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SAR repeat-pass coherence in winter for boreal forest applications. A first comparison of ASAR and JERS-1 SAR.

Leif E. B. Eriksson(1) and Christiane Schmullius(1)

(1) Friedrich-Schiller-University, Loebdergraben 32, D-07743 Jena, Germany


Interferometric coherence from the ERS-1/2 tandem mission has in several studies proved to be a useful tool for forest monitoring. After the loss of ERS-1, the focus of InSAR studies has to some extent moved to repeat-pass solutions for current and near term satellite sensors like Envisat ASAR and ALOS PALSAR. Recently published results show that 44-day repeat-pass coherence from the SAR on JERS-1 can give information about forests if the acquisitions are made during stable winter conditions, e.g. in Siberia. This paper will present the first comparison between repeat-pass coherence from ASAR and JERS-1 SAR.

SAR data from Envisat and JERS-1 have been acquired for one of the SIBERIA-II project test sites in the northern taiga in central Siberia. The acquisitions are from the winter season, which give the most favourable conditions for coherence estimation over 35 and 44 days respectively. The coherence estimation was done with an adaptive window size taking into account phase slope, texture of the averaged backscattering coefficient and the local coherence level. Initially Landsat ETM quicklook images from June 2002 have been used to give independent information about the forest coverage. In addition, forest inventory data will allow an assessment of the differences between C- band and L-band coherence for stem volume estimation.

The processed repeat-pass coherence shows relatively high values both for ASAR and JERS-1 SAR. Statistics for the coherence levels for the available land cover types will be presented. In the ASAR coherence image, which is from a more recent date than the JERS-1 coherence, a new fire scar can be identified. The study confirms that when the requirements of stability are met, coherence from repeat pass acquisitions gives exploitable coherence levels. The goal for the coming winter is to extend this study to more test sites in Siberia, but also in northern Europe.


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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry