Mapping of clear-cuts in Swedish forest using satellite images acquired by the radar sensor ALOS PALSAR

This study presents results for observing forest changes in Sweden using multi-temporal L-band satellite data and is a part of the JAXA’s ALOS Kyoto and Carbon Initiative. An extensive dataset of images acquired by the Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) is investigated for clear-cut detection in boreal forests in northern Sweden (Lat. 64°14’ N, Long. 19°50’ E). Strong forest/non-forest contrast and temporal consistency were found for the Fine Beam Dual HV-polarized backscatter during unfrozen conditions. Thus, a simple thresholding algorithm that exploits the temporal consistency of pair-wise HV-backscatter measurements has been developed for detection of clear-felled areas. When applied to an image pair acquired during favorable weather conditions, the detection algorithm identified 76% of the clear-cut pixels within a reference layer, with zero erroneously detected pixels. With further refinement, the developed methodology can be an option to present operational alternatives for clear-cut detection

ALOS PALSAR Calibration and Validation Results from Sweden

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 0.1\uba to 3\uba