The difference between SAR image and optical image

According to the imaging band Classification of the sensor, the optical image usually refers to the image data obtained by visible light and some infrared band sensors. And the SAR sensor basically belongs to the microwave frequency band, the wavelength is usually in centimeter level.
Visible images typically contain grayscale information from multiple bands to facilitate the identification of targets and classification extractions. The SAR image only records the echo information of one band, which is recorded in binary plural form, but the corresponding amplitude and phase information can be extracted by the complex data based on each pixel. The amplitude information usually corresponds to the backscattering intensity of the ground target to the radar wave, which is closely related to the target medium, water content and roughness, which is more correlated with the gray information obtained by the visible light image. The phase information corresponds to the travel distance between the sensor platform and the ground target, which is the same principle as the GPS phase ranging.
Due to the relatively low resolution of SAR imagery and low SNR, the amplitude information contained in SAR imagery is far from the imaging level of the same optical image, but its unique phase information is not available to other sensors, and phase-based interference modeling is the main application direction of SAR.
In the imaging mode, the optical image usually uses the central projection area imaging or the push broom scanning to obtain the data, but the SAR is in the signal processing need (synthetic aperture process, here does not unfold the discussion) cannot adopt the vertical downward illumination method but only through the visual active imaging mode to transmit and accepts the area radar wave, The complex cells corresponding to ground targets are synthesized by means of signal processing (focusing, compressing, filtering, etc.).
The phase information of a single SAR image has no statistical characteristics, only the amplitude information can be used for target recognition and classification applications. As mentioned above, the amplitude information is deeply affected by the noise, combined with the characteristics of SAR imagery peculiar geometric distortion (overlay, perspective contraction, multipath false target, etc.), the individual think that in the field of image segmentation, we can directly ignore the SAR image.

The difference between SAR image and optical image