Forest monitoring by using L-band coherence

Two ALOS/PALSAR polarimetry data taken in 2006 were used and examined the deforestation stage by using coherence value. Many trees were fallen by a typhoon hit on September 8, 2004 at a test site in Japan. Reforestation has started for the deforestation sites and several kinds of deforestation stages are appeared there. We classified the stands into four groups. 1) Only small stumps and branches are left. 2) Tree trunks have been carried out, but branches and stumps have been left. 3) The fallen trees have been left. 4) No trees were fallen by the typhoon (normal forest). Coherence values of HH-HH and VV-VV become ~0.39 for group 1 and ~0.30 for group 4, and show a significant difference. But the coherence values of group 2, and group 3 are ~0.3 and show almost same value as group 1. The coherence value of HH-VV and VV-HH are 0.1 lower than the one of the HH-HH and W-VV. The coherence values, which include cross polarization, such as HV-HV and HV-VV, show no difference for all groups and the value is 0.2 to 0.3. While coherence values show the difference between group 1 and group 4, sigma⁰ _HV shows wider dynamic range and is preferable to distinguish the deforested stands from forest stands.