Submitted to: National Information Management and Support System
Publication Type: Other
Publication Acceptance Date: 9/2/2005
Publication Date: 9/12/2005
Citation: Thomson, S.J., Rowland, D., Sullivan, D.G. Detection of crop water status from aerial platforms and in-field sensors. National Information Management and Support System. September 2005. 5 pgs. Interpretive Summary: Low altitude aerial platforms are being used for thermal remote sensing at three units of the USDA ARS. These sensing platforms include agricultural aircraft and Unmanned Aerial Vehicles (UAVs). Ground-based infrared temperature sensors are also being used to detect crop canopy temperature. Thermal remote sensing may be used to determine when irrigation is required by the temporal increase in the crop canopy-air temperature difference. Because of high humidity levels commonly encountered in many areas of the Southern US, however, these temperature differences can be small, necessitating very accurate sensing systems and careful consideration of weather variables. Changing cloud cover alters canopy temperature, but there is a delay between the time a cloud passes over and the time a plant shows a corresponding thermal response. In a preliminary study, attempts were made to quantify differences in canopy temperature before and after irrigation using aerial- and ground-based platforms. Thermal images from aircraft showed a distinct difference (cooler canopy) after irrigation. There was poor correlation between crop canopy-air temperature difference and readings from soil moisture sensors but good correlation between canopy temperature and sap flow readings that measure plant water use.
Technical Abstract: Two low altitude aerial platforms and one ground-based platform are being used to accommodate thermal remote sensing systems for detection of pending crop water stress in the southern U.S. The aerial platforms include an agricultural aircraft platform (instrumentation and cameras mounted in an Air Tractor 402B) and unmanned aerial vehicle (NASA ImageAire UAV). In a preliminary study, thermal crop canopy images taken from aircraft showed distinct cooling after irrigation. Ground-based thermal readings showed poor correlation with readings from soil moisture sensors, but thermal readings showed good correlation with sap flow, a direct indicator of plant water use. Procedures to account for differences in incoming solar radiation and wind need to be implemented for data obtained from both aerial and ground-based thermal sensing platforms.