| 1. |
- Soja-Woźniak, Monika, et al.
(författare)
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A Novel Statistical Approach for Ocean Colour Estimation of Inherent Optical Properties and Cyanobacteria Abundance in Optically Complex Waters
- 2017
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Eutrophication is an increasing problem in coastal waters of the Baltic Sea. Moreover, algal blooms, which occur every summer in the Gulf of Gdansk can deleteriously impact human health, the aquatic environment, and economically important fisheries, tourism, and recreation industries. Traditional laboratory-based techniques for water monitoring are expensive and time consuming, which usually results in limited numbers of observations and discontinuity in space and time. The use of hyperspectral radiometers for coastal water observation provides the potential for more detailed remote optical monitoring. A statistical approach to develop local models for the estimation of optically significant components from in situ measured hyperspectral remote sensing reflectance in case 2 waters is presented in this study. The models, which are based on empirical orthogonal function (EOF) analysis and stepwise multilinear regression, allow for the estimation of parameters strongly correlated with phytoplankton (pigment concentration, absorption coefficient) and coloured detrital matter abundance (absorption coefficient) directly from reflectance spectra measured in situ. Chlorophyll a concentration, which is commonly used as a proxy for phytoplankton biomass, was retrieved with low error (median percent difference, MPD = 17%, root mean square error RMSE = 0.14 in log(10) space) and showed a high correlation with chlorophyll a measured in situ (R = 0.84). Furthermore, phycocyanin and phycoerythrin, both characteristic pigments for cyanobacteria species, were also retrieved reliably from reflectance with MPD = 23%, RMSE = 0.23, R-2 = 0.77 and MPD = 24%, RMSE = 0.15, R-2 = 0.74, respectively. The EOF technique proved to be accurate in the derivation of the absorption spectra of phytoplankton and coloured detrital matter (CDM), with R-2 (lambda) above 0.83 and RMSE around 0.10. The approach was also applied to satellite multispectral remote sensing reflectance data, thus allowing for improved temporal and spatial resolution compared with the in situ measurements. The EOF method tested on simulated Medium Resolution Imaging Spectrometer (MERIS) or Ocean and Land Colour Instrument (OLCI) data resulted in RMSE = 0.16 for chl-a and RMSE = 0.29 for phycocyanin. The presented methods, applied to both in situ and satellite data, provide a powerful tool for coastal monitoring and management.
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| 2. |
- Askne, Jan, 1936, et al.
(författare)
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Biomass estimation in a boreal forest from TanDEM-X data, lidar DTM, and the interferometric water cloud model
- 2017
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 196, s. 265-278
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Tidskriftsartikel (refereegranskat)abstract
- The semi-empirical Interferometric Water Cloud Model, IWCM, is used to estimate above ground forest biomass, AGB, in northern Sweden, Krycklan (64 degrees N 20 degrees E). The results are based on separate analysis of 14 TanDEM-X ac-quisitions from 2011 to 2014 and a Lidar digital terrain model (DTM). 29 stands covering 272 ha and with AGB 1 ha covering 3166 ha and with AGB
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| 3. |
- Askne, Jan, 1936, et al.
(författare)
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Model-Based Biomass Estimation of a Hemi-Boreal Forest from Multitemporal TanDEM-X Acquisitions
- 2013
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:11, s. 5574-5597
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Tidskriftsartikel (refereegranskat)abstract
- Above-ground forest biomass is a significant variable in the terrestrial carbon budget, but is still estimated with relatively large uncertainty. Remote sensing methods can improve the characterization of the spatial distribution and estimation accuracy of biomass; in this respect, it is important to examine the potential offered by new sensors. To assess the contribution of the TanDEM-X mission, eighteen interferometric Synthetic Aperture Radar (SAR) image pairs acquired over the hemi-boreal test site of Remningstorp in Sweden were investigated. Three models were used for interpretation of TanDEM-X signatures and above-ground biomass retrieval: Interferometric Water Cloud Model (IWCM), Random Volume over Ground (RVoG) model, and a simple model based on penetration depth (PD). All use an allometric expression to relate above-ground biomass to forest height measured by TanDEM-X. The retrieval was assessed on 201 forest stands with a minimum size of 1 ha, and ranging from 6 to 267 Mg/ha (mean biomass of 105 Mg/ha) equally divided into a model training dataset and a validation test dataset. Biomass retrieved using the IWCM resulted in a Root Mean Square Error (RMSE) between 17% and 33%, depending on acquisition date and image acquisition geometry (angle of incidence, interferometric baseline, and orbit type). The RMSE in the case of the RVoG and the PD models were slightly higher. A multitemporal estimate of the above-ground biomass using all eighteen acquisitions resulted in an RMSE of 16% with R-2 = 0.93. These results prove the capability of TanDEM-X interferometric data to estimate forest aboveground biomass in the boreal zone.
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| 4. |
- Banda, Francesco, et al.
(författare)
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The BIOMASS level 2 prototype processor: Design and experimental results of above-ground biomass estimation
- 2020
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- BIOMASS is ESA's seventh Earth Explorer mission, scheduled for launch in 2022. The satellite will be the first P-band SAR sensor in space and will be operated in fully polarimetric interferometric and tomographic modes. The mission aim is to map forest above-ground biomass (AGB), forest height (FH) and severe forest disturbance (FD) globally with a particular focus on tropical forests. This paper presents the algorithms developed to estimate these biophysical parameters from the BIOMASS level 1 SAR measurements and their implementation in the BIOMASS level 2 prototype processor with a focus on the AGB product. The AGB product retrieval uses a physically-based inversion model, using ground-canceled level 1 data as input. The FH product retrieval applies a classical PolInSAR inversion, based on the Random Volume over Ground Model (RVOG). The FD product will provide an indication of where significant changes occurred within the forest, based on the statistical properties of SAR data. We test the AGB retrieval using modified airborne P-Band data from the AfriSAR and TropiSAR campaigns together with reference data from LiDAR-based AGB maps and plot-based ground measurements. For AGB estimation based on data from a single heading, comparison with reference data yields relative Root Mean Square Difference (RMSD) values mostly between 20% and 30%. Combining different headings in the estimation process significantly improves the AGB retrieval to slightly less than 20%. The experimental results indicate that the implemented retrieval scheme provides robust results that are within mission requirements.
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| 5. |
- Blomberg, Erik, 1987, et al.
(författare)
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A polarimetric model of topographic effects on P-band forest backscatter
- 2015
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Ingår i: Proceedings of PolInSAR 2015.
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Konferensbidrag (refereegranskat)abstract
- P-band backscatter from boreal forest is simulated using a fully polarimetric Cylinder-Over-Ground model. Trees are represented by tapered stacks of cylinders placed over lossy dielectric planar ground that is individually fitted to the topography. The results show a strong topographic dependence and also demonstrate the limitations of the odd-, even, and volume-scattering interpretation of the Pauli decomposition. BioSAR 3 SAR images, in-situ data and LiDAR-derived DCM and DTM enable a comparison with real forest backscatter through simulation of complete plots. While many features are reproduced the need for an expansion of the model to include ground and branch scattering is identified. If sufficient agreement is achieved the model will be used to further improve topographic corrections for the retrieval of above ground forest biomass from P-band SAR images.
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| 6. |
- Blomberg, Erik, 1987, et al.
(författare)
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Evaluating spaceborne L-band pol tomo SAR for forest biomass retrieval based on airborne SAR data
- 2018
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Ingår i: Proceedings of the European Conference on Synthetic Aperture Radar, EUSAR. - 2197-4403. ; 2018-June, s. 1405-1407
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Konferensbidrag (refereegranskat)abstract
- This paper presents an evaluation of L-band tomographic synthetic-aperture radar (TomoSAR) data for forest biomass retrievals. Tomograms are processed from multiple synthetic-aperture radar (SAR) data sets from the Krycklan forest site, located in the north and south of Sweden. Tomographic performance is matched to possible future spaceborne SAR configurations such as SAOCOM-CS. Ivol, the integrated volumetric backscatter between 10 m and 30 m, is found to result in improved biomass retrievals compared to those based on slope corrected SAR intensity γ0from the original airborne E-SAR system.
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| 7. |
- Blomberg, Erik, 1987, et al.
(författare)
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Forest Biomass Retrieval from BioSAR 2010 P-band SAR Data using a Regression-Based Model
- 2015
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Ingår i: IEEE International Geoscience and Remote Sensing Symposium. - 2153-6996. - 9781479979295 ; , s. 4193-4195
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Konferensbidrag (refereegranskat)abstract
- A model for retrieval of boreal forest biomass from polarimetric P-band SAR images developed using the BioSAR 2007 and BioSAR 2008 data sets is revisited and evaluated using data from BioSAR 2010. Incorporating the HV backscatter component as well as the HH/VV ratio and the ground slope, the model is noteworthy as performing well when retrieving biomass values in Remningstorp using parameters trained in Krycklan. These two Swedish test sites are separated by 720 km and represent two different types of boreal forest as well varying topography. SAR images and biomass estimates obtained from Remningstorp in 2010 provides an opportunity to test the model further. This dataset results in a qualitative reproduction of the previous result, showing the expected changes due to forest management, but with a relative overestimation of biomass. A large part of this can be explained by the timing as the new acquisitions took place during early autumn instead of spring with the associated changes in moisture conditions.
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| 8. |
- Blomberg, Erik, 1987, et al.
(författare)
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Forest Biomass Retrieval from L-Band SAR Using Tomographic Ground Backscatter Removal
- 2018
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1558-0571 .- 1545-598X. ; 15:7, s. 1030-1034
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Tidskriftsartikel (refereegranskat)abstract
- A tomographic synthetic aperture radar (TomoSAR) represents a possible route to improved retrievals of forest parameters. Simulated orbital L-band TomoSAR data corresponding to the proposed Satellites for Observation and Communications-Companion Satellite (SAOCOM-CS) mission (1.275 GHz) are evaluated for retrieval of above-ground biomass in boreal forest. L-band data and biomass measurements, collected at the Krycklan test site in northern Sweden as part of the BioSAR 2008 campaign, are used to compare biomass retrievals from SAOCOM-CS to those based on SAOCOM SAR data. Both data sets are in turn compared with the corresponding airborne case, as represented by experimental airborne SAR through processing of the original SAR data. TomoSAR retrievals use a model involving a logarithmic transform of the volumetric backscatter intensity, Ivol, defined as the total backscatter originating between 10 and 30 m above ground. SAR retrievals are obtained with slope-compensated intensity γ0using the same model. It is concluded that tomography using SAOCOM-CS represents an improvement over an airborne SAR imagery, resulting in biomass retrievals from a single polarization (HH) having a 26%-30% root-mean-square error with a little to no impact from the look direction or the local topography.
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| 9. |
- Blomberg, Erik, 1987, et al.
(författare)
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P-band Polarimetric Model of Vertical Tree Stems on Sloping Ground
- 2014
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Ingår i: Joint 2014 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2014 and the 35th Canadian Symposium on Remote Sensing, CSRS 2014; Quebec Convention CentreQuebec City; Canada; 13 July 2014 through 18 July 2014. - 9781479957750 ; , s. 80-83
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Konferensbidrag (refereegranskat)abstract
- A fully polarimetric model is implemented to simulate backscatter from boreal forest. The aim is to correct for topography on a sub-stand level during the recovery of forest properties from P-band SAR data, specifically directed at the upcoming BIOMASS mission. The model incorporates the direct, double-bounce and triple-bounce scattering from tree stems on a sloping ground. Topography is introduced by assigning an independent and arbitrarily oriented local ground plane to each tree. Simulated SAR images are produced from in-situ measurements and a high resolution digital topography model (DTM) based on LiDAR data. These were obtained during BioSAR 2010 together with the corresponding SAR images, which are used for validation.
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| 10. |
- Blomberg, Erik, 1987, et al.
(författare)
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Simulated biomass retrieval from the spaceborne tomographic Saocom-CS mission at L-band
- 2016
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292213053 ; 740
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Konferensbidrag (refereegranskat)abstract
- This paper presents an evaluation of above-ground biomass (ABG) retrieval in boreal forests using simulated tomographic synthetic-aperture radar (SAR) data corresponding to the future SAOCOM-CS (L-band 1.275 GHz) mission. Using forest and radar data from the BioSAR 2008 campaign at the Krycklan test site in northern Sweden the expected performance of SAOCOM-CS is evaluated and compared with the E-SAR airborne Lband SAR (1.300 GHz). It is found that SAOCOM-CS data produce retrievals on par with those obtained with E-SAR, with retrievals having a relative RMSE of 30% or less. This holds true even if the acquisitions are limited to a single polarization, with HH results shown as an example.
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