| 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. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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Comparison of L- and P-band biomass retrievals based on backscatter from the BioSAR campaign
- 2009
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Ingår i: Proceedings of IGARSS 2009 Symposium, Earth Observation – Origins to Applications, Cape Town, South Africa, 13-17 July, 2009. - 9781424433957 ; IV, s. 169-172
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With the continued threat of global warming, the need to obtain consistent and accurate measurements of the carbon stored in forests is strong. L- and P-band SAR backscatter data have shown to be sensitive to forest biomass, which in turn is coupled to the stored carbon. In this paper a biomass retrieval method is developed for L- and P-band using data from the BioSAR campaign conducted in Sweden during thespring 2007 over hemi-boreal forest. The results show that the use of L-band data gives an underestimation of biomass for stands with high biomass; while for P-band no such underestimation is seen. RMSEs are found to be 30-40% of the mean biomass for L-band and about 25% for P-band for stands with biomass ranging from 10 to 290 tons/ha.
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| 5. |
- Sandberg, Gustaf, 1982
(författare)
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Estimation of Forest Biomass and Faraday Rotation Using Polarimetric L-/P-band SAR
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- At present the greatest source of uncertainty in the global carbon cycle is in the terrestrialecosystems. In order to reduce these uncertainties it is necessary to provide consistent andaccurate global estimates of the biomass contained in the forests of the world. One of themost promising methods for obtaining such estimates is through polarimetric SARbackscatter measurements at L-and P-band frequencies. This thesis aims to investigate thepossibility of retrieving forest biomass from L- or P-band SAR backscatter data. It alsoconcerns SAR image calibration. Well calibrated systems are necessary to ensure that errorsin estimates of physical properties, e.g. forest biomass, are not enlarged by noise or imagedistortions. Both system distortions, such as leakage between polarization channels, anddistortions caused by the ionosphere are studied.A calibration analysis was made on data from the L-band PALSAR system onboard theJapanese ALOS satellite. The data was shown to be of good quality, especially in terms ofradiometric stability and leakage between polarization channels. Following this an analysis ofFaraday rotation, i.e. image distortions caused by the ionosphere, was made for the PALSARimages. It was shown that Faraday rotation can be measured and corrected in PALSARimage, at least if the Faraday rotation is small.Forest biomass retrieval algorithms for P- and L-band SAR backscatter were developed andevaluated using data from the BioSAR-I campaign conducted in southern Sweden in 2007. Itwas found that HV- and HH-polarized backscatter was strongly related to biomass for both LandP-band. However, the L-band backscatter was found to have decreased sensitivity tobiomass for forest stands with biomass larger than about 200 tons/ha, resulting in anincreased error in the biomass estimates. For P-band this problem was not seen, and it wasfound that the biomass on stand level could be estimated using HV- and /or HH-polarized Pbandbackscatter with an error of 20-25% of the mean biomass for stands with biomassranging from 10 to 290 tons/ha.
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| 6. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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Measurements of Faraday Rotation Using Polarimetric PALSAR Images
- 2009
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1558-0571 .- 1545-598X. ; 6:1, s. 142-146
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Tidskriftsartikel (refereegranskat)abstract
- For spaceborne synthetic aperture radar (SAR) systemsoperating at L-band frequencies or lower, the ionospheremay have a significant impact on the SAR images. The largesteffect at L-band is caused by Faraday rotation (FR). Severalstudies have modeled the effect of FR and/or devised models to measure and correct FR.With the launch of the fully polarimetric L-band system Phased Array-type L-band SAR (PALSAR), it has become possible to test both models and measurement techniques on real SAR data. In this letter, the quality of calibrated polarimetric PALSAR data is assessed, and FR is measured. It is found that residual crosstalk and channel imbalance are small in the PALSAR data. Two methods are used to measure FR, the first using in-scene distributed targets and the second using large trihedrals. The two methods show very good agreement. The measurements are compared with values of the total electron content using a linear model. It is found that the model and measurements are in good agreement, with a root-mean-square error of 0.3◦ or 15% of the mean FR angle.
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| 7. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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PALSAR Calibration Results from Sweden
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- As part of a worldwide calibration and validation campaign for the Japanese Advanced LandObserving Satellite a calibration analysis of the Phased Array type Polarimetric SAR (PALSAR)was performed. Four 5 m large trihedral corner reflectors were deployed in southern Swedenand were imaged by PALSAR on numerous occasions. The results show that the pre launchspecifications are more than met, both for the radiometric and polarimetric performance. Inparticular, the absolute radiometric accuracy in this data set was found to be better than 0.5 dB,and the cross talk was estimated to be below -35 dB.
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| 8. |
- Soja, Maciej, 1985, et al.
(författare)
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Topographic Correction for Biomass Retrieval from P-band SAR Data in Boreal Forests
- 2010
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Ingår i: Proceedings of IGARSS 2010 Symposium, Remote Sensing: Global Vision for Local Action, Honolulu, Hawaii, USA, 25-30 July, 2010. - 9781424495641 ; , s. 4776-4779
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The influence of the ground slope on radar backscatterhas been proven to be greater for lower radar frequencies dueto deeper canopy penetration. In this study, multiple heading, PbandSAR data of boreal forest in Sweden was used to find amodel for topographic correction for improved biomass retrieval.Eleven models were tested and the best model was selected. Theselected model was then used for biomass retrieval. Even bymeans of the most simplified approach, forest biomass could beestablished with a root-mean-square error of approximately 50t/ha for HV and 66 t/ha for HH.
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