Monitoring of subsurface water in wetlands in Japan based on SAR data analysis

The Earth observation satellites provide the data for wide area and in long terms. By using the microwave observation data, we can regionally detect subsurface water in any weather condition with constant intervals, which has a great advantages for hydrological monitoring.

We focus on wetlands with heavy snow during winter in Japan. We conducted the analysis of microwave data from Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard ALOS advanced Land Observing Satellite (ALOS) through years. We found considerable decrease of backscattering (NRCS: normalized radar cross section) during winter in the examined 3 snowy wetlands in Japan. Such consistent decrease of NRCS indicates more water exists under the snow cover compared with no-snow seasons.

We consider some hypotheses for the origin of the observed subsurface water. We evaluate and compare each hypothesis by introducing multiple kinds of observation data. The meteorological grid data for the snow depth is introduced and selected accordingly, considering also the wind direction and properties of snow. We estimate response time of peat and snow layers to snow fall based on correlational analyses. We try to discuss and propose the simplest permeable model for the origin of the increased water observed during winter.