Reconstruction of sparse magnetic anomaly data by integrating spatially adaptive mean compensation with patch-based sparse coding

Purpose: We aim to develop tomographic reconstruction methods that utilize prior CT volumes to improve image quality for sparse and undersampled datasets. The ability to handle such data has applications in region‐of‐interest scanning, tomosynthesis, and intraoperative imaging based on few view angles. While compressed sensing techniques like the PICCS algorithm are attractive, there are potential drawbacks. Such approaches often rely on pre‐registered prior images and the forward models for PICCS‐type algorithms tend to be simplified and ignore the noise model. We leverage the ability of likelihood‐based techniques to incorporate both prior images and sophisticated forward models. Methods: We have developed a framework for reconstruction of sparse tomographic data based on penalized‐likelihood estimation. The objective function for this approach is composed of a likelihood term that incorporates the forward model and noise; and a parameterized penalty term that discourages differences from the prior image. The penalty uses a compressed sensing norm and is parameterized to accommodate registration of the prior scan. An iterative algorithm is used to simultaneously solve for the tomographic volume and the registration parameters. The framework is general and can be used with both rigid and deformable registrations. Results: Reconstruction of sparse data using the proposed approach is demonstrated in cases where either rigid or deformable registration is employed in the reconstruction objective. We compare reconstruction results with traditional approaches where prior image data is not utilized. We find a substantial improvement in image quality with significant reduction in artifacts that are associated with the sparse data acquisitions. Conclusions: A new class of penalized‐likelihood estimator has been developed that simultaneously refines attenuation and registration estimates. The framework is general and supports both rigid and non‐rigid transformations of the prior imagery. Image quality and handling of artifacts using the proposed estimator with sparse data is superior to traditional approaches.

<p>Quantifying past motions of tectonic plates in the southwest Pacific is important because the Pacific-Antarctic ridge is the only non-destructive boundary between the Pacific plate and other major plates. However, formation of sea-ice near Antarctica impairs the collection of magnetic anomaly data that are necessary to calculate plate rotations. A detailed analysis of all ship-track magnetic data available in the southwest Pacific (61 cruises, 153 profiles, including several cruises collected after 1995) is presented here. Four different sources of uncertainty are quantified: (1) confidence of magnetic anomaly identification, (2) magnetic reversal location picking precision, (3) ship navigation precision, and (4) magnetic data quality. Finite plate rotations are calculated for the southwest Pacific (42.5 to 79 Ma) using the resulting magnetic anomaly database (1528 magnetic reversal data). Finite rotations were calculated using the Hellinger criterion, or by a new method presented here that assumes orthogonality between fracture zones and ridge segments. The new method requires less parameters and is hence able better estimate rotations in cases with an uneven distribution of sparse magnetic data. Rotations and formal uncertainties are calculated for thirty-one chrons (c20y to c33o). They confirm the existence of a three plate system (Pacific, Marie Byrd Land, Bellingshausen) in the southwest Pacific from before c31o (68.7 Ma) until c28y (62.5 Ma). After c28y, the Bellingshausen and Marie Byrd Land plates moved as a single plate.</p>

The plate tectonic history of the Easter microplate has been reconstructed by “closing” the microplate in a series of steps using the Pacific‐Nazca magnetic anomalies north and south of the microplate and the NUVEL 1 global plate motion model. After each step, the Easter microplate was rotated rigidly to match the Nazca and Pacific anomalies. Gaps and overlaps formed by this kinematic treatment indicate compressional and tensional deformation, respectively, and show that rigid plate motions are insufficient to explain the complete tectonic evolution. Analysis of the magnetic anomaly data was guided by contoured SeaMARC II, Sea Beam, and 3.5‐kHz bathymetry data and a lineament map derived from SeaMARC II side scan and Sea Beam bathymetry data. The patterns of lineaments and bathymetric structures suggest that rotational deformation of the Nazca plate is the general mechanism that accommodates the space problems arising from transfer of the Nazca plate to the microplate and rapid rotation of the microplate against the Nazca plate. Similar but smaller amounts of deformation are predicted along the southern boundary of the microplate. Prior to the origin of the microplate, the East Pacific Rise (EPR) was offset in at least two places according to the older magnetic anomalies, yet there is no evidence of linear fracture zones within the sparse data set except for occasional small consistent changes in regional depth across these age offsets. The magnetic, bathymetry, and satellite altimetry data indicate that the microplate initially formed at (or perhaps southeast of) Easter Island near a left‐lateral offset of the EPR sometime between anomaly 3 and 3'. The East Rift started propagating north from the present location of Easter Island at ∼4.5 Ma, which is ∼1.5 m.y. earlier than previously proposed. However, the magnetic data that support this interpretation are sparse and complicated by recent volcanic flows and associated rough bathymetry west of Easter Island. The geometry of the microplate changes very rapidly during its evolution. At the initial stages of development, the microplate resembles a large propagating rift system, suggesting that deformation may have been occurring throughout most of its interior up to about 2.47 Ma. At this time, the length to width of overlap ratio of the two rifts reaches a value of 3, the northward propagation slows down, the curved opening of the Southwest Rift becomes well established, and rigid rotation of the previously deformed transferred lithosphere probably starts to predominate. At this time, the offset distance between the two overlapped rifts starts to increase. Some time after 2.47 Ma and before 1 Ma, the East Rift starts propagating northwestward, probably in response to the microplate rotation, and continues up until present. Also during this time period, the East Rift breaks into a series of northward propagating rifts, each propagating into the microplate interior, thereby transferring lithosphere from the microplate to the Nazca plate and reducing the total growth rate of the microplate.

Magnetic data over the Kuwait Arch concealed by overlying Phanerozoic strata, shows a broad circular magnetic high over the Kuwait Bay area and a conspicuous E-W trending associated magnetic low on the north over the Bahrah area of nearly comparable amplitude. The gravity and seismic data shows a major high over the same area which is as per the tectonic events in the area. The present study is focused on the conspicuous magnetic low over the crestal part of the dominantly N-S trending Kuwait Arch where a comparatively complex Bahrah oil field is located. On the basis of magnetic signatures, it appears that shield elements (basic metavolcanics like basalt and rhyolite with high magnetic susceptibility) extend beneath Phanerozoic cover resulting in a dipole signature of magnetic anomaly. In order to infer the basement structures lying beneath the Bahrah and Kuwait Bay areas, magnetic anomaly data has been processed, filtered and integrated with the gravity and seismic data. To locate the observed magnetic anomalies directly over the magnetic source bodies that caused these anomalies, the Total Magnetic Intensity (TMI) data has been transformed into Reduced-To-Pole (RTP) map. The TMI data also processed for 3D Analytic Signal, produces maxima over magnetic contacts regardless of the direction of magnetization. The enhancement of magnetic anomalies associated with faults and other structural discontinuities was achieved by the application of bandpass filter (4-12km) to the TMI-RTP data which defined the best continuity and resolution of the linear features. Basement structures, faults and shear zones can easily be traced along linear features which prove the effectiveness in the interpretation. Faults and shear zones coincide with zones of significant changes in magnetic and structural characteristics. The NNE-SSW orientation of basement-involved structures over Bahrah and Kuwait Bay area are easily identified on bandpass filtered TMI-RTP data. The Bahrah oil & gas wells producing from Cretaceous/Jurassic levels are located on magnetically inferred basement highs. Basement structural highs control the structural development of the sedimentary cover. The magnetic data after integration with gravity, seismic, borehole and geologic data reveals the elements of basement structures over which the Bahrah oil field is located. This study can assist in effective placement of future wells in Kuwait Bay and Bahrah area.

Boundaries between oceanic and transitional crust in the eastern Gulf of Mexico have been delineated using detailed, accurately navigated, high‐quality aeromagnetic data. These data indicate that considerably more oceanic crust may be present than previously suggested by other geophysical data, especially seismic reflection data. The N‐S extent of oceanic crust substantially increases westward from approximately 280 km near 87°W to roughly 390 km near 90°W, indicating the proximity (<10°) of the pole of rotation. Variations in the amount of oceanic crust together with discontinuities in the magnetic anomaly patterns, interpreted as the traces of fossil transform faults or fracture zones, have been used to obtain a rough estimate of the location of the pole of rotation (24°N, 81.5°W) for the seafloor spreading phase of opening. The magnetic data have been used to develop a model for the opening of the Gulf and to identify some geometrical relationships between its conjugate continental margins. Based upon the estimated pole position, the eastern Gulf is interpreted to have opened in an approximately NNE‐SSW direction with the counterclockwise rotation of Yucatan away from North America. The seafloor spreading phase of movement accounts for about 25° of the counterclockwise motion of Yucatan. Rotating the Yucatan block clockwise by this amount to restore it to its predrift position places the Campeche Bank adjacent to the Mississippi Trough‐Louisiana shelf. Further clockwise rotation of Yucatan by an additional 30–35° about this pole restores extended crust to its original thickness and is consistent with rotations of Yucatan predicted from paleomagnetic data from Chiapas.

Investigating the applicability of the social spider optimization for the inversion of magnetic anomalies caused by dykes

Inversion of magnetic data using deep neural networks

Gülbahçe Fault Zone (GFZ) is a significant tectonic structure and seismic source for İzmir city and its surroundings. The major earthquakes occurred at the surroundings of GFZ are 2005 Seferihisar, 2020 Samos Island-Aegean Sea and 2021 Seferihisar earthquakes. In this study, the crustal thinning and tectonic stress distribution of GFZ and its surroundings were analyzed by using the new gravity and magnetic data. The correspondence analysis was applied by appraising together the magnetic and free-air anomaly data. Moreover, the average density of the subsurface structure was calculated by applying the Parasnis method. The deviatoric stress calculation was executed and the change of the physical properties that controls the gravity and magnetic anomaly of the crustal structure of the GFZ and its surroundings from north to south was investigated. Therefore, the average density values, which were obtained from gravity anomalies, were computed as 2.59 gr / cm3 in the north of the study region and it decreased to 2.06, 1.8 and 1.49 gr / cm3 towards to the south. The freeair gravity anomaly values were between 0-70 mGal and the magnetic anomalies were between -450-150 nT. The deviatoric stress values were between -0.2-0.1 MPa.

Magnetic anomaly navigation relies on high-quality magnetic anomaly maps in order to achieve accurate position information. High-quality has traditionally been defined from a geophysics perspective rather than from a navigation standpoint and this has driven the requirements for most Earth magnetic anomaly data collection. Because of the great expense required to collect magnetic anomaly data it is desirable to use existing magnetic anomaly maps for navigation. The research outlined here begins developing a framework for understanding these magnetic anomaly map errors and artifacts in terms of navigation filter performance using real-world flight data. Existing maps, such as the North American Magnetic Anomaly Database (NAMAD), are often under-sampled, aliasing high spatial-frequency components into the navigation band. In addition, much existing data collection occurred prior to the GNSS-era resulting in systematic georegistration errors within and between data sets. Map products often merge data from several collections over many years. Merging these data sets requires a good understanding of the space weather at each collection’s point in time as well as a leveling algorithm that accounts for the space weather as well at sensor positioning errors. Existing magnetic anomaly map products do not quantify these errors, and current ongoing research in investigating how to properly quantify these errors. In this work we quantify magnetic navigator performance using magnetic anomaly maps of varying quality and real collected magnetic data in several realistic navigation scenarios, and we propose map-based metrics to use to estimating magnetic navigator performance. In addition, we propose a method to estimate a map-derived first order Gauss-Markov (FOGM) process into the navigator.

<p>The Estimation of coal bituminous depth in Village of Banjaran, District of Salem, Regency of Brebes based on magnetic anomaly data has been done. The Village of Banjaran is located in the geology basin which called as Bentarsari Basin. The activities stages that carried out in this research include of magnetic data acquisition in the field, data processing, and interpretation. The interpretation of the anomalies data is done through the modeling using the Mag2DC for Window software on the local magnetic anomalies data. Based on this modeling results, then obtained six anomalous objects that can be interpreted as the subsurface rocks in the research area, which consists of sediments of gravel, sand, clay, and silt ( = 0.0020 cgs units); tuff and tuffaceous sandstone ( = 0.0069cgs units); andesite breccia, tuff, and tuffaceous sandstone ( = 0.0085cgs units); solid andesite breccia which not layered ( = 0.0115 cgs units); coarse sandstones, limestones, and sandy marl ( = 0.0109cgs units); andesite sandstone that layered with claystone and thin insertions of new coal bituminous alternately ( = 0.0008cgs units). Based on the modeling results and the geological information of this research area, it can be estimated that the coal bituminous found in the Kaliglagah formation, with its depths ranging between 104.48 m – 505.97m, and the value of the magnetic susceptibility is 0.0008 cgs units.</p>

For PET/CT systems, PET image reconstruction requires corresponding CT images for anatomical localization and attenuation correction. In the case of PET respiratory gating, multiple gated CT scans can offer phase-matched attenuation and motion correction, at the expense of increased radiation dose. We aim to minimize the dose of the CT scan, while preserving adequate image quality for the purpose of PET attenuation correction by introducing sparse view CT data acquisition.We investigated sparse view CT acquisition protocols resulting in ultra-low dose CT scans designed for PET attenuation correction. We analyzed the tradeoffs between the number of views and the integrated tube current per view for a given dose using CT and PET simulations of a 3D NCAT phantom with lesions inserted into liver and lung. We simulated seven CT acquisition protocols with {984, 328, 123, 41, 24, 12, 8} views per rotation at a gantry speed of 0.35 s. One standard dose and four ultra-low dose levels, namely, 0.35 mAs, 0.175 mAs, 0.0875 mAs, and 0.043 75 mAs, were investigated. Both the analytical Feldkamp, Davis and Kress (FDK) algorithm and the Model Based Iterative Reconstruction (MBIR) algorithm were used for CT image reconstruction. We also evaluated the impact of sinogram interpolation to estimate the missing projection measurements due to sparse view data acquisition. For MBIR, we used a penalized weighted least squares (PWLS) cost function with an approximate total-variation (TV) regularizing penalty function. We compared a tube pulsing mode and a continuous exposure mode for sparse view data acquisition. Global PET ensemble root-mean-squares-error (RMSE) and local ensemble lesion activity error were used as quantitative evaluation metrics for PET image quality.With sparse view sampling, it is possible to greatly reduce the CT scan dose when it is primarily used for PET attenuation correction with little or no measureable effect on the PET image. For the four ultra-low dose levels simulated, sparse view protocols with 41 and 24 views best balanced the tradeoff between electronic noise and aliasing artifacts. In terms of lesion activity error and ensemble RMSE of the PET images, these two protocols, when combined with MBIR, are able to provide results that are comparable to the baseline full dose CT scan. View interpolation significantly improves the performance of FDK reconstruction but was not necessary for MBIR. With the more technically feasible continuous exposure data acquisition, the CT images show an increase in azimuthal blur compared to tube pulsing. However, this blurring generally does not have a measureable impact on PET reconstructed images.Our simulations demonstrated that ultra-low-dose CT-based attenuation correction can be achieved at dose levels on the order of 0.044 mAs with little impact on PET image quality. Highly sparse 41- or 24- view ultra-low dose CT scans are feasible for PET attenuation correction, providing the best tradeoff between electronic noise and view aliasing artifacts. The continuous exposure acquisition mode could potentially be implemented in current commercially available scanners, thus enabling sparse view data acquisition without requiring x-ray tubes capable of operating in a pulsing mode.

Interpretation on the magnetic anomalies data has been done in the Widarapayung coast area, District of Binangun, Regency of Cilacap to identify distribution of iron sand. The acquisition of magnetic intensity data in this area has been done in December 2015 and May 2016 using Proton Precession Magnetometer (PPM) with type of GSM-19T. The research area extends on the geographic positions of 109.2501°BT – 109.2702°E and 7.6781°LS – 7.6986°S. Magnetic anomalies data modeling is done with using Mag2DC for Windows software so obtained some subsurface anomalous objects model. The anomaly object model having a value of magnetic susceptibility of 0.0093cgs unit is interpreted as iron sand interspersed with silt, clay, sand, and gravel from the alluvium formation. This formation is lain at a depth of 1.709 to 11.966m and a length of 1576.7m. The iron sand contained in this formation is estimated prospects for exploitation. Based on the interpretation results, alluvium formation is also found at a depth of 1.140 to 30.769m, which expected be composed of silt, clay, sand, and gravel with a magnetic susceptibility value of 0.0051cgs unit. The content of iron sand in this 2<sup>nd</sup> alluvium formation is expected to be relatively small.

The transformation of magnetic anomalies to magnetic potential or pseudo-gravity simplifies the complexities of magnetic anomaly interpretation. We present new pseudo-gravity maps, derived from EMAG2v3 data, for the South Atlantic Ocean and adjacent continent to reveal insights into crust and lithosphere composition.The pseudo-gravity transformation of the full-field magnetic anomaly consists of three steps: (i) reduction to the pole (RTP); (ii) integration to determine magnetic potential; and (iii) scaling to determine the pseudo-gravity, assuming a constant ratio of density contrast to magnetization. This transformation produces a gravity-like anomaly that would be observed if the magnetization were replaced by a density distribution of proportional magnitude. We use magnetic data from the public domain EMAG2 v3 as the primary input. The South Atlantic region was divided into 90 tiles of 5º to account for regional variations in magnetic inclination and declination. An important assumption for the transformation is that the magnetization is induced. The pseudo-gravity mapping shows large amplitude positive anomalies consistent with the assumption of induced magnetization; negative anomalies identify areas of remnant magnetization. In the oceanic domain, alternating positive and negative anomalies reflect magnetic reversals and are not an artifact.On the South American plate, the Rio-Grande-Rise exhibits three distinct high positive pseudo-gravity anomalies, reflecting thick magmatic crust. The São-Paulo-Plateau in the Santos Basin, Florianópolis-Ridge and Torres-High also show high positive anomalies. The Campos Basin has lower-amplitude positive anomalies, suggesting localized magmatic crust. In the continents, high-amplitude positive anomalies correlate with magmatic intrusion. The high positive pseudo-gravity anomalies form an NW-SE arc from magmatic material in the Paraná Basin to the São-Paulo-Plateau, continuing through the Florianópolis-Ridge and Rio-Grande-Rise.Strong positive anomalies along the Namíbia-Ridge, Walvis-Ridge, and southwestern African margin form a "7"-shaped uniform anomaly, corresponding to magmatic crust. In contrast, the oceanic crust offshore Orange Basin shows a north-south region of negative anomalies. No significant anomalies are seen in the Tristan-Gough Guyot Province (nor are they seen on the Vitória-Trindade or Tristan-Gough Guyot Province hot-spot tracks).A comparison of the pseudo-gravity map with crustal thickness from gravity inversion shows that many large, high-amplitude positive pseudo-gravity anomalies in the oceanic domain correlate strongly with anomalously thick crust (>12.5 km thickness) on the Rio-Grande-Rise, São-Paulo-Plateau, Florianópolis-Ridge, Namíbia-Ridge and Walvis-Ridge. Plate reconstruction of pseudo-gravity anomalies and crustal thickness suggest that the Namíbia-Ridge and western Florianópolis-Ridge, both with thick magmatic crust, have a common origin at approximately 110 Ma but were later separated by the Florianópolis-Fracture-Zone. The spatial relationship of observed high positive pseudo-gravity anomalies on magmatically intruded crust in the South American and African continents, the hybrid or magmatic crust on their rifted margins and thickened magmatic crust within the South Atlantic shows the major role of mantle inheritance in their origin.

The Oldest Ice Reconnaissance (OIR) airborne geophysical survey in East Antarctica was flown over approximately 170,000 km2 of the Dome Fuji region in 2016/17. The survey’s results support new insights into the subglacial geology and its meaning for the tectonic histories of the supercontinents Rodinia and Gondwana. The new magnetic and radar-derived bed topography data are integrated with previously acquired magnetic and gravity data, allowing the mapping of crustal domains within and beyond the survey’s limits. The magnetic data reveal three distinct domains within the survey region, delineated by N–S oriented boundaries, partly aligned with gravity domains following upward continuation transformations for both datasets. Additionally, four primary sets of magnetic lineaments were identified, exhibiting correlations with topographic and gravity patterns. These correlations indicate the continuation of the Tonian Oceanic Arc Super Terrane (TOAST) southward of its previously known southern limit. Moreover, an E–W-trending magnetic anomaly, the Elbert magnetic anomaly, suggests the suture between the recently-proposed subglacial Valkyrie craton and the TOAST. Furthermore, the analysis reveals a broad scale shear zone, named here the OIR shear zone, which formed as a result of oblique collision of the Ruker and Valkyrie cratons during the amalgamation of Gondwana.

As an effective physical field feature to perceive ferromagnetic targets, magnetic anomaly is widely used in covert marine surveillance tasks. However, its practical usability is affected by the complex marine magnetic noise interference, making robust magnetic anomaly detection (MAD) quite a challenging task. Recently, learning-based detectors have been widely studied for the discrimination of magnetic anomaly signal and achieve superior performance than traditional rule-based detectors. Nevertheless, learning-based detectors require abundant data for model parameter training, which are difficult to access in practical marine applications. In practice, target magnetic anomaly data are usually expensive to acquire, while rich marine magnetic noise data are readily available. Thus, there is an urgent need to develop effective models to learn discriminative features from the abundant marine magnetic noise data for newly appearing target anomaly detection. Motivated by this, in this paper we formulate MAD as a single-edge detection problem and develop a self-supervised marine noise learning approach for target anomaly classification. Specifically, a sparse autoencoder network is designed to model the marine noise and restore basis geomagnetic field from the collected noisy magnetic data. Subsequently, reconstruction error of the network is used as a statistical decision criterion to discriminate target magnetic anomaly from cluttered noise. Finally, we verify the effectiveness of the proposed approach on real sea trial data and compare it with seven state-of-the-art MAD methods on four numerical indexes. Experimental results indicate that it achieves a detection accuracy of 93.61% and has a running time of 21.06 s on the test dataset, showing superior MAD performance over its counterparts.