Altitude measurement using laser beam reflected from water surface

In this paper altitude measurement from water surface using laser beam is presented. Research data indicate that the reflection of infrared waves from water surface is about zero and it is less than 2% for visible radiations. Phase-shift and heterodyne technique was used for the measurement, and the laser beam ( mW p nm 10 , 700 = = l ) was modulated by a sine wave having a fixed frequency. The optimum design and low-noise elements made it possible to detect a light power about 20 nW at operating frequency.