The operation of a surface acoustic wave spectrum analyser and digital integrator is reviewed. Expressions are derived for signal to noise ratio in the measured voltage spectrum with an approximation for the general case and rigorous treatment for the low signal case. A previous calibration study is re-evaluated to provide a final calibration for the atmospheric backscatter data accumulated by the airborne LATAS (laser true airspeed) coherent laser radar system.

A coherent lidar system based on a 3W CW CO2 laser has been installed on an aircraft positioned to look forward and down. A monostatic optical geometry is employed and the optical system incorporates a scanning mechanism that generates a line scan in the horizontal plane perpendicular to the aircraft. This scan pattern, coupled with the aircraft motion, produces a 2D coverage of the ground. The laser reflections from terrain features are collected and 2D images of the ground generated based on the amplitude of the return signals. A flight programme has been conducted and active images of a range of natural terrain and man made objects collected. This paper will describe the coherent laser system, its aircraft installation, signal processing and results obtained from the flight trial programme.

A new anemometer will be described for application to a wide range of difficult flow problems. This comprises a combined optical fringe and two-spot optical system of very great flexibility and a 10 ns "burst correlator" which can record and process bursts of individual photons from single particle transits. Operation is by photon correlation followed by Fourier cosine transformation at turbulence frequencies up to 10 KHz.

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.