This page provides updates
to the snow/ice and snow-free land surface temperature retrieval procedure
detailed in Key et al. (1997). The coefficients are based on modelled radiances
in the 11 and 12 um bands using Arctic and Antarctic temperature and humidity
profiles and angular emissivity models for snow. The equations do not include
a bias term to account for differences between modelled and actual radiances.
This has not been necessary for NOAA-14, which as validated extensively
with surface data from the SHEBA experiment. It may or may not be necessary
for other platforms. See Key et al. (1997) for additional details.
For ice/snow surface temperature
(IST) retrieval from the AVHRR and MODIS we use the equation
where
Ts is
the estimated surface temperature (K),
T11 and
T12 are the
brightness temperatures (K) at 11 um (AVHRR channel 4, MODIS band 31) and
12 um (AVHRR channel 5, MODIS band 32) and
q is the sensor scan
angle. Coefficients
a, b, c , and
d are derived for the following
temperature ranges:
T11 < 240K, 240K <
T11
< 260K,
T11 > 260K.
where
T11 and
T12 are the brightness temperatures of the 11 and 12 um channels
in Kelvin and the subscript
nadir and
forward refer to the
two viewing angles.
The regression model for snow-free
land using the AVHRR and ATSR is:
where
e is
the emissivity at the wavelength denoted by the subscript. Note: ATSR-2
coefficients have not been developed for snow-free land.
Key, J., J. Collins,
C. Fowler, and R. Stone, 1997. High-latitude surface temperature estimates
from thermal satellite data. Remote Sensing Environ., 61, 302-309.
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