Overview
Measuring soil moisture might seem to be one of the problems that should be tackled using the so-called remote sensing technology. And indeed many attempt to do just that. But research shows that none of the existing satellite-based imaging techniques can provide scientists and engineers with enough information to calculate the soil moisture deep enough to provide accurate measurements for the relevant root zone of the plants in agriculture.
Remotely sensed shortwave infrared (SWIR) transformed reflectance (TRSWIR), the normalized difference vegetation index (NDVI), and other such parameters can be successfully used to estimate soil moisture at the surface level for large areas and can definitely be applied to problems like drought detection or irrigation in low-income areas but modern farming, especially with plants that exhibit deep root zones, requires a much higher precision in measuring soil moisture at larger depths which are physically hidden from the satellite cameras.
Accurate only up to 5cm below surface
A review of remote sensing methods applied to soil moisture estimation performed at the University of New Brunswick in Canada points out that remote sensing methods can be relatively successful at estimating moisture for up to 5cm below the surface. And even that is only given that there isn't much vegetation constraining the view above the soil. Anything deeper "can be considered as another challenge".
10 years have passed since that review but not much has changed besides there being more companies offering satellite-based solutions that promise results they cannot deliver. The reason for that is that the farm's root zone is a much more complicated system than one that could be solved by observing the surface of the soil. No matter how advanced the machinery, the only way one can estimate the moisture accurately deep within the soil is by performing a measurement at the relevant depth. And that's exactly what soil moisture sensors do.
Read more about our soil moisture sensors.