Within the County GSAs, monitoring of evapotranspiration (ET) and evapotranspiration of applied water (ETAW) will be done with satellite technology provided by Irriwatch using SEBAL (Surface Energy Balance Algorithm for Land). Quality assurance and quality control would be performed by both Irriwatch, Davids Engineering and by Madera County staff. Resources and frequently asked questions are at the bottom of this page.
SEBAL (Surface Energy Balance Algorithm for Land) was developed by Dr. Wim Bastiaanssen of The Netherlands. SEBAL uses spectral radiances recorded by satellite-based sensors, plus ordinary meteorological data, to solve the energy balance at the Earth’s surface. SEBAL computes actual evapotranspiration (ETa) for each pixel in a multispectral satellite image by applying radiative, aerodynamic and energy balance physics in 25 computational steps incorporated into 19 models.
Conceptual Schematic of the Surface Energy Balance
SEBAL is a remote sensing algorithm that converts raw satellite data into radiation, heat and water vapor transfer fluxes to calculate the energy balance at the land surface. The actual evapotranspiration (ET) is the desired output, and it is determined from the radiation and heat fluxes. The radiation component considers all forms of incoming and reflected solar radiation to determine net radiation (net energy in). The heat flux component describes the heating rate of soil and air during the daytime. All energy that is not used for heating the soil and air is used to evaporate water, or ET. So, the net energy is dissipated in either heating the soil and air or evaporating water, and this dissipation depends on the soil moisture conditions. Wet land surfaces have a high ET and a low heat flux. Dry land surfaces have a low ET and a high heat flux. Satellite measurements of land surface temperature are fundamental for computing this energy balance.
IrriWatch is a daily irrigation scheduling and crop production information service that uses SEBAL model outputs. The main objective is to inform growers about the irrigation status of fields and recommend irrigation activities of the day. Growers with weekly schedules can check the need for corrective actions. For instance, the urgency of certain fields to receive water immediately or whether desirable stress levels are still ok. Sometimes mild stress is desirable, but the stress should not adversely impact the crop production. Besides irrigation advice for the day, also the status of the fields from yesterday are portrayed. This helps in understanding whether soil moisture and soil water potential in the root zone are still in the pre-defined range. If soil moisture signatures show a low and irregular value, then the grower sees that the current irrigation schedule is not appropriate. If soil moisture signatures are high, then water could be conserved. IrriWatch shows the accumulated crop production and ET values, and also applied water and Nitrogen status. This info together with the allocation helps growers making decisions on the timing and amounts of irrigation. The data portal is suitable for planning and monitoring. The App is developed mainly to check today’s situation.
Enrollment Presentation to MAWA: 12/17/2020
IrriWatch Set up and use training 1/20/2021 from 10-11:30
MAWA, FB and County GSAs on Irrigation Management 5/3/2021 at 10-11:30 a.m.; Powerpoint Presentation