GROUND PENETRATING RADAR MEASUREMENTS OF BOG DEPOSITS (A CASE STUDY OF THE ZAONEZHSKII PENINSULA, KARELIA)
P.A. RYAZANTSEV1, P.A. IGNASHOV2
1Department of Multidisciplinary Scientific Research, Karelian Scientific Center, Russian Academy of Sciences, 185910, Petrozavodsk, ul. Pushkinskaya, 11, Russia
chthonian@yandex.ru
2Institute of Biology, Karelian Scientific Center, Russian Academy of Sciences, 185910, Petrozavodsk, ul. Pushkinskaya, 11, Russia
paul.ignashov@gmail.com
Keywords: геофизическая проницаемость, торф, сапропель, радарограмма, картирование, диэлектрическая проницаемость, Заонежский полуостров, geophysical penetrability, peat, sapropel, GPR profile, mapping, dielectric permittivity, Zaonezhskii Peninsula
Abstract
The capabilities of Ground Penetrating Radar (GPR) in the study of bog massifs are discussed. The foundations of this method, a historical summary of its use, and a brief overview of problems dealt with in peatland study are provided. A detailed analysis is made of the influence of main peat parameters, such as density, moisture content, ash content, and the degree of decomposition, on the electromagnetic wave transmission rate, and on the formation of reflection boundaries. Literature sources were used to generalize electrophysical properties for peat deposits of different types. Data obtained show a presence of substan tial differences. The performance of GPR is demonstrated by results of our experimental studies on bog systems of the Zaonezhs kii Peninsula (Central Karelia). Using the Tolvuiskoe bog as an example, experience in studying the structure of the deposit and determining its boundaries is outlined. Radargrams were used to determine the three-layer structure, including peat, sapropel and varve clays, which is characteristic for the bogs in the study area. Each of the layers identified is characterized by a spe cific GPR complex, providing a means of uniquely identifying it on the radiogram. In addition, intermediate differences were determined, which are due to changes in moisture content and in the degree of decomposition. Data obtained for the depth of the layers were compared with biostratigraphic sections. The accuracy of determining the boundaries was of the order of ±0.2 m, which is comparable with the resolution of the 150 MHz GPR antenna used. Radargrams for the Tolvuiskoe bog were compared with GPR profiles for the Karasozerskoe, Gan’kovskoe and Padmozerskoe bogs to reveal a similarity in their structure. This confirmed the theory of their identical origin caused by the transgression of Lake Onega. Furthermore, some differences were noted, indicating local changes in the growth conditions of the bog massifs.
|
