Iranian Studies and Experiences Related to Water Resource Management Using Remote Sensing Data
Islamic Republic Of Iran Ministry Of Energy »EvapoTranspiration (ET)«
27 February 2018 Water Research Water Research Institute Neamat Karimi Institute Outline
➢ ❶ Introduction ❷ ET Estimation Algorithms ❸ Data Used ❹ Accuracy Assessment and Results
Water Research Institute Introduction Evapotranspiration (ET) is the sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere. ET is a main component of the water cycle because about 65% of precipitation is globally evacuated through ET.
Water Research Institute Introduction
Many water resources and agricultural management applications require the knowledge of surface evapotranspiration (ET) over a range of spatial and temporal scales. However, it is impractical to obtain ET using ground-based observations over large area. Satellite remote sensing is a promising tool to estimate the spatial distribution of ET with minimal use of in situ observational data. The objective of this project is to map ET spatial distribution over large areas using primarily remote sensing data.
Water Research Institute Outline
❶ Introduction ➢ ❷ ET Estimation Algorithms ❸ Data Used ❹ Accuracy Assessment and Results
Water Research Institute EvapoTranspiration Estimation Algorithms
1) One-source energy balance models which are based on defining the maximum and minimum ET over the study areas and estimating the ET of other pixels by interpolating the surface properties and conditions: SEBAL, SEBS, SEBI and METRIC
2) Two-source energy balance models which distinguish the contribution of soil and vegetation covers on surface energy balance and total amount of ET: ALEXI
3) Models based on distributions in surface temperature– vegetation index triangle/trapezoid space.
Water Research Institute What is the Energy Balance Algorithms?
The basis of all energy balance models:
The energy driving the hydrological cycle (ET) is equal to the incoming energy minus:
the energy going to heating of the soil and air the energy reflected back to space.
Soil and air + Energy In Energy Out + ET
ET=Energy In-(Energy for Soil + Air + Energy Out) Water Research Institute What is the Energy Balance Algorithms?
ET is calculated as a “residual” of the energy balance
Rn(radiation from sun and sky) H (heat to air) ET
ET = R n - G - H Basic Truth: Evaporation consumes Energy G (heat to ground)
Water Research Source: Rick Allen, University of Idaho Institute ET = Rn - G - H
Sensible heat flux is the rate of heat loss to the air by convection and conduction, due to a temperature difference.
Ta
H ra
T C. dT ns H p rah
Water Research Institute Outline
❶ Introduction ❷ ET estimation algorithm ➢ ❸ Data Used ❹ Accuracy Assessment and Results
Water Research Institute Satellite Images and Algorithms Used
Energy Balance algorithms needs both short wave and thermal bands
Several images can use images from: NASA-Landsat (30 m, 16 days) - since 1982 NOAA-AVHRR (1 km, daily) - since 1980’s NASA-MODIS (500 m, daily) - since 1999
Algorithms: - ‘SSEBop’ - ‘SEBAL’ - ‘ETLook’ -‘Modified EB’
Water Research Institute Outline
❶ Introduction ❷ ET Estimation Algorithm ❸ Data Used ➢ ❹ Accuracy Assessment and Results
Water Research Institute Validation with Scintillometer Sensible Heat Flux
Transmitter Receiver
Water Research Institute Validation of Net Radiation (Rn)
700 Y=0.9831.X+13.12
) R2=0.91 2 600
500
400
300 Net Radiation Net (W/m Moderate Net Radiation (W/m2)
200 Measured Net Radiation (W/m2)
100 133 140 156 165 172 181 197 204 213 220 229 236 245 Number of Julian Day in 2016
Water Research Institute Validation of Sensible Heat Flux (H)
400
Measured H with Scintillometer Estimate H from Observation dT
300 )
2 200
100
0 133 140 156 165 172 181 197 204 213 220 229 236 245
Sensible Flux Heat (w/m -100 Y=0.96.X+17.2 R2=0.83 -200 Number of Julian Day in 2016
Water Research Institute Validation of Final Evapotranspiration (ET)
۰.۹۰ y = 1.0972x - 0.0439 R2 = 0.88 ۰.۸۰ RMSE=0.09 ۰.۷۰
۰.۶۰
۰.۵۰
۰.۴۰
۰.۳۰
۰.۲۰
ET Estimated by modified model (mm/day) model modified by Estimated ET ۰.۱۰
۰.۰۰ ۰.۹۰ ۰.۸۰ ۰.۷۰ ۰.۶۰ ۰.۵۰ ۰.۴۰ ۰.۳۰ ۰.۲۰ ۰.۱۰ ۰.۰۰ ET Measured by Scintillometer (mm/day)
Water Research Institute Monthly Changes of ET Over Esfahan Basin
Water Research Institute Annual ET of Different Land Use/ Land Cover (2016)
992 ۱۰۰۰1000 750 ۸۰۰800
513 ۶۰۰ 600 387 ۴۰۰ 272 271 400 238
Annual Annual (mm/year) ET ۲۰۰ 112 83 200 ۰
باغ 0
برنج
مراتع
دیمکشت دیم
Rice
Trees
بهارهکشت مرجعگیاه مرجع
Alfalfa
پاییزهکشت دوگانهکشت دوگانه
Fall Crop Fall
Orchards
Dual Crop Dual
Spring Crop Spring
DryFarming
Range Lands Range درختیهای مجتمع های درختی
Water Research Institute Seasonal ET of Iran
Water Research Institute http://wrr-wri.ir/ Alamkouh Glacier, Iran Water Research Institute