Influence of Organic Matter in Soils on Radar-Wave Reflection: Sedimentological Implications

Abstract

Soils are excellent reflectors of ground-penetrating radar (GPR) signals because of the ability of organic matter to hold water. In this paper, GPR profiles of an eolian sedimentary succession are combined with textural, dielectric, and moisture-retention characteristics to illustrate the influence of soil moisture on radar-wave reflection. Organic matter in this succession varies strongly, from Ͻ 0.15% for clean sand to 7% for the most prominent soil, whereas grain-size distributions are comparable. Moisture-retention curves show a complex relationship between suction potential (pF) and volumetric water content (). As a result of their uniform pore-size distribution, clean sand and weakly developed soils with Ͻ 1% organic matter experience a sudden loss of water between pF 1.5 and pF 1.8, going directly from saturated to almost dry conditions. In contrast, the most prominent soil shows a more gradual decrease in with increasing suction potential. It follows that the dielectric contrast between clean sand and this soil increases sharply above pF 1.5, reaches a maximum value at field-capacity conditions, and then decreases slowly. Synthetic GPR images for different suction potentials show that field-capacity conditions, when reflection coefficients are high, are favorable for tracing one single soil. Dry sediments are preferable when imaging widely spaced soils, whereas saturated sediments are best when imaging closely spaced soils.

Depositional Models of Braided Rivers

“…Ground-penetrating radar reflection data are acquired in real time by moving transmitting and receiving antennae together along lines in a grid. The GPR reflections are due to changes in dielectric permittivity (and less commonly due to magnetic permeability), related to the amount and type of pore-filling material, sediment texture and composition (Van Dam & Schlager, 2000;Kowalsky et al, 2001Kowalsky et al, , 2004Van Dam et al, 2002;Lunt et al, 2004a,b). As reflections are primarily caused by changes in pore-water saturation or volume, which are closely related to sediment texture and composition, reflections give a record of sedimentary strata.…”

GPR in sediments: advice on data collection, basic processing and interpretation, a good practice guide

“…Smith and Jol 1992;Huggenberger 1993;Bristow 1995aBristow , 1995bBristow et al 1996;Woodward et al 2003). Detailed field and lab studies of radar reflections in sediments have also been carried out for this purpose (Topp et al 1980;Knoll 1996;Van Dam and Schlager, 2000;Van Dam et al 2002a, 2002b). In addition, Van Dam et al (2003) conclude that variations in water content associated with small scale textural changes in sediments are responsible for the changes in permittivity that cause reflection of radar signals.…”

Strength of landmine signatures under different soil conditions: implications for sensor fusion

“…The dielectric properties of the soil are strongly influenced by the water content, as the dielectric constant of water (80) is a factor 20 times as large as most soil constituents (Topp et al 1980, Peplinski et al 1995, Borchers et al 2000, Van Dam and Schlager 2000, Van Dam et al 2002b). The relationship between soil water content and bulk electromagnetic properties can be described by simple regression functions, or pedotransfer functions, that sometimes include information about bulk density, particle size distribution and the effect of bound water (Topp et al 1980, Jackson 1987, Bohl and Roth 1994, Heimovaara et al 1994).…”