| 1. |
- Ahmed, Mohamed, et al.
(författare)
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Dynamic response of NDVI to soil moisture variations during different hydrological regimes in the Sahel region
- 2017
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 38:19, s. 5408-5429
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Tidskriftsartikel (refereegranskat)abstract
- Over the last few decades, the African Sahel has become thefocus of many studies regarding vegetation dynamics and theirrelationships with climate and people. This is because rainfalllimits the production of biomass in the region, a resource onwhich people are directly dependent for their livelihoods. In thisstudy, we utilized a remote-sensing approach to answering thefollowing two questions: (1) how does the dynamic relationshipbetween soil moisture and plant growth vary across hydrologi-cal regimes, and (2) are vegetation-type-dependent responsesto soil moisture availability detectable from satellite imagery? Inorder to answer these questions, we studied the relationshipbetween monthly modelled soil moisture as an indicator forwater availability and the remotely sensed normalized differ-ence vegetation index (NDVI) as a proxy for vegetation growthbetween a“recovery rainfall period”(1982 to 1997) and a“stable rainfall period”(1998 to 2013), at different time lagsacross the Sahel region. Using windowed cross-correlation, wefind a strong significant positive relationship between NDVI andsoil moisture at a concurrent time and at NDVI lagging behindsoil moisture by 1 month for grassland, cropland, and decid-uous shrubland vegetation–the dominant vegetation classes inthe Sahel. South of the Sahel (the Sudanian and Guinean areas),wefind longer optimal lags (soil moisture lagged by 1–3 months) in association with mixed forest and deciduousshrubland. Wefind no major significant change in optimal lagbetween the recovery and stable periods in the Sahelian region;however, in the Sudanian and Guinean areas, we observe atrend towards shorter time lags. This change in optimal lagsuggests a vegetation change, which may be a response to aclimatic shift or land-use change. This approach of identifyingspatiotemporal trends in optimal lag correlations between mod-elled soil moisture and NDVI could prove to be a useful tool formapping vegetation change and ecosystem behaviour, in turnhelping inform climate change mitigation approaches and agri-cultural planning
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| 2. |
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| 3. |
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| 4. |
- Archer, Jenny, et al.
(författare)
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Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:11, s. 2973-2985
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.
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| 5. |
- Ardö, J., et al.
(författare)
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On the accuracy of the global positioning system-a test using a hand-held receiver
- 1992
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 13:16, s. 3229-3233
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to evaluate the accuracy of location (x, y and z) using a Magellan GPS NAV 1000 receiver. The position of a known reference point was compared with 50 fix points measured in two-dimensional (2D) mode (x, y) and with 50 fix points measured in three-dimensional (3D) mode (x, y and z). The mean errors and the root mean square errors (RMSE) in the Euclidian distances between the reference poinl and the measured fix points were 17.9m and 20.0m respectively for the 2D measurements, and 25.7m and 34.8m respectively for the 3D measurements. The mean error in elevation was 0-2 m and the corresponding RMSE was 39.1 m. The study indicates a significant difference in the total error (Euclidian distance) between points obtained with different signal qualities and different geometric qualities. The error in the Euclidian distance never exceeded 44.0 m using 2D mode, which suggests that the Magellan GPS NAV 1000 receiver should be a useful supportive tool for many remote sensing applications.
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| 6. |
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| 7. |
- Ban, Yifang, et al.
(författare)
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Fusion of Quickbird MS and RADARSAT SAR data for urban land-cover mapping : object-based and knowledge-based approach
- 2010
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Ingår i: International Journal of Remote Sensing. - : Taylor & Francis. - 0143-1161 .- 1366-5901. ; 31:6, s. 1391-1410
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this research is to evaluate Quickbird multi-spectral (MS) data, multi-temporal RADARSAT Fine-Beam C-HH synthetic aperture radar (SAR) data and fusion of Quickbird MS and RADARSAT SAR for urban land-use/land-cover mapping. One scene of Quickbird multi-spectral imagery was acquired on 18 July 2002 and five-date RADARSAT fine-beam SAR images were acquired during May to August 2002. Quickbird MS images and RADARSAT SAR data were classified using an object-based and rule-based approach. The results demonstrated that the object-based and knowledge-based approach was effective in extracting urban land-cover classes. For identifying 16 land-cover classes, object-based and rule-based classification of Quickbird MS data yielded an overall classification accuracy of 87.9% (kappa: 0.868). For identifying 11 land-cover classes, object-based and rule-based classification of RADARSAT SAR data yielded an overall accuracy: 86.6% (kappa: 0.852). Decision level fusion of Quickbird classification and RADARSAT SAR classification was able to take advantage of the best classifications of both optical and SAR data, thus significantly improving the classification accuracies of several land-cover classes (25% for pasture, 19% for soybeans, 17% for rapeseeds) even though the overall classification accuracy of 16 land-cover classes increased only slightly to 89.5% (kappa: 0.885).
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| 8. |
- Ban, Yifang, et al.
(författare)
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Orbital effects on ERS-1 SAR temporal backscatter profiles of agricultural crops
- 1998
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 19:17, s. 3465-3470
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Tidskriftsartikel (refereegranskat)abstract
- Multi-temporal radar backscatter characteristics of crops and their underlying soils were analysed for an agricultural area in south-western Ontario, Canada using nine dates of ERS-1 SAR imagery acquired during the 1993 growing season. From the calibrated data, SAR temporal backscatter profiles were generated for each crop type. The results indicate that small changes in incidence-angle can have strong impacts on radar backscatter. Thus, attention must be given to local incidence-angle effects when using ERS-1 SAR data,especially when comparing backscatter coefficients of the same area from different scenes or different areas within the same scene.
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| 9. |
- Baron, P., et al.
(författare)
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HO2 measurements in the stratosphere and the mesosphere from the sub-millimetre limb sounder Odin/SMR
- 2009
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 30:15-16, s. 4195-4208
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents observations of the hydroperoxy radical (HO 2 ) performed by the Odin/SMR instrument from the middle stratosphere to the upper mesosphere (35-90 km). The data set covers the period from October 2003 to December 2005 on a basis of one observation period of 24 hours each month. Odin/SMR can provide two zonal maps of HO 2 per day, with a vertical resolution of 10 km. The non-standard processing applied to the retrievals is described. The consistency between HO 2 observations from three periods in August 2004 demonstrates the robustness of the retrieval method. It also shows that the measurements are sensitive enough to detect changes in the middle and upper mesosphere. The retrieval needs further improvements for studying stratospheric variations. © 2009 Taylor & Francis.
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| 10. |
- Beck, P S A, et al.
(författare)
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A ground-validated NDVI dataset for monitoring vegetation dynamics and mapping phenology in Fennoscandia and the Kola peninsula
- 2007
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 28:19, s. 4311-4330
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Tidskriftsartikel (refereegranskat)abstract
- An NDVI dataset covering Fennoscandia and the Kola peninsula was created for vegetation and climate studies, using Moderate Resolution Imaging Spectroradiometer 16-day maximum value composite data from 2000 to 2005. To create the dataset, ( 1) the influence of the polar night and snow on the NDVI values was removed by replacing NDVI values in winter with a pixel- specific NDVI value representing the NDVI outside the growing season when the pixel is free of snow; and ( 2) yearly NDVI time series were modelled for each pixel using a double logistic function defined by six parameters. Estimates of the onset of spring and the end of autumn were then mapped using the modelled dataset and compared with ground observations of the onset of leafing and the end of leaf fall in birch, respectively. Missing and poor-quality data prevented estimates from being produced for all pixels in the study area. Applying a 5 km x 5 km mean filter increased the number of modelled pixels without decreasing the accuracy of the predictions. The comparison shows good agreement between the modelled and observed dates ( root mean square error = 12 days, n = 108 for spring; root mean square error = 10 days, n = 26, for autumn). Fennoscandia shows a range in the onset of spring of more than 2 months within a single year and locally the onset of spring varies with up to one month between years. The end of autumn varies by one and a half months across the region. While continued validation with ground data is needed, this new dataset facilitates the detailed monitoring of vegetation activity in Fennoscandia and the Kola peninsula.
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| 11. |
- Beltrán-Abaunza, José M., et al.
(författare)
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Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas
- 2017
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 38:7, s. 2004-2028
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to highlight how satellite data can be used for an improved understanding of ecological processes in a narrow coastal bay. The usefulness of the Medium Resolution Imaging Spectrometer (MERIS) data (2003-2011) as a complement to the in situ monitoring in Himmerferdenn (HF) bay is used as an example that can also be applied to other coastal areas. HF bay is one of the most frequently monitored coastal areas in the world, allowing for a rigorous comparison between satellites and ship-based monitoring data. MERIS data was used for the integration of chlorophyll-a (chl-a) over each waterbody in the HF area, following the national waterbody classification by the Swedish Meteorological and Hydrological Institute (SMHI). Chl-a anomaly maps were produced for the bay and its adjacent areas. The maps could be used to show events with high chl-a, both with natural causes (e.g. a Prymnesium polylepis bloom observed in summer 2008) and of anthropogenic causes (e.g. failure in the local sewage treatment plant resulting in a strong spring bloom in 2006). Anomaly maps thereby allow to scan larger coastal stretches to discriminate areas that may require additional sampling by ship, or to identify areas that do not differ much from the median value of the MERIS time series.
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| 12. |
- Brown, Ian A.
(författare)
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Assessing eco-scarcity as a cause of the outbreak of conflict in Darfur : a remote sensing approach
- 2010
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 31:10, s. 2513-2520
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Tidskriftsartikel (refereegranskat)abstract
- The conflict in Darfur, Western Sudan, is frequently represented in the media as a dispute over access to resources by competing communities. Environmental degradation is often cited as either a causal or a contributory factor to the outbreak of the conflict and its prolongation. In this paper, Normalized Difference Vegetation Index (NDVI) data are used as a measure of 'eco-scarcity' to assess the notion that the outbreak of conflict was the result of competition for resources between communities. It is shown that there is no evidence in the vegetation mapping for a worsening of the ecological situation in Western and Northern Darfur states around the outbreak of the conflict. On the contrary, the years prior to the outbreak of the conflict experienced better than average vegetation growth in the context of the past 25 years.
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| 13. |
- Connolly, J., et al.
(författare)
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Detecting recent disturbance on montane blanket bogs in the Wicklow Mountains, Ireland, using the MODIS enhanced vegetation index
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 32:9, s. 2377-2393
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Tidskriftsartikel (refereegranskat)abstract
- Irish peat soils are extensive, covering approximately 14-20% of the national land area. They contain between 53% and 62% of the national soil organic carbon stock. Montane blanket bog covers approximately 25% or 242650ha of the total peatland area in Ireland and is the dominant peatland type covering the upland area of Wicklow. Blanket bogs are very sensitive systems and have experienced much disturbance in Ireland due to overgrazing, burning, drainage, forestry and turf cutting. It has been estimated that disturbance of blanket bog, on a national area basis, ranges from 74% to 82% and in Wicklow is 57%. Disturbance can be detrimental to stocks of soil organic carbon in peatlands. Monitoring disturbance in peatlands, which tend to cover large, remote areas, is difficult and expensive using conventional surveying methods. Satellite remote sensing offers a way to gather data for these areas. In this paper a method of determining the probability of disturbance is presented. This method uses the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) in combination with univariate image differencing along with thresholding and binary logistic regression. A probability map was produced depicting the geospatial patterns and pressures on the peatland soil organic carbon stock in Wicklow. Peat soils in higher and steeper areas were more disturbed and the primary disturbance in between 2000 and 2005 was fire. Lower, flatter areas did not experience as much disturbance probably because they are wetter. The consumer's and producer's accuracy for the map was 76% and 42%, respectively.
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| 14. |
- Drake, V. Alistair, et al.
(författare)
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Heading variations resolve the heading-direction ambiguity in vertical-beam radar observations of insect migration
- 2021
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 42:10, s. 3873-3898
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Tidskriftsartikel (refereegranskat)abstract
- Vertical-beam entomological radars provide precise measurements of the body alignment of individual overflying insects but are unable to distinguish which of the two axial directions the insect is heading towards. Insects migrating at altitude typically show common alignment, although with a broad spread. We show here that when observations from multiple individual insects are available, and the insects have airspeeds of about 2 ms–1 or greater, the spread in heading directions allows the heading ambiguity to be resolved (though at the sample rather than the individual level). A vector analysis of radar-measured track direction, track speed, and heading will provide consistent results for all the insects in a sample only when the heading direction is chosen correctly. With the heading then resolved, the analysis can continue to estimation of representative values for the airspeed of the insects in the sample and for the speed and direction of the wind they were flying in. This general approach can be implemented in two different ways, which we term the ‘cluster’ and ‘projection’ methods. When applied to an intense migration of large insects, probably moths, these methods produced highly consistent results from hour to hour and from one 150 m height interval to the next. Simulations show that the methods are not liable to directional bias and reveal when they are rendered ineffective by small sample sizes or low insect airspeeds; they also indicate that the cluster method handles small sample sizes better than the projection method, and its use is therefore recommended. A comparison with two previously proposed methods that use meteorological data to resolve the ambiguity shows that the new methods are more reliable. Use of this objective means of resolving the heading ambiguity will increase confidence in radar-based studies of the orientation behaviour of insect migrants and their responses to cues like sky illumination patterns, the Earth’s magnetic field, and wind.
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| 15. |
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| 16. |
- Elmqvist, Bodil, et al.
(författare)
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Land use studies in drylands: an evaluation of object-oriented classification of very high resolution panchromatic imagery
- 2008
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 29:24, s. 7129-7140
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Tidskriftsartikel (refereegranskat)abstract
- Object-oriented classification approaches offer an alternative to per-pixel methods for assessment of land use and land cover. Combining object-oriented approaches with very high resolution imagery may provide enhanced possibilities for applications requiring land use and land cover data. The aim of this study is to evaluate the application of object-oriented classification of panchromatic very high resolution data in African drylands, where sizes and shapes of fields are varied, and intercropping practised, which might lead to difficulties in image segmentation. The results show that region-based segmentation is sensitive to the proportion of spectral and shape information and the best results were gained when the segmentation was based on predominately spectral information. The accuracy (Kappa value of 0.6) for the object-oriented classification was significantly higher than that for per-pixel classification. However, both the segmentation and the classification were time-consuming based on a trial and error process.
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| 17. |
- Eriksson, Patrick, et al.
(författare)
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Efficient forward modelling by matrix representation of sensor responses
- 2006
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 27:9-10, s. 1793-1808
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Tidskriftsartikel (refereegranskat)abstract
- The polarization, frequency and spatial responses of the sensor can be considered by calculating the Stokes vector of monochromatic pencil beam radiances for a set of frequencies and viewing directions, and weight these radiances with the instrument responses. This paper presents a highly efficient solution for this calculation procedure. The basic idea is to pre-calculate a matrix that represents the mapping from polarisation, frequency and spatial values to measured data. Sensor impacts can then be included by a simple matrix multiplication. The full sensor matrix can be obtained by determining the response matrix for the sensor parts individually. Data reduction methods can also be incorporated. A simple method for optimizing the calculation grids is further presented. The described approach for sensor modeling has been implemented in two public available softwares for atmospheric radiative transfer simulations.
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| 18. |
- Evgenieva, Tsvetina, et al.
(författare)
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Three-point observation in the troposphere over Sofia-Plana Mountain,Bulgaria
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:24, s. 9343-9363
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Tidskriftsartikel (refereegranskat)abstract
- Based on a novel combination of approaches and instruments, this article presents campaign-based results from atmospheric boundary layer (ABL) height and aerosol optical depth (AOD) measurements carried out at two different experimental sites in Sofia, as well as from three-point measurements of aerosol number concentrations. Several instruments (lidar (developed by the IE), ceilometer, aerosol particle counter, sun photometer and meteorological sensors) were used in this study. Based on joint interpretation of the instruments' data we assess the influence of the atmospheric aerosol in the planetary boundary layer and the significant influence of aerosol layers and high clouds on AOD values. Measurements of AOD in the city basin gave values in the range 0.22-0.41 for cloud-free skies, and up to around 0.8 under partly cloudy conditions. The information obtained during the two campaigns indicates that aerosol particle concentrations were lower in park areas than along heavy-traffic thoroughfares in the city, but higher than in the mountain area. In conclusion, our study demonstrates the potential of employing a broad array of instruments for the study of boundary layer and aerosol over large, valley-situated and heavily urbanized city areas.
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| 19. |
- Feng, Wenqing, et al.
(författare)
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A novel change detection approach based on visual saliency and random forest from multi-temporal high-resolution remote-sensing images
- 2018
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 39:22, s. 7998-8021
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a novel change detection (CD) approach for high-resolution remote-sensing images, which incorporates visual saliency and random forest (RF). First, highly homogeneous and compact image super-pixels are generated using super-pixel segmentation, and the optimal segmentation result is obtained through image superimposition and principal component analysis. Second, saliency detection is used to guide the search of interest regions in the initial difference image obtained via the improved robust change vector analysis algorithm. The salient regions within the difference image that correspond to the binarized saliency map are extracted, and the regions are subject to the fuzzy c-means (FCM) clustering to obtain the pixel-level pre-classification result, which can be used as a prerequisite for super-pixel-based analysis. Third, on the basis of the optimal segmentation and pixel-level pre-classification results, different super-pixel change possibilities are calculated. Furthermore, the changed and unchanged super-pixels that serve as the training samples are automatically selected. The spectral features and Gabor features of each super-pixel are extracted. Finally, super-pixel-based CD is implemented by applying RF based on these samples. Experimental results on Quickbird, Ziyuan 3 (ZY3), and Gaofen 2 (GF2) multi-spectral images show that the proposed method outperforms the compared methods in the accuracy of CD, and also confirm the feasibility and effectiveness of the proposed approach.
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| 20. |
- Feng, Wenqing, et al.
(författare)
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Building extraction from VHR remote sensing imagery by combining an improved deep convolutional encoder-decoder architecture and historical land use vector map
- 2020
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 41:17, s. 6595-6617
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Tidskriftsartikel (refereegranskat)abstract
- Building extraction has attracted considerable attention in the field of remote sensing image analysis. Fully convolutional network modelling is a recently developed technique that is capable of significantly enhancing building extraction accuracy. It is a prominent branch of deep learning and uses advanced state-of-the-art techniques, especially with regard to building segmentation. In this paper, we present an enhanced deep convolutional encoder-decoder (DCED) network by incorporating historical land use vector maps (HVMs) customized for building extraction. The approach combines enhanced DCED architecture with multi-scale image pyramid for pixel-wise building segmentation. The improved DCED network, together with symmetrical dense-shortcut connection structures, is employed to establish the encoders for automatic extraction of building features. The feature maps from early layers were fused with more discriminative feature maps from the deeper layers through ‘Res path’ skip connections for superior building extraction accuracy. To further reduce the occurrence of falsely segmented buildings, and to sharpen the buildings’ boundaries, the new temporal testing image is segmented under the constraints of an HVM. A majority voting strategy is employed to ensure the homogeneity of the building objects as the post-processing method. Experimental results indicate that the proposed approach exhibits competitive quantitative and qualitative performance, effectively alleviating the salt-and-pepper phenomenon and block effects, and retaining the edge structures of buildings. Compared with other state-of-the-art methods, our method demonstrably achieves the optimal final accuracies.
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| 21. |
- Flygare, Ann-Marie, 1964-
(författare)
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A comparison of contextual classification methods using Landsat TM
- 1997
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Ingår i: International Journal of Remote Sensing. - : Taylor & Francis Group. - 0143-1161 .- 1366-5901. ; 18:18, s. 3835-3842
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Tidskriftsartikel (refereegranskat)abstract
- The performance of contextual classification methods is evaluated using Landsat TM data. Classes of pixels adjacent to the pixel to be classified are assumed to be conditionally independent given the class of the pixel to be classified. An assumption of autocorrelated spectral reflectance is made in three of the methods. Methods that utilize information from one image and images from two different occasions are compared. Our results indicate that an autocorrelation method utilizing images from two different occasions performs optimally.
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| 22. |
- Gilichinsky, Michael, et al.
(författare)
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Histogram matching for the calibration of kNN stem volume estimates
- 2012
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 33, s. 7117-7131
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we have tested HM for the calibration of kNN total stem volume raster maps to the reference distribution captured by a forest inventory (FI) from 106 stands in Stromsjoliden, in the north of Sweden. The available field FI data set comprises 1084 circular plots, divided into a reference data set and an evaluation data set of total stem volume observations. The reference data set was used for the creation of a cumulative frequency histogram of total stem volume and the evaluation data set was used to assess the accuracy of volume estimates, before and after HM. The HM adjusted the cumulative distribution of the kNN data set to the distribution of the reference observations and resulted in a distribution of kNN estimates of total stem volume, which corresponded closely to that of the evaluation data set. The results show that the variation range of the kNN stem volume estimates can be extended by HM both on the pixel and stand levels. The extension of the range of estimates towards the range provided by the field observations allows improvement of kNN volume estimation for use in forest management planning based on stand-level analysis, given that the reference stem volume distribution can be estimated accurately, for example, using field data from NFI.
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| 23. |
- Gilichinsky, Michael, et al.
(författare)
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Mapping ground lichens using forest inventory and optical satellite data
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:2, s. 455-472
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Tidskriftsartikel (refereegranskat)abstract
- Lichen is a major forage resource for reindeer and may constitute up to 80% of areindeer’s winter diet. The reindeer grazing area in Sweden covers almost half of thecountry, with reindeer using mountainous areas in the summer and forested areas inthe winter. Knowledge about the spatial distribution of ground lichens is importantfor both practical and decision-making purposes. Since the early 1980s, remotesensing research of lichen cover in northern environments has focused on reindeergrazing issues. The objective of this study was to use lichen information collected inthe Swedish National Forest Inventory (NFI) as training data to classify opticalsatellite images into ground lichen cover classes. The study site was located within thereindeer husbandry area in northern Sweden and consisted of the common areabetween two contiguous Satellite Pour l’Observation de la Terre (SPOT)-5 scenesand one Landsat-7 Enhanced Thematic Mapper Plus (ETMþ) scene. Three classificationmethods were tested: Mahalanobis distance, maximum likelihood andspectral mixture analysis. Post-classification calibration was applied using a membershipprobability threshold in order to match the NFI-measured proportions oflichen coverage classes. The classification results were assessed using an independentlycollected field dataset (229 validation areas). The results demonstrated highclassification accuracy of SPOT imagery for the classification of lichen-abundantand lichen-poor areas when using theMahalanobis distance classifier (overall accuracy84.3%, kappa ¼ 0.68). The highest classification accuracy for Landsat wasachieved using a maximum likelihood classification (overall accuracy 76.8%, kappa¼ 0.53). These results provided an initial indication of the utility of NFI data astraining data in the process of mapping lichen classes over large areas.
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| 24. |
- Granholm, Ann-Helen, et al.
(författare)
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Estimating vertical canopy cover using dense image-based point cloud data in four vegetation types in southern Sweden
- 2017
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 38, s. 1820-1838
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Tidskriftsartikel (refereegranskat)abstract
- This study had the aim of investigating the utility of image-based point cloud data for estimation of vertical canopy cover (VCC). An accurate measure of VCC based on photogrammetric matching of aerial images would aid in vegetation mapping, especially in areas where aerial imagery is acquired regularly. The test area is located in southern Sweden and was divided into four vegetation types with sparse to dense tree cover: unmanaged coniferous forest; pasture areas with deciduous tree cover; wetland; and managed coniferous forest. Aerial imagery with a ground sample distance of 0.24 m was photogrammetrically matched to produce dense image-based point cloud data. Two different image matching software solutions were used and compared: MATCH-T DSM by Trimble and SURE by nFrames. The image-based point clouds were normalized using a digital terrain model derived from airborne laser scanner (ALS) data. The canopy cover metric vegetation ratio was derived from the image-based point clouds, as well as from raster-based canopy height models (CHMs) derived from the point clouds. Regression analysis was applied with vegetation ratio derived from near nadir ALS data as the dependent variable and metrics derived from image-based point cloud data as the independent variables. Among the different vegetation types, vegetation ratio derived from the image-based point cloud data generated by using MATCH-T resulted in relative root mean square errors (rRMSE) of VCC ranging from 6.1% to 29.3%. Vegetation ratio based on point clouds from SURE resulted in rRMSEs ranging from 7.3% to 37.9%. Use of the vegetation ratio based on CHMs generated from the image-based point clouds resulted in similar, yet slightly higher values of rRMSE.
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| 25. |
- Granholm, Ann-Helen, et al.
(författare)
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The potential of digital surface models based on aerial images for automated vegetation mapping
- 2015
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 36, s. 1855-1870
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Tidskriftsartikel (refereegranskat)abstract
- Segmentation of vegetation patches was tested using canopy height models (CHMs) representing the height difference between digital surface models (DSMs), generated by matching digital aerial images from the Z/I Digital Mapping Camera, and a digital elevation model (DEM) based on airborne laser scanner data. Three different combinations of aerial images were used in the production of the CHMs to test the effect of flight altitude and stereo overlap on segmentation accuracy. Segmentation results were evaluated using the standard deviation of photo-interpreted tree height within segments, as well as by visual comparison to existing maps. In addition, height percentiles extracted from the CHMs were used to estimate tree heights. Tree height estimation at the segment level yielded root mean square error (RMSE) values of 2.0 m, or 15.1%, and an adjusted coefficient of determination (adjusted R2) of 0.94 when using a CHM from images acquired at an altitude of 1200 m above ground level (agl) and with an along-track stereo overlap of 80%. When a CHM based on images acquired at 4800 m agl and an overlap of 60% was used, the corresponding results were an RMSE of 2.2 m, or 16.0%, and an adjusted R2 of 0.92. Tree height estimation at the plot level was most accurate for densely forested plots dominated by coniferous tree species (RMSE of 2.1 m, or 9.8%, and adjusted R2 of 0.88). It is shown that CHMs based on aerial images acquired at 4800 m agl and with 60% along-track stereo overlap are useful for the segmentation of vegetation and are at least as good as those based on aerial images collected at a lower flight altitude or with greater overlap.
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| 26. |
- Hannerz, Fredrik, et al.
(författare)
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Assessment of remotely sensed and statistical inventories of African agricultural fields
- 2008
-
Ingår i: International Journal of Remote Sensing. - : Informa plc. - 0143-1161 .- 1366-5901. ; 29:13, s. 3787-3804
-
Tidskriftsartikel (refereegranskat)abstract
- This paper critically examines different sources of remotely sensed and statistical inventories of African agricultural fields. Substantial discrepancies are found across alternative sources of information in both the extent and location of agricultural fields. In one-third of the countries, the difference between lowest and highest field extent estimate exceeds 25% of the total country area, and the maximum difference at the continental level is 2.6 million km2. Much of the disagreement between land-cover maps arises from areas of low cropping density. These inconsistencies have important implications when using these data directly, e.g. for the assessment of land cover changes, or indirectly in economic or physical models, and indicate a need to explicitly quantify uncertainties arising from the limitations in land-cover data. They also highlight the need for development of regional land information systems for baseline development and informed policy decisions.
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| 27. |
- Holmgren, Johan, et al.
(författare)
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Tree crown segmentation in three dimensions using density models derived from airborne laser scanning
- 2022
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 43, s. 299-329
-
Tidskriftsartikel (refereegranskat)abstract
- This article describes algorithms to extract tree crowns using two-dimensional (2D) and three-dimensional (3D) segmentation. As a first step, a 2D-search detected the tallest trees but was unable to detect trees located below other trees. However, a 3D-search for local maxima of model fits could be used in a second step to detect trees also in lower canopy layers. We compared tree detection results from ALS carried out at 1450 m above ground level (high altitude) and tree detection results from ALS carried out at 150 m above ground level (low altitude). For validation, we used manual measurements of trees in ten large field plots, each with an 80 m diameter, in a hemiboreal forest in Sweden (lat. 58 degrees 28' N, long. 13 degrees 38' E). In order to measure the effect of using algorithms with different computational costs, we validated the tree detection from the 2D segmentation step and compared the results with the 2D segmentation followed by 3D segmentation of the ALS point cloud. When applying 2D segmentation only, the algorithm detected 87% of the trees measured in the field using high-altitude ALS data; the detection rate increased to 91% using low-altitude ALS data. However, when applying 3D segmentation as well, the algorithm detected 92% of the trees measured in the field using high-altitude ALS data; the detection rate increased to 99% using low-altitude ALS data. For all combinations of algorithms and data resolutions, undetected trees accounted for, on average, 0-5% of the total stem volume in the field plots. The 3D tree crown segmentation, which was using crown density models, made it possible to detect a large percentage of trees in multi-layered forests, compared with using only a 2D segmentation method.
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| 28. |
- Huo, Langning, et al.
(författare)
-
Individual tree detection using template matching of multiple rasters derived from multispectral airborne laser scanning data
- 2020
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 41, s. 9525-9544
-
Tidskriftsartikel (refereegranskat)abstract
- Multispectral airborne laser scanning (MS-ALS) provides information about 3D structure as well as the intensity of the reflected light and is a promising technique for acquiring forest information. Data from MS-ALS have been used for tree species classification and tree health evaluation. This paper investigates its potential for individual tree detection (ITD) when using intensity as an additional metric. To this end, rasters of height, point density, vegetation ratio, and intensity at three wavelengths were used for template matching to detect individual trees. Optimal combinations of metrics were identified for ITD in plots with different levels of canopy complexity. The F-scores for detection by template matching ranged from 0.94 to 0.73, depending on the choice of template derivation and raster generalization methods. Using intensity and point density as metrics instead of height increased the F-scores by up to 14% for the plots with the most understorey trees.
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| 29. |
- Kari, Elina, et al.
(författare)
-
Retrieval of suspended particulate matter from turbidity - model development, validation, and application to MERIS data over the Baltic Sea
- 2017
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 38:7, s. 1983-2003
-
Tidskriftsartikel (refereegranskat)abstract
- Suspended particulate matter (SPM) causes most of the scattering in natural waters and thus has a strong influence on the underwater light field, and consequently on the whole ecosystem. Turbidity is related to the concentration of SPM which usually is measured gravimetrically, a rather time-consuming method. Measuring turbidity is quick and easy, and therefore also more cost-effective. When derived from remote sensing data the method becomes even more cost-effective because of the good spatial resolution of satellite data and the synoptic capability of the method. Turbidity is also listed in the European Union's Marine Strategy Framework Directive as a supporting monitoring parameter, especially in the coastal zone. In this study, we aim to provide a new Baltic Sea algorithm to retrieve SPM concentration from in situ turbidity and investigate how this can be applied to satellite data. An in situ dataset was collected in Swedish coastal waters to develop a new SPM model. The model was then tested against independent datasets from both Swedish and Lithuanian coastal waters. Despite the optical variability in the datasets, SPM and turbidity were strongly correlated (r = 0.97). The developed model predicts SPM reliably from in situ turbidity (R-2 = 0.93) with a mean normalized bias (MNB) of 2.4% for the Swedish and 14.0% for the Lithuanian datasets, and a relative error (RMS) of 25.3% and 37.3%, respectively. In the validation dataset, turbidity ranged from 0.3 to 49.8 FNU (Formazin Nephelometric Unit) and correspondingly, SPM concentration ranged from 0.3 to 34.0 g m(-3) which covers the ranges typical for Baltic Sea waters. Next, the medium-resolution imaging spectrometer (MERIS) standard SPM product MERIS Ground Segment (MEGS) was tested on all available match-up data (n = 67). The correlation between SPM retrieved from MERIS and in situ SPM was strong for the Swedish dataset with r = 0.74 (RMS = 47.4 and MNB = 11.3%; n = 32) and very strong for the Lithuanian dataset with r = 0.94 (RMS = 29.5% and MNB = -1.5%; n = 35). Then, the turbidity was derived from the MERIS standard SPM product using the new in situ SPM model, but retrieving turbidity from SPM instead. The derived image was then compared to existing in situ data and showed to be in the right range of values for each sub-area. The new SPM model provides a robust and cost-efficient method to determine SPM from in situ turbidity measurements (or vice versa). The developed SPM model predicts SPM concentration with high quality despite the high coloured dissolved organic matter (CDOM) range in the Baltic Sea. By applying the developed SPM model to already existing remote sensing data (MERIS/Envisat) and most importantly to a new generation of satellite sensors (in particular OLCI on board the Sentinel-3), it is possible to derive turbidity for the Baltic Sea.
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| 30. |
- Khan, Aamir
(författare)
-
Role of epicuticular wax in the regulation of plant growth and health as measured by spectral indices
- 2021
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 42, s. 3498-3510
-
Tidskriftsartikel (refereegranskat)abstract
- Using remote sensing technology for exploring the trait of interest can provide better results without damaging the plants and are comparatively economic. Traditional methods are available for quantification of different pigments and chemicals present in plants, yet these methods do not allow repeated measurements on the same plant throughout development. The reflected values from plant surfaces are a direct representation of plant physiology including plant morphological factors. The hyperspectral imaging indices for vegetation and water-stressed canopies provided a better indication of each genotype proficiency, thus improving their selection efficiency. The presence of epicuticular wax (EW) influences the reflectance from leaf surface which depends on the presence of leaf pigments including carotenoids, photosynthetic light use efficiency biochemical structures, and water content as they absorb the incident light necessary for photosynthesis. The results obtained suggested decrease carotenoid reflectance index (CRI) and photochemical reflectance index (PRI) values for high wax lines indicating the low concentration of stress-related pigments thus improving plant health and extended maturation. The high waxy lines decreased for plant senescence reflectance index (PSRI) and reduce canopy stress at grain filling and maturation growth stages. A positive correlation between high epicuticular wax (EW) and yield was found confirming previous study. A positive correlation between high epicuticular wax (EW) lines and yield indicated its important role in preventing yield losses under drought conditions.
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| 31. |
- Knudby, Anders, et al.
(författare)
-
Remote sensing of seagrasses in a patchy multi-species environment
- 2011
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:8, s. 2227-2244
-
Tidskriftsartikel (refereegranskat)abstract
- We tested the utility of IKONOS satellite imagery to map seagrass distribution and biomass in a 4.1 km2 area around Chumbe Island, Zanzibar, Tanzania. Considered to be a challenging environment to map, this area is characterized by a diverse mix of inter- and subtidal habitat types. Our mapped distribution of seagrasses corresponded well to field data, although the total seagrass area was underestimated due to spectral confusion and misclassification of areas with sparse seagrass patches as sparse coral and algae-covered limestone rock. Seagrass biomass was also accurately estimated (r2 = 0.83), except in areas with Thalassodendron ciliatum (r2 = 0.57), as the stems of T. ciliatum change the relationship between light interception and biomass from that of other species in the area. We recommend the use of remote sensing over field-based methods for seagrass mapping because of the comprehensive coverage, high accuracy and ability to estimate biomass. The results obtained with IKONOS imagery in our complex study area are encouraging, and support the use of this data source for seagrass mapping in similar areas.
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| 32. |
- Kolios, Stavros, et al.
(författare)
-
Achieving downscaling of Meteosat thermal infrared imagery using artificial neural networks
- 2013
-
Ingår i: International Journal of Remote Sensing. - : Taylor & Francis. - 0143-1161 .- 1366-5901. ; 34:21, s. 7706-7722
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents the successful application of artificial neural networks (ANNs) for downscaling Meteosat Second Generation thermal infrared satellite imagery. The scope is to examine, propose, and develop an integrated methodology to improve the spatial resolution of Meteosat satellite images. The proposed approach may contribute to the development of a general methodology for monitoring and downscaling Earth's surface characteristics and cloud systems, where there is a clear need for contiguous, accurate, and high-spatial resolution data sets (e.g. improvement of climate model input data sets, early warning systems about extreme weather phenomena, monitoring of parameters such as solar radiation fluxes, land-surface temperature, etc.). Moderate Resolution Imaging Spectroradiometer (MODIS) images are used to validate the downscaled Meteosat images. In terms of the ANNs, a multilayer perceptron (MLP) is used and the results are shown to compare favourably against a linear regression approach.
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| 33. |
- Koppel, Kalev, et al.
(författare)
-
Sensitivity of Sentinel-1 backscatter to characteristics of buildings
- 2017
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 38:22, s. 6298-6318
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, Sentinel-1 interferometric wide swath (IW) mode backscatter is analysed with respect to physical parameters of buildings in Tallinn, Estonia. Dependence on height, alignment, density, shape, and material is shown and discussed. Distribution of backscatter was estimated with respect to each of the parameters, and a correlation matrix of all physical parameters and backscatter values was computed. Height has the strongest effect on backscatter values for both polarization bands, while shape and alignment to orbit has weaker effect on the backscatter. Relationship of co-polarized and cross-polarized backscatter with how a building is aligned with respect to the satellite’s look angle indicates that double bounce from wall–ground interactions is still the dominant scattering mechanism detected by Sentinel-1 in IW mode with 20 m resolution. In order to establish possible detection problems related to specifically oriented buildings at different latitudes, dihedral backscatter is modelled for buildings of oblong and square shapes. Results from this study should be used to improve existing and develop new urban area detection methods based on Sentinel-1 data.
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| 34. |
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| 35. |
- Larsson, Richard
(författare)
-
A note on modelling of the oxygen spectral cross-section in the Atmospheric Radiative Transfer Simulator – Zeeman effect combined with line mixing in the Earth’s atmosphere
- 2014
-
Ingår i: International Journal of Remote Sensing. - 0143-1161 .- 1366-5901. ; 35:15, s. 5845-5853
-
Tidskriftsartikel (refereegranskat)abstract
- A new module to the Atmospheric Radiative Transfer Simulator is presented that models the strong oxygen spectral band at 60 GHz. The module handles the line mixing effect and works with or without additionally calculating the Zeeman effect. It is shown how the module may be internally reduced to calculations of the Zeeman effect at higher altitudes, and to calculations of the line mixing effect at lower altitudes. The article ends with a short discussion on what is being done to validate the module, and what may be done to refine the theoretical description of line mixing in the simulator.
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| 36. |
- Lindberg, Eva, et al.
(författare)
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Estimation of tree lists from airborne laser scanning by combining single-tree and area-based methods
- 2010
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 31, s. 1175-1192
-
Tidskriftsartikel (refereegranskat)abstract
- Individual tree crown segmentation from airborne laser scanning (ALS) data often fails to detect all trees depending on the forest structure. This paper presents a new method to produce tree lists consistent with unbiased estimates at area level. First, a tree list with height and diameter at breast height (DBH) was estimated from individual tree crown segmentation. Second, estimates at plot level were used to create a target distribution by using a k-nearest neighbour (k-NN) approach. The number of trees per field plot was rescaled with the estimated stem volume for the field plot. Finally, the initial tree list was calibrated using the estimated target distribution. The calibration improved the estimates of the distributions of tree height (error index (EI) from 109 to 96) and DBH (EI from 99 to 93) in the tree list. Thus, the new method could be used to estimate tree lists that are consistent with unbiased estimates from regression models at field plot level.
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| 37. |
- Lindström, Johan, et al.
(författare)
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Influence of solar zenith angles on observed trends in the NOAA/NASA 8-km Pathfinder normalized difference vegetation index over the African Sahel
- 2006
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 27:9-10, s. 1973-1991
-
Tidskriftsartikel (refereegranskat)abstract
- The strong systematic change in solar zenith angles (SZA) due to annual orbital drift of the NOAA satellites has raised the suspicion of the influence of residual illumination on the calibrated normalized difference vegetation index (NDVI) derived from the Pathfinder AVHRR Land (PAL) database. The aim of this work is to analyse if trends in AVHRR NDVI from 1982 to 2000 over the Sahel region in Africa depend on variations in SZA. The analysis uses both ordinary least squares regression and cointegration to analyse possible linear dependencies between NDVI and SZA on a per satellite basis. Tests for integration and cointegration fail to find any significant evidence for either. This, together with the ability of simple deterministic models to explain primarily SZA constitutes evidence against integration and cointegration, indicating that linear relationships can be examined using ordinary linear regression. Regression gives no consistent relationship between NDVI and SZA and the explanatory power (R 2) of the regression is low (on average 0.08). However there is some evidence for downward bias in NDVI due to nonlinear interactions between NDVI and SZA when SZA is large (>= 80 degrees) leading to the conclusion that PAL data from the year 2000 should not be used for analyses in these environments.
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| 38. |
- Lorenz, Henning, 1972-
(författare)
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Integration of Corona and Landsat Thematic Mapper data for bedrock geological studies in the high Arctic
- 2004
-
Ingår i: International Journal of Remote Sensing: An official journal of the Remote Sensing and Photogrammetry Society. - : Informa UK Limited. - 0143-1161. ; 25:22, s. 5143-5162
-
Tidskriftsartikel (refereegranskat)abstract
- The Severnaya Zemlya Archipelago near the continental edge in the Russian high Arctic is one of few land-areas along the Eurasian Arctic margin. It is of particular interest for investigating the Arctic's tectonic history. This study focuses on the Palaeozoic bedrock of October Revolution Island.In the Russian high Arctic detailed topographic maps and aerial photography often are not available. The potential of low-cost satellite imagery as a substitute is shown in this study. High-resolution Corona KH-4A panchromatic satellite imagery and Landsat TM multispectral data have been integrated. In combination with field-investigations in key-areas, these data provide the basis for new interpretations of the geology. Corona images were digitized and georeferenced to provide a basis for conventional and digital geological mapping. Merging Corona and Landsat TM data resulted in a high-resolution multispectral image of enhanced interpretability. Lithological contacts have been traced, supported by a bedrock-image extracted from the Landsat TM data. Stereoscopic coverage of the Corona KH-4A photographic sensor allowed a structural interpretation. All results were integrated into a geological interpretation of southern October Revolution Island which provides an encouraging platform for further work in the high Arctic.
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| 39. |
- Mantovani, Matteo, 1974, et al.
(författare)
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DInSAR investigation in the Pärvie endglacial fault region, Lapland, Sweden
- 2013
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 34:23, s. 8491-8502
-
Tidskriftsartikel (refereegranskat)abstract
- Northern Fennoscandia bears witness to the Pleistocene glaciation in the form of a seriesof large faults that have been shown to have ruptured immediately after the retreat ofthe ice sheet, about 9500 years ago. The largest one, known as the Pärvie fault, consistsof a 155 km long linear series of fault scarps forming north–northeast-trending, thatstretch west of Kiruna, Lapland. End-glacial intra-plate faults of this extent are veryrare in the continental crust and the Pärvie system represents one of the major faultzone structures of this type in the world. Seismological evidence shows that there isstill noticeable seismic activity, roughly one event of magnitude 2 per year that can beattributed to the fault. Nevertheless assessing its state of activity is a difficult task dueto the extent and remoteness of the area. This study is aimed at the determination ofcrustal motion around the Pärvie fault zone using the differential inter-ferometric syntheticaperture radar (DInSAR) technique, based on images acquired with the EuropeanSpace Agency (ESA) satellites European Remote Sensing (ERS) 1, ERS-2, and theEnvironmental Satellite (ENVISAT). We present results achieved in terms of deformationof the crystalline bedrock along different sectors of the fault where high levels ofcoherence were obtained, even from image pairs several years apart. This finding doesnot exclude deformation in other segments, as observing conditions are not always asfavourable in terms of data availability.
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| 40. |
- Margold, Martin, 1981-, et al.
(författare)
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Evaluation of data sources for mapping glacial meltwater features
- 2012
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 33:8, s. 2355-2377
-
Tidskriftsartikel (refereegranskat)abstract
- The meltwater system of disintegrating ice sheets provides an important source of information for the reconstruction of ice-retreat patterns during deglaciation. Recent method development in glacial geomorphology, using satellite imagery and digital elevation models (DEMs) for glacial landform mapping, has predominantly been focused on the identification of lineation and other large-scale accumulation features. Landforms created by meltwater have often been neglected in these efforts. Meltwater features such as channels, deltas and fossil shorelines were traditionally mapped using stereo interpretation of aerial photographs. However, during the transition into the digital era, driven by a wish to cover large areas more economically, meltwater features were lost in most mapping surveys. We have evaluated different sets of satellite images and DEMs for their suitability to map glacial meltwater features (lateral meltwater channels, eskers, deltas, ice-dammed lake drainage channels and fossil shorelines) in comparison with the traditional mapping from aerial photographs. Several sets of satellite images and DEMs were employed to map the landform record of three reference areas, located in northwestern Scotland, northeastern Finland and western Sweden. The employed satellite imagery consisted of Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Satellite Pour l’Observation de la Terre (SPOT) 5 and Indian Remote Sensing (IRS)1C, and the DEMs used were from NEXTMap Britain, Panorama, National elevation data set of Sweden and National Land Survey of Finland. ASTER images yielded better results than the panchromatic band of Landsat 7 ETM+ in all three regions, despite the same spatial resolution of the data. In agreement with previous studies, this study shows that DEMs display accumulation features such as eskers suitably well. Satellite images are shown to be insufficiently detailed for the interpretation of smaller features such as meltwater channels. Hence, satellite imagery and DEMs of intermediate resolution contain meltwater system information only at a general level that allows for the identification of landforms of medium to large sizes. It is therefore pertinent that data with an appropriate spatial and spectral resolution are accessed to fulfil the need of a particular mapping effort. Stereointerpretation of aerial photographs continues to be an advisable method for local meltwater system reconstructions; alternatively, it can be replaced by mapping fromhigh-resolution DEMs such as NEXTMap Britain. For regional to sub-continental reconstructions, the use of ASTER satellite imagery is recommended, because it provides both spectral and spatial resolutions suitable for the identification of meltwater features on a medium to large scale.
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| 41. |
- McCarthy, Jenny, et al.
(författare)
-
Ecoregion classification in the Okavango Delta, Botswana from multitemporal remote sensing
- 2005
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 26:19, s. 4339-4357
-
Tidskriftsartikel (refereegranskat)abstract
- The Okavango inland Delta in Botswana is characterized by a high spatial and temporal variation in vegetation patches and flooding. Predicting the effects of escalating development projects in this pristine wildlife area is hampered by a lack of accurate maps. Efforts using traditional statistical methods have been futile. The processes forming this highly dynamic environment, however, give rise to a well-documented consistency in the land cover pattern at scales ranging from single island architecture to an overall gradient in wetland, flood plain and island occurrence. We conducted a classification in a two-step process starting with statistical methods, and then refining using indices and flooding data. The indices and flooding data were created and selected to make possible the inferring of knowledge about the patterns at different scales through declarative IF ... THEN ... statements. The initial statistical classification achieved a best result of 46% accuracy for 10 classes, whereas the rule-based classification achieved an accuracy of 63%. Application of the derived classification for mapping islands and topography shows a surprisingly high accuracy.
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| 42. |
- Morozov, Evgeny, et al.
(författare)
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A spaceborne assessment of cyclone impacts on Barents Sea surface temperature and chlorophyll
- 2015
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 36:7, s. 1921-1941
-
Tidskriftsartikel (refereegranskat)abstract
- A pilot satellite-based investigation of modulations exerted upon mixed-layer phytoplankton fields by cyclones was performed for the first time across a selected part of the Arctic Ocean, the Barents Sea (BS). Resorting to a synergistic approach, cyclones were first identified from NCEP/NC.R data for the summer period during 2003-2013, and their propagation throughout the BS was further surveyed. The above-water wind force was retrieved from QuikSCAT data. These data were further accompanied by ocean colour data from SeaWiFS and MODIS to examine the spatial and temporal distributions of surficial phytoplankton chlorophyll concentration (chl) dynamics along the trajectory of the cyclone's footprint across the sea. Sea surface temperature was retrieved from MODIS data. The specific trajectory of cyclone passage across the BS area, depression depth, and wind speed proved to be conjointly the main factors determining the sign, amplitude, and duration of modulations of phytoplankton chl. The spaceborne data obtained over more than a decade indicate that, on balance, the cyclone passage led to increase in chl within the cyclone footprint area. On average, this increase did not exceed 1-2 mu g l(-1), which is nevertheless appreciable given that the mean chl within the cyclone footprint rarely exceeded 1 mu g l(-1). However, chl enhancement within the footprint area lasted only within the range of a few days to a fortnight, with the footprint area generally accounting for about 14% of the BS area. During the vegetation season (April-August, rarely till mid-September), the number of cyclones prone to optical and infrared remote sensing was about 2-3. In light of the above, arguably the cyclones studied are hardly capable of boosting annual primary productivity in the BS. Moreover, it can be conjectured that the same conclusion can be drawn with respect to the pelagic Arctic tracts that are generally less productive and more extensively cloud-covered than the BS. However, this supposition requires further studies in order to advance our understanding of the actual role of cyclones in modulation of Arctic Ocean productivity and ecosystem functioning.
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| 43. |
- Mård Karlsson, Johanna, 1979-, et al.
(författare)
-
Quality analysis of SRTM and HYDRO1K : a case study of flood inundation in Mozambique
- 2011
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:1, s. 267-285
-
Tidskriftsartikel (refereegranskat)abstract
- Many countries still lack national digital elevation models (DEMs) and have to rely on global datasets, which can negatively influence the reliability of flood model results. Mozambique is considered the most risk prone country for floods in Southern Africa. In this study a quality and accuracy assessment of two global DEMs (Shuttle Radar Topography Mission (SRTM) and HYDRO1K) is presented for a simple static flood inundation model of lower Limpopo Basin. This is accomplished with a local fit and vertical accuracy assessment of global datasets on a local scale as well as simulations of flood extent in the floodplain carried out by filling the DEMs with water according to the 2000 flood event. The results from the vertical accuracy assessment show that global DEMs can be used on a local scale. However, flood simulations performed on original DEMs contain inadequacies and are misleading with both under-and overestimation of the flooded area, while simulation performed on locally fitted DEMs shows a better agreement with the actual event. This study clearly shows that DEMs with questionable accuracy and resolution should be used with great caution in flood inundation modelling because they could result in deceptive model predictions, and lead to devastating after-effects in risk prone areas.
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| 44. |
- Nilsson, Mats, et al.
(författare)
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Estimating annual cuttings using multi-temporal satellite data and field data from the Swedish NFI
- 2009
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 30, s. 5109-5116
-
Tidskriftsartikel (refereegranskat)abstract
- Many countries have ongoing national forest inventories (NFIs) that provide reliable information on current forest conditions and changes in the forest landscape. These inventories are often based on data collected using field inventory procedures and the results are presented in terms of forest statistics for different geographical areas. The Swedish NFI has decided to combine their field data with optical satellite data by using post-stratification to obtain improved and unbiased estimates of forest variables. The method has been shown to reduce the sampling error (standard error) by 10-35% for variables such as stem volume and forest area. The objective of this study is to investigate the effect on sampling error for the estimated annual clear-felled area when the NFI plots are post-stratified by cuttings mapped from multi-temporal satellite images. Clear-felled areas mapped by the Swedish Forest Agency using image pairs (SPOT and Landsat) from the years 2001/2002, 2002/2003, 2003/2004, and 2004/2005 were used to post-stratify the NFI plots. The study area covers approximately a 1.3 Mha forest land area in Coastal Vasterbotten. It was found that the sampling error (standard error) for the annually clear-felled area was reduced by 31% using post-stratification compared to use of field data alone.
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| 45. |
- Niu, Xin, et al.
(författare)
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Multi-temporal RADARSAT-2 polarimetric SAR data for urban land-cover classification using an object-based support vector machine and a rule-based approach
- 2013
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 34:1, s. 1-26
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated multi-temporal polarimetric synthetic aperture radar (SAR) data for urban land-cover classification using an object-based support vector machine (SVM) in combinations of rules. Six-date RADARSAT-2 high-resolution polarimetric SAR data in both ascending and descending passes were acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008. The major land-use/land-cover classes include high-density residential areas, low-density residential areas, industrial and commercial areas, construction sites, parks, golf courses, forests, pasture, water, and two types of agricultural crops. Various polarimetric SAR parameters were evaluated for urban land-cover mapping and they include the parameters from Pauli, Freeman and Cloude-Pottier decompositions, the coherency matrix, intensities of each polarization, and their logarithm forms. The multi-temporal SAR polarimetric features were classified first using an SVM classifier. Then specific rules were developed to improve the SVM classification results by extracting major roads and streets using shape features and contextual information. For the comparison of the polarimetric SAR parameters, the best classification performance was achieved using the compressed logarithmic filtered Pauli parameters. For the evaluation of the multi-temporal SAR data set, the best classification result was achieved using all six-date data (kappa = 0.91), while very good classification results (kappa = 0.86) were achieved using only three-date polarimetric SAR data. The results indicate that the combination of both the ascending and the descending polarimetric SAR data with an appropriate temporal span is suitable for urban land-cover mapping.
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| 46. |
- Niu, Xin, et al.
(författare)
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RADARSAT-2 fine-beam polarimetric and ultra-fine-beam SAR data for urban mapping : comparison and synergy
- 2016
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 37:12, s. 2810-2830
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this article is to investigate the capabilities of multitemporal RADARSAT-2 fine-beam polarimetric synthetic aperture radar (SAR) data and RADARSAT-2 ultra-fine-beam C-band single-polarization HH SAR (C-HH SAR) data for detailed urban land-cover mapping using a contextual approach. With an adaptive Markov random field and a spatially variant finite mixture model, contextual information was effectively explored to improve the mapping accuracy. A texture enhancement in FMM was further proposed to improve the classification accuracy. Moreover, a rule-based approach exploring object features and spatial relationships was employed to extract road, street, and park. Three-date RADARSAT-2 fine-beam polarimetric SAR (PolSAR) and three-date RADARSAT-2 ultra-fine-beam C-HH SAR data over the Greater Toronto area were used for the evaluation. For 10 major classes, the overall accuracy (OA) is 51% for C-HH SAR data and 79% for PolSAR data. Compared with C-HH SAR, PolSAR data produced better results for identifying various urban patterns. Although with multi-date, the C-HH SAR data showed low capability to distinguish high-density residential area and industry commercial area (Ind.). Considerable low-density residential area (LD) was misclassified as forest. Identification of the construction site (Cons.) and golf course were poor. Nevertheless, the efficiency of the multitemporal C-HH SAR textures for distinguishing the built-up areas was observed. By texture enhancement with the synergy of the PolSAR and C-HH SAR data, the mapping results could be significantly improved, especially for LD, forest, and crops. The OA is improved by 2.7% for PolSAR data, and 11.1% for C-HH SAR data. Road, street, and park could be extracted by the rule-based approach with OA about 77% for 13 classes.
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| 47. |
- Olsson, Håkan
(författare)
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A method for using Landsat time series for monitoring young plantations in boreal forests
- 2009
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 30, s. 5117-5131
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Tidskriftsartikel (refereegranskat)abstract
- A time series of Landsat Enhanced Thematic Mapper Plus (ETM+) imagery was used to investigate its potential contribution to characterization of young forest plantations in northern Sweden (latitude 65 degrees N, longitude 16 degrees E). The time series image data were first bandwise relatively normalized, using image statistics from forest areas. It was shown that the difference in reflectance development between different types of forest plantations could be characterized by fitting a linear regression model through the bandwise spectral mean values for each stand, starting 5 years after the final felling. The coefficients of this regression model can be used to improve statistically based characterizations of young forest, compared to using data from the most recent image only. This result is useful for screening stands that might be in need of precommercial thinning (PCT), as well as for improving forecasts of expected forest development for whole forest-dominated landscapes consisting of several estates.
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| 48. |
- Olsson, Lennart, et al.
(författare)
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Fourier series for analysis of temporal sequences of satellite sensor imagery
- 1994
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 15:18, s. 3735-3741
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Tidskriftsartikel (refereegranskat)abstract
- Fourier Series and the derivative were used in this study for analysing time series of remotely-sensed data. The technique allows fundamental characteristics of time series data to be quantified. In Fourier analysis a function in space or time is broken down into sinusoidal components, or harmonics. The first and second harmonics are a function of the mono or bi-modality of the curve, demonstrated in the study on Global Vegetation Index data classified into typical mono and bi-modal vegetation index zones. The last harmonic explains close to 100 per cent of the variance in the curve. Other important parameters of the time series, such as extreme points and rate of change, can be extracted from the derivative of the Fourier Series. Fourier Series may form a basis for a quantitative approach to the problem of handling temporal sequences of remotely-sensed data.
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| 49. |
- Ouedraogo, Issa, et al.
(författare)
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Systematic and random transitions of land-cover types in Burkina Faso, West Africa
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32, s. 5229-5245
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Tidskriftsartikel (refereegranskat)abstract
- In-depth statistical analysis of forest transition between land-cover types over time can reveal the dominant signals of landscape transformation, which are needed in order to develop appropriate land management strategies. We applied a recently developed methodology to analyse the transition matrix of six land-cover classes, derived from 1986 and 2002 Landsat images of an area of 15 675 km(2) in southern Burkina Faso. Results show that most landscape transformations followed a systematic process. In addition, some transitions occurred as an apparently random process, probably caused by uncommon or sporadic events. Degradation of woodland to shrub-/grassland over 15.7% of the landscape, increases in biomass from woodland to dense forest on 10% of the landscape and conversion of 6% of the landscape from shrub-/grassland to cropland were the dominant signals of forest-cover transitions. From a planning perspective, the dominance of systematic processes should facilitate regional land-use planning and sustainable forest management in a context of immigration and agricultural intensification.
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| 50. |
- Patil, S. D., et al.
(författare)
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On the variation of the tropospheric ozone over Indian region in relation to the meteorological parameters
- 2009
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 30:11, s. 2813-2826
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Tidskriftsartikel (refereegranskat)abstract
- Using monthly mean satellite measurements of TOMS/SBUV tropospheric ozone residual (TOR) data and meteorological parameters (tropopause height (TPH), 200hPa geopotential height (GPH) and outgoing longwave radiation (OLR)) during 1979-2001, seasonal variability of TOR data and their association with meteorological parameters are outlined over the Indian region. Prominent higher values of TOR (44-48DU, which is higher than the globally averaged 31.5DU) are observed over the northern parts of the country during the summer monsoon season (June-September). Similar to the TOR variation, meteorological parameters (tropopause height, 200hPa geopotential height and outgoing longwave radiation) also show higher values during the summer monsoon season, suggesting an in phase relationship and strong association between them because of deep convection present during summer monsoon time. The monthly trends in TOR values are found to be positive over the region. TOR has significant positive correlations (5% level) with GPH, and negative correlations with OLR and TPH for the month of September. The oxidation chains initiated by CH4 and CO show the enhanced photochemical production of ozone that would certainly become hazardous to the ecological system. Interestingly, greenhouse gases (GHG) emissions were found to have continuously increased over the Indian region during the period 1990-2000, indicating more anthropogenic production of ozone precursor gases causing higher level of tropospheric ozone during this period.
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