| 1. |
- Fransson, Johan E.S., et al.
(författare)
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Estimation of Forest Stem Volume using ALOS-2 PALSAR-2 Satellite Images
- 2016
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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
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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.
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| 2. |
- Elyouncha, Anis, 1978, et al.
(författare)
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Wind-wave effect on ATI-SAR measurements of ocean surface currents in the Baltic Sea
- 2016
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Ingår i: 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. ; 2016-November, s. 3982-3985
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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.
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| 3. |
- Carvajal, Gisela, 1983, et al.
(författare)
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Correlation between Synthetic Aperture Radar Surface Winds and Deep Water Velocity in the Amundsen Sea, Antarctica
- 2013
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:8, s. 4088-4106
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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.
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| 4. |
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| 5. |
- Eriksson, Leif, 1970, et al.
(författare)
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Stem volume estimation for boreal forest using ALOS PALSAR
- 2007
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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-
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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.
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| 7. |
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| 8. |
- Folkesson, Klas, 1976, et al.
(författare)
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Model-based compensation of topography effects for improved stem volume retrieval from CARABAS-II VHF-band SAR images
- 2009
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 47:4, s. 1045-1055
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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.
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| 9. |
- Folkesson, Klas, 1976, et al.
(författare)
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Stem volume retrieval at stand level using multiple low-frequency SAR images
- 2003
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Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS), Toulouse, France, 21-25 July. - 0780379292 ; IV, s. 2556-8
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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
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| 10. |
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