Look-ahead radar and horizon sensing for coal cutting drums and horizontal directional drills

An earth-penetrating radar method, comprising:

• using a near measurement mode and a far measurement mode for predistortion and calibration of a transmitted waveform and a carrier suppression;
• setting a radar first to near measurement mode to measure near-antenna signals reflected from a first interface by setting a phase of a modulation signal to θm to 0 (π) during a calibration;
• processing a near measurement mode, wherein a first sideband is tuned off and a magnitude and phase are a measurement of a second sideband alone;
• repeating a measurement for an opposite sideband;
• adjusting magnitudes of said sidebands to be equal in value and adjusting the phase θm to produce 0-degrees;
• adjusting θc is adjusted to zero to compensate for a frequency response in the radar and antennas;
• then switching to a far measurement mode that sets
• θ
• m
• =
• π
• 2
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• 
• or
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• 3
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• such that any first interface reflection is suppressed
• using polarized antennas for any additional suppression;
• and
• using a software-defined transceiver for phase-coherent detection of the depth of said second interface reflection.

An earth-penetrating radar, comprising:

• a power amplifier and antenna for launching corrected versions of coherent pairs of said first and second continuous wave frequencies into a geologic heterogeneous media with different constituent electrical parameters for causing first, second, etc. interface reflected waves to be received;
• a receiver and antenna for collecting signals reflected from a first interface and other signals reflected or scattered from buried objects and interfaces of material with contrasting electrical parameters;
• a down-converter and coherent demodulator for coherent demodulating of an in-phase I=cos(θm+ωmτ1)cos(ωc+ωcmτ1)+cos(θm+ωcmτ2)cos(θcm+ωcτ2)+ . . . , and Q=cos(θm+ωmτ1)sin(θc+ωchτ1)+cos(θm+ωmτ2)sin(θc+ωcmτ2)+ . . . , where θm is a processor-controllable phase shift (π/2, 0, 3π/2, 2π) . . . , ωm is the modulation frequency of a double-sideband suppressed carrier or phase-modulated signal, and θc is a carrier phase with a frequency of ωcm;
• a processor for determining the magnitude of each reflection as M=|cos(θm+ωmτ)| for each pair of transmitting continuous waves, wherein τ1 represents the echo delay time occurring for reflections from the surface near the antenna and τ2 represents the echo delay time occurring for more distant reflections from buried objects and interfaces;
• a device for predistortion that results in a modulation signal phase θm being set to zero when π1=0 in a far measurement mode calibration process, and a predistorted modulation signal phase is set to a near measurement mode and then measured in a far measurement mode to determine a distance (R) to a second interface by measuring ωmτ in the intermediate frequency.