ABSTRACT:
An improved model for the absortion
absorption of the atmosphere near the 22 GHz water vapor line is presented.
The Van-Vleck-Weisskopf line shape is used with
a simple parameterized version of the model from Liebe for the water
vapor absorption spectra and a scaling of the model
from Rosenkranz for the 20-32 GHz oxygen absorption. Radiometric
brightness temperature measurements from two sites
of contrasting climatological properties (San Diego, CA and
West Palm Beach, FL ) were used as ground truth
for comparison with in situ radiosonde derived brightness temperatures.
The retrieval of the new model’s four parameters,
related to water vapor line strength, line width and continuum absorption,
and far-wing oxygen absorption, was performed using
the Newton-Raphson inversion method. In addition, the Hill line
shape asymmetry ratio was evaluated on several
currently used models to show the agreement of the data with the new model,
and rule out atmospheric vapor absorption models
near 22 GHz given by Waters and Ulaby, Moore and Fung which are
based on the Gross line shape. Results show
a 23% improvement in the difference between modeled and measured
brightness temperature from the atmosphere compared
to current models.