Instrumental and Atmospheric Considerations in the Development and Application of an Airborne/Spaceborne Water Vapor DIAL System

Abstract

The Differential Absorption Lidar (DIAL) technique can be used to measure concentration profiles of many atmospheric gases1. Atmospheric water vapor (H2O) has been measured with the DIAL technique from ground-based2-4 and airborne systems5. In the DIAL technique, two laser wavelengths are transmitted near simultaneously, one "on" the peak of the H2O absorption line and another away from, or "off" the peak. In the range resolved DIAL measurement, H2O concentration between two ranges is calculated using the well known DIAL equation1, which is a function of the on and off signals at the two ranges and the effective H2O differential, absorption cross section. Random errors due to noise in the detected signal and systematic errors due to uncertainties in the knowledge of the effective cross section, Δσ, contribute to inaccuracy in the DIAL measurements. The development of a DIAL system must give full consideration to these two sources of error and any known systematic offsets can be at least partially compensated for in the DIAL data analysis phase. A brief discussion of these effects is given in this paper, and a more detailed description of these effects is given in Ismail and Browell6.