Mixed topographic and shallow bathymetric mapping via multi-stop single photoelectron laser ranging

Airborne laser swath mapping (ALSM) systems collect thousands of range measurements per second, enabling efficient high-resolution surface mapping. Low signal-to-noise ratio (LSNR) detection techniques allow for implementation of light detection and ranging (LIDAR) instrumentation on platforms with prohibitive power, size, and weight restrictions. The viability of single-wavelength photon counting techniques applied to mixed target detection and shallow-water bathymetry has not been previously investigated in detail.;The system design process for constructing a LSNR LIDAR system is described, with emphasis on component selection as related to theoretical performance. Cost-effective microchip lasers are now commercially available that produce sub-nanosecond pulse widths and stable peak energies (>1 muJ at 10 kHz). In order to detect backscattered laser radiation at low power levels, detector elements must be capable of single photon sensitivity; a high gain (10 5), fast response (sub-250 ps rise time) detector is therefore central to photon counting operation. Micro-channel plate photomultiplier tubes (MCP-PMTs) are capable of attaining these specifications with simultaneous two-dimensional detection over an array.;The University of Florida's prototype LSNR LIDAR sensor -- the Coastal Area Tactical-mapping System (CATS) -- was constructed with these major components in mind. The instrument is designed to operate in a fixed-wing aircraft flying 600 m above ground level, producing 3 muJ output pulses at 8 kHz to allow for 20 cm spatial resolution by scanning a 10x10 array of laser beamlets. Ground-based field testing results yield 10 cm range accuracy and small-scale feature identification at variable scan settings.;Experimental data is presented establishing the ability to record multiple returns from the same laser pulse. Evaluation of system dead time shows that the minimum separation distance required to discriminate multiple scattering objects is 15 cm, indicating the possibility of seamless topographic / bathymetric mapping with no gap at the waterline. Data collected during tests display vertical structure in shallow water areas based on fixed threshold crossings at very low signal levels. A major concern for the binary detection strategy is dark / atmospheric / crosstalk noise producing false-positive measurements. Potential causes of image ghosting are described, and data collection / processing solutions based on local density estimation are explored. LIDAR depth estimates from airborne profiles are compared to on-site measurements, and near-shore submerged feature identification is presented.;Analysis of CATS data confirms simulation estimates of decimeter-scale spatial resolution for hybrid topographic and shallow bathymetric mapping. Dark noise production and atmospheric scattering in daylight operation at maximum signal amplification does not significantly impede feature identification procedures. In order to combat the high variability in dynamic range, modifications to the detector structure may be necessary to reduce anomalous effects.