Lidar-radar heterodyne receiver for underwater imaging applications

High spatial resolution, LIDAR images of underwater targets from air and submersed platforms are plagued by poor signal-to-noise ratios (SNR), arising from strong scattering in the turbid media of seawater. A hybrid system that combines the detection and coherent signal processing techniques of conventional RADAR with the optical propagation characteristics of LIDAR improves target detectability and image contrast. For this application the receiver should have a good response at the RF modulation frequency of 1 GHz and a large dynamic range to detect return signals from deep targets in highly scattering waters. Radiation Monitoring Devices, Inc. (RMD) proposes to develop an avalanche photodiode (APD) based receiver system to increase the SNR by at least ten fold and the dynamic range by more than 20 dB over existing PMT based receiver modules. The novel receiver will operate on gain modulation and heterodyne detection techniques in order to offer improved system response at the required high modulation frequency (~1 GHz). By leveraging previous experience with high performance receiver systems, RMD's highly qualified research team will design, fabricate and deliver an APD-based receiver module with ~ 1 GHz bandwidth, ~ 60dB dynamic range and a superior SNR to NAVAIR for evaluation.