Ground-penetrating radar study of the Rahivere peat bog, eastern Estonia

Abstract

The current case study presents results of the ground-penetrating radar (GPR) profiling at one of the Saadjärve drumlin field interstitial troughs, the Rahivere bog, eastern Estonia. The study was conducted in order to identify the bog morphology, and the thickness and geometry of the peat body. The method was also used to describe the applicability of GPR in the evaluation of the peat deposit reserve as the Rahivere bog belongs among the officially registered peat reserves. Fourteen GPR profiles, ~ 100 m apart and oriented perpendicular to the long axis of the depression, covering the bog and its surrounding areas, were acquired. In order to verify the radar image interpretation as well as to evaluate the velocity of electromagnetic waves in peat, a common source configuration was utilized and thirteen boreholes were drilled on the GPR profiles. A mean value of 0.036 m ns–1 corresponding to relative dielectric permittivity of 69.7 was used for the time–depth conversion. Radar images reveal major reflection from the peat–soil interface up to a depth of about 4 m, whereas drillings showed a maximum thickness of 4.5 m of peat. Minor reflections appear from the upper peat and mineral soil. According to the borehole data, undecomposed peat is underlain by decomposed one, but identifying them by GPR is complicated. Mineral soil consists of glaciolimnic silty sand in the peripheral areas of the trough, overlain by limnic clay in the central part. The calculated peat volumes (1 200 000 m3) were found to exceed the earlier estimation (979 000 m3) that was based solely on drilling data. Ground-penetrating radar, as a method that allows mapping horizontal continuity of the sub-peat interface in a non-destructive way, was found to provide detailed information for evaluating peat depth and extent

Ground-penetrating radar study of the Cena Bog, Latvia: linkage of reflections with peat moisture content

“…Results of this research disagree with the generally-accepted opinion that it is possible to explain all obtained reflections from bogs on the basis of volumetric moisture content changes only (Holden et al, 2002;Slater & Reeve, 2002;Comas et al, 2004;Kettridge et al, 2008;Plado et al, 2011;de Oliveira et al, 2012 As it was not possible to relate some of the obtained reflections directly with any of the determined properties of peat (moisture content, ash content, the degree of decomposition, botanical composition), other more complex mechanisms must be considered. For example, bound water has significantly different electromagnetic properties from free water (Kaatze, 2011).…”

“…It is generally accepted that reflections are related to peat moisture content changes (Holden et al, 2002;Slater and Reeve, 2002;Comas et al, 2004;Kettridge et al, 2008;Plado et al, 2011;de Oliveira et al, 2012). Further, several authors (Slater & Reeve, 2002;Kettridge et al, 2008;Comas et al, 2011) argue that changes in peat moisture content are related to other properties of peat, such as ash content, density, botanical composition and degree of decomposition.…”

“…Further, several authors (Slater & Reeve, 2002;Kettridge et al, 2008;Comas et al, 2011) argue that changes in peat moisture content are related to other properties of peat, such as ash content, density, botanical composition and degree of decomposition. Thereby, GPR can potentially be used for identification peat boundaries of various properties, e.g., to correlate GPR signal reflections with boundaries of peat layers characterised by different degree of decomposition (Kettridge et al, 2008;Plado et al, 2011) or different botanical composition (Hanninen, 1992;Sass et al, 2010). These results are, however, not unambiguous as there is still no widely-accepted opinion about the effect of various peat properties on the propagation and reflection of the GPR signal.…”

A ground-penetrating radar study of the Vaidasoo bog (Estonia): no crater structure exists

“…Prism2 soft ware was used for data pro cess ing, which in cluded (i) a bandpass fil ter with the aim to re move oc ca sional low-fre quency in ter fer ence and (ii) time-depend ent gain. To con vert two-way travel time mea sured by radar de vice to a depth-scale, ve loc i ties of 0.036 m ns -1 for peat-cov ered ar eas (Plado et al, 2011) eas cov ered by min eral soil (wet sand; Da vis and Annan, 1989), were used. In ter pre ta tion of the GPR im ages is sup ported by the drill ing data.…”

Cenas tīrelī iegūto radiolokācijas signālu analīze

“…Signāli tika konstatēti, korelēti ar ģeoloģiskā griezuma raksturīgām virsmām un sekmīgi pielietoti kūdras novērtējumam vienkāršiem izmantošanas veidiem. Turpmākajos gados padziļināti pētījumi nesekoja un iemesli, kāpēc radiolokācijas signāla atstarojums ir izveidojies, ir skaidroti salīdzinoši vienkāršoti.Bieži vien ir ticis pausts viedoklis, ka iegūtie radiolokācijas signāli ir saistīti ar nogulumu mitruma daudzuma izmaiņām griezumā [2,3]. Tāpat līdzšinējos pētījumos bieži vien tiek atzīmēts, ka iegūtie radiolokācijas signāli var būt saistīti ar kūdras humifikācijas pakāpes izmaiņām griezumā [4,5].…”