Ground-based energy flux measurements for calibration of the Advanced Thermal and Land Application...
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Ground-based energy flux measurements for calibration of the Advanced Thermal and Land Application Sensor (ATLAS)1
Eric W. Harmsen and Richard Díaz Román, Dept. of Agricultural and Biosystems Engineering University of Puerto Rico, Mayagüez, PR 00681, [email protected]
(787)834-2575, Fax: (787)265-3853
ABSTRACT 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). Short-term measurements (10-second) of micro-meteorological parameters, including soil heat flux, soil temperature, soil moisture and net radiation were measured. Wind speed, relative humidity and air temperature were measured at two vertical positions above the ground. Vertical differences in soil water tension (negative pressure) were also measured continuously. This poster presents results from the ground-based study.
Large differences in relative humidity were observed between 20 and 200 cm heights above the turf grass, whereas temperature differences were small. Estimates of evapotranspiration are presented based on the Penman-Monteith method.
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 poster is to present estimates of reference evapotranspiration during the ATLAS fly-over.
METHODOLOGYField MeasurementsClimatological data were saved on a Campbell Scientific (CS) CR10X datalogger every 10 second. Measurements of air temperature and relative humidity were measured at 30 cm and 200 cm heights, respectively, using a single CS HMP45C sensor. Net radiation was measured using a CS NR Lite Net Radiometer. Wind speed was measured at 30 cm and 300 cm
_______1 This material is based on research supported by the NOAA-CREST and NASA-EPSCoR (NCC5-595 ).
above the ground, respectively. The upper sensor was a MET One 034B wind speed and direction sensor. The lower wind speed was measured using a HOBO wind speed sensor. Soil water content was measured using a CS616 Water Content Reflectometer. Soil temperature was measured using two TCAV Averaging Soil Temperature probes, and the soil heat flux at 8 cm below the surface was measured using a HFT3 Soil Heat Flux Plate. Soil heat flux at the soil surface was estimated using the average soil temperature, soil heat flux at 8 cm and water content data.
Reference EvapotranspirationThe reference evapotranspiration was estimated using the Penman-Monteith equations (Allen et al., 1998) at 4-minute intervals:
ETo
0.408 Rn G 37
T 273
u2 es ea
1 0.34 u2
.
where ETo = reference evapotranspiration (mm/hr) Δ = slope of the vapor pressure curve (KPaoC-1), Rn = net radiation (mm/hr), G = soil heat flux density (mm/hr), γ = psychrometric constant (KPaoC-1), T = mean daily air temperature at 2 m height (oC), u2 = wind speed at 2 m height (m/s), es is the saturated vapor pressure and ea is the actual vapor pressure (KPa). The equation applies specifically to a hypothetical reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 s/m and a solar reflectivity of 0.23.
RESULTSFigure 1-7 show the measured climatological data collected on February 11, 2004. Figure 8 shows the estimated reference evapotranspiration based on the field measurements. 1 Second Readings of RH (%)
Instrument is at 200 cm Height
Instrument is at 30 cm Height
Figure 1. One-second measurements of relative humidity.
RH for a single sensor at 30 cm and 200 cm from the groundFebruary 11, 2004
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
Time
Rela
tive
Hum
dity
(%)
200 cm30 cm
Figure 2. Measured relative humidity from 10 AM to 6 PM on February 11, 2004.
Air Temperature for a single sensor at 30 cm and 200 cm from the groundFebruary 11, 2004
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
Time
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ativ
e H
umdi
ty (%
)
200 cm30 cm
Figure 3. Measured air temperature from 10 AM to 6 PM on February 11, 2004.
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
Time
Win
d Sp
eed
(m/s
)
Wind Speed at 300 cm and 30 cm above the groundFebruary 11, 2004
Figure 4. Measured wind speed from 10 AM to 6 PM on February 11, 2004. The lower values
were from the sensor at 20 cm from the ground.
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
Time
Net R
adia
tion
(W/m
2)
Net Radiation on the Day of the Fly-OverFebruary 11, 2004
Figure 5. Measured net radiation from 10 AM to 6 PM on February 11, 2004.
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
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Soil
Heat
Flu
x (W
/m2)
Soil Temperature on the Day of the Fly-OverFebruary 11, 2004
Figure 6. Measured wind speed from 10 AM to 6 PM on February 11, 2004.
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10:00 AM 11:12 AM 12:24 PM 1:36 PM 2:48 PM 4:00 PM 5:12 PM
Time
Soil
Heat
Flu
x (W
/m2)
Soil Heat Flux on the Day of the Fly-OverFebruary 11, 2004
Reference EvapotranspirationFebruary 11, 2004
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10:00 11:12 12:24 13:36 14:48 16:00 17:12 18:24
Time(hr)
ETo
(mm
/hr)
Time of ATLASfly-over
Figure 7. Measured soil temperature from 10 AM to 6 PM on February 11, 2004.
Figure 8. Calculated reference evapotranspiration from 10 AM to 6 PM on February 11, 2004. The total
depth of the reference evaporation for the 8-hr period was 3.6 mm.