Abstract

To establish natural aerosol backscatter coefficients over extended regions of the globe, the Geophysics Laboratory (GL) of the US Air Force Systems Command and the Royal Signals and Radar Establishment (RSRE) of Great Britain have joined in a co-operative program of lidar observations utilizing both ground based and airborne instrumentation. A preliminary account of the measurement programme in the South Atlantic has been given in Reference 1. Aircraft measurements have been made with a CO₂ 10.6µm coherent lidar mounted in the bomb bay of a Royal Aircraft Establishment Canberra bomber operating throughout complex test flights to above 50,000 feet. At the surface, simultaneously and in the near vicinity of the aircraft flight path, altitude profiles of backscatter were acquired by a coherent CO₂ lidar and a doubled and tripled YAG lidar provided by Phillips Laboratory. In addition to the lidar, the aircraft carried particle size probes under the wings. Supporting meteorological data were obtained from local sonde launches, and from the Air Force Air Weather Service and the British Meteorological Office. The airborne system provides essentially an in situ measurement, sampling approximately 100 metres ahead of the aircraft with a sensitivity threshold of 8 × 10^-12m^-1 - sterad^-1. The range gated systems on the ground have altitude resolution of 150 or 300 metre, power levels of the order of 100 millijoule (IR and visible) per pulse, and pulse repetition frequencies of 100 and 10 per second. Field measurements have been completed from Ascension Island in the South Atlantic [Oct-Nov 1988 (aircraft only) and Jun/Jul 1989], from Keflavik, Iceland [May 1990 (aircraft only)], and Terceira, Azores [March 1990 (aircraft only) and Aug 1990]. Two specimen results are shown in Figures 1 and 2. Comparisons of LWIR and visible data, of airborne and ground based data, and results of particle probe measurements will be presented.

© 1991 Optical Society of America