Data acquisition and processing of space borne lidar system

This paper discusses the various requirements of data acquisition and processing for Space Borne Lidar (Light Detection and Ranging) system being developed in Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum for the study of aerosols and clouds in the troposphere and lower stratosphere (0-40 km). The lidar system will be housed in a polar orbiting satellite at an altitude of 600 kin with a period of approximately 90 minutes providing global coverage. The lidar operates by transmitting a laser pulse down (nadir looking) and receiving the backscatter returns from the atmosphere. The laser source operates at dual wavelengths of 1064 and 532 nm with a pulse repetition rate of 5110 Hz with energy of 100 mJ. The receiving system consists of a 265 mm Fresnel lens telescope followed by backend optics and detector systems. The data acquisition system uses three channels with two types of photo detectors, namely photo multiplier tube and avalanche photo diode and operate either in analog (current) mode or discrete pulse (photon counting) mode. The data acquisition system has to handle signals of wide dynamic range (4-5 decades) and acquire the backscattered signal intensity with good spatial resolution. The analog channel will receive and digitize the 1064 nm signal with 16 bit resolution and the photon counting channels will count the 532 nm signal upto 200 MHz rate. The data backed up onboard is telemetered down to ground station during periods of visibility of satellite.