REMOTE SENSING METHODS FOR MEASUREMENT OF SOIL AND CROP WATER STATUS IN A HUMID ENVIRONMENT

Authors: Sassenrath, Gretchen; PRINGLE, H - DREC; ALARCON-CALDERON, V - MSU

Submitted to: The Environmental Protection Agency Conference on Spectral Remote Sensing of Vegetation
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2003
Publication Date: 3/15/2003
Citation: SASSENRATH COLE, G.F., PRINGLE, H.C., ALARCON-CALDERON, V.J. REMOTE SENSING METHODS FOR MEASUREMENT OF SOIL AND CROP WATER STATUS IN A HUMID ENVIRONMENT. THE ENVIRONMENTAL PROTECTION AGENCY CONFERENCE ON SPECTRAL REMOTE SENSING OF VEGETATION. 2003. Session 4, Paper 3, p.4.

Interpretive Summary: Presently, producers in the Mid-South have adopted no standard method to monitor soil moisture or crop water stress for irrigation purposes. In order to maintain acceptable productivity levels in the region, irrigation is becoming increasingly important. This increased reliance on irrigation has contributed to a decline in the ground water. Confounding this loss of ground water is the common occurrence of surface flooding from inadequate drainage. We are interested in developing a rapid detection method for determining soil water and crop water status for irrigation scheduling and water management. We are exploring visible and thermal remote imagery for its potential in estimating available soil water and detecting crop water status. Several limitations exist that limit the adaptation of remote imagery in humid growing environments. Atmospheric conditions, including the high humidity and cloud cover, interfere with reflectance measurements and thermal emissivity. Moreover, differences in canopy structure and soil reflectance will alter the measured spectra. As a first step in developing reliable remote imagery systems, we are using synthetic spectra, built from individual components that contribute to the canopy spectra. These synthetic spectra can be generated from a variety of individual conditions. The spectra compare well with remote images of the entire canopy obtained from aerial sources. The spectra will be used to explore the individual contribution of various factors to the canopy spectra.

Technical Abstract: With the increased need to insure adequate crop production, producers are increasingly relying on supplemental irrigation. Remote sensing has potential as an accurate indicator of crop moisture status. While the water potential of the soil and individual leaves or plants can be measured with a fair degree of accuracy, extrapolation from these well-defined measures for a small portion of a field to an estimate of whole field canopy water status is error-prone. Moreover, changes in canopy structure and leaf angle alter the reflectance from the individual leaves, and introduce deviations in the recorded spectra due to increases in reflectance from the soil and lower canopy layers. These factors, together with atmospheric distortions, alter the reflectance spectra of a crop canopy from that recorded for individual leaves or plants within that canopy. This study explores the feasibility of remote sensing in the thermal and visible regions for detecting the onset of water stress in cotton canopies under the humid growing conditions of the Mid-South. Soil water availability was altered in research plots through changes in tillage and irrigation. A spectroradiometer and an infrared thermometer were mounted on a boom for rapid scanning of the crop canopy. Concurrent measurements of insolation, air temperature and spatial position were taken. The measured individual leaf spectral characteristics were then approximated by Fourier transformations, and randomly mixed and visualized using an imaging software package. The resultant synthetic spectra were remarkably similar to remote images of crop fields obtained from aerial sources. The spectra will be used to explore the individual contribution of various factors to the canopy spectra.