Zhurnal Radioelektroniki - Journal of Radio Electronics. eISSN 1689-1719. 2020. No. 1
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Full text in Russian (pdf)

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DOI 10.30898/1684-1719.2020.1.7

UDC 621.369.9
 

Measuring moisture in the surface layer of mineral soil at two frequencies

 

K. V. Muzalevskiy

Kirensky Institute of Physics, Federal Research Center KSC Siberian Branch Russian Academy of Sciences, Akademgorodok 50, bld. 38, Krasnoyarsk, Russia

 

The paper is received on December 4, 2019

 

Abstract. In this work, the possibility of remote sensing of moisture in the mineral topsoil at a frequency of 5.4 GHz (C-band) and at a frequency of 0.63 GHz (P-band) was experimentally investigated. Bistatic scheme for measuring of the reflection coefficient at a fixed angle of 25° on horizontal and vertical polarization was used. Due to the wide radiation pattern of the used antennas, the radio impulse method was used to separate in the time domain the direct and reflected signals from the soil cover. As the receiving and transmitting antennas the pair of horn (5.4 GHz) and pair log-periodic (0.63 GHz) antennas were used. Radio impulses were generated in an unreal time scale using an Agilent N9918A FieldFox vector network analyzer. The technique for measuring the reflection coefficient consisted in the measurement of the  maximum of the envelope of the radio impulse, reflected from the soil cover, relative to the maximum of the envelope of the radio impulse reflected from the metal screen placed on the soil cover. It is experimentally established that the soil moisture, which was remotely measured at a frequency of 5.4 GHz, in the approximation of a homogeneous dielectric half-space, with a correlation coefficient of 0.780-0.897 and a standard deviation of 1.3-2.3% (depending on wave polarization) is consistent with the soil surface moisture measured by the contact method in a layer of 0-0.5 cm. Using the frequency of 5.4 GHz as the main one for retrieving soil surface moisture needs additional verification in various conditions of roughness of the soil surface and vegetation cover. The proposed model of the soil moisture profile in the form of a piecewise-linear function allows remotely measuring on two-frequencies soil moisture in topsoil with a correlation coefficient of 0.758 and a standard deviation of 2.4% relative to the soil moisture measured by the contact method. The author sees the indisputable advantage of using ultra-wideband (UWB) pulsed signals, the spectrum of which is concentrated in the megahertz frequency range, for the further development of technology for remote measurement of moisture profiles in the arable layer of agricultural soils. The use of ultra-wideband electromagnetic pulses with a continuous spectrum in the megahertz frequency range will allow us to solve the multi-parameter problem of restoring the moisture profile in the arable layer of agricultural soils. In the future, the UWB technology of pulsed sounding due to the availability of miniature electronic devices can be implemented for platforms of an ultra-light unmanned aerial vehicle with the aim of mapping moisture in the arable layer of agricultural soils.

Key words: radiolocation, soil moisture.

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For citation:

Muzalevskiy K.V. Measuring moisture in the surface layer of mineral soil at two frequencies. Zhurnal Radioelektroniki – Journal of Radio Electronics. 2020. No. 1. Available at http://jre.cplire.ru/jre/jan20/7/text.pdf
DOI  10.30898/1684-1719.2020.1.7