4.3. Detecting the phenological stages on a regional scale
The mixed pixel effect and topography may affect the spectral characteristics in satellite image. However, we focused on areas where most of each grid is used as paddy fields. Generally such areas are located on plains formed by alluviation. Therefore, there is little topographic and mixed pixel effect on the results.
The area of a parcel of paddy fields is less than about 5000 m2 in Japan. The 500-m resolution of MODIS data is too coarse to show an individual parcel. Given that our objective in this study is to estimate the regional characteristics of rice phenology, it is appropriate to use MODIS data with a 500-m resolution for monitoring paddy fields on a regional scale. Additionally, compared with the resolution of NOAA/AVHRR (ca. 1.1 × 1.1 km) and SPOT/VEGETATION (ca. 1 × 1 km), the resolution of the MODIS image is higher and offers an advantage in determining regional crop phenology