| 1. |
- Eriksson, Leif, 1970, et al.
(författare)
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ALOS PALSAR calibration and validation activities in Sweden
- 2008
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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
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Eriksson, Leif, 1970, et al.
(författare)
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ALOS PALSAR Calibration and Validation Results from Sweden
- 2007
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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
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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.
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| 3. |
- 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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| 4. |
- Fransson, J.E.S., et al.
(författare)
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Detection of clear-cuts using ALOS PALSAR satellite images
- 2008
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Ingår i: Proceedings of the European Conference on Synthetic Aperture Radar, EUSAR. - 2197-4403. ; 1-4
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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.
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| 5. |
- Fransson, J.E.S., et al.
(författare)
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Detection of forest changes using ALOS PALSAR satellite images
- 2007
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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
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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.
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| 6. |
- Fransson, J.E.S., et al.
(författare)
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Mapping of Wind-Thrown Forests Using VHF/UHF SAR Images
- 2007
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Ingår i: IEEE 2007 International Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27 2007. ; DOI: 10.1109/IGARSS.2007.4423313, s. 2350-2353
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- SAR images from the Swedish airborne CARABAS-II and LORA systems have been visually analyzed over simulated wind-thrown forest at both single tree and stand level. In ideal conditions, the results show that LORA is more accurate than CARABAS-II at detecting wind-thrown trees, regardless of tree size and direction of the fallen trees relative to flight heading. Furthermore, the visible single trees in the LORA images appeared more distinct than in the CARABAS-II images, which could be explained by the high resolution in the LORA images. Based on visual interpretation, it is likely that the detection of wind-thrown forests could be improved using VHF/UHF SAR images acquired both prior to and after a storm event.
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| 7. |
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| 8. |
- Kononov, Anatoliy, 1951, et al.
(författare)
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Statistical Analysis of VHF-Band Tree Backscattering Using Forest Ground Truth Data and PO Scattering Model
- 2011
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 49:8, s. 3035-3046
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes the statistical properties of thevery high frequency (VHF)-band radar backscattering from coniferous trees by incorporating forest ground truth data into a physical-optics (PO) model that assumes horizontally transmit and receive polarizations and dominant double-bounce scattering from vertical stems standing on an undulating ground surface. The analysis shows that a statistically adequate model for the tree backscattering amplitude can be presented as a mixture of generalized gamma or lognormal distribution, and the mixture model can be reduced to a single density model if the trees withtrunk volumes exceeding an appropriate threshold are to be taken into account. The generalized gamma density is shown to provide an appreciably better fit to the exceedance functions associated with the PO model data than that for the lognormal density. The results can be used to design statistically adequate models of forest clutter for VHF synthetic aperture radar systems.
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| 9. |
- Magnusson, M., et al.
(författare)
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Estimation of forest stem volume using ALOS PALSAR satellite images
- 2007
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Ingår i: IEEE Geoscience and Remote Sensing Symposium (IGARSS 2007), Barcelona, Spain, July 23-27, 2007. ; DOI: 10.1109/IGARSS.2007.4423813, s. 4343-4346
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A first evaluation of ALOS PALSAR data for forest stem volume estimation has been performed at a coniferous dominated test site in Sweden. In total, 7 Fine Beam Single polarization (FBS, look angle 34.3°, HH-polarization) and 7 Polarimetric (PLR, look angle 21.5°, HH-, HV-, VH-, and VV-polarization) SAR images were used. In total, 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 using one of the FBS images acquired in the winter season. The corre-sponding RMSEs for the PLR images with HH-, HV-, VH-, and VV-polarization were 65%, 65%, 62%, and 81%, respectively. The better results for FBS compared to PLR mode could be explained by particularly favorable weather conditions at image acquisition, or by the higher ground resolution in the FBS images, which makes small stands less sensitive to errors in geo-coding.
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| 10. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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A Physical-optics Model for Predicting VHF/UHF-band HH-pol Backscatter from Coniferous Forests in Undulating Terrain
- 2007
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Ingår i: 5th International Symposium on Retrieval of Bio- and Geophysical Parameters from SAR Data, Bari, Italy, September 25-28, 2007, ESA, Istituto di Studi sui Sistemi Intelligenti per l`Automazione.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A physical optics based model for predicting backscatter from coniferous forest in the VHF- and UHF frequency bands is presented. It models the forest as a collection of stems standing on a well characterized undulating ground surface. The model is valid for SAR systems transmitting and receiving horizontal polarization (HH) and is useful for assessing the importance of ground topography in SAR images.SAR data from the airborne systems CARABAS-II (22-82 MHz) and LORA (230-470 MHz) and forest characterization on individual tree level were used to validate the model. It was found that the model was able to predict much of the backscatter variations due to surface topography. At best, coefficients of determination (R2) of 0.44 and 0.65 for the CARABAS and LORA case were found. In comparison it should be noted that R2 drops to about 0.1 if a flat ground is assumed. These results indicate that it is essential to consider ground topography when predicting HH-polarized SAR images in these frequency bands.The model failed to predict the absolute values of the backscatter intensity. Probable explanations are the lack of attenuation effects in the model and/or the value chosen for the dielectric constant of the stems.In the near future efforts will be placed into the task of extending the model to include more polarizations, especially HV. This includes e.g. adding the backscatter from branches and leaves/needles, accounting for attenuation effects and including random small scale variations in the surface description.
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