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, Kiyomi Morino, R. Scott Murray, John Osterberg, Edward P. Glenn

Research output: Contribution to journalArticlepeer-review

55 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)1273-1297
Number of pages25
JournalRemote Sensing
Volume1
Issue number4
DOIs
StatePublished - Dec 2009
Externally publishedYes

Keywords

  • Evaporative fraction
  • Remote sensing
  • Saltcedar
  • Sap flux
  • Stomatal conductance
  • Transpiration

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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