Remote Sens. 2009, 1(4), 1273-1297; doi:10.3390/rs1041273
Article

An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method

Pamela L. Nagler 1,* email, Kiyomi Morino 2 email, R. Scott Murray 3 email, John Osterberg 4 email and Edward P. Glenn 3 email
1 US Geological Survey, Southwest Biological Science Center, Sonoran Desert Research Station, 1110 E. South Campus Drive, Room 123, Tucson, AZ 85721, USA 2 Laboratory of Tree Ring Research, 105 West Stadium, University of Arizona, Tucson, AZ 85721, USA 3 Environmental Research Laboratory, University of Arizona, 2601 East Airport Drive, Tucson, AZ 85706, USA 4 US Bureau of Reclamation, Denver Federal Center, Denver, CO 80225, USA
* Author to whom correspondence should be addressed.
Received: 13 October 2009; in revised form: 19 November 2009 / Accepted: 3 December 2009 / Published: 10 December 2009
(This article belongs to the Special Issue Global Croplands)
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Abstract: We used the Enhanced Vegetation Index (EVI) from MODIS to scale evapotranspiration (ETactual) over agricultural and riparian areas along the Lower Colorado River in the southwestern US. Ground measurements of ETactual by alfalfa, saltcedar, cottonwood and arrowweed were expressed as fraction of potential (reference crop) ETo (EToF) then regressed against EVI scaled between bare soil (0) and full vegetation cover (1.0) (EVI*). EVI* values were calculated based on maximum and minimum EVI values from a large set of riparian values in a previous study. A satisfactory relationship was found between crop and riparian plant EToF and EVI*, with an error or uncertainty of about 20% in the mean estimate (mean ETactual = 6.2 mm d−1, RMSE = 1.2 mm d−1). The equation for ETactual was: ETactual = 1.22 × ETo-BC × EVI*, where ETo-BC is the Blaney Criddle formula for ETo. This single algorithm applies to all the vegetation types in the study, and offers an alternative to ETactual estimates that use crop coefficients set by expert opinion, by using an algorithm based on the actual state of the canopy as determined by time-series satellite images.
Keywords: sap flux; transpiration; stomatal conductance; evaporative fraction; remote sensing; saltcedar

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MDPI and ACS Style

Nagler, P.L.; Morino, K.; Murray, R.S.; Osterberg, J.; Glenn, E.P. An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method. Remote Sens. 2009, 1, 1273-1297.

AMA Style

Nagler PL, Morino K, Murray RS, Osterberg J, Glenn EP. An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method. Remote Sensing. 2009; 1(4):1273-1297.

Chicago/Turabian Style

Nagler, Pamela L.; Morino, Kiyomi; Murray, R. Scott; Osterberg, John; Glenn, Edward P. 2009. "An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method." Remote Sens. 1, no. 4: 1273-1297.

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