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www.sea-technology.com August 2015 / st 23 Bathymetric Mapping From a Small UAV Compact, Lightweight Lidar System By Dr. John W. McLean overall system weight. Unmanned fight testing of PILLS 2.0 is scheduled for late summer 2015. Under sponsorship of the Offce of Naval Research (ONR), Arete has developed and demonstrated a com- pact, lightweight lidar system to perform bathymetric and topographic mapping from a small UAV. This system, called PILLS, delivers a capability that is comparable to, or bet- ter than, that provided by manned systems, but in a pack- age that is an order-of-magnitude smaller, lighter and lower power. Measurement performance includes mapping over a 1,000-ft. swath, 1-m sample spacing and better than 25-cm absolute vertical measurement precision. In addition, full waveform processing allows precise measurement of both water surface elevation and bottom depth, so no contem- poraneous tidal measurements are required for precision bathymetry. The initial fight demonstrations, conducted in 2013, were performed from manned aircraft (commercial photo- grammetry aircraft) to avoid the complexities of UAV inte- gration and operations. Full waveform lidar data along with associated platform position and attitude data were record- ed in fight, and topographic and bathymetric maps (point clouds) were generated post-fight. Post-fight data analysis of the lidar data veri- fed that the ranging precision was within re- quirements for pre- A irborne lidar systems have become standard survey tools for both topographic and bathymetric mapping, and topographic systems suitable for small UAVs are now becoming available. In order to penetrate to signifcant depths in water, bathymetric lidars require a much larger power-aperture product than topographic lidars, which adds additional challenges for UAV operations. In this ar- ticle, a new compact, lightweight lidar system is described that overcomes these diffculties, delivering a combined topobathy capability suitable for a small UAV. The system is designed to provide a measurement capa- bility comparable to current manned systems, but in a con- fguration suitable for a small unmanned aircraft. Measure- ment performance includes 1-m horizontal sampling, better than 2-m horizontal registration (absolute), and 25-cm verti- cal precision. The system weighs less than 30 lb., consumes less than 250 W (peak) and occupies less than 1 ft 3 . The system is currently confgured for the Navy's RQ-21A small tactical unmanned aerial system (STUAS), but the modular design is readily adaptable to a wide variety of manned and unmanned aircraft. In contrast to other lidar systems, a scannerless design based on a pushbroom imaging approach is used. The frst- generation bathymetric system (pushbroom imaging lidar for littoral surveillance - PILLS 1.0) was completed in 2012. The second-generation system is currently in integration and includes onboard, real-time processing and reductions in The PILLS integrated lidar system for bathymetry and topography as confgured to ft within the payload bay of the RQ-21A STUAS.