interval of 
inclination, 
roughness 
and vapour 
¥ 
potential 
difference 
n potential 
and free 
derived by 
perature 
As is the 
smperature 
calculated 
rived from 
ependance 
results. Aq 
igger than 
cg, 1 and 
| holds and 
d for each 
ut from the 
  
Finally, sensible heat flux is calculated by equation (5), 
and the value is written to an output image. 
Fig. 2 shows sensible heat flux, as it was modeled over 
the study area. 
  
  
  
Niulla 20.7, 986 
Fuehlbarer VWaermestrom 
Xon ml 
  
0 25 50 75 100 125 150 
    
  
  
  
Schnee/bebaut 
  
Masser 
  
175 Z00 Z25 250 275 300 325 350 375° 
Inklination € 2 
EI To € IL o. H.wert 
  
„500 
   
  
  
Fig. 2. Sensible heat flux 
9. ENERGY BUDGET MODEL 
9.1 Soil heat flux 
As for the day of satellite overpass no measured data for 
sensible heat flux were available, verification was 
performed by integrating the calculated data into an 
energy budget model. 
All energy budget terms of equation (9), except ground 
heat flux, evapotranspiration and sensible heat flux, were 
at hand and well determined by ground truth and 
calibration. 
Using a method described by Daughtry, Kustas and 
Moran (Daughtry/Kustas/Moran, 1990), soil heat flux 
could easily be derived at pixel resolution and calibrated 
to the data from Abisko Station (Storl, 1992). 
The method applied is described in detail in Storl, 1992. 
9.2 Evapotranspiration 
The only term left to be calculated is evapotranspiration. 
This parameter was modeled in a way, that would give 
665 
good results over specific land use classes as heaths 
and meadows, for which the assumptions of the applied 
evaporation model hold. Several authors have shown, 
that specially in subpolar ecosystems, equilibrium 
evaporation is a good aproximation to actual 
evapotranspiration for a wide variety of conditions, 
counting with sufficient water supply (Davies, 1972, 
Rouse/Stewart, 1972, Mc Naughton/Black, 1973, Mc 
Naughton, 1976) 
Equilibrium evaporation is written as: 
XL 
Ay 
  
Eq (Q*-G) (13) 
Where A is the inclination of the saturation curve for 
vapor pressure, Q* is the radiation balance, G the 
ground heat flux and y the psycrometric constant. 
9.3 Ratio H/(Q*-G) 
The first condition that has to hold, if the sensible heat 
flux H is modeled with accuracy, is that the ratio 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996