M-Sequence Pulse-Compression Underground Survey Radars

Abstract

A method of coded pulse compression employing two maximal length sequences (M-seq.) which are the same in code but generated by slightly different clock frequencies is newly applied to subsurface radars. This method practically gains the sensitivity of the signal without any sacrifice of resolution.The M-seq. pulse-compression underground survey radars are theoretically analyzed and the design criteria are obtained. The waveform made by phase modulation of the M-seq. over the carrier synchronized by the clock frequency generating the M-seq. is found to be more effective than the original M-seq. as transmitting wave.Two prototypes, the surface scanning underground radar and the cross bore-hole radar, are tested and confirmed to be highly sensitive with enough resolution, showing their promising prospect such as inspection of buried pipes in the deeper underground and more precise survey of stratum structure than the conventional subsurface radars with mono-pulse.

Coded pulse signal subsurface radar

“…Examples of correlation receivers for subsurface radar include the sliding correlation type [11] and the delay correlation type [9,12]. In the sliding correlation type, two identical coded signal generators at RF frequencies are needed.…”

“…For that reason, it is difficult to construct matched filters. Hence, pulse compression is realized with a correlation receiver that generates the output waveform equivalent to that of the matched filter processing [11,12]. In this paper, we derive the S/N improvement ratio at the input and output of such a correlation receiver when the M-sequence coded pulse signals proposed here are used.…”

“…To this end, (1) software processing [10,13] and (2) sliding correlation scheme [11,14] have been reported for subsurface radar. Method (1) has a low utilization efficiency of the signal and the S/N improvement is poor because the correlation processing is carried out after the received signals are converted to a lower frequency range by sampling.…”

Archaeological survey using pulse compression subsurface radar

“…This subsurface radar solves the difficulties of the conventional model because the detection range is determined by the average power of the signal, not by the peak power, and the range resolution is determined by the bandwidth of the transmitting signal, not by the pulse width. A coded signal or a modulated pulse is used for the pulse compression technique instead of a narrow shaped pulse (Fernett et al, 1970;Barton, 1975;Brookner, 1978;Olver et al, 1982;Arai and Suzuki, 1983a,b;Suzuki et al, 1987;Arai et al, 1992;Nagamune and Tezuka, 1994). A linear frequency modulation (FM) chirp radar uses the pulse compression technique.…”