Parameterization of METRIC Model for Forestry Applications: A Case Study of Doon Valley, India.
Abstract
Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model is a surface energy balance based method aimed at estimation of evapotranspiration (ET). It is dominantly used to estimate the ET of agricultural crops. Complex canopies like forests have a mixture of the sunlit canopy, shaded canopy, sunlit soil, and shaded soil surfaces and it reflects a different fraction of solar radiation and tends to have a different surface temperature. Individual trees cast shadows on their neighbors which may reduce the apparent reflection leading to low albedo estimates. Nadir looking satellites like Landsat points vertically downward and therefore sees only radiation that is emitted or reflected in a completely vertical/upward direction. For Forest ET estimation several extensions of the existing model are required in terms of change in the computation of albedo (α), surface temperature (Ts), and momentum roughness length (Zom) techniques. In the present study, the METRIC model is applied on 12 cloud-free Landsat 8 images of the year 2018 to estimate ET from Shorea robusta forest in Doon valley. The METRIC model was parameterized for better representation of forest canopy. The total hemispherical albedo is computed using solar zenith angle and bidirectional albedo estimated from the Landsat data. The computation of Ts requires three-source condition, thus segregating the temperature of the canopy (Tc), shaded ground surface (Tshadow), and sunlit ground surface (Tsunlit). The estimation of the Zom for tall vegetation is based upon the Perrier equation which uses LAI and canopy height. The adjustments to the Ts and Zom provide an improved sensible heat transfer estimation within the METRIC model and thus, better estimates of ET. The ET results with and without parameterization of METRIC were compared to analyze the impact of parameterization and model sensitivity towards these parameters. Results showed the improvement in ET estimation after applying necessary modifications.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH008.0021P
- Keywords:
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- 1814 Energy budgets;
- HYDROLOGY;
- 1818 Evapotranspiration;
- HYDROLOGY;
- 1855 Remote sensing;
- HYDROLOGY;
- 1895 Instruments and techniques: monitoring;
- HYDROLOGY