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.
*«»»**' '’•¿¿of v
a«»» ’. • .•
‘ ' Tv—
. • . .V,
Pam*
_ .Vf" M v4- k HR
*****
; -,
'"SiXiXWif •
hxmmS y
, . X..: \
fc ■****• t.
..y*. -
***** 8uO*tn*-\
fd**'>***. ■ Tjfr**
\ fituwi&S
,w »¿v <"»■
I ' C *—
«">
"■"w- D
V
Ilf
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).
520000
—I—
540000
1
520000
Figure 2: Suitable area for calibration.