Contactless soil moisture estimation using radiofrequency signals

A method of contactless moisture estimation of soil, the method comprising:

• emitting, via a first antenna and into the soil, radiofrequency (RF) signals at each of a plurality of frequency increments (δf) ranging from a lower frequency (fs) to an upper frequency (fe);
• determining a channel frequency response (CFR) for each of the plurality of frequency increments (δf) by measuring an amplitude attenuation and a phase change of reflected RF signals detected by a plurality of second antennas, wherein the CFR for each of the plurality of frequency increments (δf) is in a frequency domain;
• determining a power delay profile (PDP) for each of the plurality of second antennas based on the CFR of each of the plurality of frequency increments (δf), wherein the PDP for each of the plurality of second antennas is determined by taking the CFR in the frequency domain for each frequency from fs to fe in increments of δf, and then mapping the CFR in the frequency domain for each frequency from fs to fe to a time domain by taking an inverse fast Fourier transform (IFFT) of all [(fe−fs)/δf]+1 CFR values;
• extracting a subset of the reflected RF signals associated with the emitted RF signals by performing peak detection of the PDP of each of the plurality of second antennas;
• and
• for each layer of the soil and for each of the subset of reflected RF signals, determining:
• i) a wavelength of the reflected RF signal in a layer, ii) an estimated depth of the layer, iii) a dielectric permittivity of the layer based on the wavelength in the layer, and iv) an estimated moisture content of the layer based on the dielectric permittivity.

A non-transitory computer readable medium having instructions stored thereon that, when executed by a computing device, cause the computing device to:

• operate a radiofrequency (RF) generator to emit, via a first antenna and into a medium, RF signals at each of a plurality of frequency increments (δf) ranging from a lower frequency (fs) to an upper frequency (fe);
• determine a channel frequency response (CFR) for each of the plurality of frequency increments (δf) by measuring an amplitude attenuation and a phase change of reflected RF signals detected by the plurality of second antennas, wherein the CFR for each of the plurality of frequency increments (δf) is in a frequency domain;
• determine a power delay profile (PDP) for each of the plurality of second antennas based on the CFR of each of the plurality of frequency increments (δf), wherein the PDP for each of the plurality of second antennas is determined by taking the CFR in the frequency domain for each frequency from fs to fe in increments of δf, and then mapping the CFR in the frequency domain for each frequency from fs to fe to a time domain by taking an inverse fast Fourier transform (IFFT) of all [(fe−fs)/δf]+1 CFR values;
• extract a subset of the reflected RF signals associated with the emitted RF signals by performing peak detection of the PDP of each of the plurality of second antennas;
• and
• for each layer of the medium and for each of the subset of reflected RF signals, determine:
• i) a wavelength of the reflected RF signal in a layer, ii) an estimated depth of the layer, iii) a dielectric permittivity of the layer based on the wavelength in the layer, and iv) an estimated moisture content of the layer based on the dielectric permittivity.