Abstract
Vegetation-Soil-Water (VSW) index was applied for four sets of SPOT/HRV data collected during the 1997 rice-growing season. Objectives of this study were to examine relationships among V, S, and W indices in rice planting fields and develop new area estimation model with VSW index. Study area was located at the Saga Plains, Kyushu district in Japan. End-member points for the VSW index were determined from the four images, which were converted into reflectance factors with the 6S code. For planted rice fields, there was a negative linear relationship between the V and W indices on July 23 and between S and W indices on June 17. Linear regression lines were derived for these two relationships and used to estimate the area of the rice fields. Assuming the pixels for rice planting fields distributed around these regression lines, pixels were sampled around the lines. An optimal pixel sampling range was decided by the result of comparison between the estimated area and ground measurement points (5.47 ha). The result indicated that 2.9 times of root mean squared error achieved most suitable sampling range to estimate the area of rice fields. Consequently, our new developed model with VSW index showed -1.8% on the total estimated error ratio.
