Sensor height effects on calculated reference evapotranspiration.
ABSTRACT Automated weather stations are becoming commonly used to measure and reduce climatic data. Unfortunately, standards do not exist for sensor installation height. Therefore, sensor height for the measurement of air temperature, relative humidity and wind speed was evaluated to determine their effects on calculated reference ET. Air temperature and relative humidity were measured at 1.5 m and 2.0 m above ground; wind speed was measured at 2.0 m and 3.0 m heights. Alfalfa reference ET (E^^) was calculated from daily climatic data and for 3-, 7-, and 10-day periods using the modified Penman equation. Ejj. calculated from 2.0 m air temperature and relative humidity data was 2.2% greater than E^j. calculated from 1.5 m data for daily time periods; for 10-day periods, E^^ (2.0 m temp/rh data) was 1.6% greater. Wind speed measured at 3.0 m and estimated at the 2.0 m height produced minor differences (less than 1%) in E^^ calculations when compared to E^^ calculated with 2.0 m measured wind. Reference ET calculated with 3.0 m measured wind compared to E^j. calculated with 2.0 m measured wind was 2.8% greater for daily periods and 2.3% greater for 10-day periods.