Measurement of the integrated water vapor content in the atmosphere by a radiometric method.

An improved version of a two-wavelength radiometric method is described by which the total water vapor amount along an optical path may be determined by the use of a radiometer and a source at the two ends of the optical path. The method requires two transmission measurements: one at 1.14 microm (at the center of an absorption band) and another at 1.06 microm (an atmospheric window). The spectral transmittance is calculated using the FASCODE computer code, convolved with the source, filter, and detector response curves of the transmissometer. Good agreement (1-7%) is obtained with experimental observations of this quantity as a function of total water vapor amount. The method was verified for horizontal paths of up to 10 km.