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Remote Sens. 2012, 4(2), 439-455; doi:10.3390/rs4020439

Satellite NDVI Assisted Monitoring of Vegetable Crop Evapotranspiration in California’s San Joaquin Valley

1,2,*  and 3
1 Division of Science & Environmental Policy, California State University, Monterey Bay, Seaside, CA 93955, USA 2 Earth Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA 3 USDA/ARS Water Management Research Unit, Ft. Collins, CO 80526, USA
* Author to whom correspondence should be addressed.
Received: 23 December 2011 / Revised: 21 January 2012 / Accepted: 22 January 2012 / Published: 6 February 2012
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Reflective bands of Landsat-5 Thematic Mapper satellite imagery were used to facilitate the estimation of basal crop evapotranspiration (ETcb), or potential crop water use, in San Joaquin Valley fields during 2008. A ground-based digital camera measured green fractional cover (Fc) of 49 commercial fields planted to 18 different crop types (row crops, grains, orchard, vineyard) of varying maturity over 11 Landsat overpass dates. Landsat L1T terrain-corrected images were transformed to surface reflectance and converted to normalized difference vegetation index (NDVI). A strong linear relationship between NDVI and Fc was observed (r2 = 0.96, RMSE = 0.062). The resulting regression equation was used to estimate Fc for crop cycles of broccoli, bellpepper, head lettuce, and garlic on nominal 7–9 day intervals for several study fields. Prior relationships developed by weighing lysimeter were used to transform Fc to fraction of reference evapotranspiration, also known as basal crop coefficient (Kcb). Measurements of grass reference evapotranspiration from the California Irrigation Management Information System were then used to calculate ETcb for each overpass date. Temporal profiles of Fc, Kcb, and ETcb were thus developed for the study fields, along with estimates of seasonal water use. Daily ETcb retrieval uncertainty resulting from error in satellite-based Fc estimation was < 0.5 mm/d, with seasonal uncertainty of 6–10%. Results were compared with FAO-56 irrigation guidelines and prior lysimeter observations for reference.
Keywords: crop coefficient; water use; NDVI; Landsat; fractional cover crop coefficient; water use; NDVI; Landsat; fractional cover
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Johnson, L.F.; Trout, T.J. Satellite NDVI Assisted Monitoring of Vegetable Crop Evapotranspiration in California’s San Joaquin Valley. Remote Sens. 2012, 4, 439-455.

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