Mapping Soil Moisture: Using Thermal Imagery to Make Practical Agronomic Decisions.

Soil moisture is a key factor in many management decisions, including planting and replanting, irrigation timing, and the design of variable-rate fertilizer and seeding prescriptions. On many production fields, soil moisture is monitored via a single sensor placed at a representative location, qualitatively assessed during field scouting, or not noted at all. While field-level estimates of soil moisture are valuable, managing variation within a field is essential for any management strategy attempting to efficiently allocate inputs and maximize yield.

Planetary Resources is developing a mid-wave infrared (MWIR) sensor (3-5μm), the first commercially available sensor of its kind, as part of our Earth observation satellite constellation. Prior to the deployment of the constellation in 2018, we are conducting extensive field-testing of the sensor with a focus on the development of agriculturally useful data products. The first of these is a relative soil moisture index based on the soil brightness temperature measured by the MWIR instrument.

During the 2016 growing season, we conducted a field campaign to collect aerial imagery of irrigated corn, wheat, and potato fields in Eastern Washington state. Our ground truth measurements include soil moisture, soil temperature, percent canopy cover, and canopy temperature. Preliminary analysis of the early season data shows a correlation between the MWIR data and soil moisture that is particularly evident in the center-pivot watering patterns.

Here we present analysis results from the full season data evaluating the relationship between MWIR observations and soil moisture throughout the season. We present the utility of MWIR imagery in constructing a relative soil moisture index for bare soil and early canopy coverage and an evaluation of the resulting data product.