Two factors of microwave characteristics are of importance ; frequency (or wavelength) and polarization,In microwave remote remote sensing , various wavelengths (or frequency) such as L band, C band, X band, P band etc,Will be used ranging from millimeter wavelengths (1 mm- 1cm) up to about 30 cm.According to the wavelength or frequency,specular reflection will occur, so that the surface roughness can be detected if multi-frequency radar images are compared