ISSUES OF OPTIMAL SOIL MOISTURE CONTROL BASED ON DUAL-BAND SENSORS

Abstract

The water content in the soil is spatially heterogeneous, which depends on climatic factors, land use, topography and properties of the soil itself. Currently, radio frequency soil moisture meters are the most common. The technical documentation of these devices indicates that the measurement error in them can reach 1 %. However, as the results of known experimental measurements show, such a result is achieved only after calibration with respect to a specific type of soil. Calculations show that in the absence of such calibration, the error can grow up to 15 %. In this regard, spectral methods of measuring soil moisture are more advantageous. The wellknown results of the conducted studies show that in this method the main interfering factor is the content of organic substances in the soil and taking into account only the phosphorus content in the soil makes it possible to achieve a measurement error of 6.5 %. This circumstance emphasizes the prospects of exploring additional ways to increase the efficiency of spectral methods for measuring the moisture content in the soil. The question of the optimal construction of a soil moisture monitoring network based on contact dualband optical soil moisture sensors operating in the NIR and SWIR ranges is formulated and solved. It is shown that the use of the usual averaging of the measurement results obtained on two ranges of the sensor when measuring with a constant frequency can lead to an inaccurate result due to differences in the dynamic ranges of optical signals at the detector inputs caused by the non-identity of the humidification conditions of the sub-field. The possibility of choosing an adaptive measurement mode is shown when sub-stages with a large dynamic range of humidity changes should be measured with a higher frequency, proportional to the specified dynamic range, which is equivalent to the implementation of an adaptive measurement mode.