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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
| Landsat TMS Band 6
n ASTER BAND 12
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| Landsat Calibration
| 3
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ASTER Calibration nl
| Thermal Atmospheric Correction |
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Emissivity Hormalization |
o Temp image of Study Area Me) |
Figure 3. Methodology used in current investigation
3.1 Landsat and ASTER Calibration
Initially we perform Landsat Calibration to convert
Landsat TM and ASTER, and digital numbers to
spectral radiance or exoatmospheric reflectance
(reflectance above the atmosphere) using published
post-launch gains and offsets. The spectral radiance
(L3) is calculated using the following equation:
Ly = MIN, +] ee 5; VOCAL -OCALMIN)
Where: QCAL is the calibrated and quantized scaled
radiance in units of digital numbers
LMIN, is the spectral radiance at QCAL = 0
LMAX, is the spectral radiance at QCAL =
QCALMAX
LMIN, and LMAX, are derived from values
published in Chander, Markham, and Helder (2009).
The resulting radiance (L;) is in units of watts per
square meter per steradian per micrometer (W/
(n *sr*um)).
The exoatmospheric reflectance (p,) is calculated
using the following equation:
Where:
L, is the spectral radiance
d is the Earth-Sun distance in astronomical units
ESUN, is the mean solar exoatmospheric irradiance.
ENVI uses the ESUN, values from the Landsat 7
Science Data Users Handbook for Landsat 7 ETM+.
ENVI uses the ESUN, values from Chander and
Markham (2003) for Landsat TM 4 and 5.
6, is the solar zenith angle in degrees.
3.2 Thermal Atmospheric Correction
Thermal image data must be converted to radiance
before performing the atmospheric correction;
Thermal Atmospheric Correction requires for
approximation and it removes the atmospheric effect
contributions from thermal infrared radiance data.
Following the approach of (Johnson et. al. 1998)
determines the wavelength that most often exhibits
the maximum brightness temperature. This
wavelength is then used as the reference wavelength.
Only spectra that have their brightest temperature at
this wavelength are used to calculate the atmospheric
compensation. At this point, for each wavelength, the
reference blackbody radiance values are plotted
against measured radiances. A line is fitted to the
highest points in these plotted data and the fit is
weighted to assign more weight to regions with
denser sampling. The compensation for this band is
then applied as the slope and offset derived from the
linear regression of these data with their computed
blackbody radiances at the reference wavelength.
3.3 Converting to Emissivity and Temperature
(Emissivity Normalization)
The radiation emitted from a surface in the thermal
infrared wavelengths is a function of both the surface
temperature and emissivity. The emissivity relates to
the composition of the surface and is often used for
surface constituent mapping.
