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Proceedings of the Symposium on Global and Environmental Monitoring

5. The assumption that radiometric surface
temperature equals surface air temperature is not
generally valid. In fact a considerable
temperature discontinuity may exist in the lowest
meter of the atmosphere during the day. In the
present case satellite derived surface
temperatures range as high as 55 C, while air
temperatures, even in mid July, are mostly below
40 C. This implies that the assumed temperature
distribution T(p) = T (1 - k 6p/p) is
substantially incorrect.
Three potential sources of additional information
may be considered: a) The sounder data from the
HIRS may be used to extrapolate downward through
the atmosphere (Davis and Tarpley, 1983); or b)
one may use reported air temperatures from
weather stations, with a resultant sampling
problem in many areas of the world, or c) the
estimated temperature of vegetated areas may be
used to approximate air temperature at shelter
height (Price, 1990). The last method uses only
coincident AVHRR data, but also requires further
analysis because few AVHRR picture elements
represent pure vegetation cover in many areas
such as the U.S.
Further work is needed to establish the value of
the procedure describe here for routine use in
computations of the energy and moisture budgets
at the earth's surface.
A procedure has been described for relating
variability of AVHRR channels 4 and 5 to moisture
and temperature. The method is an approximate
procedure which is probably not competitive with
conventional meteorological data in many areas.
Its utility in practice will depend on the
ability to screen the data for clouds, and to
reduce errors associated with the various
approximations. The principal advantage of the
method is its capability to routinely process
AVHRR data for the considerable information it
contains about the earth's surface energy and
moisture budget, and for possible correction of
vegetation index calculations for atmospheric
moisture. The method needs to be verified
against an independent measure after the approach
has been incorporated in a conventional sounding
Davis, P.A., and J.D. Tarpley, 1983, Estimation
of shelter temperatures from operational
satellite sounder data, J. of Clim. and Appl.
Met., 22:369-376.
Price, J.C., 1984, Land surface temperature
measurements from the split window channels of
the NOAA 7 Advanced Very High Resolution
Radiometer, J. Geophys. Res., 89, pp 7231-7237.
Price, J.C., 1990, Using spatial context in
satellite data to Infer regional scale
évapotranspiration, IEEE Trans, on Geosci. and
Remote Sens., in press.
Kleespies, T. J., and L. M. McMillan, 1987, An
Extension of the Split Window Technique for the
Retreival of Précipitable Water: Experimental
Verification, Contribution of NESDIS Authors to
the International Workshop on Remote Sensing
Retreival Methods, Williamsburg, VA., pp 335-345.
Kneizys, F. X., E. P. Shettle, W.O. Gallery, L.
H. Chetwynd, Jr., L. W. Abreu, J.E.A. Selby, R.
W. Genn, and R. A. McClatchey, 1980, Atmospheric
Transmittance/Radiance: Computer Code Lowtran 5,
Envir.Res. Paper 697, pp 57-60, Air Force Geophys
Lab., Hanscom AFB, Mass.
Price, J. C., 1989, Estimating évapotranspiration
over large areas, IGARSS'89/12th Canadian
Symposium on Remote Sensing, 4, pp 2138-2141.
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