We discuss the optimization of components in a single-wavelength airborne laser bathymeter that is intended for a low-power unmanned aerial vehicle platform. The theoretical minimum energy requirement to detect the submerged sea floor in shallow (< 5 m) water using a low signal-to-noise ratio (LSNR) detection methodology is calculated. Results are presented from tests of a prototype light detection and ranging (LiDAR) instrument that was developed by the University of Florida, Gainesville. A green wavelength (532 nm), 100-beamlet, low-energy (35-nJ/beamlet), short-pulse (480 ps) laser ranging system was operated from a low-altitude (500-m) aircraft, with a multichannel sensor that is capable of single photoelectron sensitivity and multiple stops. Data that were collected during tests display vertical structure in shallow-water areas based on fixed threshold crossings at a single-photon sensitivity level. A major concern for the binary detection strategy is the reliable identification and removal of noise events. Potential causes of ranging errors related to photomultiplier tube afterpulsing, impedance mismatching, and gain block overdrive are described. Data collection/processing solutions based on local density estimation are explored. Previous studies on LSNR performance metrics showed that short (15-cm) dead time could be expected in the case of multiple scattering objects, indicating the possibility of seamless topographic/bathymetric mapping with minimal discontinuity at the waterline. LiDAR depth estimates from airborne profiles are compared to on-site measurements, and near-shore submerged feature identification is presented.Index Terms-Airborne laser swath mapping (ALSM), bathymetry, light detection and ranging (LiDAR), photonics.

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One century after the Wright brothers proved it was possible to build a piloted heavier‐than‐air “flying machine,” several airlines will soon, perhaps as early as October 2005, begin to operate the largest passenger aircraft ever built, the Airbus A380. The A380 is nearly half again as large, in terms of passenger floor space, as the Boeing 747‐400. It can be configured to hold as many as 840 passengers, and it has a takeoff weight of 550,000 kg, a maximum range of 15,000 km, and a cruising speed of Mach 0.85. The remarkable advances in aeronautics realized during the past century make it difficult to understand how anyone, let alone Simon Newcomb, one of the most prominent U.S. scientists at the turn of the twentieth century, could have opposed efforts by Samuel Pierpont Langley to build a piloted winged aircraft for the military. Newcomb argued that Langley was doomed to failure because the technology required to build such an aircraft was not then available, and he bemoaned the “waste” of scarce government funds toward the effort.

Microgal gravimetry's unique ability to sense mass anomalies and movements beneath the surface of the Earth makes it a promising technology for science and engineering, particularly when it is used with Global Positioning System geometrical measurements. It is rapidly becoming the method of choice for measuring postglacial rebound, monitoring active volcanoes, modeling subsurface cavities, detecting changes in aquifers, and studying changes in the Arctic and Antarctic ice masses. More than 50 scientists and students from 14 nations recently met at a Chapman Conference to discuss microgal gravimetry and its applications.