Atmospheric Lidar with Cross-Track Scanning

An eye-safe, multispectral cross-track scan subsystem with a large receiver aperture and a narrow FOV is proposed for the NASA Cloud Physics Lidar (CPL) to increase the horizontal scan area coverage. The /-14 degree cross-track scan capability will cover /- 5 km from nadir at a 20 km altitude. The cross-track scanner uses a bidirectional scan pattern, which collects 10,000 data points per cross track scan at a 5 kHz transmitter rep rate. Solar background is reduced with narrow bandpass filters and a narrow transmitter linewidth with center wavelength control. The scanner accounts for the return pulse lag angle due to pulse time of flight. The existing CPL vertical resolution is maintained at 30 m. Photon counting SPAD detectors and PMT's are used with photon counting modules and multichannel scalers, which support eye-safe operation. The compact receiver telescope design is achieved with a configuration that uses a fixed primary mirror and a scanning secondary mirror, which directs the return signal through a Coude path to the the detector optics bench. The multispectral lidar uses polarization discrimination on two of the three receiver channels, and the optics design supports a 100 urad receiver Instantaneous Field Of View to minimize the solar background noise.