Marine Magnetometer Processing (original) (raw)
Related papers
Developing magnetometer techniques to identify submerged archaeological sites
Camidge, K., P. Holt, C. Johns, L. Randall & A. Schmidt 2010. Developing magnetometer techniques to identify submerged archaeological sites (5671 DT). Historic Environment Service, Environment and Heritage, Cornwall County Council Report No: 2010R012. , 2010
Marine magnetic surveying has become a standard technique for mapping the location of ferrous material on the seabed. Existing guidance documents are concerned principally with data collection methods. The aim of the project was to acquire a better understanding of magnetic data and thus develop our ability to interpret these data with increased confidence.
High Resolution Marine Magnetic Survey of Shallow Water
The purpose of this paper is to present a system developed for detection and accurate mapping of ferro-metallic objects buried below the seabed in shallow waters. The system comprises a precise magnetic gradiometer and navigation subsystem, both installed on a non-magnetic catamaran towed by a low-magnetic interfering boat. In addition we present the results of a marine survey of a near-shore area in the vicinity of Atlit, a town situated on the Mediterranean coast of Israel, about 15 km south of Haifa. The primary purpose of the survey was to search for a Harvard airplane that crashed into the sea in 1960. A magnetic map of the survey area (3.5 km2 on a 0.5 m grid) was created revealing the anomalies at sub-meter accuracy. For each investigated target location a corresponding ferro-metallic item was dug out, one of which turned to be very similar to a part of the crashed airplane. The accuracy of location was confirmed by matching the position of the actual dug artifacts with the magnetic map within a range of ± 1 m, in a water depth of 9 m.
High Resolution Marine Magnetic Survey of Shallow Water Littoral Area
Sensors, 2007
The purpose of this paper is to present a system developed for detection and accurate mapping of ferro-metallic objects buried below the seabed in shallow waters. The system comprises a precise magnetic gradiometer and navigation subsystem, both installed on a non-magnetic catamaran towed by a low-magnetic interfering boat. In addition we present the results of a marine survey of a near-shore area in the vicinity of Atlit, a town situated on the Mediterranean coast of Israel, about 15 km south of Haifa. The primary purpose of the survey was to search for a Harvard airplane that crashed into the sea in 1960. A magnetic map of the survey area (3.5 km 2 on a 0.5 m grid) was created revealing the anomalies at sub-meter accuracy. For each investigated target location a corresponding ferro-metallic item was dug out, one of which turned to be very similar to a part of the crashed airplane. The accuracy of location was confirmed by matching the position of the actual dug artifacts with the magnetic map within a range of ± 1 m, in a water depth of 9 m.
Study of marine magnetic field
2007
Measurement of the Earth’s magnetic field in the marine areas (marine magnetic field) is one of the most widely used marine geophysical techniques. Data about the variation of the marine magnetic field has various applications. The conventional uses are to determine depth of burial and trend of magnetized basement rocks, which in turn yields overburden thickness, basin demarcation and information about the underlying structures. Marine magnetic data are used as one of the tool to differentiate areas underlain by continental and oceanic crusts. Other usages are in the fields of marine archaeological investigations or search of sunken ferrous objects (such as ships). However, the most important use of marine magnetic data is to address questions pertaining to geodynamics.
Malta Archaeological Review, 2021
In 2010 a magnetometer survey was conducted off the north-eastern coast of Malta, concentrating on Mellieħa and Salina bays. The aim was to identify potential target anomalies along the shoreline, with areas of interest marked in both bays. Ground-truthing surveys conducted by divers in Mellieħa Bay in 2011 and 2012 confirmed the presence of scattered cultural remains, and allowed for the re-identification of the so-called ‘Mortar Wreck’ site, first excavated by Honor Frost in 1967. A follow-up magnetometer survey was conducted in 2014 within the context of the University of Malta underwater field school, and consequently resulted in the exclusion of Salina Bay for further survey. The 2014 survey concentrated on Mellieħa bay and sought to further positively identify or reject potential anomalies first documented in the 2010 survey. The 2014 survey results revealed the possibility of substantial target anomalies within the bay.
There are various strategies for magnetic surveying
There are various strategies for magnetic surveying. Most are designed to capture a wide range of sources from near surface to deep subsurface structure. Magnetics, particularly magnetic gradiometry, is often used for discovering small objects at very shallow depths that have environmental or archaeological importance.
Over 400,000 shells of different calibers were dumped in Burgas Bay after the end of WWI. The operation, under the coordination of the British forces, was completed without the dumping areas to be clearly mentioned and mapped, allowing us today to assume that they can be anywhere in Burgas Bay. Many other shells were also dumped in the sea at the end of WWII. During the first phase of expansion of Burgas harbor, carried out between 2001 and 2006, a great deal of unexploded ammunition, originating from both WWI and WWII, was discovered and recovered by the dredging operations. Prior to the start of the second expansion phase, the Burgas port authorities ordered a detailed geophysical search to be carried out and cover a 90,000 sq.m surface where dredging activities are planned, aiming to identify sites where items such as UXO, wrecks, pipes, anchors and other metal objects lying on the sea floor and/or buried in shallow sediments could disturb and even endanger the dredging. The high-resolution marine magnetic mapping carried out in August 2016 by a team comprising both Romanian and Bulgarian specialists entirely covered the area of interest. The search was conducted in a totally unfriendly magnetic environment, dominated by huge variations of the total geomagnetic field due to the numerous outcropping or shallow intrusions of Paleozoic and Late Cretaceous ages, to lens of “black sands” with high contents of titanomagnetite minerals, resulted from the physical decomposition of the magmatites and not least to the large pile of steel pipeline sections stored on the neighboring quay. Still, the careful analysis of the magnetic analytic signal as well as the individual analysis of each marine magnetic line were able to highlight the presence of over 75 potential target areas where the presence of UXO-type items, possibly dumped or lost ferrous objects, accumulations of ammunition, etc. on the seabed or shallowly buried in sediments was highly likely. The indexed target sites became subsequently subject for scuba diving inspection which confirmed the existence of ferrous objects within all selected sites and brought to surface over 2,000 artillery shells and other items.
Application of the Magnetic Method to Explore for Shipwrecks on the South African Coast
Many ships that foundered on the South African coast have yet to be discovered. In most cases of previously discovered wrecks, incorrect published coordinates necessitate relocation of wrecks to facilitate recreational or salvage activities. Some of these wrecks present beautiful dive sites and offer interesting discoveries ranging from rum bottles to perfectly preserved ammunition dating back to before the Anglo-Zulu war. Other wrecks offer incredible stories that enrich our South African cultural heritage. And some offer rich treasure. Magnetic surveys effectively detect shipwrecks but require proper design. A standard airborne survey might suffice for detecting an old steam ship but older wooden wrecks, such as the Britannia (1826), require hi-res airborne surveys or better. Boat-borne surveys are used for searching for wrecks in shallow waters and may be complimented by cheaply available side-scan sonar equipment. In areas where hazards prevent boat access a small drone equipped with a fluxgate magnetometer offers good value. Where storms have washed up wrecks onto the beach a ground-magnetic survey offers potential success as well as some other attractions. Such is the case with the current search for the Haarlem, a Dutch ship that foundered in Table Bay in 1647, an event that was directly responsible for Jan van Riebeeck's relocation to the Cape some years later.