The TV receiving antenna receives the modulated video signal. After frequency conversion, intermediate frequency amplification, detection and video amplification, the electron gun of the picture tube emits an electron beam that varies with the video signal. When the electron beam bombards the screen, the kinetic energy of high-speed electrons will be converted into light energy, and bright spots will appear on the screen, while the secondary electrons bombarded by high-speed electrons will be captured by the grid. The electron beam scans rapidly on the fluorescent screen. Because of the persistence of the fluorescent screen and human vision, you can see the whole picture, or you can remake it into a photo with a camera.
(2) Optical mechanical scanning:
The scanning system used in mechanical scanning imaging is mostly parabolic focusing system-Ka seglin optical system, which focuses the electromagnetic radiation of ground objects on the detector.
The instantaneous field of view of the optical scanning system is very small, and the scanning mirror only collects the radiation energy at this point. Using its own rotation or swing, it forms a one-dimensional linear scan, and with the movement of the platform, it realizes the plane scan of the ground objects and achieves the purpose of collecting the electromagnetic radiation of the regional ground objects.
(3) Solid-state scanning imaging: an imaging method of scanning the target object through the movement of the remote sensing platform. At present, the commonly used detection element is electronic coupling device CCD, which is a detection element that uses the amount of charge to represent the signal size and transmits the signal through coupling. It has a series of advantages such as wide sensing spectral range, small distortion, small volume, light weight, low system noise, high sensitivity, low dynamic power consumption, long service life and high reliability.