A differential absorption technique in the near infra-red to determine precipitable water

• Published in: Atmospheric environment (1994) Vol. 28; no. 5; pp. 977 - 987
• Main Authors: Cuomo, V., Serio, C., Esposito, F., Pavese, G.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 1994; Elsevier Science
• Subjects: absorption spectra; aerosol; Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; infra-red; Precipitable water; Precipitable water; absorption spectra; infra-red; aerosol; Aerosols; Radiometry; Measurement method; Differential absorption; Absorption spectrum
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/1352-2310(94)90257-7

The analysis of an improved version of a radiometric method is described by which the total water amount over the entire atmospheric column may be determined by the use of a moderate resolution grating spectrometer. The method requires transmission measurements of solar spectral irradiance at differentially absorbing channels located in the wing of a water vapour band. Two water vapour bands are investigated: the 0.9- and l.4-μm H z0 bands. Since the method is based on the establishment of ratios of optical signals at given channels, there is no need for absolute calibration. Using an extensive set of rawinsonde temperature and water vapour mixing ratio profiles along with LOWTRAN 7 code, empirical curves between precipitable water and ratios of solar direct irradiance at differentially absorbing channels have been derived. The interrelationship with atmospheric aerosol has been particularly analysed. The method which has been proposed is based on observing the extinction of solar beam irradiance at four adjacent wavelengths rather than at two as it is habit. The result is a good independence of the method on the aerosol atmospheric load.