An Optical Rain Gauge Based on Forward Scattering

A novel approach to the real-time quantitative measurement of rainfall rate is proposed and investigated. The proposed method relies on the sensing of coherence degradation. suffered by a laser beam propagating through rain. A simple model explaining the system operation principle is presented and the necessary data processing algorithm is derived. Further, possible implementations of the suggested rain gauge are discussed. It is shown that the ground-based rain gauge is more easily realizable and may provide better accuracy than the satellite-assisted gauge. A 1-km ground-based rain gauge would require lasertransmitter power of the order of 3 mW; such, and much higher, powers are easily generated by modern lasers. Finally, the possible impact of multiple scatterings, absorption, aerosols/hydrometeors, and of the atmospheric turbulence on the proposed device is discussed. It is shown that with proper system design none of the aforementioned factors should impair the operation of the proposed rain gauge. Adequate system-design parameters are as follows: minimum receiver diameter is 0.1 mm; maximum receiver diameter is 16 mm; wavelength of operation is 0.63 ¿m; intermediate frequency is 1 MHz; and system bandwidth is 1 kHz.