Thermal infrared earth observation for operational irrigation management
Authors: Werner Florian , Ziliani Matteo , Abello Albert 
Published: February 2023

Irrigation water use in agriculture is a major drain on the world&#8217;s freshwater reserves. Optimizing irrigation water use and accurately assessing crop responses to water stress in near-real-time is becoming increasingly important due to more extreme weather conditions and increasing water scarcity promoted by climate change. Canopy temperature measured by thermal infrared (TIR) is an excellent indicator of crop water stress due to its close relation to relative transpiration rate. Satellites equipped with TIR sensors can provide a cost-efficient global solution for irrigation management and crop water stress monitoring. However, current TIR satellite data products are only available at either high spatial or high temporal resolution, but not both. Hydrosat is launching a 16+ satellite constellation to provide high-resolution global TIR data products every day, multiple times per day. Hydrosat&#8217;s data will be a game changer in agricultural monitoring and management, enabling detailed and fully remote sub-field-level irrigation management everywhere in the world.Assimilating daily crop water stress derived from TIR measurements into soil water balance models provides multiple unique advantages: 1) &#160;Knowledge of the current crop stress increases the reliability of water balance calculations even if physical soil parameters are not known precisely; 2) actual applied water amounts can be estimated, alerting to issues arising from malfunction of irrigation equipment; and 3) crops can be safely maintained at reduced soil moisture, making full use of water reserves in the soil and controlling pathogens which thrive under moist conditions.Field trials were carried out in Europe, United States, and South Africa, where different crops (including potatoes, tomatoes, maize, soybeans, and dry beans) were studied under various irrigation regimes. Daily thermal infrared data and soil water balance models were employed to estimate crop water stress and soil water content, which provided an optimized irrigation schedule based on the actual current water deficit.Soil water balance calculations accurately reproduced the volumetric soil water content measured with soil probes, and on two occasions identified malfunctions in the irrigation systems. Beyond yield increases and cost reductions from reduced water consumption and pumping times, precision control of irrigation also has interesting applications in conditions where meticulous control of canopy moisture is required. Potatoes and tomatoes affected by late blight during field trials in South Africa were grown under standard irrigation and under Hydrosat&#8217;s optimized irrigation schedule targeting a low surface soil moisture. Blight infection under standard irrigation resulted in drastic yield losses, while optimized irrigation was able to maintain over 80% of the yield obtained in the previous year without blight infection. For tomatoes, which only showed very mild symptoms of blight, the optimized irrigation schedule still achieved a 40% yield increase compared to standard irrigation. In these examples, water balance modeling based on thermal infrared data can turn almost complete crop loss into a reasonable crop yield.