Environmental Engineering Reference
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If we adopt emissivity correction to this equation, then
LST ¼ c
1
þ c
2
T
11
þ c
3
W
sec
θ þ c
4
1
ð
ε
11
Þ
(19.55)
19.4 Forward Simulations and Regression Coefficients
19.4.1 Forward Simulations
In order to derive regression coefficients in our algorithms and test and compare
algorithm accuracy, forward simulations using radiative transfer model, such as the
MODerate-resolution atmospheric TRANsmission (MODTRAN), are performed to
generate a comprehensive simulation dataset.
The MODTRAN atmospheric radiative transfer model (Berk et al.
2000
) has
been widely used in satellite remote sensing studies for about three decades. It is a
moderate spectral resolution model, up to cm-1 in frequency. The radiative transfer
simulation procedure is illustrated in Fig.
19.5
.
In order to account for the wide range of different atmospheric and surface
conditions, a large number of simulations for each season need to be performed
with variations in:
• Geometry of the problem (solar zenith angle, viewing, and azimuth angles).
• Atmospheric conditions (profiles of ozone, water vapor, aerosols).
• Surface conditions (spectral characteristics of the surface).
• Characteristics of the instrument (spectral response of the satellite sensors); the
GOES spectral response functions can be obtained from the NOAA/NESDIS
To make the simulations applicable to all possible conditions, the atmospheric
(height, temperature, and relative humidity) profiles with the matched surface
height, pressure, temperature, and relative humidity from the Global NCEP Reanal-
ysis (NRA) climatology (long-term mean) are used as the input.
In order to represent the variability in solar geometry, the solar zenith angel
(SZA) are calculated according to the latitude, longitude, Julian day, GMT time;
thus, the values at global coverage may vary from 0
to 180
.
To consider the effects of satellite zenith angles, simulations were performed for
five zenith angle bins as satellite viewing zenith angle (VZA: 0, 2, 4, 6, 8), which is
equal to satellite zenith angle (SZA: 0, 12.8, 26.38, 41.75, 62.44).
In order tomake the GOES forward simulations applicable to different sensors with
different spectral response functions (SRF), we performed simulations to a wide
spectral range from 3 to 14
m with 10 cm-1 resolution. Therefore, the input surface
reflectance/emissivity was not for a specific channel, but was for full spectra. We used
μ
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