Evapotranspiration on Terrestrial Eastern Asia Estimated by Satellite Remote Sensing

Kenlo NishidaInstitute of Agricultural and Forest Engineering,

University of Tsukuba

kenlo@sakura.cc.tsukuba.ac.jp

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.