Abstract 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.
[1]
E Raz,et al.
Measurement of the integrated water vapor content in the atmosphere by a radiometric method.
,
1987,
Applied optics.
[2]
F. Volz.
Economical Multispectral Sun Photometer for Measurements of Aerosol Extinction from 0.44 mum to 1.6 mum and Precipitable Water.
,
1974,
Applied optics.
[3]
Bo G Leckner,et al.
The spectral distribution of solar radiation at the earth's surface—elements of a model
,
1978
.
[4]
J H Perluissi,et al.
New LOWTRAN band model for water vapor.
,
1989,
Applied optics.
[5]
G. Paltridge,et al.
Radiative processes in meteorology and climatology
,
1976
.
[6]
V. Cuomo,et al.
Determining Ångström's Turbidity Coefficients: An Analysis with a Wide-Range Grating Spectrometer
,
1993
.
[7]
Gary J. Jedlovec,et al.
Precipitable water estimation from high-resolution split window radiance measurements
,
1990
.