SAR

Methodology
Paddy fields are waterlogged during the rice transplanting period. SAR is a microwave-based active sensor that transmits microwaves to the target and then records the backscatter. The microwaves undergo specular reflection when encountering water or a smooth ground surface. This reduces the backscatter coefficient of SAR in a water-covered area, providing an estimation method for a rice paddy area, as the backscatter coefficient is very low just after transplanting. The paddy is waterlogged during the transplanting period. Just after transplanting, the rice plants are very small and the microwaves can penetrate the plant bodies, giving the same reflectivity as that of a body of water. During the growing period, the microwaves are unable to penetrate the rice bodies, causing the backscatter coefficient to increase. When other crops are planted in paddy fields, the crops are flooded with water in neither the transplanting period nor the growing period, though some rice production control fields are waterlogged to protect against weed growth. Identification of the rice planted fields therefore requires two scenes of SAR data: the detection of areas of water, followed by no detection of water. Fields that exhibit this pattern are assumed to be paddies planted with rice.