evapotranspiration on terrestrial eastern asia estimated by satellite remote sensing kenlo nishida...
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Evapotranspiration on Terrestrial Eastern Asia Estimated by Satellite Remote Sensing
Kenlo NishidaInstitute of Agricultural and Forest Engineering,
University of Tsukuba
Evapotranspiration (ET) from land in the eastern Asia was estimated with satellite remote sensing. The algorithm is a simple two-source model consisting of ET from bare land and ET from vegetation. ET from vegetation was estimated by combination of Penman-Monteith equation and the complementary relationship (relationship between actual evaporation and potential evaporation of Penman and Proestley-Taylor). ET from bare land was estimated by VI-Ts diagram. By applying this method to NOAA/AVHRR and Terra/MODIS sensors, distribution of evaporation fraction was mapped in a regional scale.
JWH02/04P/D-002 1400-027 PosterIUGG 2003, July 4, Sapporo
MOD16 Evapotranspiration Project
- MOD16 is a project for operational estimation of terrestrial evapotranspiration (ET) by a satellite sensor (Aqua/MODIS)
- MOD16 algorithm is applicable not only for Aqua/MODIS but also for Terra/MODIS, ADEOS2/GLI, and NOAA/AVHRR etc.
- Currently, the algorithm has been established. (Nishida et al., 2003)
- Tests have been done mainly on North America.
- In this study, we test MOD16 logic with NOAA/AVHRR data for Eastern Asia.
Nishida, K., Nemani, R. R., Running, S. W., Glassy, J. M. (2003): An operational remote sensing algorithm of land surface evaporation. Journal of Geophysical Research D, in press
Nishida, K., Nemani, R. R., Running, S. W., Glassy, J. M. (2003): Development of an evapotranspiration index from Aqua/MODIS for monitoring surface moisture status. IEEE Transactions of Geoscience and Remote Sensing, 41(2), 493-501.
Actual landscape: mixture of forest, farm, grassland, road, etc.
Simplification (Two-source model)
Fraction of vegetation: fveg
Fraction of bare soil: 1.0 - fveg
ET = fveg ET veg + (1 - fveg) ET soilETveg
ETbare
Qveg Qbare
EF = fveg ------- EFveg + (1 - fveg) ------ EFbare
Q Q
MOD16 ET Logic (1): Conceptual Frame
Q
ETEF GRQ n
Net radiation (radiation absorbed
on the land)
Available Energy
Ground heat transfer
MOD16 ET Logic (2): Estimating EFveg
α ΔEFveg = ------------------------------------
Δ + γ ( 1 + rc / 2 ra)
Assuming complementary relationship (ET + PETPM = 2PETPT; PETPM=Penman’s PET; PETPT=Priestley-Taylor’s PET), we can get:
Psychrometric constant (slightly change with T)
Derivative of saturated vapor pressure curve (change with T)
Constant. 1.26
Canopy resistanceAerodynamic resistance
1 / rc = f1(T) f2(VPD) f3(PAR) f4() / rcMIN
Soil waterSolar radiation
Humidity
Temperature
1 / rc = f1(T) f3(PAR) / rcMINImplementation
Change of VI
MOD16 ET Logic (3): Estimating EFbare
Tbare max – Tbare
EFbare= ----------------------
Tbare max – Tbare min VI-Ts diagram (Nemani & Running, 1989; 1993)
VI
Ts
VImaxVImin
Tveg=Tbare min
Tbare max
Tbare
VI
Window
satellite image
Warm Edge
Air temperature
Wind speed
Qbare0 – ET
Tbare = ------------------------------------ + Ta
4εσTa3 (1- CG) + Cp/ra bare
Channel reflectance
Thermal IR
Satellite data
fveg
VI-Ts diagram
Ta
ra
rc
Ta
PAR
Tbare max
Tbare
Ta
EFbare
EFveg
VIalbedo
OrbitTa
Rd
PAR
Qbare
Qbare0
Qveg
EF
U50m
ra
rc
MOD16 ET Logic (4): Data Stream
Ts
Radiative transfer model
Radiation budget
Energy budget
Conductance model
Penman-Monteith &Complementary relation
VITs
VI
Rd Ta
albedo
Qbare
Tbare max
Ta
-------------------------------------------------------------------------------------------------------------------------------------- site (symbol) type data size R 2 bias standard error-------------------------------------------------------------------------------------------------------------------------------------- Harvard Forest DBF 28 0.75 -0.05 0.13 Walker Branch DBF 29 0.88 0.01 0.13 Willow Creek DBF 8 0.80 -0.14 0.18 WLEF Tower DBF 17 0.89 -0.18 0.20 Blodgett ENF 11 0.30 -0.12 0.21 Duke Forest ENF 13 0.70 0.04 0.19 Howland ENF 20 0.84 -0.02 0.10 Metolius ENF 15 0.20 -0.12 0.23 Bondville Crop 37 0.81 -0.07 0.19 Ponca Crop 6 0.36 -0.10 0.31 Little Washita Grass 20 0.86 0.04 0.14 Shidler Grass 10 0.91 -0.03 0.12 Ski Oaks Shrub 16 0.29 -0.07 0.17 all sites --- 230 0.74 -0.05 0.17 --------------------------------------------------------------------------------------------------------------------------------------
Test in USA
Comparison of estimated EF by AVHRR and observed EF at
AmeriFlux sites
Nishida et al., 2003, JGR
Test in Eastern Asia
Data
- NOAA/AVHRR 1km-10day composite, 1999, by Iwate University(Yokoyama, Lei, and Purevdorj, 2002)
- Land Cover Dataset, Asian Association on Remote Sensing (AARS)0.5minute grid
EF EFv
fv
EFb
1999/01
EF
EFEF
EFv
EFv
EFv
fv
fv
fv
EFb
EFb
EFb
1999/02
1999/03 1999/04
EF EF
EF EF
EFv
EFv
EFv
EFv
fv
fv
fv
fv
EFb
EFb
EFb
EFb
1999/05 1999/06
1999/07 1999/08
EF
EF
EF EF
EFv
EFv
EFv EF
v
fv
fv
fv f
v
EFb
EFb
EFb EF
b
1999/09 1999/10
1999/11 1999/12
Validation at Takayama Flux Site
Courtesy for field data: Dr. Saigusa, AIST
Validation at EGAT Tower
Courtesy for field data: Dr. Toda, Hokkaido Univ.
Evaluation of Water Budget
Gain: precipitationGPCC, global, monthly, 1deg
Loss: evapotranspirationEF * (Rn-G)
Rn: NCEP reanalysis
G: Moran, 1989 G=0.58 exp(-2.13NDVI)
Gain – Loss = Budget
(vertical only)
1999/01 1999/02 1999/03 1999/04
1999/05 1999/06 1999/07 1999/08
1999/09 1999/10 1999/11 1999/12
mm/month
Conclusion
- MOD16 logic was tested in Eastern Asia, 1999, with NOAA/AVHRR composite.
- Validation with ground observation data from two sites showed consistent accuracy with North America.
- In combination of radiation and precipitation data, MOD16 EF product provides vertical water budget, which has implication on water resource monitoring.
Acknowledgements: Dr. Liping Lei in Basic Engineering Co., Ltd. allowed me to use AVHRR composite dataset. Mr. W. Takeuchi in the University of Tokyo arranged the AVHRR datasets. Dr. N. Saigusa in AIST provided me with energy flux data taken in Takayama flux site. Drs. M. Toda and N. Ohte carried out the energy flux observation in EGAT Tower site with a support from GAME(GEWEX Asian Monsoon Experiment)-Tropics. The MOD16 algorithm development was supported by JSPS Fellowship for Study Abroad as well as NASA and Numerical Terradinamic Simulation Group (NTSG) of University of Montana.