The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
The ASD field spectrometer is measuring in the range of 325 - 
1075 nm. This range is covering the spectral range of Proba 
CHRIS hyperspectral image data. The field spectrometer 
measurements are collected randomly over the study area (Fig. 
1). Before going to the field, the measurement sites are defined 
from a Terra ASTER image (27.04.2001) and ancillary data 
including different surface covers and accessible sites. As many 
as possible sites have been chosen. At the field study 106 sites 
are measured. Samples of the geological materials covering the 
surface of the site are collected at 30 sites to be measured with a 
laboratory spectrometer. Throughout the field study, at some 
days there have been no stable weather conditions. This has to 
some extent affected the field study. Due to this, before each 
spectral measurement the spectrometer has been calibrated and 
hand specimens collected. 
M-ai* W3?ts intm .«-«w 
»3JS*t M*WB M-361 J.r«B 
Figure 1. Proba CHRIS image of the study area with field 
measurement sites (yellow asterisks) 
Not all the field measurement sites had laboratory samples. The 
laboratory measurements of the hand specimens are done to 
verify spectral details and provide information for removing 
artifacts from the field and image data. After receiving the 
image data it has been observed that some of the image is cloud 
covered and cloud shadowed. These no data areas have even 
included some field measurement sites. 
METHODOLOGY 
The Proba CHRIS image mode 1 with the acquisition angle -55 
has been covering the study area. In the image data the missing 
pixels have been filled and stripes have been removed using the 
HDFclean program (Cutter, M., A., 2006). The clouds and 
cloud shadows have been masked. 
The Proba CHRIS image data is atmospherically corrected to 
remove the effects of scattering and absorption of the 
atmosphere and to convert from radiance values received at the 
sensor to reflectance values of the imaged surface materials. 
Three different atmospheric correction methods are used 
(Bertels, et al., 2006 and Van der Meer, et al., 2001): 
1) Scene derived correction: IARR 
The internal average relative reflectance normalizes the image 
to a scene average spectrum. This shifts all spectral radiances to 
the same relative brightness. The resulting spectral values 
represent reflectance relative to the average spectrum. 
2) Ground-calibrating method: Empirical Line 
Calibration 
The technique is used to force image data to match selected 
field reflectance spectra. It requires field or laboratory 
reflectance spectra of at least two uniform ground targets. For 
each spectral band a linear regression is calculated between the 
reference spectra and the image spectra. 
3) Radiative transfer model: 6S 
The 6S (Second Simulation of the Satellite Signal in the Solar 
Spectrum) model is used to predict the atmospheric radiative 
properties and to model the radiance at the sensor (Vermote, et 
al., 1997). 
After calculating reflectance values of the Proba CHRIS image 
the backscatter response curves are derived for different surface 
materials to integrate the image, field and laboratory spectral 
data. These data are used to create a spectral library of the study 
area for the end member selection. 
Following these, the dimensionality, the inherent redundancy 
and noise in Proba CHRIS data is reduced by the principal 
components transform, minimum noise fraction. Then the 
reference spectra and the image spectra are compared and a 
spectrum match, spectral angle mapper, is applied. The spectral 
angle mapper is a spectral classification that matches pixels to 
the reference spectra. The algorithm determines the spectral 
similarity between two spectra by calculating the angle between 
the spectra. Following the classification process the lithological 
map of the (^ankiri-Eldivan area is produced and verified with 
the ancillary data. 
RESULTS AND DISCUSSION 
At first, the atmospherically corrected Proba CHRIS 
hyperspectral image data is compared with field and laboratory 
spectra. Three different methods have been used for the 
calibration of the hyperspectral image data: IARR, empirical 
line calibration and 6S. The results of the internal average 
relative reflectance correction have not matched the field and 
laboratory spectra. There are a few green agricultural areas and 
a small forest area in the study area. The vegetation and the 
small dam lakes caused strong absorption and affected the result. 
The empirical line calibration requires at least two reference 
targets: white and dark. In the image area there are good white 
targets but none dark target with field spectroscopy data is 
supplied for the empirical line calibration. This caused a minor 
mismatch with the field and laboratory spectra. 
The best atmospheric correction has been the 6S radiative 
transfer model. 6S is quite effective but needs a lot of input 
parameters to execute the program. Some of these parameters 
need additional field measurements. Nevertheless, the program 
has let choose between default parameters. 
Wavelenghts 
range (nm) 
Xa 
Xb 
Xc 
Total 
irradiance 
405.0-486.9 
0.0031 
0.2242 
0.19069 
1372.602 
486.9-586.9 
0.0028 
0.1078 
0.13097 
1439.093 
586.9-697.8 
0.003 
0.0581 
0.09385 
1263.639 
697.8-749.0 
0.0036 
0.041 
0.07557 
1044.318 
749.0-1008.8 
0.0052 
0.0265 
0.05653 
712.782 
Table 1. Coefficients for atmospheric correction simulated 
using 6S code 
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