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Estimating total evaporation at the field scale using the SEBS model and data infilling procedures

S Gokool, K.T. Chetty, G.P.W. Jewitt, A Heeralal

Abstract


The spatial representativeness of total evaporation estimates (ET) acquired from conventional approaches is limited, as these techniques generally provide site-specific values. The use of satellite earth observation has shown a great deal of potential in capturing spatially representative hydro-meteorological flux data and therefore represents a practical alternative for estimating ET. However, one of the challenges facing ET estimation using satellite earth observation data is the effect of clouds, which reduce the number of satellite images available for use. The objectives of this paper were firstly to validate satellite-derived ET estimates against estimates acquired from a surface renewal system and, secondly, to assess the feasibility of two infilling techniques to create a daily satellite-derived ET time series. The Surface Energy Balance System (SEBS) model was used to derive daily ET using MODIS imagery. Two infilling approaches, the Kcact approach and a linear interpolation approach, were evaluated by comparing their respective values against in-situ ET measurements, as well as SEBS ET estimates derived using MODIS. The results showed that SEBS ET estimates were approximately 47% higher and produced R2 and RMSE values of 0.33 and 2.19 mm∙d-1, respectively, compared to in-situ ET values. The ET estimates obtained by applying the Kcactapproach and the linear interpolation approach compared favourably with the in-situ ET values, producing RMSE values of 0.9 mm∙d-1 and 0.6 mm∙d-1, respectively. However, comparisons of ET estimates acquired by applying the Kcact approach and the linear interpolation approach against the SEBS ET indicated a poor match, yielding RMSE values of 1.96 mm∙d-1 and 1.54 mm∙d-1, respectively.

Keywords: satellite earth observation, SEBS Model, ET, infilling, surface renewal system




http://dx.doi.org/10.4314/wsa.v42i4.18
AJOL African Journals Online