Estimating the relative water content of leaves in a cotton canopy.

Authors: VANDERBILT, V.C. - GODDARD SPACE FLIGHT CENTER; DAUGHTRY, CRAIG; KUPINSKI, M. - UNIVERSITY OF ARIZONA; BRADLEY, C. - UNIVERSITY OF ARIZONA; FRENCH, ANDREW; BRONSON, KEVIN; CHIPMAN, R. - UNIVERSITY OF ARIZONA; DAHLGREN, R. - NATIONAL AERONAUTICS AND SPACE ADMINISTRATION (NASA)

Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: 8/31/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reliable measurements of plant water status are crucial for managing limited water supplies for sustainable crop production. Direct measurements of plant were status are reliable for a single plant or small plots, but are time-consuming and impractical for agricultural fields and large areas. Most remotely sensed estimates of plant water status have relied on near infrared or thermal infrared measurements that are generally tied to plant physiology. Infrared indices are based on the physics of water-light interaction, not upon plant physiology, which is a key limitation. Thermal indices are based on the principles of evaporative cooling and plant foliage temperature relative to the surrounding air temperature which is tied to plant physiology. However, thermal indices do not work well in humid regions where evaporative cooling is limited. Leaves, when water-stressed, may droop or curl and often appear gray compared to fully hydrated leaves that typically appear turgid and vivid green. Light reflected by interiors of individual corn leaves is linearly related to the leaf relative water content. Here we report results for extending our laboratory research to the canopy scale. We anticipate the knowledge gained at the canopy scale will be applicable to analysis remotely sensed imagery from aircraft and satellite sensors.

Technical Abstract: Remotely sensing plant canopy water status remains a long term goal of remote sensing research. Established approaches to estimating canopy water status — the Crop Water Stress Index, the Water Deficit Index, the Equivalent Water Thickness and the many other indices — involve measurements in the thermal or reflective infrared. Here we report plant water status estimates based upon analysis of polarized visible imagery of a cotton canopy measured by Ground Multiangle SpectroPolarimetric Imager (GroundMSPI). Such estimators potentially provide access to the plant hydrological photochemistry that manifests scattering and absorption effects in the visible spectral region.