Remotely Surface Reflectance Data for Irrigation Scheduling of Southern New Mexico Pecan Orchards

Demand for New Mexico’s limited water resources coupled with periodic drought has increased the necessity for developing advanced sensing technologies to optimize irrigation scheduling and drought monitoring of pecan orchards.  The objective of this study was to use remotely-sensed surface reflectance derived from a hand-held spectroradiometer (ASD Fieldspec Pro Full Range Spectroradiometer), Landsat-7 Enhanced Thematic Mapper (ETM+), and Earth Observing One-Advanced Land Imager (EO-1 ALI) to detect moisture status of pecan trees exposed to cyclic flood irrigations.  The study was conducted simultaneously on two southern New Mexico mature pecan orchards in 2012.  Irrigation cycles were synchronized with satellite overpasses. In situ measurements of canopy spectral reflectance and pecan stem water potential (Ψ_smd) were taken shortly after irrigation and near the end of a flood irrigation dry-down cycle.  In situ measurement of canopy reflectance at near infrared wavelengths (750, 960, 1050, 1075, and 1260 nm) correlated positively with Ψ_smd, whereas short wave infrared (SWIR) surface reflectance within the range 1450 to 2500 nm did not differ between well-watered trees and those at the end of irrigation cycle.  Near infrared reflectance recorded by the ETM+ and EO-1 ALI sensors correlated with Ψ_smd, but unlike the in situ data, SWIR reflectance data from these satellite sensors was also significantly correlated with Ψ_smd .  Our results suggest that remotely-sensed data from both satellite sensors and hand-held spectroradiometers can be used to detect moisture status of pecan orchards, but the difference in scale of observation needs further interpretation.