In terms of the imaginary system, it is a general term for various types of remote sensor systems that acquire remote sensing images of objects without photography. Scanning is usually used for imaging, tape recording or indirect recording on film. According to the structure of the system, the scanning method and the detector parts are roughly divided into:
1. Optomechanical scanning. Such as multi-spectral scanners. The mirror is used to scan the object surface, and the image data is output after being split, detected and photoelectrically converted.
2. Electronic scanning. For example, a return beam guiding TV camera, is an image-side scanning method. The process is optical imaging on the target surface of the light guide, and the signal is amplified and output after being scanned by the electron beam.
3. Robust self-scanning. For example, the photoelectric scanning sensor of the French SPOT satellite is also an image scanning method. The object is imaged by an objective lens on a detector array consisting of  a plurality of charge coupled devices (CCDs) that are photoelectrically converted and output.
4. Antenna scanning. Such as side-view radar, which is an active remote sensing imaging system that is a surface scanning method. It transmits the microwave beam through the antenna and receives an echo reflected by the scene, which is demodulated and output.