Soil moisture/water content monitoring (spatial and temporal) is a critical component of farm management decision primarily for crop/plant growth and yield improvement, but also for optimization of practice such as tillage and field treatments. Satellite humidity probes do not deliver the relevant resolution for farming purposes. Ground moisture probes only provide punctual measurements and do not reflect the true spatial variability of soil moisture.

Previous studies have demonstrated that variations of the nature of the ground/soil (i.e. moisture/water content amongst others parameters) modify the properties of reflected waves resulting in variations of amplitude and phase of the signal-to-noise ratio (SNR) recorded by a Global Navigation Satellite System (GNSS) receiver. Ground based studies analyzing the time variations of SNR measurements linked to dielectric constant of the surrounding soil established a method to recover local fluctuations of soil moisture content.

This method was adapted to airborne application and trialed on low level flying GyroLAG’s light and affordable aircraft also used for other airborne remote sensing agri-surveying work (e.g. magnetic and gamma spectrometry soil zoning). Data processing chain was adjusted to the specifics of the airborne dynamic context. Spatial resolution of 45 m was achieved for the specific test conditions (120-140 km/hr flying speed and 50-100 m agl survey height). Comparison with isolated in situ measurements of soil moisture proved to be poor at less than 75% correlation. A second test is now planned to be performed over a single farm/pivot with validation over a regular grid of in situ measurements of soil moisture.