36 
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
1. A high-reflectance results in higher signal-to-noise ratio 
(SNR) which, in return, increases overall accuracy. 
2. The higher the spatial uniformity of the area, the lesser the 
effects of generalizing the reflectance data to the size of 
the full test site. 
3. Spectral uniformity of the site eases the calibration 
procedure. 
4. Temporal uniformity of the site eases the calibration 
procedure. 
5. The site should have little or no vegetation that can 
deteriorate spectral and temporal uniformity. 
6. Higher elevation reduces the error due to aerosols. 
7. A Lambertian site surface is preferable since it decreases 
errors caused by different solar and view geometry. 
8. High probability of cloud free days provides more time for 
calibration studies. 
9. A longer distance to densely populated areas and/or 
industrial facilities decreases the effect of anthropogenic 
aerosols. 
10. A location far from the seas or other large water bodies 
minimizes the influence of atmospheric water vapor. 
11. Having a site in an arid region minimizes probability of 
precipitation and this in turn may change the surface 
BRDF. Also, in arid regions, the probability of a cloudy 
weather is minimum. 
12. Having a large site minimizes the unwanted effects of 
scattering of light from areas outside the target area. 
13. Easy access to the site is an advantage. 
14. Instrumented test sites are preferable. 
In line with the criteria listed above, generally deserts and salt 
lakes are preferable radiometric calibration sites. The Railroad 
Valley in Nevada, USA, the La Crau test site in France, Ivanpah 
Playa in Nevada, USA, White Sands Missile Range in New 
Mexico, USA, Lake Frome in Australia, Uyuni Salt Flats in 
Bolivia are among such sites. 
3. TUZGOLU 
In this section, while presenting the information about Tuz Golti 
test site, CEOS WGCV template for cal/val sites will be taken 
as a guideline. 
Core Site / Description of the Site: 
Tuz Golii, a permanent endorheic lake, is located in the arid 
central plateau of Turkey in Central Anatolia (Figure 1). Being 
a natural reserve area, the site is a salt flat at an elevation of 905 
m above the sea level. The evaporates are mainly halite and 
gypsum, with minor amounts of polyhalite and coelestine 
(Camur, et al., 1996). There is virtually no vegetation in the salt 
flat but it is surrounded by arable fields and salt-steppes. There 
are salt mines and saltwork pools operating at the margins of 
the lake. 
The suitable area selection analysis was conducted by using the 
MODIS (LPDAAC, 2007) satellite images of July and August 
(2004-2006), which is the most suitable period for the site, for 
calibration studies. In Figure 2, the red region is 324.026 km 2 
and illustrates available homogenous area throughout July- 
August. The yellow region has an area of 195.092 km 2 and 
gives an idea about regions which are likely to be dry, in July- 
August period. Thanks to the large size of the area, the lake can 
be used for calibration/validation of satellites with sensors from 
low to high resolution. The method used for determining the 
usable area is described in the next section. 
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Figure 1: Location map of Tuz Golii salt lake, Turkey on 
Europe Map (Map courtesy of www.map-of-europe.us/, image 
courtesy of GLCF). 
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Figure 2: Suitable area for calibration.