| 1. |
- Vu, Viet Thuy, et al.
(författare)
-
RFI Suppression in Ultrawideband SAR Using an Adaptive Line Enhancer
- 2010
-
Ingår i: IEEE Geoscience and Remote Sensing Letters. - : IEEE. - 1545-598X .- 1558-0571. ; 7:4, s. 694-698
-
Tidskriftsartikel (refereegranskat)abstract
- In this letter, we propose an approach to suppress radio-frequency interference (RFI) in ultrawideband (UWB) low-frequency synthetic aperture radar (SAR). According to the proposal, RFI is suppressed by using an adaptive line enhancer controlled by the normalized least mean square algorithm. The approach is tested successfully on real UWB low-frequency SAR data. In order to keep the computational burden down, possible ways to integrate the RFI suppression approach into SAR imaging algorithms are also suggested.
|
|
| 2. |
- Ankel, Martin, 1996, et al.
(författare)
-
Bistatic noise radar: Demonstration of correlation noise suppression
- 2023
-
Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8792 .- 1751-8784. ; 17:3, s. 351-361
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudo-random noise, generated digitally at the receiver and transmitter units. Correlation losses, due to non-linearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.
|
|
| 3. |
- Ankel, Martin, 1996, et al.
(författare)
-
Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
-
Ingår i: 20th European Radar Conference, EuRAD 2023. ; , s. 213-216
-
Konferensbidrag (refereegranskat)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
|
|
| 4. |
- Ankel, Martin, 1996, et al.
(författare)
-
Implementation of a coherent real‐time noise radar system
- 2023
-
Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792.
-
Tidskriftsartikel (refereegranskat)abstract
- The utilisation of continuous random waveforms for radar, that is, noise radar, has been extensively studied as a candidate for low probability of intercept operation. However, compared with the more traditional pulse-Doppler radar, noise radar systems are significantly more complicated to implement, which is likely why few systems exist. If noise radar systems are to see the light of day, system design, implementation, limitations etc., must be investigated. Therefore, the authors examine and detail the implementation of a real-time noise radar system on a field programmable gate array. The system is capable of operating with 100% duty cycle, 200 MHz bandwidth, and 268 ms integration time while processing a range of about 8.5 km. Additionally, the system can perform real-time moving target compensation to reduce cell migration. System performance is primarily limited by the memory bandwidth of the off-chip dynamic random access memory.
|
|
| 5. |
- Askne, Jan, 1936, et al.
(författare)
-
Biomass estimation in a boreal forest from TanDEM-X data, lidar DTM, and the interferometric water cloud model
- 2017
-
Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 196, s. 265-278
-
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
|
|
| 6. |
- Askne, Jan, 1936, et al.
(författare)
-
Biomass growth from multi-temporal TanDEM-X interferometric synthetic aperture radar observations of a boreal forest site
- 2018
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 10:4
-
Tidskriftsartikel (refereegranskat)abstract
- Forest growth estimation is important in forest research and forest management, but complex to analyze in diverse forest stands. Twelve summertime TanDEM-X acquisitions from the boreal test site, Krycklan, in Sweden, with a known digital terrain model, DTM, have been used to study phase height and aboveground biomass change over 3.2 years based on the Interferometric Water Cloud Model, IWCM. The maximum phase height rate was determined to 0.29 m/yr, while the mean phase height rate was 0.16 m/yr. The corresponding maximum growth rate of the aboveground dry biomass, AGB, was 4.0 Mg/ha/yr with a mean rate of 1.9 Mg/ha/yr for 27 stands, varying from 23 to 183 Mg/ha. The highest relative AGB growth was found for young stands and high growth rates up to an age of 150 years. Growth rate differences relative a simplified model assuming AGB to be proportional to the phase height were studied, and the possibility to avoid a DTM was discussed. Effects of tree species, thinning, and clear cutting were evaluated. Verifications using in situ data from 2008 and a different in situ dataset combined with airborne laser scanning data from 2015 have been discussed. It was concluded that the use of multi-temporal TanDEM-X interferometric synthetic aperture radar observations with AGB estimates of each individual observation can be an important method to derive growth rates in boreal forests.
|
|
| 7. |
- Askne, Jan, 1936, et al.
(författare)
-
Boreal Forest Properties from TanDEM-X Data Using Interferometric Water Cloud Model and Implications for a Bistatic C-Band Mission
- 2021
-
Ingår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. - 2151-1535 .- 1939-1404. ; 14, s. 8627-8637
-
Tidskriftsartikel (refereegranskat)abstract
- Data from TanDEM-X in single-pass and bistatic interferometric mode together with the interferometric water cloud model (IWCM) can provide estimates of forest height and stem volume (or the related above-ground biomass) of boreal forests with high accuracy. We summarize results from two boreal test sites using two approaches, i.e., 1) based on model calibration using reference insitu stands, and 2) based on minimization of a cost function. Both approaches are based on inversion of IWCM, which models the complex coherence and backscattering coefficient of a homogeneous forest layer, which includes gaps where free-space wave propagation is assumed. A digital terrain model of the ground is also needed. IWCM is used to estimate forest height or stem volume, since the two variables are assumed to be related through an allometric equation. A relationship between the fractional area of gaps, the area-fill, and stem volume is also required to enable model inversion. The accuracy of the stem volume estimate in the two sites varies between 16% and 21% for height of ambiguity <100 m. The results clearly show the importance of using summer-time acquisitions. Based on the TanDEM-X results at X-band, C-band data from the ERS-1/ERS-2 tandem mission are revisited to investigate the potential of a future bistatic C-band interferometric mission. Out of nine ERS-1/ERS-2 pairs, only one pair was found to be acquired at summer temperatures, without precipitation and with high coherence. A simulated bistatic phase height is shown to give approximately the same sensitivity to stem volume as TanDEM-X.
|
|
| 8. |
- Askne, Jan, 1936, et al.
(författare)
-
Model-Based Biomass Estimation of a Hemi-Boreal Forest from Multitemporal TanDEM-X Acquisitions
- 2013
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:11, s. 5574-5597
-
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.
|
|
| 9. |
- Askne, Jan, 1936, et al.
(författare)
-
On the Sensitivity of TanDEM-X-Observations to Boreal Forest Structure
- 2019
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 11:14
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of forests is important to observe for understanding coupling to global dynamics of ecosystems, biodiversity, and management aspects. In this paper, the sensitivity of X-band to boreal forest stem volume and to vertical and horizontal structure in the form of forest height and horizontal vegetation density is studied using TanDEM-X satellite observations from two study sites in Sweden: Remningstorp and Krycklan. The forest was analyzed with the Interferometric Water Cloud Model (IWCM), without the use of local data for model training, and compared with measurements by Airborne Lidar Scanning (ALS). On one hand, a large number of stands were studied, and in addition, plots with different types of changes between 2010 and 2014 were also studied. It is shown that the TanDEM-X phase height is, under certain conditions, equal to the product of the ALS quantities for height and density. Therefore, the sensitivity of phase height to relative changes in height and density is the same. For stands with a phase height >5 m we obtained an root-mean-square error, RMSE, of 8% and 10% for tree height in Remningstorp and Krycklan, respectively, and for vegetation density an RMSE of 13% for both. Furthermore, we obtained an RMSE of 17% for estimation of above ground biomass at stand level in Remningstorp and in Krycklan. The forest changes estimated with TanDEM-X/IWCM and ALS are small for all plots except clear cuts but show similar trends. Plots without forest management changes show a mean estimated height growth of 2.7% with TanDEM-X/IWCM versus 2.1% with ALS and a biomass growth of 4.3% versus 4.2% per year. The agreement between the estimates from TanDEM-X/IWCM and ALS is in general good, except for stands with low phase height.
|
|
| 10. |
|
|
| 11. |
- Banda, Francesco, et al.
(författare)
-
BIOMASS L2 Prototype Processor : Current Status
- 2019
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 9781538691540 ; , s. 5996-5999
-
Konferensbidrag (refereegranskat)abstract
- The ESA BIOMASS mission will be the 7th Earth Explorer measuring the above-ground biomass (AGB) in the world's forests. The current ESA Level-2 (L2) implementation study focuses on defining and implementing the main algorithms for forest parameter retrieval from BIOMASS data. After the first year of L2 study innovative results were achieved: the development of ground cancellation, in particular, has proved to be huge value, since it removes from the data the effects of environmental variability and contributions unrelated to the forest carried in the ground scattering. In this paper the current processor implementation and validation activities of the L2 team will be described.
|
|
| 12. |
- Banda, Francesco, et al.
(författare)
-
The BIOMASS level 2 prototype processor: Design and experimental results of above-ground biomass estimation
- 2020
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:6
-
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.
|
|
| 13. |
|
|
| 14. |
- Bennet, Patrik, 1995, et al.
(författare)
-
Diurnal Cycles of L-Band Tomographic SAR Backscatter in a Boreal Forest During Summer: Observations by the Borealscat Tower Radar
- 2023
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; 2023-July, s. 2195-2198
-
Konferensbidrag (refereegranskat)abstract
- The BorealScat tower radar experiment, in Remningstorp, Sweden, acquired tomographic L-band backscatter time series over a boreal forest stand consisting of Norway spruce (Picea abies). Data from summer 2018 is analysed in this study, where diurnal cycles with variations up to more than 1 dB are identified for HH and VV polarizations. The HH cycle has its minimum at night, its maximum at noon and mainly occurs in the middle layers of the forest. Conversely, the VV cycle has its maximum at night, its minimum at noon and is most apparent in the upper and lower forest layers, especially during June and July. The cycles are compared with vapour-pressure deficit (VPD), an indicator of favourable transpiration conditions, and they are seen to co-vary closely. The VV cycle compares well to that seen for P-band in a previous study and is speculated to originate from stem water content variations. The HH cycle cannot be directly connected to stem water content, but is indicated to follow a currently unknown transpiration related phenomena.
|
|
| 15. |
- Blomberg, Erik, 1987, et al.
(författare)
-
A polarimetric model of topographic effects on P-band forest backscatter
- 2015
-
Ingår i: Proceedings of PolInSAR 2015.
-
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.
|
|
| 16. |
- Blomberg, Erik, 1987, et al.
(författare)
-
Evaluating P-Band TomoSAR for Biomass Retrieval in Boreal Forest
- 2021
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 59:5, s. 3793-3804
-
Tidskriftsartikel (refereegranskat)abstract
- P-band synthetic aperture radar (SAR) is sensitive to above-ground biomass (AGB) but retrieval accuracy has been shown to deteriorate in topographic areas. In boreal forest, the signal penetrates through the canopy to interact with the ground producing variations in backscatter depending on ground topography, forest structure, and soil moisture. Tomographic processing of multiple SAR images Tomographic SAR (TomoSAR) provides information about the vertical backscatter distribution. This article evaluates the use of P-band TomoSAR data to improve AGB retrievals from backscattered intensity by suppressing the backscattered signal from the ground. This approach can be used even when the tomographic resolution is insufficient to resolve the vertical backscatter profile. The analysis is based on P-band data from two campaigns: BioSAR-1 (2007) in Remingstorp, southern Sweden, and BioSAR-2 (2008) in Krycklan (KR), northern Sweden. BioSAR airborne data were also processed to correspond as closely as possible to future BIOMASS TomoSAR acquisitions, with BioSAR-2-based results shown. A power law AGB model using volumetric HV polarized backscatter performs best in KR, with training residual root mean-squared error (RMSE) of 30%-36% (27-33 t/ha) for airborne data and 38%-39% for simulated BIOMASS data. Airborne TomoSAR data suggest that both vertical and horizontal tomographic resolution are of importance and that it is possible to greatly reduce AGB retrieval bias when compared with airborne P-band SAR backscatter intensity-based retrievals. A lack of significant ground slopes in Remningstorp reduces the benefit of using TomoSAR data which performs similar to retrievals based solely on P-band SAR backscatter intensity.
|
|
| 17. |
- Blomberg, Erik, 1987, et al.
(författare)
-
Evaluating spaceborne L-band pol tomo SAR for forest biomass retrieval based on airborne SAR data
- 2018
-
Ingår i: Proceedings of the European Conference on Synthetic Aperture Radar, EUSAR. - 2197-4403. ; 2018-June, s. 1405-1407
-
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.
|
|
| 18. |
- Blomberg, Erik, 1987, et al.
(författare)
-
Forest Biomass Retrieval from BioSAR 2010 P-band SAR Data using a Regression-Based Model
- 2015
-
Ingår i: IEEE International Geoscience and Remote Sensing Symposium. - 2153-6996. - 9781479979295 ; 2015-November, s. 4193-4195
-
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.
|
|
| 19. |
- Blomberg, Erik, 1987, et al.
(författare)
-
Forest Biomass Retrieval from L-Band SAR Using Tomographic Ground Backscatter Removal
- 2018
-
Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1558-0571 .- 1545-598X. ; 15:7, s. 1030-1034
-
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.
|
|
| 20. |
- Blomberg, Erik, 1987, et al.
(författare)
-
P-band Polarimetric Model of Vertical Tree Stems on Sloping Ground
- 2014
-
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
-
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.
|
|
| 21. |
- Blomberg, Erik, 1987, et al.
(författare)
-
Simulated biomass retrieval from the spaceborne tomographic Saocom-CS mission at L-band
- 2016
-
Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292213053 ; 740
-
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.
|
|
| 22. |
- Carvajal, Gisela, 1983, et al.
(författare)
-
Comparison between current fields detected with infrared radiometry and modeled currents around Sweden
- 2013
-
Ingår i: 33rd IEEE International Geoscience and Remote Sensing Symposium (IGARSS); 2013, Melbourne. - 9781479911141 ; , s. 1270-1273
-
Konferensbidrag (refereegranskat)abstract
- The understanding of the relationship between surface currents derived from weather models and remote sensing data is essential in order to produce an improved and integrated surface current information of high quality and resolution. The large availability of satellite derived infrared radiometer data at the high latitudes of the coastal waters surrounding Sweden makes the Maximum Cross Correlation (MCC) method a feasible alternative to produce real time measurements of surface currents. This work compares current retrievals from the MCC method and model data around Sweden. Our results indicate a similar magnitude for both sources of current fields in most of the locations. However, there exist small discrepancies in the localization of the larger current values. Also, the MCC retrievals generally present more features than the modeled ones. Possible reasons for these discrepancies might be the MCC detection of circulation patterns not predicted by the model, or the depreciation in the MCC performance due to the influence of diurnal variability of the sea surface temperature, wind driven mixing due to upwelling or tides.
|
|
| 23. |
- Carvajal, Gisela, 1983, et al.
(författare)
-
Correlation between Synthetic Aperture Radar Surface Winds and Deep Water Velocity in the Amundsen Sea, Antarctica
- 2013
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:8, s. 4088-4106
-
Tidskriftsartikel (refereegranskat)abstract
- The recent observed thinning of the glacier ice shelves in the Amundsen Sea (Antarctica) has been attributed to warm deep currents, possibly induced by along-coast winds in the vicinity of the glacial ice sheet. Here, high resolution maps of wind fields derived from Synthetic Aperture Radar (SAR) data have been studied and correlated with subsurface measurements of the deep water velocities in the Amundsen Sea area. Focus is on periods with low ice coverage in 2010 and 2011. In 2010, which had comparatively low ice coverage, the results indicate a more rapid response to wind forcing in the deep currents than in 2011. The SAR wind speed maps have better spatial resolution than available reanalysis data, and higher maximum correlation was obtained with SAR data than with reanalysis data despite the lower temporal resolution. The maximum correlation was R = 0.71, in a direction that is consistent with wind-driven Ekman theory. This is significantly larger than in previous studies. The larger correlation could be due to the better spatial resolution or the restriction to months with minimum ice coverage. The results indicate that SAR is a useful complement to infer the subsurface variability of the ocean circulation in remote areas in polar oceans.
|
|
| 24. |
- Carvajal, Gisela, 1983, et al.
(författare)
-
Retrieval and assessment of sub-mesoscalewind velocity vectors with Synthetic Aperture Radar
- 2011
-
Ingår i: IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011. Vancouver, 24-29 July 2011. - 9781457710056 ; , s. 2041-2044
-
Konferensbidrag (refereegranskat)abstract
- Wind vector fields are currently available from different sources at mesoscale resolutions (2 km to 200 km). The commonly provided wind resolution on 25 km imposes a limit in coastal areas and in the study of small-scale phenomena occurring in the ocean surface. Since wind is the driving force of the ocean, the study of its behavior in sub-mesoscale (
|
|
| 25. |
- Carvajal, Gisela, 1983, et al.
(författare)
-
Retrieval and Quality Assessment of Wind Velocity Vectors on the Ocean With C-Band SAR
- 2014
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - : Institute of Electrical and Electronics Engineers (IEEE). - 0196-2892 .- 1558-0644. ; 52:5, s. 2519-2537
-
Tidskriftsartikel (refereegranskat)abstract
- Wind vector fields derived from synthetic aperture radar (SAR) sensors show variations at smaller scales than most other globally available surface wind sources. However, few studies have been devoted to the investigation of the accuracy of SAR-derived wind fields at different scales and how they compare with other wind data. In order to investigate these issues, an algorithm for the retrieval of SAR-derived wind vectors has been developed, and a quality assessment between the retrievals and in situ, scatterometer, and numerical weather model (NWM) wind data has been performed. The implemented wind retrieval algorithm detects streak features in the SAR image to estimate wind directions and inverts wind speeds using CMOD-IFR2, CMOD5, or CMOD5.N geophysical model functions. In addition, a regularization method for filtering outliers in the wind direction retrievals is used. Retrievals compared with in situ data indicated better performance at offshore locations for wind speed inversions with CMOD5.N. The bias and standard deviation for offshore regularized wind directions and CMOD5.N speeds are 9 degrees and 25 degrees and -0.1 and 1.4 m/s, respectively. The comparison with the scatterometer and NWM wind data has been performed for retrievals at 5-, 10-, and 20-km resolution. The results indicate a better agreement of the coarser retrievals with the reference data. Nevertheless, mapping of smaller scale features requires wind directions from the SAR image itself.
|
|
| 26. |
- d'Alessandro, M. Mariotti, et al.
(författare)
-
Interferometric Ground Notching of SAR Images for Estimating Forest Above Ground Biomass
- 2018
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 9781538671504 ; 2018-July, s. 8797-8800
-
Konferensbidrag (refereegranskat)abstract
- The effectiveness of SAR tomography in estimating forest Above Ground Biomass (AGB) has been repeatedly demonstrated in the recent years. For tropical rain-forests, analysis from the Paracou test site reveals that the best results are achieved when the backscattered power coming from 30m above the ground is considered. As suggested in previous papers, the most likely reason is that ground scattering acts as a disturbing factor for forest biomass retrieval, as it depends on a number of parameters (like topography, moisture), that do not relate to forest biomass. In this paper we further test this hypothesis by proposing the concept of interferometric ground notching. By taking the difference between two phase calibrated, ground-steered, SAR SLC images a third image is obtained where ground scattering contributions are canceled out, hence the name ground-notched SLC. Results indicate that ground-notched data can effectively retain the features of vegetation-only scattering, including its polarimetric signature and correlation with AGB.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Empirical Relationship Between the Doppler Centroid Derived From X-Band Spaceborne InSAR Data and Wind Vectors
- 2022
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 60
-
Tidskriftsartikel (refereegranskat)abstract
- One of the challenges in ocean surface current retrieval from synthetic aperture radar (SAR) data is the estimation and removal of the wave-induced Doppler centroid (DC). This article demonstrates empirically the relationship between the dc derived from spaceborne X-band InSAR data and the ocean surface wind and waves. In this study, we analyzed over 300 TanDEM-X image pairs. It is found that the general characteristics of the estimated dc follow the theoretically expected variation with incidence angle, wind speed, and wind direction. An empirical geophysical model function (GMF) is fit to the estimated dc and compared to existing models and previous experiments. Our GMF is in good agreement (within 0.2 m/s) with other models and data sets. It is found that the wind-induced Doppler velocity contributes to the total Doppler velocity with about 15% of the radial wind speed. This is much larger than the sum of the contributions from the Bragg waves (~0.2 m/s) and the wind-induced drift current (~3% of wind speed). This indicates a significant (dominant) contribution of the long wind waves to the SAR dc. Moreover, analysis of dual-polarized data shows that the backscatter polarization ratio (PR=σ⁰VV/σ⁰HH) and the dc polarization difference (PD=|dcVV|-|dcHH|) are systematically larger than 1 and smaller than 0 Hz, respectively, and both increase in magnitude with incidence angle. The estimated PR and PD are compared to other theoretical and empirical models. The Bragg scattering theory-based (pure Bragg and composite surface) models overestimate both PR and PD, suggesting that other scattering mechanisms, e.g., wave breaking, are involved. In general, it is found that empirical models are more consistent with both backscatter and Doppler data than theory-based models. This motivates a further improvement of SAR dc GMFs.
|
|
| 30. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Joint retrieval of ocean surface wind and current vectors from satellite SAR data using a Bayesian inversion method
- 2021
-
Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 260
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method for joint retrieval of the ocean surface wind and current vectors using the backscatter and the Doppler frequency shift measured by spaceborne single-beam single-polarization synthetic aperture radar (SAR). The retrieval method is based on the Bayesian approach with the a priori information provided by atmospheric and oceanic models for surface wind and currents, respectively. The backscatter and Doppler frequency shift are estimated from the along-track interferometric SAR system TanDEM-X data. The retrieval results are compared against in-situ measurements along the Swedish west coast. It is found that the wind retrieval reduces the atmospheric model bias compared to in-situ measurements by about 1 m/s for wind speed, while the bias reduction in the wind direction is minor as the wind direction provided by the model was accurate in the studied cases. The ocean model bias compared to in-situ measurements is reduced by about 0.04 m/s and 12 circle for current speed and direction, respectively. It is shown that blending SAR data with model data is particularly useful in complex situations such as atmospheric and oceanic fronts. This is demonstrated through two case studies in the Skagerrak Sea along the Swedish west coast. It is shown that the retrieval successfully introduces small scale circulation features detected by SAR that are unresolved by the models and preserves the large scale circulation imposed by the models.
|
|
| 31. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Measurements of Sea Surface Currents in the Baltic Sea Region Using Spaceborne Along-Track InSAR
- 2019
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 57:11, s. 8584-8599
-
Tidskriftsartikel (refereegranskat)abstract
- The main challenging problems in ocean current retrieval from along-track interferometric (ATI)-synthetic aperture radar (SAR) are phase calibration and wave bias removal. In this paper, a method based on differential InSAR (DInSAR) technique for correcting the phase offset and its variation is proposed. The wave bias removal is assessed using two different Doppler models and two different wind sources. In addition to the wind provided by an atmospheric model, the wind speed used for wave correction in this work is extracted from the calibrated SAR backscatter. This demonstrates that current retrieval from ATI-SAR can be completed independently of atmospheric models. The retrieved currents, from four TanDEM-X (TDX) acquisitions over the Öresund channel in the Baltic Sea, are compared to a regional ocean circulation model. It is shown that by applying the proposed phase correction and wave bias removal, a good agreement in spatial variation and current direction is achieved. The residual bias, between the ocean model and the current retrievals, varies between 0.013 and 0.3 m/s depending on the Doppler model and wind source used for wave correction. This paper shows that using SAR as a source of wind speed reduces the bias and root-mean-squared-error (RMSE) of the retrieved currents by 20% and 15%, respectively. Finally, the sensitivity of the sea current retrieval to Doppler model and wind errors are discussed.
|
|
| 32. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Phase calibration of TanDEM-X ATI-SAR data for sea surface velocity measurements
- 2017
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; 2017-July, s. 922-925
-
Konferensbidrag (refereegranskat)abstract
- It has been demonstrated that Along Track Interferometric (ATI) SAR is a useful tool to retrieve ocean surface currents. The ATI SAR provides an interferometric phase (hereafter called phase) which is directly related to the Line-Of-Sight (LOS) component of the surface velocity. The accuracy of ocean currents retrieval is highly dependent on the phase processing. For instance, a properly processed phase must equal zero over static targets. The measured TanDEM-X phase rarely (if ever) satisfies this condition which indicates a phase offset independent of the surface properties. The offset can be either due to a phase synchronization issue or to using inaccurate orbital and attitude information in the processing. The objective of phase calibration is the estimation and the removal of the offset and possible trends from the measured phase. In this paper, the topographic phase is simulated using a Digital Elevation Model (DEM) and baseline information. The calibration is carried out by estimating the average of the phase over land, after topography correction, and subtracting the estimated value from the measured phase. Finally, the residual phase trend is removed using a second order polynomial fitting.
|
|
| 33. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Using Sentinel-1 Ocean Data for Mapping Sea Surface Currents Along the Southern Norwegian Coast
- 2019
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 9781538691540 ; , s. 8058-8061
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the capability of Sentinel-1 data to map ocean surface currents in the Skagerrak Sea, with a focus on the Norwegian Coastal Current (NCC), is investigated. Post-processing methods for removing artefacts in the data and improving of the geophysical interpretation are suggested. Scalloping is one major artefact, which significantly degrades the quality of the velocity maps. Two methods, in spatial and spectral domain, for correcting this effect are proposed. It is also found that the radial velocity provided in the Sentinel-1 ocean data is biased, hence land is used as a reference to correct for the absolute and inter-beam bias. Finally, the retrieved (corrected) velocity is compared to a regional ocean circulation model (ROMS). It is shown that there is a good agreement between the ocean model and the retrieved velocity with values of ≈ 0.8 m/s in the core of the NCC.
|
|
| 34. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Wind direction ambiguity removal using along-track InSAR: A case study
- 2018
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; 2018-July, s. 3262-3265
-
Konferensbidrag (refereegranskat)abstract
- The main problem in wind retrieval using SAR imagery is the lack of the wind direction information. A few methods have been proposed to extract the wind direction from SAR images. The main limitation of these methods is the 180 degrees ambiguity in the direction. Usually, an external source of wind direction is used to remove this ambiguity. This study exploits the Along-track Interferometric SAR (ATI-SAR) phase to demonstrate its usefulness to tackle this problem. A method is proposed to remove the wind direction ambiguity using the ATI-SAR phase information. This is based on the fact that the interferometric phase is related to the sea surface motion direction. Depending on the sign convention, the phase is positive/negative for advancing/receding target respectively. This effect is used to assist the wind extraction algorithm to select the most plausible direction. The results show a very good agreement with atmospheric model and visual investigation.
|
|
| 35. |
- Elyouncha, Anis, 1978, et al.
(författare)
-
Wind-wave effect on ATI-SAR measurements of ocean surface currents in the Baltic Sea
- 2016
-
Ingår i: 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. ; 2016-November, s. 3982-3985
-
Konferensbidrag (refereegranskat)abstract
- Along-Track Interferometric (ATI) SAR has demonstrated through several studies a capability to detect ocean surface currents. One of the most challenging problems in ocean surface current retrieval using SAR is the removal of the wind-wave contribution. The phase difference provided by ATI-SAR technique is directly related to the radial velocity of the moving ocean surface. In order to infer the current-only velocity from the total phase the wind-wave contribution need to be removed. This is achieved by simulation of SAR Doppler spectra from given wind fields. This paper investigates the effect of the local wind on ATI-SAR phase. A study case, where the backscatter modulation is dominated by the wind variation, is illustrated using TanDEM-X data over the Baltic Sea. It is shown that retrieving high resolution winds from SAR data using an empirical wind model and using the retrieved winds as input to the SAR imaging model improves the simulated SAR signatures.
|
|
| 36. |
- Eriksson, Leif, 1970, et al.
(författare)
-
ALOS PALSAR calibration and validation activities in Sweden
- 2008
-
Ingår i: Proceedings of The First Joint PI Symposium of ALOS Data Nodes for ALOS Science Program in Kyoto, Kyoto, Japan, 19 - 23 November, 2007. - 1349-113X. - 9784906653041 ; JAXA-SP-07-012
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 37. |
- Eriksson, Leif, 1970, et al.
(författare)
-
ALOS PALSAR Calibration and Validation Results from Sweden
- 2007
-
Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27, 2007. ; DOI: 10.1109/IGARSS.2007.4423115, s. 1589-1592
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In 2006 calibration activities for ALOS PALSAR wereconducted in Sweden. Four five-metre trihedral corner reflectorsand three smaller dihedral reflectors were deployed and operatedduring eight months. 23 PALSAR scenes were acquired over thecalibration site allowing an evaluation of the quality and temporalstability of the data. Results show that the co-polarized datahave been stable during the whole calibration period with variationsin the trihedral responses lower than 0.7 dB. The measuredresolution in azimuth was 4.4 m and in slant range 4.7 m forsingle polarization images and 9.5 m for polarimetric data. Forthe cross-polarized data large variations in the dihedral responseswere found. It is assumed that this is caused by a larger sensitivityto pointing errors. For the polarimetric data, estimation ofFaraday rotation gave values ranging from 0.1º to 3º.
|
|
| 38. |
- Eriksson, Leif, 1970, et al.
(författare)
-
Stem volume estimation for boreal forest using ALOS PALSAR
- 2007
-
Ingår i: 5th International Symposium on Retrieval of Bio- and Geophysical Parameters from SAR Data for Land Applications, Bari, Italy, September 25-28, 2007, ESA, Istituto di Studi sui Sistemi Intelligenti per l´Automazione. ; , s. CD-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An evaluation of ALOS PALSAR data for standwise forest stem volume estimation has been performed at a Swedish test site. The site is dominated by coniferous tree species. SAR data from three operational PALSAR modes, including single, dual and quad polarization, have been analyzed. In total, images from 18 different dates were included. Altogether, 56 forest stands with stem volume in the range of 45-650 m3 ha-1 (average 325 m3 ha-1) were analyzed by relating backscatter intensity to field data. The estimation accuracy of stem volume at stand level was calculated in terms of root mean square error (RMSE). For the best case investigated an RMSE of 30% was obtained for one of the single polarization images acquired in the winter season. In this case no saturation was observed for high stem volumes. The corresponding RMSEs for the dual and quad polarization images were between 62%, and 81%. The better results for single polarization might be explained by particularly favourable weather conditions at image acquisition. An extended evaluation will be performed to verify the cause.
|
|
| 39. |
|
|
| 40. |
|
|
| 41. |
|
|
| 42. |
- Folkesson, Klas, 1976, et al.
(författare)
-
Model-based compensation of topography effects for improved stem volume retrieval from CARABAS-II VHF-band SAR images
- 2009
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 47:4, s. 1045-1055
-
Tidskriftsartikel (refereegranskat)abstract
- A limiting factor that has been identified for stem-volume retrieval in coniferous forests using VHF synthetic aperture radar is that the backscatter varies depending on ground topography. On sloping ground, the backscatter from a forest is reduced, since the dominant groundtrunk double-bounce scattering mechanism is changed. This leads to underestimation of stem volume, and the variations caused by topography can obscure real variations in stem volume. By using multiple images acquired with different flight headings and combining the image information with ground-topography data in a model-based inversion method, we are able to compensate for the ground-topography influence on the backscatter. The inversion method is based on image segmentation and the optimal estimation method. Using four or more images from the CARABAS-II system and a coarse digital elevation model with 50-m horizontal grid, the stem volume can be retrieved with an average root-mean-square error (rmse) of less than 60 $\hbox{m}^{3}\hbox{ha}^{-1}$ for stem volumes in range of 80700 $\hbox{m}^{3}\hbox{ha}^{-1}$ (in terms of above-ground biomass, this is equivalent to an rmse of less than 40 $\hbox{ton} \cdot\hbox{ha}^{-1}$ over the range of 50400 $\hbox{ton} \cdot\hbox{ha}^{-1}$). The retrieval accuracy is similar to that previously obtained for similar forests standing on flat and horizontal ground.
|
|
| 43. |
- Folkesson, Klas, 1976, et al.
(författare)
-
Stem volume retrieval at stand level using multiple low-frequency SAR images
- 2003
-
Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS), Toulouse, France, 21-25 July. - 0780379292 ; IV, s. 2556-8
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper the ground slope effect on stem volume retrieval from VHF-band SAR images has been studied using multiple co-registered images acquired from different flight headings. Accurate measurements of the topography were used as additional input data to a model of the backscatter amplitude variation with ground slope and aspect angle. Modeling this topographical effect on the radar backscatter provides a base for improvement of the stem volume retrieval
|
|
| 44. |
|
|
| 45. |
- Fransson, J.E.S., et al.
(författare)
-
Detection of clear-cuts using ALOS PALSAR satellite images
- 2008
-
Ingår i: Proceedings of the European Conference on Synthetic Aperture Radar, EUSAR. - 2197-4403. ; 1-4
-
Konferensbidrag (refereegranskat)abstract
- The objective of this study is to make a first evaluation of the possibilities to detect forest clear-cuts using high-resolution ALOS PALSAR FBD (Fine Beam Dual polarization) satellite images. New operational applications for mapping of changes in forest cover are of interest for government authorities in Sweden and in other countries with similar needs. The study was conducted in southern Sweden and included seven old coniferous stands located on flat terrain. Three of the stands were clear-felled and the remaining stands were left untreated for reference. Altogether, six PALSAR FBD images (look angle 34.3°, HH- and HV-polarization) acquired during the summer and fall seasons were analyzed. The difference in backscattering coefficient between the reference and the clear-felled stands was on average 2.4 dB and 2.9 dB for the HH- and HV-polarization, respectively. When comparing the backscattering coefficient before and after clear-felling the drop was found to be 1.7 dB and 2.3 dB for the HH- and HV-polarization, respectively.
|
|
| 46. |
- Fransson, J.E.S., et al.
(författare)
-
Detection of forest changes using ALOS PALSAR satellite images
- 2007
-
Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27, 2007. ; DOI: 10.1109/IGARSS.2007.4423308, s. 2330-2333
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A controlled experiment has been performed to quantify the ability to detect clear-cuts using ALOS PALSAR data. The experiment consisted of 8 old spruce dominated stands with a size of about 1.5 ha, located at a test site in southern Sweden. Four of the stands were clear-felled and the remaining stands were left untreated for reference. A time series of PALSAR images were acquired prior to, during, and after treatment, including 7 Fine Beam Single polarization (FBS, look angle 34.3°, HH-polarization) SAR images. The results clearly show that the clear-felled stands could be separated from the reference stands. The drop in backscattering coefficient between the reference and the clear-felled stands was on average 2.1 dB. This implies that ALOS PALSAR data potentially can be used for large-scale mapping of changes in forest cover.
|
|
| 47. |
|
|
| 48. |
- Fransson, Johan E.S., et al.
(författare)
-
Estimation of Forest Stem Volume using ALOS-2 PALSAR-2 Satellite Images
- 2016
-
Ingår i: Proceedings of 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. - 9781509033324 ; 2016-November, s. Art no 7730388, Pages 5327-5330
-
Konferensbidrag (refereegranskat)abstract
- © 2016 IEEE. A first evaluation of ALOS-2 PALSAR-2 data for forest stem volume estimation has been performed at a coniferous dominated test site in southern Sweden. Both the Fine Beam Dual (FBD) polarization and the Quad-polarimetric mode were investigated. Forest plots with stem volume reaching up to a maximum of about 620 m 3 ha -1 (corresponding to 370 tons ha -1 ) were analyzed by relating backscatter intensity to field data using an exponential model derived from the Water Cloud Model. The estimation accuracy of stem volume at plot level (0.5 ha) was calculated in terms of Root Mean Square Error (RMSE). For the best case investigated an RMSE of 39.8% was obtained using one of the FBD HV-polarized images. The corresponding RMSE for the FBD HH-polarized images was 43.9%. In the Quad-polarimetric mode the lowest RMSE at HV- and HH-polarization was found to be 43.1% and 66.1%, respectively.
|
|
| 49. |
- Fransson, Johan E.S., et al.
(författare)
-
Estimation of Stem Density in Hemi-Boreal Forests using Airborne Low-Frequency Synthetic Aperture Radar
- 2020
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; , s. 4152-4155
-
Konferensbidrag (refereegranskat)abstract
- In this study, Synthetic Aperture Radar (SAR) backscatter data from the Swedish airborne CARABAS-II and LORA systems were used to estimate stem density. The analysis were performed at the test site Remingstorp, located in the south of Sweden, consisting mainly of coniferous in hemi-boreal forests. In total, ten 80 m × 80 m forested areas, where all trees were measured in situ, with stem densities in the range of 278-552 stems and stem volumes in the range of 70-550 m3 ha-1 were analysed. SAR data from CARABAS-II and LORA were acquired in 2006 with nine unique flight headings. Local maxima of the backscatter were used to estimate stem density. The results were compared with in situ data and the accuracy in terms of root mean square error (RMSE) for CARABAS-II and LORA were found to be 81 stems (20.9%) and 82 stems (20.2%), respectively, in the best cases. The accuracy assessment of the stem density were performed after averaging images from each SAR system. This was done in order to suppress noise to a greater extent compared to using single images. The results show a potential to estimate stem density with low-freqency SAR data for the benefit of forest management.
|
|
| 50. |
- Fransson, Johan E.S., et al.
(författare)
-
Estimation of stem volume in hemi-boreal forests using airborne low-frequency Synthetic Aperture Radar and lidar data
- 2013
-
Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 2153-6996 .- 2153-7003. - 9781479911141 ; , s. 161-164
-
Konferensbidrag (refereegranskat)abstract
- Synthetic Aperture Radar (SAR) backscatter data from the Swedish airborne CARABAS-II and LORA systems were used to estimate stem volume at stand level. The study was performed in hemi-boreal forests at the Remningstorp test site, located in southern Sweden. In total, ten 80 m × 80 m stands, where all trees were measured in situ, with stem volumes in the range of 70-530 m 3 ha-1 (on average 347 m3 ha-1) were analyzed. SAR data from CARABAS-II and LORA were acquired from two different years, with nine unique flight headings that were repeated for each system and year. Regression analysis was used to estimate stem volume and the accuracy was assessed in terms of Root Mean Square Error (RMSE). As a first step, stem volume was estimated for each flight heading separately. The accuracy assessment was then performed by weighting the separate estimates for each system and year inversely proportionally to the variance about the regression function. The best results for CARABAS-II and LORA showed a relative RMSE of 7% and 24% of the mean stem volume, respectively. In a previous study, stem volume was estimated using LiDAR data and the same forest stands, resulting in an RMSE of about 12%. In conclusion, the estimation accuracy of stem volume using combined low-frequency CARABAS SAR images was found to be superior to that from using LiDAR data for the stands investigated.
|
|
