Simplified calculations for accuracy of a lidar dial system to measure atmospheric H2O vapor and temperature

A simple method is given for computing the relative errors in H2O vapor and T (temperature) profiles measured by a ground-based differential lidar system: The analysis is based on a simplified model of the earth's atmosphere, which allows one to write exact mathematical expressions for the lidar return signals which can be evaluated in closed form. Error computations can be made from these expressions with a small pocket calculator to an accuracy of a few percent. Error estimates are given for a lidar system used to measure H2O and T profiles from the ground up to a 5-km altitude. The results are given for an ideal system with no instrument noise and for a system using quantum detectors with detector-amplifier noise and less than unity quantum efficiency. The relative merits of the photomultiplier tube and silicon diode as detectors are also assessed using this technique of error analysis. Regions of useful operation for these detectors are defined in terms of the signal energy of the lidar return and the noise equivalent power of the detector.