Dr. Guangning Yang

Space laser altimeters provide high precision global elevation data needed for a broad range of science objectives, including determining ice sheet and glacier heights, sea ice thickness, vegetation structure and land flight (ToF) of laser pulses and the return laser pulse energy, to retrieve surface height and reflectivity at the laser wavelength. NASA has a 30-year history of operating laser altimeters in orbit to measure the elevation of the Earth’s surface and its change.  We present the lidar design and airborne demonstration of a concurrent artificially-intelligent spectrometry and adaptive lidar system (CASALS). A 1040 nm seed laser cycles through 256 wavelength steps while pulsing at 144 kHz. The wavelength stepped pulse train is efficiently amplified by fiber amplifiers and subsequently diffracted by a grating to illuminate 256 resolvable footprints on the surface. High laser peak power is retained for each footprint to improve performance. The footprints are imaged by a receiver (RX) telescope onto an entrance slit and reimaged onto an exit slit by a grating monochromator that rejects solar photons spatially and spectrally for all footprints. The footprints are subsequently relayed onto a 2x8 linear HgCdTe avalanche photodiode detector array whose 8 outputs are time-division multiplexed to two fast digitizers. The digitized waveforms are range-gated and streamed to a solid-state drive for post processing. The design increases coverage while reducing the power consumption owing to the fast non-mechanical steering of the efficiently generated laser beam, imaging the footprints across the nearly noiseless detector array, and the RX signal multiplexing. The lidar airborne demonstration was performed around ~4.5 km altitude where the 256 tracks span a swath of ~58 m.  preliminary results of gapless 3D imaging of various surfaces are presented. The airborne demonstration validates the lidar design and performance. Spaceborne CASALS lidar design configurations are discussed for future surface topography and vegetation missions.

Biography:

Guangning Yang received his Ph.D. degree in Electrical Engineering from Drexel University, USA. For the past 18 years he has worked at NASA Goddard Space Flight Center on lidar and laser ranging. He was the Product Development Lead on photon counting detector for the ATLAS laser altimeter instrument on the ICESat-2 mission, Principal Investigator (PI) for the Laser Communications Relay Demonstration (LCRD) Optimetrics Experiment, and PI for the CASALS lidar development. He co-invented the CASALS lidar system. Prior to joining NASA, he worked at telecommunication industries for terminal hardware design and development for both submarine and terrestrial applications.