A Three-Dimensional Index for Characterizing Crop Water Stress

Jessica Torrion,Wenxuan Guo,Andy Cranmer,Stephan Maas,James Bordovsky

doi:10.3390/rs6054025

Jessica Torrion, Wenxuan Guo + Show 3 more

Open Access

https://doi.org/10.3390/rs6054025

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Abstract

The application of remotely sensed estimates of canopy minus air temperature (Tc-Ta) for detecting crop water stress can be limited in semi-arid regions, because of the lack of full ground cover (GC) at water-critical crop stages. Thus, soil background may restrict water stress interpretation by thermal remote sensing. For partial GC, the combination of plant canopy temperature and surrounding soil temperature in an image pixel is expressed as surface temperature (Ts). Soil brightness (SB) for an image scene varies with surface soil moisture. This study evaluates SB, GC and Ts-Ta and determines a fusion approach to assess crop water stress. The study was conducted (2007 and 2008) on a commercial scale, center pivot irrigated research site in the Texas High Plains. High-resolution aircraft-based imagery (red, near-infrared and thermal) was acquired on clear days. The GC and SB were derived using the Perpendicular Vegetation Index approach. The Ts-Ta was derived using an array of ground Ts sensors, thermal imagery and weather station air temperature. The Ts-Ta, GC and SB were fused using the hue, saturation, intensity method, respectively. Results showed that this method can be used to assess water stress in reference to the differential irrigation plots and corresponding yield without the use of additional energy balance calculation for water stress in partial GC conditions.

Highlights

The Crop Water Stress Index (CWSI) method for assessing water stress in plants is based on the observation that plant stomata close as a natural crop response to the depletion of soil moisture
Measurement of Tc-Ta at a few locations may not provide an adequate indication of water stress conditions that are representative of a field, if the field contains appreciable spatial heterogeneity in soil moisture conditions resulting from variation in soil physical properties
An alternative is the use of satellite- or aircraft-based remote sensing imagery within the thermal infrared (TIR) spectral range, which is capable of capturing the spatial variability in surface temperature

Summary

Introduction

The Crop Water Stress Index (CWSI) method for assessing water stress in plants is based on the observation that plant stomata close as a natural crop response to the depletion of soil moisture. The resulting decrease in latent heat flux from the plants gives rise to an increase in leaf and canopy temperature. Canopy temperature (Tc) minus air temperature (Ta) has been shown to be an effective indicator of crop water stress [1]. The application of Tc-Ta to irrigation management can be achieved through the use of commercially available infrared sensors that can be mounted in the field. Measurement of Tc-Ta at a few locations may not provide an adequate indication of water stress conditions that are representative of a field, if the field contains appreciable spatial heterogeneity in soil moisture conditions resulting from variation in soil physical properties. An alternative is the use of satellite- or aircraft-based remote sensing imagery within the thermal infrared (TIR) spectral range, which is capable of capturing the spatial variability in surface temperature

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