Biomedical Engineering Reference
In-Depth Information
Conversion of Thermal Band Digital Number
into At-Sensor Radiance
The digital number (DN) has linear relationship with radiance. For calculation of
radiance, upper and lower bounds of radiance are required to be known which is
available in calibration parameter file (CPF). CPF contains all the processing
parameters, which were downloaded from internet for specific date of satellite
overpass. There are 15 radiometric and 11 geometric parameters. Radiometric
parameters include detectors gain, bias, scaling parameters, etc. Conversion of DN
into spectral radiance was performed using USGS [
1
] method as follows.
Radiance
ðÞ¼
L
max
L
min
½
ð
Þ =
255
DN
þ
L
min
Conversion of Spectral Radiance to At-Sensor Temperature
At-sensor radiance was converted to a more useful variable namely the effective
at-sensor temperature of viewed Earth-atmosphere system. The ETM+ thermal
band data was converted from spectral radiance to at-sensor temperature assuming
unity emissivity following the method given by Schott and Volchok [
2
], Wukelic
et al. [
3
].
o
ðÞ¼
K
2
=
ln
T
B
½
ð
K
1
þ
L
Þ =
L
:
Conversion of At-Sensor Brightness Temperature to LST
Estimation of LST from radiance directly does not represent a true surface
temperature but a mixed signal or the sum of different fraction of energy.
These fractions include energy emitted from the ground [
4
], upwelling radiance
from the atmosphere, as well as downwelling radiance from the sky integrated
over the hemisphere above the surface (Fig.
2
).
Results and Discussion
Land Cover and Land Surface Temperature
Significant variation in near surface temperature exists among different land cover
categories (Figs.
3
and
4
) in both the seasons (May and August). Among different
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