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

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

Lower Silurian biostratigraphy of the Viirelaid core, western Estonia

The distribution of five groups of fossils in the upper Llandovery (Telychian) and Wenlock of the Viirelaid core section, Estonia, is presented and discussed in terms of their biozones (conodonts and chitinozoans) and mutual positions (scolecodonts, ostracods, and brachiopods). Graphical correlation of the Viirelaid and Paatsalu sections shows a stronger linear correlation for zonal conodonts than for chitinozoans and scolecodonts. In the given case, this is caused by different nature of zones: chitinozoan zones are based on appearances and/or disappearances of ordinal taxa whereas conodont zonation corresponds, as a rule, to evolutionary succeeding species in the Pterospathodus lineage. At the same time, the positions of chitinozoan zones in the Viirelaid, Ruhnu, Aizpute, and Paatsalu cores are oscillating with respect to conodont zones

Georadar Eestis: välitöödest avaandmete taaskasutuseni

Väitekirja elektrooniline versioon ei sisalda publikatsiooneGeoradar on geofüüsikaline seade, mis võimaldab uurida pinnast kaudselt. Maapinda suunatud ja erinevatelt pindadelt tagasipeegeldunud signaalidest koostab radar pidevad läbilõiked (pildid). Koos paljanditest ja puursüdamikest saadud otseste vaatlusandmetega aitavad radaripildid täiendada meie ettekujutust maapõuest. Doktoritöö selgitab georadari potentsiaali erinevates settekeskkondades ning teeb ettepanekuid seadme laialdasemaks kasutamiseks. Autori kogemustele ja kirjandusallikatele tuginedes on soovitatav georadarit tarvitada geoloogilisel kaardistamisel ja maavarauuringutel. Seade aitab piiritleda turba, liiva, kruusa, moreeni ja lubjakivi levikut ning kirjeldada mitmesuguseid rikkestruktuure. Samuti on võimalik täpsustada maavarade levikut, mahtu ja kvaliteeti. Keerulisema maapõueehituse korral saab georadariga optimeerida puurimiskulusid ning suurendada kaevandamistulusid. Doktoritöö annab ülevaate Eesti radariuuringutest. Töö aluseks oleva nelja uuringu andmed on avalikustatud Maa-ameti geoportaalis. Lähiaastatel plaanib Maa-amet võtta kasutusele riikliku kaardistusplatvormi Geo3D, mille maapõuemudelisse on oodatud kõikide radariuuringute info. Suurema ühtlustatud andmekogumiga saaks arendada masinõpet, mis aitaks säästa radaripiltide tõlgendamisele kuluvat aega. Piltidel tuvastatud objektid koos muude Geo3D avaandmetega on väärtuslikuks sisendiks järgnevatele pinnaseuuringutele.Ground-penetrating radar is a geophysical device for indirect subsurface studies. Signals transmitted into the ground, and reflected back from different surfaces, allow the construction of continuous cross-sections (radar images). Hence the geological realm, generally known from the boreholes and outcrops, obtains a more consistent perception. The thesis specifies the radar potential in various depositional environments and provides recommendations for its additional applications. Based on the author's experiences and examined references, more intensive radar usage is promoted in two fields – geological mapping and mineral resource estimations. The method can successfully reveal the distribution of peat, sand, gravel, till, carbonate rocks, as well as various deformation structures. Similarly, the tool enables to adjust the mineral resource's spatial extent, quality, and quantity. In more complicated circumstances, the exploration costs can be decreased, whereas the extraction profits may increase with radar engagement. The thesis gives an overview of the Estonian radar surveys. The results of the four case studies are shown in the Estonian Land Board's geoportal. In the coming years, the Land Board will launch the new mapping environment Geo3D. All the radar interpretations are welcome to the Geo3D subsurface module. Larger standardised datasets allow developing machine learning procedures, thus reduce analysis time. Objects identified in the radar images along with other Geo3D open data become valuable inputs for the subsequent geological explorations.https://www.ester.ee/record=b555190

Investigations of the Rahivere peat deposit by ground-penetrating radar

Rahivere turbamaardla uuringud georadariga Magistritöö käsitleb 2009. a veebruaris Vooremaa idaossa jäävas Rahivere turbamaardlas teostatud georadari uuringuid. Rahivere turbamaardla paikneb voortevahelises nõos ning tema pindala on 53,63 ha ja aktiivseks reservvaruks 97 000 tonni. Maardlale ja selle vahetusse ümbrusesse rajati keskmiselt 100 meetriste intervallide tagant 13 kirde-edelasuunalist radariprofiili ja üks loode-kagu suunaline profiil kogupikkusega 9 km. Mõõtmisteks kasutati Läti päritolu georadarit „Zond 12e“ sagedusel 300 MHz. Radargrammidel eristub turbakihi lamam valdavalt pideva ja selge peegeldusena, mis paikneb võrreldes servadega nõo keskosas oluliselt sügavamal (üle 4 m). Radargrammide alusel määratud turba paksuse ning elektromagnetlainete levikukiiruse kontrollimiseks puuriti maardla piiresse erinevatele profiilidele käsipuuriga kokku 10 auku. Maardla leiti koosnevast vähelagunenud (ülal) ja hästilagunenud (all) turbast. Turba lamamiks on liiv ja aleuroliit (nõo servaaladel) ning limnilise tekkega savi (nõo keskosas). Radargrammid interpreteeriti kasutades turba permitiivsusena väärtust 69,5 ning saadud andmepunktide alusel loodi arvutiprogrammiga ArcGIS turba levikut kirjeldavad pinnad ja arvutati turba mahud. Pinna genereerimiseks sobivaima meetodi leidmiseks katsetati erinevaid interpolatsioonitehnikaid. Lisaks erinevate meetodite võrdlemisele analüüsiti pinnale arvutatud mahu seost tema tegemiseks kasutatud informatsiooni hulgaga. Selleks tehti iga meetodiga 3 pinda: esiteks kõikide profiilide andmepunktidega (14 profiili), teiseks iga teise profiili andmepunktidega (6 profiili) ning kolmandaks iga kolmanda profiili andmetega (4 profiili). Sobivaimaks vahendiks pinna loomisel võib pidada andmepunktide triangulatsiooni (ArcGISi TIN). Leiti, et optimaalseks georadari profiilide vahekauguseks maardla turbamahu leidmiseks on 200 meetrit. SUMMARY Investigations of the Rahivere peat deposit by ground-penetrating radar Ivo Sibul Rahivere peat deposit lies in the eastern part of Vooremaa drumlin field. According to the Estonian records of mineral resources of the Environmental Registry it has an area of 53,63 hectares and reserves of 97 thousand tons. Calculation of these reserves is based solely on borehole data. Current study proposes an alternative method for peat volume calculation. Fourteen georadar profiles were created in Rahivere peat bog, covering the area of peat deposit and it’s nearest vicinity. Thirteen of the profiles were NE-SWoriented and juxtaposed approximately 100 meters from each other; one profile connects 4 profiles perpendicularly. Latvian „Zond 12e” ground-penetrating radar at the frequency of 300 MHz and common offset method was utilized during field work. Additionally, common mid-point technique (antennae 300 & 500 MHz) provided some information for estimating the dielectrical permittivity of peat (69,5). Radargrams reveal that thickness of the peat deposits extends four meters in the centre of the valley. In order to verify the radargrams’interpretation as well as the evaluated velocity of electromagnetic waves in peat, ten boreholes (depth from 1,75 to 5,5 m) were drilled manually upon the profiles. According to the borehole data, minerotrophic peat, where present, is covered by the ombrotrophic one. Mineral soil consists of silt and sand in the peripheral areas of the valley and limnoglacial clay in the central part. Peat thickness data were introduced as a point feature class into ArcGIS geodatabase. These spatially coordinated points were source data for some wellknown interpolation methods (spline, natural neigbor, IDW, kriging, TIN). The aim of generating raster and TIN surfaces was peat volume calculation. At first, all the georadar information was used. Then, data points were reduced by eliminating 8 of the profiles and finally, only 4 of them attended in the processing. Distance between the profiles was 100, 200 and 300 meters, respectively. Calculated peat volumes correspond well with official information. TIN method is given the preference after comparing the isolines of the surfaces. 200 m step is suggested as the optimum for georadar profiling in peat deposits