NOBUYUKI MINO

The backscattering behavior of the improved grasslands is investigated with the ERS-1 SAR (C-band with VV polarization, 23 degrees incident angle) data of a dairy farming area in Japan. Capabilities of ERS-1 SAR data to detect two major management procedures, which are grass renovation and grass mowing, are discussed using a field based interpretation approach. Our results show that renovated grasslands with high surface roughness and high soil moisture content have extremely high backscattering coefficients, whereas the others do not show such high coefficients. The SAR-derived grass renovation map using backscattering signatures is almost consistent with the results from Landsat TM data. However, mown grasslands show a backscattering signature that is similar to those of unmown grasslands. Detection of grass mowing practices is still difficult using ERS-1 SAR data alone. Grass renovation is a very important procedure for improving grasslands productivity. In dairy farming areas where optical data often hindered, the success in monitoring grass renovation using ERS-1 SAR data is considered to be very useful.

In this study, we attempted to monitor the changes in the type of grassland use and advancement of grass mowing utilizing satellite data. On the satellite images acquired during the growing seasons, grasslands just after mowing showed the distinctive reflectance characteristics. Using these characteristics, we analyzed the changes in grassland-use and advancement of pasture mowing on Konsen plain, Hokkaido during a decade. This analysis clarified that of grasslands area for grazing decreased, and mowing time became earlier in the study site. Ground survey of the study site supported the result of satellite monitoring. These results prove the usefulness of satellite remote sensing for monitoring the grassland management.

Once grassland productivity decreases, grass-renovation, accompanied by plowing and seeding, needs to be conducted to improve its productivity. Years after grass-renovation is one index indicating grassland productivity. In this study, the monitoring of grass-renovation status using satellite data is discussed. By extracting 1-year grassland and renovated grassland from each satellite image, we compiled a Grass-renovation years map (1985-1994) . Renovation years from satellite data agreed with that from ground survey with high accuracy, showing that satellite remote sensing is very useful for survey of grass-renovation status.

Satellite remote sensing provides wide-ranging and temporal information on grasslands, which are indispensable for proper grassland management. In this study the satellite monitoring of annual changes of grasslands is discussed. By applying a new method which utilizes a Grassage Standard Map to a study area in Konsen Plain, Hokkaido, Japan, increases in reflectance according to the aging of grasslands were identified from the data observed in May. The increases were considered to be a result of dead leaf accumulation on the ground surface of grasslands. In the June data, sudden decreases of reflectance in the near infrared and middle-infrared bands were identified within the 4 years period after the grass-renovation. The decreases may be a result of changes in grass biomass and grass species composition. The results demonstrate the significance of the new method for grassland monitoring.