M. Shiobara et al., OPTICAL DEPTH MEASUREMENTS OF AEROSOL, CLOUD, AND WATER-VAPOR USING SUN PHOTOMETERS DURING FIRE CIRRUS IFO-II, Journal of applied meteorology, 35(1), 1996, pp. 36-46
Optical depths in the visible to infrared spectral region were obtaine
d from solar extinction measurements with two sun photometers during t
he First ISCCP Regional Experiment Phase II Cirrus Intensive Field Obs
ervation in Kansas. A method is described to correct sun photometry fo
r gaseous absorption and is extended to estimate the water vapor amoun
t. The approach uses a prior computation of gaseous absorption for the
narrowband-pass sun photometry, parameterized with the slant-path abs
orber amount. These produce correction coefficients for gaseous absorp
tion, as determined by LOWTRAN 7 models. Near-infrared channels were c
alibrated by modified Langley plots taking account of gaseous absorpti
on. After the correction and calibration, the aerosol optical depths a
t the wavelengths of 0.4-4 mu m were obtained for clear sky conditions
. The aerosol optical depth at the wavelength lambda = 0.5 mu m was 0.
1-0.2 during the campaign. The cloud optical depth at lambda = 0.5 mu
m was obtained for cirrus events on 26 November and 5 December 1991 af
ter correction of multiple scattering effects involved in sun photomet
ry. The column amount of water vapor was estimated from the 0.94-mu m-
channel measurement and compared with results from radiosonde measurem
ents. The comparison has shown a good agreement within a 10% differenc
e during the campaign when the equivalent water vapor amount ranges fr
om 0.3 to 1.2 g cm(-2).