The airborne backscatter measurements at 10.6 μm, from the South Atlantic Backscatter Lidar Experiment (SABLE) and the Global Atmospheric Backscatter Lidar Experiment (GABLE) programs over the Atlantic, are gathered together and presented. Plots of backscatter versus altitude are shown for 80 flight sequences. These data comprising about 4×105 measurements from over 180 flight hours is statistically analyzed. The material is distributed in altitude (1 km) and backscatter (half decade) intervals and presented in tabular and histogram form for six principal regions and seasons: South Atlantic summer, South Atlantic winter, far‐North Atlantic spring, mid‐Atlantic spring/summer, and Northeast Atlantic winter and summer. Several features of the results are discussed, including the incidence of low backscatter and drop‐outs and the remarkably high incidence of thin cirrus in the southern tropical winter season. The compendium should provide a climatology of atmospheric backscatter at 10.6 μm for regions of the Atlantic during the relatively clean atmospheric period 1988–1990.

During the period 1988–1990, studies of atmospheric aerosol have been made over the Atlantic. These include measurement programs out of Ascension Island (8°S, 14°W), the Azores (38°N, 25°W), Iceland (63°N, 23°W), and from the United Kingdom over the Northeast Atlantic. For these studies the equipment deployed included an airborne backscatter lidar (operating at 10.6 μm), airborne particle‐sounding probes, ground‐based lidars (operating at 10.6, 0.53, and 0.35 μm), balloon radiosondes, and a Sun‐tracking photometer. In addition, standard meteorological information has been incorporated along with, when appropriate, data from the SAGE II limb‐sounding satellite. The present paper thus introduces an overview of the program together with an outline of the technology, measurement characteristics, and performance of the airborne equipment that determined the strategic planning of much of the work. The measurements themselves, made in the relatively clean period for the atmosphere before the Mount Pinatubo eruption, will be presented in a subsequent series of papers.

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.

Signal fluctuations from coherent lidar systems have been considered both theoretically and experimentally by many authors in different wavelength regimes. At 10.6µm Hardesty et al [1] considered characteristics of coherent lidar returns from calibration targets and aerosols; Flamant et al [2] used a pulsed CO2 lidar to study speckle effects from various rough surfaces and Letalick et al [3] measured signal amplitude distributions for a FM-cw CO2 laser radar. In other studies Vaughan et al [4] employed correlation analysis to study signal fluctuations from a moving belt.

The Air Force’s Phillips and Wright Laboratories are engaged in developing and applying coherent lidar/ladar technology from ground and aircraft based platforms with a vision for possible future space based sensors. An overview of current programs in the areas of imaging, wind profiling, DIAL, laser technology, and modeling will be presented.