Development of a Procedure for Estimating Crop Evapotranspiration over Short Periods
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Transcript of Development of a Procedure for Estimating Crop Evapotranspiration over Short Periods
Development of a Procedure for Estimating Crop
Evapotranspiration over Short Periods
Dr. Jorge Gonzalez, ProfessorDept. of Mechanical Engineering
Santa Clara University.
Eric Harmsen, Associate Professor Richard Diaz, Research Assist.Dept. of Agr. and Biosystems Eng. Civil Engineering Department
University of Puerto Rico University of Puerto Rico
Acknowledgements NASA-EPSCoR (NCC5-595), NOAA-CREST, USDA-
TSTAR, NASA-URC, and UPRM-TCESS.
Individuals: Javier Chaparro, Antonio Gonzalez, Jose Paulino-Paulino, and Dr. Ricardo Goanaga of the USDA Tropical Agricultural Research Station in Mayaguez, PR.
The ATLAS Sensor was provided by NASA Stennis Space Center and the Lear Jet Plane was provided by NASA Glenn Research Center.
Water Use
Agriculture is the greatest consumer of water in society.
It is estimated that 69% of all water withdrawn on a global basis is used for agriculture.
Water Losses
Large losses of irrigation water are common.
Irrigation efficiencies on the order of 50% are typical.
The ability to estimate short-term latent heat fluxes (i.e., crop water use) from remotely sensed data is an essential tool for managing the worlds future water supply.
However, validation of these sensors is necessary.
ATLAS
Objective
To describe a relatively inexpensive method for estimating short-term (e.g., hourly) actual evapotranspiration.
Present validation results for the method
Present application example results from two field studies conducted in Puerto Rico.
Combine
Humidity Gradient
and Generalized
Penman-Monteith Methods
Methodology
Generalized Penman-Monteith Method (GPM)
ET = evapotranspirationΔ = slope of the vapor pressure curve Rn = net radiationG = soil heat flux densityρa = air densitycp = heat capacity of airλ = psychrometric constant T = mean daily air temperature at 2 m heightu2 = wind speed at 2-m heightes = saturated vapor pressure and ea is the actual vapor pressurers and ra = bulk surface resistance and aerodynamic resistance, respectively.
ET
Rn G a cpes ea
ra
1rs
ra
.
Simplified representation of the (bulk) surface resistance and aerodynamic resistances for water vapor flow (from Allen et al., 1989).
Aerodynamic Resistance (ra)
ra = aerodynamic resistancezm = height of wind measurement zh = height of the humidity measurementd = zero plane displacementh = crop heightk = von Karman’s constantuz = wind speed at height z
ra
u2
.ra
lnzm d 0.123h
lnzh d
0.0123h
k2u2
.
Humidity Gradient Method (HGM)
ET = evapotranspirationρa = density of aircp = heat capacity of airρw = density of waterρvL = water vapor density at height LρvH = water vapor density at height Hrs = bulk surface resistancera = aerodynamic resistance = ζ / u2
u2 = wind velocity at 2 m
ETa cp
w
vL vH ra rs
.
Elevator Device
Method Validation
Eddy-Covariance System
Eddy Covariance System
Eddy Covariance System
ET Station
ET Results - UF Agr. Experiment Station - April 6th, 2005
0.0
0.2
0.4
0.6
0.8
8:30 AM 10:54 AM 1:18 PM 3:42 PM 6:06 PM
Time
Eva
po
tran
spir
atio
n (m
m/h
r) .
Penman-Monteith Method
Humidity Gradient Method
RH results over a 15-minute periodUF Agr. Experiment Station April 6th, 2005
0.5
1
1.5
2
2.5
2:15 PM 2:17 PM 2:20 PM 2:23 PM 2:26 PM 2:29 PM
Time
Squ
are
Wa
ve
40
44
48
52
56
60
Re
lativ
e H
um
idty
(%
) .
SW
RH
Actual Vapor Pressures and Actual Vapor Pressure DifferencesUF Agr. Experiment Station - April 6th, 2005
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0.1
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8:00 AM 10:24 AM 12:48 PM 3:12 PM 5:36 PM
Time
Act
ua
l Va
po
r P
ress
ure
D
iffe
ren
ce (
KP
a)
.
0.0
0.5
1.0
1.5
2.0
2.5
Act
ua
l Va
po
r P
ress
ure
(K
Pa
) .Actual Vapor Pressure Difference
Up Position Actual Vapor Pressure
Dow n Position Actual Vapor Pressure
Comparison: eddy covariance system and ET station
U of F Agr. Experiment Station April 5th and 6th, 2005
1
Date Method
Daily ET
(mm) Kc ζ rs
(s/m)
PM - ETo 4.37 208 70 Eddy Covariance 3.92 0.90 4/5/2005
ET station 4.11 0.94 191 157
PM - ETo 4.06 208 70 Eddy Covariance 3.78 0.93 4/6/2005
ET station 3.66 0.90 191 160 2
Comparison: eddy covariance system and ET station
U of F Agr. Experiment Station April 5th, 2005
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0.2
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0.6
0.8
8:30 AM 10:54 AM 1:18 PM 3:42 PM
Time
Eva
po
tra
nsp
ira
tion
(m
m/h
r) .
EToEddy Covariance SystemPM ET
Comparison: eddy covariance system and ET station
U of F Agr. Experiment Station April 6th, 2005
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0.2
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1.0
8:30 AM 10:54 AM 1:18 PM 3:42 PM 6:06 PM
Time
Eva
potr
ansp
iratio
n (m
m/h
r) . ETo
Eddy Covariance System
ET Station
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100
150
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250
300
1.5 1.7 1.9 2.1 2.3 2.5
Actual Vapor Pressure (KPa)
He
igh
t ab
ove
gro
un
d (
cm)
.
Grass
Sugar Cane
Monteith and Unsworth, 1990
Vapor Pressure
0
50
100
150
200
250
300
27.0 28.0 29.0 30.0 31.0 32.0
Temperature (oC)
He
igh
t a
bo
ve
gro
un
d (
cm
) .
Sugar cane
Grass
Monteith and Unsworth, 1990
Temperature
Application Example No. 1
Estimation of ET and aerodynamic resistancefor sugarcane, Lajas, PR
Estimated ET for a sugarcane plot November 9, 2004, Lajas, PR
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7:00 AM 8:12 AM 9:24 AM 10:36 AM 11:48 AM 1:00 PM 2:12 PM 3:24 PM 4:36 PM 5:48 PM
Time
Eva
potr
ansp
iratio
n (m
m/h
r) .
HG method
GPM method
Average of HG and GPMmethods
ET = 1.3 mm/day and ζ = 305
Estimated surface and aerodynamic resistances for a sugarcane plot November 9, 2004, Lajas, PR
y = 12564x2 - 12139x + 3065.7
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200
400
600
800
1000
1200
7:00 AM 9:24 AM 11:48 AM 2:12 PM 4:36 PM 7:00 PM
Time
Re
sist
an
ce (
s/m
) .
Aerodynamic Resistance
Surface Resistance
Poly. (Surface Resistance)
Measured Net Radiation for a sugarcane plot Oct. 31st and Nov. 9, 2004 Lajas, PR
-200
-100
0
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200
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400
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700
6:00:00 8:24:00 10:48:00 13:12:00 15:36:00 18:00:00
Time
Net
Rad
iatio
n (W
/m2)
.
31-Oct-04
9-Nov-04
Application Example No. 2The ATLAS Mission On February 11th, 2004, the ATLAS was used to
evaluate the Urban Heat Island Effect within the San Juan Metropolitan area.
A ground-based study was conducted at the University of Puerto Rico Agricultural Experiment Station in Rio Píedras.
The ATLAS Mission
Estimated ET for a grass-covered field Nov. 11, 2004, Rio Piedras, PR
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1.0
1.2
10:00 AM 11:55 AM 1:50 PM 3:45 PM 5:40 PM
Time
ET
(m
m/h
r)
GPM method
HG method
Average of GPM and HG methods
ET = 3.7 mm/day and ζ = 208 and rs = 90 sm-1
0.53 mm/hr
Time of fly-over 2:25 PM
Remote Sensing ET Equation
ETa cp
v vs rs
.
ρv is the vapor density of the air measured at the ground surface.
ρvs is the actual vapor pressure based on the corrected remotely sensed surface temperature
ATLAS-Estimated Surface Temperature for a grass-covered field Nov. 11, 2004, Rio Piedras, PR
1
2
60
52
46
39
33
26
19
12
6
Degrees oC
Pixel No.
Surface Temperature
(C)1 122 198 32.502 124 200 32.463 122 201 33.164 121 201 32.505 119 199 32.506 120 200 32.507 123 198 31.038 119 197 33.469 123 199 33.94
10 120 202 32.9811 118 199 36.2212 123 203 32.94
Average = 33.02
Pixel Location
Area of the station
ATLAS surface temperature correction: 33.0 oC – 29.8 oC= 4.2 oC
60
52
46
39
33
26
19
12
6
Degrees oC
Areal Photo Surface
Temperature
31.78 oC
33.95 oC
4
5
y = -0.1542x + 33.496
R2 = 0.4706
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31
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Distance from Ocean (ft)
Air
Tem
per
atu
re (
C)
Temperature and ET variation with distance from the ocean
The estimated ET varied 0.1 mm/hr over the 20 km transect.
0 4 8 12 16 2024
26
28
30
Corrected Surface TemperatureAir Temperature
Distance from Ocean (km)
Tem
pera
ture
(C
)
0 5 10 15 200.3
0.45
0.6
0.75
Distance from Ocean (km)E
T (
mm
/hr)
Relative Cost Comparison of Direct ET Methods
WeighingLysimeter
EddyCovariance
Bowen Ratio Systemdescribed in
this paper
Evapotranspiration Measurement System
Re
lati
ve
Co
st
+
Future Work Additional method validation. Utilize the ET station to estimate
evapotranspiration rates and factors (ra, rs, Kc, Ks).
Deploy numerous stations around Puerto Rico to validate/calibrate remote sensing estimates of surface temperature, ET and the surface energy balance.