Monitoring of Plant growth and Snow Cover in the Ishikari Plains by Microwave Remote Sensing

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This study started with the purpose of demonstrating the usefulness of microwave Remote Sensing for a monitoring of wide area through the investigation of plant growth and snow cover in the Ishikari plains by a microwave Synthetic Aperture Radar (SAR) onboard the Japanese Earth Resource Satellite 1 (JERS-l) and through the development of the algorithm for extracting information about plant growth and snow cover.The Normalized Radar Cross Section (NRCS) of rice paddies in the Ishikari plains shows a large value in sumner and in winter. Since NRCS is proportional to the received power of the radar, a large NRCS means that the strength of radar echo becomes large. A large NRCS in summer is understandable because of a volume scattering from growing rice, but a large NRCS in winter is a puzzle because the literatures reported the contrary. To solve this puzzle, the later part of this study was devoted to a theoretical investigation.Since JERS-l SAR uses a low frequency (1.275 GHz) of L band … More microwave, dry snow cover is almost transparent to the wave, which means that the attenuation of the wave due to dry snow cover can be negligible. Dry snow cover, however, has a refraction effect on the wave making a steeper incidence from snow to the soil. This steeper incidence increases NRCS because NRCS depends on the angle of incidence. (Here, the roughness of soil surface is assumed to be the same for with and without the snow cover, and the water content of soil is also assumed to be the same for with and without the snow cover.)When snow cover becomes wet, NRCS decreases because the water in the snow attenuates the wave. But the wet snow supplies water to the soil, making the water content of soil increase. When the water content of soil increases, the impedance of soil increases ; the increased impedance of soil enhances the impedance mismatch between snow and soil, so that the scattering from the soil increases. For wet snow cover, the above two competitive mechanisms, viz. , attenuation due to wet snow and increase of scattering due to a larger water content of soil, can make it possible that NRCS with snow cover is larger than that without snow cover.The above method for analyzing the L band SAR data may be extended to the analysis of higher frequency data when the volume scattering effect is included in the analysis Less