The Hull Coherent DIAL Programme
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An experimental programme to exploit the advantages of coherent laser radars has been in progress at Hull since January, 1976. A 10 μm, coherent laser radar system has a much greater range capability along a near horizontal tropospheric path than either a uv-visible system or an infrared system employing direct detection. Further advantages of a coherent system operating at 10 μm include eye-safety, immunity to solar background radiation, good all-weather performance and the need to transmit relatively small amounts of energy. The inherent capability for high spectral resolution enables Doppler measurements to be made. Here we consider some problems in the application of these systems to differential absorption lidar (DIAL) and discuss briefly work in our laboratory.
KeywordsCoherent System Unstable Resonator Fractional Bias Differential Absorption Lidar Lidar Equation
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References and Footnotes
- (6).Where the bandwidth of the pulse is large compared with atmospheric Doppler shifts the frequency-time correlation properties of the return are described by the radar ambiguity function. For simple pulses the correlation time is about the pulse duration; unfortunately except for chirp-free SLM operation laser pulses are not simple.Google Scholar
- (7).Ambiguity considerations suggest that the notion of obtaining temporally independent returns from essentially the same scatter volume is possible in principle provided the pulse bandwidth is much greater than the reciprocal pulse duration and pulse compression (matched) filters are not used. How closely the ideal can be realised in practice is not considered here. An alternative approach would of course be aperture (spatial) averagino which is demanding technically as use is made of a photodetector array; the conclusions here would be essentially unaffected.Google Scholar
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