Abstract

The sensitivity advantages of coherent detection can potentially be employed to make range-resolved differential absorption lidar (DIAL) measurements of atmospheric species even when transmit pulse energies are relatively low. By operating in a shot-noise-limited mode, coherent lidars often obtain average carrier-to-noise ratios (CNR's) as much as 30 dB higher than would be measured with equivalent direct-detection systems. This apparent advantage in average CNR is at least partially offset by the characteristically large fluctuation in the instantaneous received irradiance due to target speckle effects.¹ To measure mean backscattered-signal irradiance accurately, the variance due to these fluctuations must be reduced to an acceptable level by averaging.

© 1983 Optical Society of America