The article is devoted to the development of a method for determining the moisture content of the upper layers of agricultural lands on the basis of mathematical modeling of a radar signal reflected from the soil. For the radar study of the moisture content of agricultural lands, it is proposed to use remote sensing using relatively inexpensive unmanned aerial vehicles (UAVs) of a multi-rotor type (a bistatic system consisting of a radar transmitter and a radar receiver placed on two UAVs). At the same time, it is necessary to ensure a high probability of correct determination of soil moisture to a depth exceeding the groundwater level. In remote sensing, the reflection coefficient from the air-soil interface depends on the dielectric properties of the top soil layer and the polarization of the sounding signal. When modeling the reflected signal, it is advisable to represent the earth's surface as a flat-layered structure, the upper part of which will be represented by vegetation and heterogeneities followed by the area with a relatively constant dielectric constant value to the groundwater level and then the area with a linearly increasing conductivity. Studies have shown that the Brewster effect in soils manifests itself when the probe signal is perpendicularly polarized. When the soil surface is irradiated with a perpendicularly polarized radar signal at Brewster's angle, the required penetration depth of the probing signal is ensured, at which the reflected signal will contain enough information about the percentage of moisture in the upper soil layers. The information contained in changes in the amplitude and phase of the reflected radio signal is related to the structure and dielectric properties of the upper soil layers. On the basis of this information, rational agro-technical measures can be justified, both operational (watering, fertilization) and long-term (reclamation, drainage).

Objectives of this article are to create a method that should identify distortion of navigation signals using supplementary information obtained whilst processing the navigation parameters in the calculator of the navigation receiver. To develop this method, a comparative evaluation of the actual data of the navigation measurements with the calculated data values and a Bayesian probabilistic approach for detecting the navigation field distortion and identifying the interference. Test of results of the developed method showed that it enables a highly reliable assessment of the state of the navigation field and, if distorted, the identification of the distortion type: normal (undistorted) condition; abnormal state: when abnormally high errors appear spasmodically in the positioning estimation within individual measuring channels of the navigation receiver; slightly distorted state leading to a slow change in positioning accuracy; active spoofing manifested in the substitution of positioning coordinates. The article provides a new method for processing navigation parameters allowing to detect the fact of the navigation fields (NF) distortion and identify the interference effect on the navigation receiver (NR) of UAV.