Direct-detection Ladar Research Articles

Ladar scene projector for a hardware-in-the-loop simulation system.

In order to test a direct-detection ladar in a hardware-in-the-loop simulation system, a ladar scene projector is proposed. A model based on the ladar range equation is developed to calculate the profile of the ladar return signal. The influences of both the atmosphere and the target's surface properties are considered. The insertion delays of different channels of the ladar scene projector are investigated and compensated for. A target range image with 108pixels is generated. The simulation range is from 0 to 15km, the range resolution is 1.04m, the range error is 1.28cm, and the peak-valley error for different channels is 15cm.

Acquisition algorithm for direct-detection ladars with Geiger-mode avalanche photodiodes

An optimal algorithm for detecting a target using a ladar system employing Geiger-mode avalanche photodiodes (GAPDs) is presented. The algorithm applies to any scenario where a ranging direct detection ladar is used to determine the presence of a target against a sky background within a specified range window. A complete statistical model of the detection process for GAPDs is presented, including GAPDs that are inactive for a fixed period of time each time they fire. The model is used to develop a constant false alarm rate detection algorithm that minimizes acquisition time. Numerical performance predictions, simulation results, and experimental results are presented.

Optical-fiber preamplifiers for ladar detection and associated measurements for improving the signal-to-noise ratio

In an effort to increase achievable postdetection signal-to-noise ratios (SNRs) of continuous-wave, 1-μm all-solid-state ladar systems, a prototype rare-earth-doped optical-fiber amplifier has been included in the optical return signal path of both a heterodyne and a direct-detection ladar system. We provide numerical predictions for SNR increases according to our previously developed theory. We also detail our experimental efforts and provide the results of SNR measurements for four distinct cases: direct ladar detection with and without a fiber amplifier, and heterodyne ladar detection with and without a fiber amplifier. Experimentally measured increases in SNRs for ladar systems incorporating an optical-fiber amplifier are then compared with our earlier predictions. Specifically, we have found that for direct detection with a fiber amplifier in place, the predicted SNR increase is 42.0 dB, and we have measured an increase of 36.5 dB. Similarly, for heterodyne ladar detection with a fiber amplifier, the predicted SNR increase is 3.8 dB, and we have measured an increase of 8.0 dB.