X-B8, 2012 
  
Sun 
Azimuth 
37.80 
  
  
154.75 
  
87.15 
  
  
  
current 
nfrared region 
emperature of 
The infrared 
be converted 
e Emissivity 
]iance is then 
methodology 
igure 3. Both 
re processed 
  
)10 Band 6 
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 
  
Y 
| Landsat Calibration 
  
  
  
| 3 
  
ES | 
ASTER Calibration nl 
| Thermal Atmospheric Correction | 
  
Ÿ 
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.