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•Requires local ETref (Weather station network) <br />•Provides ETcb – must add in soil evaporation to get ETp <br />•Must estimate crop stress to get ETa (e.g., via soil water balance) <br />Advantages of the SIMS / Reflectance Approach <br />•Reflectance data freely available from multiple satellites (e.g., <br />Landsat 7/8, Sentinel-2A)  operational reliability & data continuity <br />•Reflectance data available at field scales (30 m) <br />•Relatively simple calculations - fully automated computations <br />•NDVI/Fc/Kcb interpolates well between point measurements <br />•Extensible framework for satellite data processing <br />•ETcb represents biological demand for water by the plant <br />Limitations of the SIMS / Reflectance Approach <br />Combination of energy balance (e.g., METRIC) and reflectance (e.g., <br />SIMS) approaches provides robust, long-term strategy for sustaining <br />operational use.