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B. Determining the Time for Weather Data and Reference Evapotranspiration (ET r )This section describes how the instantaneous wind speed and the reference ET at thesatellite overpass time are determined from hourly (or shorter) weather data. Thisprocedure assumes that one has hourly (or shorter) meteorological data from a weatherstation. Refer to part 2D in “The Theoretical Basis of SEBAL” for the selection of weatherstations and required weather data.B-1. Data InvestigationAny data from a weather station must be studied to determine what time interval itrepresents. The table below shows weather data obtained from the following weatherstation: (6/20/2000, Aberdeen Idaho weather station in the Agrimet Public Weather System,http://mac1.pn.usbr.gov/agrimet/). ETr was computed using the REF-ET software(Appendix 3).ASCEDoY HrMn Year Tmax Tmin Rs Wind DewP stPMETrC C W/m2 m/s C mm/h172 0 0 10.9 10.9 0 1.7 8.8 0.00172 100 0 10.2 10.2 0 2.3 7.3 .01172 200 0 10.3 10.3 0 4.1 3.6 .04172 300 0 9.3 9.3 0 1.3 2.6 .01172 400 0 7.3 7.3 0 .3 3.6 -.02172 500 0 5.8 5.8 0 1.0 3.1 .02172 600 0 3.6 3.6 1 1.2 2.0 .01172 700 0 3.7 3.7 64 1.7 1.6 .05172 800 0 5.7 5.7 156 1.9 2.6 .10172 900 0 10.7 10.7 415 .4 2.8 .25172 1000 0 12.9 12.9 591 .7 1.2 .38172 1100 0 14.7 14.7 747 1.8 .3 .54172 1200 0 16.2 16.2 868 3.4 .9 .68172 1300 0 17.6 17.6 941 4.5 .5 .79172 1400 0 18.8 18.8 964 6.2 1.5 .87172 1500 0 20.3 20.3 939 4.5 .3 .87172 1600 0 21.2 21.2 869 4.8 -.3 .87172 1700 0 21.7 21.7 619 5.4 .2 .76172 1800 0 22.2 22.2 469 5.6 1.6 .69172 1900 0 22.0 22.0 402 5.7 .7 .66172 2000 0 20.9 20.9 226 3.9 1.4 .41172 2100 0 19.1 19.1 69 3.7 2.5 .12172 2200 0 17.1 17.1 3 3.8 .8 .10172 2300 0 14.6 14.6 1 3.3 2.0 .06When using these data, one must ask two questions:1. Was daylight savings time, DST, applied to the time of record?58