Detection of forest changes using ALOS PALSAR satellite images

Fransson, Johan E. S.; Magnusson, Mattias; Olsson, Håkan; Eriksson, Leif E. B.; Sandberg, Gustaf; Smith-Jonforsen, G.; Ulander, Lars M. H.

doi:10.1109/igarss.2007.4423308

Cited by 22 publications

(18 citation statements)

References 8 publications

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“…For such range of angles, the backscatter decreased by less than 1 dB for the JERS-1 configuration (38 • incidence angle at midswath) and less than 2 dB for the SIR-C configuration (55…”

Section: ) Krycklan Test Sitementioning

confidence: 96%

Signatures of ALOS PALSAR L-Band Backscatter in Swedish Forest

Santoro

Fransson

Eriksson

et al. 2009

IEEE Trans. Geosci. Remote Sensing

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Abstract-The Phased Array type L-band Synthetic ApertureRadar onboard the Advanced Land Observing Satellite has, since its launch, been acquiring an extensive data set of images over two forest test sites in Sweden. The sites of Remningstorp (Lat. 58• 30 N, Long. 13• 40 E) in the south and Krycklan (Lat. 64• 14 N, Long. 19• 50 E) in the north of Sweden are characterized by hemiboreal and boreal forests, respectively. In this paper, we have investigated the signatures of standwise backscatter measurements from forests with different growth stages in relation to polarization, environmental conditions, image viewing geometry, and spatial resolution. The HV backscatter presented stronger sensitivity to the forest growth stage than the HH and VV backscatter. Under unfrozen conditions, the dynamic range of fine-beam data acquired at 34.3• was 8-9 dB for the HV polarization and 6-7 dB for the HH polarization. At 21.5• , in the polarimetric mode, the dynamic range was 6, 7, and 9 dB at VV, HH, and HV polarizations, respectively. Regardless of the specific polarization, the backscatter was temporally consistent under unfrozen conditions, with a small increase of backscatter in regrowing young forest for wet conditions. Under thawing and frozen conditions, repeated measurements were available only for the HH backscatter at 34.3• . For thawing conditions, the backscatter level was similar to the unfrozen conditions even though the signatures differed depending on temperature dynamics, snow-cover properties, and precipitation. Under frozen conditions, the signatures varied depending on temperature. For images acquired when the temperature was well below the freezing point, the backscatter was low, and the dynamic range was small (2-4 dB); nonetheless, the measurements were consistent. Images acquired when temperature was close to the freezing point presented a behavior similar to unfrozen conditions. The sensitivity of the backscatter to the image viewing geometry for different growth stages was studied for data acquired under dry unfrozen conditions. The backscatter difference increased for increasing look angle because of the increase in volume scattering and the decrease of ground-surface backscatter. The largest difference was observed at 41.5• with 2.5-4-dB difference for the HH and 4-5-dB M. Santoro is with Gamma Remote Sensing AG, 3073 Gümligen, Switzerland (e-mail: santoro@gamma-rs.ch).J. E. S.

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“…For such range of angles, the backscatter decreased by less than 1 dB for the JERS-1 configuration (38 • incidence angle at midswath) and less than 2 dB for the SIR-C configuration (55…”

Section: ) Krycklan Test Sitementioning

confidence: 96%

Signatures of ALOS PALSAR L-Band Backscatter in Swedish Forest

Santoro

Fransson

Eriksson

et al. 2009

IEEE Trans. Geosci. Remote Sensing

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“…Given the high yearly growth rate of stem volume in the region (7.5 m 3 /ha/year [32]), the stem volumes were updated each year with stand-wise yearly growth factors available with the forest field inventory data. Stands where forest was felled at some time between 2006 and 2010 [33,34] were excluded from the analysis of images acquired after the felling. For Krycklan, stem volume was available for 1131 forest stands; inventory was undertaken during 2007 and 2008 with the same approach as for Remningstorp.…”

Section: Test Sitesmentioning

confidence: 99%

Reviewing ALOS PALSAR Backscatter Observations for Stem Volume Retrieval in Swedish Forest

2015

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Between 2006 and 2011, the Advanced Land Observing Satellite (ALOS) Phased Array L-type Synthetic Aperture Radar (PALSAR) instrument acquired multi-temporal datasets under several environmental conditions and multiple configurations of look angle and polarization. The extensive archive of SAR backscatter observations over the forest test sites of Krycklan (boreal) and Remningstorp (hemi-boreal), Sweden, was used to assess the retrieval of stem volume at stand level. The retrieval was based on the inversion of a simple Water Cloud Model with gaps; single estimates of stem volume are then combined to obtain the final multi-temporal estimate. The model matched the relationship between the SAR backscatter and the stem volume under all configurations. The retrieval relative Root Mean Square Error (RMSE) differed depending upon environmental conditions, polarization and look angle. Stem volume was best retrieved in Krycklan using only HV-polarized data acquired under unfrozen conditions with a look angle of 34.3° (relative RMSE: 44.0%). In Remningstorp, the smallest error was obtained using only HH-polarized data acquired under predominantly frozen conditions with a look angle of 34.3° (relative RMSE: 35.1%). The relative RMSE was below 30% for stands >20 ha, suggesting high accuracy of ALOS PALSAR estimates of stem volumes aggregated at moderate resolution.

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“…SAR data used in those studies are from experimental (Ranson and Sun 1997;Rignot et al 1997;Saatchi et al 1997) and commercial SAR missions (Fransson et al 2007;Santos et al 2008). SAR has the capability of acquiring data throughout the year irrespective of cloud coverage, while optical sensing is often affected by the presence of cloud cover in the desired seasons and time.…”

Section: Introductionmentioning

confidence: 99%