Open AccessOne of the problems of location and remote sensing laser systems is the overload of photoreceiver because of the intensive clutter from the backscatter (towards the lidar) signal in the lidar “near zone. The intensive clutter arises from elastic scattering of laser radiation by aerosol particles, which are always available in the earth's atmosphere.
To solve this problem the long-range high-speed laser systems use mechanical shutters to disable physically a receiving optical channel for a time of the possible arrival of the backscatter signal from the "near zone". The easiest way to solve the problem of the photo-receiver overload in the "near zone" here is to use a biaxial circuit of location where a laser beam comes in sight of photo-receiver only within a certain predetermined range. This location circuit allows us to reduce the intensity of the atmospheric aerosol-based radiation scattered in the lidar "near zone" and avoid the clutter of the photo-receiver.
The size of the lidar clutter zone can be estimated by comparing a detected signal, caused by scattering the atmospheric aerosol laser pulse of lidar, with a maximum output current of the photo-receiver.
The clutter zone (and its size) depends on many factors, namely: factors that are directly or indirectly dependent on the wavelength of the radiation (atmospheric factors, i.e. index of attenuation and scattering of the atmosphere, scattering indicatrix, radiation energy of the laser pulse, the photo-receiver parameters - spectral sensitivity, gain, maximum output current, etc.) as well as geometric factors (distance between the optical axes of the source and the receiver, divergence of laser radiation, fields in sight of photo-receiver, size of transmitting aperture and receiving lens).
The calculation results of UV and visible spectral bands show that with a small base, depending on the photomultiplier (PMT) parameters (gain, maximum anode current) and the atmosphere parameters, conditions for arising clutter zone of lidar photo-receiver may be implemented or not. In the more transparent atmosphere at a lower PMT gain and a higher value of the PMT maximum anode current the sizes of the clutter zone are less (or it is absent). At a wavelength of 0.355 μ the size of the clutter zone is mostly more than at the wavelength of 0.532 μ.
With increasing base between the optical axes of the source and receiver the clutter zone is reduced, and the results of calculations enable selecting a base value to ensure a lack of the clutter zone in a certain range of parameter values of the PMT and the Earth's atmosphere.