A for vegetated surface G 020 R for bare surface

Since, H, G and Rn are instantaneous, it is necessary to apply a procedure to integrate to daily totals. The evaporative fraction (Brutsaert and Sugita, 1992) is the energy used for evaporation process divided by the total amount of energy available for the evaporation process.

LH LE

Although, the H and LE fluctuate strongly on daily basis, the evaporative fraction behaves steady during day time. Then, the link between the instantaneous and the integrated daily case is given by

The final equation that can be used to evaluate the daily ET is based on the evaporative fraction -

Figure 6 illustrates flow chart for a daily ET model based on remote sensing data. Various researchers investigated several approaches of ET modeling using satellite data using Landsat TM and NOAA - AVHRR data (for reference see Chen et al., 2003). ET and Rn estimated from Landsat TM data following surface energy balance modeling approach for western part of Doon Valley is presented in Fig. 7 (Saha and Pande, 1995b).

Figure 6: Flow chart for daily regional ET estimation using satellite data

SvftPO-

TPflMSP I PflT ] Oil

SvftPO-

TPflMSP I PflT ] Oil

Figure 7: Evapotranspiration image of part of western Doon Valley generated by processing of Landsat - TM data

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