Lidar measurements of spike returns from clear air are presented. These spikes occur infrequently (approximately one in hundred returns) but provide returns that are significantly stronger (occasionally an order of magnitude larger) than the average aerosol backscatter signal. The spike density is 5.7e-3 spikes m-3 for backscattering cross sections estimates to be between 0.003 and 0.080 mm2 sr-1. A modified form of the lidar equation which includes returns from large particulates is presented and the probability distribution for the spike magnitudes is derived from five million measurements.
Measurements and simulations of a dual gas-cell system, which uses Raman scattering to convert infrared laser radiation from 1064 to 1560 nm, are presented. The cells contain deuterium at a pressure of ~25 atm. A beamsplitter is used to distribute the energy from the YAG laser between the seed and pump cells. The laser light is focused into the seed cell, which generates a lower-power, backward-propagating, pulse. This seed pulse and a laser pulse counterpropagate in the pump cell to generate a stronger 1560-nm pulse. The goal is to create a single pulse without any shorter pulses or oscillations. Simulation results are presented, which indicate that a beamsplitter directing 25% of the laser energy into the seed cell and the rest into the pump cell is optimal for 1560-nm generation. Laboratory testing of a dual-cell system using a 32% beamsplitter shows the generation of a 1560-nm pulse with 250 mJ/pulse with an efficiency of 35%.
Over a thousand measurements of optical refraction across the Chesapeake Bay were made between November 1999 and June 2001. A survey station was placed on the western side of the bay south of Chesapeake Beach MD and used to view lights on Tilghman Island MD on the eastern side at a range of 16.2 km. In addition, the survey station viewed buoys at ranges of 690, 1420, 2050, 2790, 3440, and 4180 m. The heights for the survey station measurements were 2.3, 3.5, 5.4, 12.7, 27.7, and 37 m above the mean water level and the lights were located at 4.7, 9.5, 13.7, 27.0 m above the water level. When weather and work schedules permitted, observations were made twice a day (just after sunrise and at noon). Survey station measurements of the closest buoy are used to estimate the water level. Observations of air-sea temperature difference measured by the mid-bay buoy in the Chesapeake Bay Observing Station (CBOS) are compared with the elevation angles. The elevation angles and air-sea temperature differences (ASTD) are analyzed over an annual cycle. The elevation angles and the non-dimensional curvature of the refractive rays are compared with the ASTD.
A lidar system, developed to map atmospheric extinction under the flight path of a P-3 aircraft, was tested during the Key 90 experiment. Using a modified Cassegrainian telescope, the return signals from both wide and narrow field of view are detected. Optical depth and extinction profiles are derived from these signals. The instrument design, data analysis, and measurements from Key 90 are discussed.
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