Performance of a 1319 nm laser radar using RF pulse compression

Spaceborne lidars have been shown to provide data on surface elevation, vegetation canopy heights, and aerosol characteristics. Satellites carrying lidars for measuring ice sheet surface elevation and vegetation canopy heights are scheduled to be launched in the next few years. To achieve the necessary resolution and sensitivity, lidars on these satellites will use short duration, high peak power transmit pulses. Because of their high peak power, these lidars must be operated with a low pulse repetition frequency (PRF). The high peak power operation results in limited lidar lifetime and the low PRF provides insufficient spatial samples along the satellite track. To overcome these limitations of high peak power systems, at the University of Kansas we have developed a low peak power laser radar using modern RF techniques and fiber-optic technologies developed in support of the communication industry. We used RF pulse compression to achieve the sensitivity needed for spaceborne applications and have increased the PRF to provide more dense sampling. We have developed and reported preliminary results of a fiber-optic-based, laser radar that applies RF pulse compression and digital signal processing techniques to improve receiver sensitivity and range measurement capabilities. With our improved super-heterodyne receiver, we have achieved receiver sensitivities below -100 dBm with transmit pulses with 40 μs duration, 260 MHz bandwidth, and a 4 kHz PRF. These parameters are sufficient for altimeter operation from a satellite. We have modified the receiver architecture, performed detailed system simulations, developed a new data acquisition system, and conducted laboratory tests to verify simulation results. We present the system design, results of performance analyses and tests. We also show details on the two-stage down-conversion receiver with envelope detection and present issues concerning telescope-to-optical fiber coupling