Impulse radar sounding in permafrost

Abstract

A VHF impulse radar system operating on the ground is a viable technique for mapping the near‐surface geological structure and electrical properties of permafrost. A fixed antenna configuration transported over the surface yields a reconnaissance map of two‐way travel times for subsurface reflectors. Wide‐angle reflection and refraction (WARR) sounding determines propagation velocity versus depth when performed in layered areas. To obtain a WARR sounding, one measures travel time versus antenna separation. These techniques were field tested in the Tuktoyaktuk region of the Mackenzie River delta, N.W.T. Data recording was on a graphic display for initial field analysis and on analog magnetic tape for subsequent processing. Reconnaissance surveying has mapped structural features at various depths between 3 and 30 m. The electrical loss of the soils at a site limits the penetration depth. Clays and silts attenuate the radar signal more than sands and gravels. WARR soundings have determined dielectric constant versus depth in layered areas. While impulse radar is useful in delineating geological structure, core drilling is required to determine the geological composition.

High‐resolution seismic and ground penetrating radar–geophysical profiling of a thermokarst lake in the western Lena Delta, Northern Siberia

“…Antenna spacing was changed with constant increments of 1 m to offsets of 100 m at maximum. This generated an antenna-separation versus travel-time plot, from which the propagation velocity of subsurface materials can be deduced (Annan and Davis, 1976). These profiles were recorded at characteristic sites such as deep basins or the shallow margins ( Figure 3).…”

“…These activities complement shallow seismic (Chirp) measurements collected as a presurvey of the sediment fill in the preceding summer season (see Figure 1). GPR sounding is an established technique for permafrost investigations (Annan and Davis, 1976;Arcone et al, 1998;Judge et al, 1991;Robinson et al, 1997;Hinkel et al, 2001), active layer surveys (Doolittle et al, 1990) and lake-sediment profiling (Mellet, 1995). Mellet (1995) and Moorman and Michel (1997) have shown the potential of the GPR method for surveying sediments through a lake-ice cover.…”

Improved method to determine radio-echo sounding reflector depths from ice-core profiles of permittivity and conductivity

“…Most direct measurements of wave speeds are derived from ice-core profiles of density or permittivity (Robin and others, 1969;Clough and Bentley, 1970;Kovacs and others, 1995;Richardson and others, 1997;Eisen and others, 2002) or tomography between boreholes or pits (Fortin and Fortier, 2001;Kravchenko and others, 2004). Indirect measurements depend on knowledge of reflector depth and travel time, as is needed for down-hole radar methods (Jezek and Roeloffs, 1983;Clarke and Bentley, 1994), or on a defined survey geometry for wide-angle reflection measurements (Annan and Davis, 1976) and common-midpoint surveys (Fisher and others, 1992;Hempel and others, 2000;Murray and others, 2000;Eisen and others, 2002).…”

Airborne River-Ice Thickness Profiling with Helicopter-Borne UHF Short-Pulse Radar

“…The Xadar unit triggers pulses at a pulse repetitition frequency (PRF) of 50 kHz and compiles the received pulses into 8 scans per second. Before compilation, the received UHF signals are sampled and converted to an audio-frequency facsimile to allow recording on cassette magnetic tape (see Morey (1974) or Annan and Davis (1976) for more complete operating descriptions). A variety of time-range gain (TRG) functions may be applied to the scans to suppress the higher-amplitude early returns (especially the direct coupling between transmit and receive antennae) and enhance the lower-amplitude later returns.…”