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Parametric classification of ferromagnetic bottom objects based on an image analysis of magnetic anomaly map

100%

Bodus-Olkowska I. , Uriasz J.

tom No. 28

18--28

The magnetic properties of ferromagnetic objects or naturally occurring minerals such as ores can be detected and mapped using magnetic field theory studies. Magnetometry water area survey are commonly used for the purposes of detecting the oil or gas pipelines, shipwrecks and their equipment (i.e. anchors or engines), wrecks of airplanes or cars, barrels, containers, unexploded ordnances and mines and other metal debris. It is possible by detecting the magnetic anomalies they induce. The following article is presenting the stages of geoclassification of the bottom objects based on the analysis of a magnetic anomaly map. In order to determine the conditions and parameters of geoclassification, a catalog of ferrous seabed bottom features was previously developed. The catalog is dedicated to inland water areas and contains the characteristics of features potentially possible to meet in these waters along with the parameters of the magnetic anomaly they induce: e.g. spatial dimensions (length, width, area, perimeter, value ratio) together with the value of the generated anomaly itself. The further part of the article presents the map segmentation process, carried out for the purpose of detecting the areas covered by an anomaly and then dimensioning it along with the classification procedure. The whole process is summarized with the verification of the correctness of the method's operation on modeled and real anomalies.

Geological setting of the Milejowice-Janowice diabase intrusion: insights into post-Caledonian magmatism in the Holy Cross Mts., Poland

88%

Kowalczewski Z.

tom Vol. 48, No 2

135--146

Near Milejowice and Janowice in the eastern part of the Łysogóry Unit of the Holy Cross Mts., Poland, a SW-NE trending diabase has been identified intruding Lower Palaeozoic strata. This intrusion causes amagnetic anomaly, with delta T values of 48-112 gamma. It is orientated perpendicular to the regional strike. Boreholes encountered one to three component dykes 2.0 to more than 10.0 m thick inclined at 75-90 degrees Celsius, generally towards the east. They are hydrothermally altered and affected by surface weathering. The intrusion is located along two independent transverse faults, "skipping" from one to another irrespective of their strike. The intrusive zone is strongly tectonically disturbed, S-curved and disrupted by faults into segments and sub-segments. Most of the diabases are slicken-sided, and locally cataclased and mylonitized. The Milejowice-Janowice diabases probably formed in the Early Devonian, i.e. late Lochkovian-early Pragian, as post-tectonic igneous rocks belonging to within-plate, continental basalts according to Krzemiński (2004). Their origin may be referred tomagmatism triggered by the extension of the Baltica passivemargin during the final Late Silurian-Early Devonian phase of its collision with eastern Avalonia. A complex and at least two-phase development ofmagmatism in the Holy Cross Mts. is envisaged.

Magnetic interpretation utilizing a new inverse algorithm for assessing the parameters of buried inclined dike‑like geological structure

75%

Essa K. S. , Elhussein M.

tom Vol. 67, no. 2

533--544

A new algorithm has been established to interpret magnetic anomaly data due to inclined dike-like structure. This algorithm uses first horizontal derivative anomalies attained from magnetic anomaly data utilizing filters of sequential window lengths. The final estimated parameters are the half-width, the depth, angle of magnetization and amplitude factor of an inclined dike-like geological structure. A minimum variance criterion is used for selecting the most suitable variables. This algorithm has been realized to theoretical data without and with random noise. The effects of interference due to near structures have additionally been studied. The method was then applied to two field examples from Turkey and Peru, which demonstrate its effectiveness and accurateness. Thus, it is a respectable correspondence among the model parameters retrieved from this approach, drilling information, and the outcomes published in the literature. For example, in Turkey, we applied the technique to gauge the source variables and also the results were precise to w = 64.74 m and h = 87.65 m (2% and 3% errors, respectively) based on information from Aydin and Gelişli (Jeofizik 10:41–49, 1996).