Abstract: To understand the spatial representation of flux measurement of the eddy covariance system in the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), footprint was analyzed during representative seasons (summer and winter) from March 2007 to February 2011 by FSAM (Flux Source Area Model). The results indicated that wind direction and atmospheric stability have important effect on footprint. 1) The analysis at different wind directions showed that the location of the maximum footprint function (X_m) in winter was farther from the observation point than that in summer; the source area was the largest in SW, and smallest in NW in both summer and winter; the source area in summer was bigger than that in winter at all directions except for NE. 2) The analysis under different atmospheric stabilities showed that X_m was the farthest from the observation point under stable condition and nearest under unstable condition; the source area was the largest under stable condition and smallest under unstable condition; the source area in summer was bigger than that in winter under all atmospheric stabilities. 3) Moreover, the results showed that the flux measurements of SACOL were representative of two types of topography: flat terrain and mountain terrain.

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