University of Florida (UF) researchers are developing an airborne laser swath mapping (ALSM) unit based on a paradigm referred to as photon counting ALSM, or PC-ALSM. In the PC-ALSM approach relatively low energy (few micro-joule) laser pulses are used to illuminate a surface 'patch' of terrain a few meters in extent. Reflected photons are imaged onto a multi-channel photomultiplier tube, to achieve high resolution (few decimeter) contiguous coverage of the terrain. A multi-channel multi-stop timing unit records both noise and signal events within a range gated window, and the noise events are filtered out of the data during post flight processing. A first generation PC-ALSM sensor, the Coastal Area Tactical-mapping System (CATS), is being developed with funding from the Office of Naval Research (ONR). The CATS sensor will be tested and operated from the UF Cessna 337 aircraft, which is equipped with a commercial ALSM unit. However, the ultimate goal of the UF research is to verify that PC-ALSM offers the possibility of developing a high resolution airborne laser mapping unit small and light enough, and with sufficient energy efficiency, to operate from a UAV.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.