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Ground-based energy flux measurements for calibration of the Advanced Thermal and Land Application Sensor (ATLAS) Eric Harmsen, Associate Professor Dept. of Agricultural and Biosystems Engineering Richard Diaz, Undergraduate Research Assistant Department of Civil Engineering INTRODUCTION The ability to estimate short-term fluxes of water vapor from a growing crop are necessary for validating estimates from high resolution remote sensing techniques, such as NASA’s Advanced Thermal and Land Applications Sensor (ATLAS). On February 11th, 2004, the ATLAS was used to evaluate the Urban Heat Island Effect within the San Juan Metropolitan area. To validate energy flux estimates from ATLAS, a ground study was conducted at the University of Puerto Rico Experiment Station in Rio Píedras (located within the metropolitan area). Objectives To support modeling efforts related to the Urban Heat Island problem. To obtain ground-based measurements and/or estimates of energy fluxes to validate the ATLAS estimates. The specific objective of this presentation is to present estimates of reference evapotranspiration during the ATLAS fly-over. Estimating Latent heat flux from ATLAS cp VDa VDs LE Rs . ρ = density of air Cp = specific heat of air VDa = water vapor density of the air VDs = saturated water vapor density of the air at the vegetation canopy, temperature measured from ATLAS channel 4 γ = psychrometric constant, and Rs = stomatal resistance Reference Evapotranspiration 900 0.408 Rn G u2 es ea T 273 ET o 1 0.34 u2 where ETo is the Latent heat flux or Reference Evapotranspiration Δ is the slope of the vapor pressure curve (kPa oC-1), Rn is net radiation (MJ m-2 d-1), G is the soil heat flux density (MJ m-2 d-1), g is the psychrometric constant (kPa-1), T is mean daily air temperature at 2 m height (oC), u2 is wind speed at 2-m height, es is the saturated vapor pressure (kPa-1) and ea is the actual vapor pressure (kPa-1). Penman-Monteith Equation The equation applies specifically to a hypothetical reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 sec m-1 and an albedo of 0.23. Vapor Flux Equation a cp VD0.2 VD2 q w 400 Rs u2 q = vapor flux ρa = density of air ρw = density of water VD0.2 = absolute vapor density at 0.2 m VD2 = absolute vapor density at 2 m Rs = reference grass stomatal resistance u2 = wind velocity at 2 m . Results One-second reading of RH Instrument is at 30 cm Height Instrument is at 200 cm Height Relative Humidity Differences RH for a single sensor at 30 cm and 200 cm from the ground February 11, 2004 Relative Humdity (%) 70 65 60 55 50 200 cm 30 cm 45 40 35 10:00 AM 11:12 AM 12:24 PM 1:36 PM Time 2:48 PM 4:00 PM 5:12 PM 75 31 70 RH % 60 29 55 50 28 45 35 30 25 10:09 AM 27 RH TEMP 40 26 25 11:21 AM 12:33 PM 1:45 PM 2:57 PM Time (Hr) 4:09 PM 5:21 PM Temp (C) 30 65 Air Temperature Differences Air Temperature for a single sensor at 30 cm and 200 cm from the ground February 11, 2004 30 Relative Humdity (%) 29.5 29 28.5 28 27.5 27 200 cm 30 cm 26.5 26 25.5 25 10:00 AM 11:12 AM 12:24 PM 1:36 PM Tim e 2:48 PM 4:00 PM 5:12 PM Net Radiation on the Day of the Fly-Over February 11, 2004 Net Radiation (W/m2) 750 650 550 450 350 250 150 50 -50 10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM Time Soil Heat Flux on the Day of the Fly-Over February 11, 2004 50 Soil Heat Flux (W/m2) 45 40 35 30 25 20 15 10 5 0 10:00 AM 11:12 AM 12:24 PM 1:36 PM Time 2:48 PM 4:00 PM 5:12 PM Wind Speed at 300 cm and 30 cm above the ground February 11, 2004 8 7 Wind Speed (m/s) 6 5 300 cm 4 3 2 20 cm 1 0 10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM Time Soil Temperature on the Day of the Fly-Over February 11, 2004 30 Soil Heat Flux (W/m2) 29 28 27 26 25 24 23 22 21 20 10:00 AM 11:12 AM 12:24 PM 1:36 PM Time 2:48 PM 4:00 PM 5:12 PM Reference Evapotranspiration Penman-Monteith Reference Evapotranspiration February 11, 2004 Vapor Flux Equation ETo and q (mm/hr) 1.000 0.800 0.600 0.400 0.200 0.000 10:00 11:12 12:24 Time of ATLAS fly-over 13:36 14:48 Time(hr) 16:00 17:12 18:24 Future Work Related to ATLAS Latent and sensible heat fluxes will be estimated by several methods for comparison with the ATLAS estimates. The ATLAS ground surface temperature data are expected to be available in September 2004.