Manfred Schroeder 
  
  
30 T T T T T 
"standard deviation 18m" 
reflectance [96] 
tA 
T 
1 
  
  
0 1 1 1 1 1 1 1 1 
0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 
wavelength [um] 
  
Fig.4: Average reflectance and standard deviation of the 400m x 400m calibration site of La Crau for 18m x 18m 
ground pixel size. 
MOMS and SPOT ground pixels have a square size of 18 m respectively 20 m. A Daedalus image processed to 
18 m ground resolution as seen by SPOT and MOMS is shown in Fig. 2 (right). The reflectance standard 
deviation of this 18 m ... pixel image (Fig. 4) is reduced by a factor of 2 in comparison to the 0.8 m ... pixel image 
and is in the order of 4,4 %. This is a measure of the spatial homogeneity of the test site as seen from SPOT and 
MOMS. It is assumed that the reflectance curve derived for 2" July is also valid for 29" June. 
3.3 Comparison of reflectance data sets 
The CIMEL ground radiometer was used the 29" June before and after SPOT overpass. It was hand held and 
scanned the whole area and acquired a sequence of several hundred values, with an instantaneous foot print of 
approx. 10 by 10 cm?. A measurement of a BaSO4 white reference was used to convert the data into directional 
hemispherical reflectance. The mean value allow a comparison at three wavelengths with the spectral reflectance 
curve obtained with corrected Daedalus data. The results are in good agreement (Fig. 5). The standard deviation 
of the CIMEL measurements shows the variability of the site at the measurement scale. 
30 
  
25 
  
  
  
  
  
  
15 | re 
albedo (%) 
  
  
  
  
  
  
  
  
  
DLR extended with Daedalus 300m 
  
  
| + LISE radiometer (29 june 98) 
0 deer ee EE 
400 450 500 550 600 650 700 750 800 850 900 
wavelength (nm) 
  
  
  
  
  
Fig. 5: Ground reflectance of La Crau test site. (The reason that the reflectance measured with the ZEISS 
radiometer (see Fig.3) is higher than the average reflectance obtained from the corrected Daedalus data is due to 
the fact that the ZEISS measurements were made in the Measuring Box only, which has a lighter tone than the 
average Calibration Area .) 
  
282 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.