Gravity and magnetic data processing further constrained inversion for 3D modelling and tonnage calculation

The paper defines the blind source separation (BSS) problem, demonstrates the mathematic model and conditions for its solving, and explains the uncertainty of its solving. The paper analyses the algorithm of independent component analysis (ICA), proving EFFICA more suitable for engineering data processing. The paper illustrates the application of EFFCIA to the gravity and magnetic data processing and simulated experiments. The results show the advantage of ICA application in denoising and extraction of weak signal over the traditional gravity and magnetic data processing, worth further research.

Potensoft: MATLAB-based software for potential field data processing, modeling and mapping

<p>We investigate the use of cross-validation (CV) techniques to estimate the accuracy of equivalent-source (also known as equivalent-layer) models for interpolation and processing of potential-field data. Our preliminary results indicate that some common CV algorithms (e.g., random permutations and k-folds) tend to overestimate the accuracy. We have found that blocked CV methods, where the data are split along spatial blocks instead of randomly, provide more conservative and realistic accuracy estimates. Beyond evaluating an equivalent-source model's performance, cross-validation can be used to automatically determine configuration parameters, like source depth and amount of regularization, that maximize prediction accuracy and avoid over-fitting.</p><p>Widely used in gravity and magnetic data processing, the equivalent-source technique consists of a linear model (usually point sources) used to predict the observed field at arbitrary locations. Upward-continuation, interpolation, gradient calculations, leveling, and reduction-to-the-pole can be performed simultaneously by using the model to make predictions (i.e., forward modelling). Likewise, the use of linear models to make predictions is the backbone of many machine learning (ML) applications. The predictive performance of ML models is usually evaluated through cross-validation, in which the data are split (usually randomly) into a training set and a validation set. Models are fit on the training set and their predictions are evaluated using the validation set using a goodness-of-fit metric, like the mean square error or the R² coefficient of determination. Many cross-validation methods exist in the literature, varying in how the data are split and how this process is repeated. Prior research from the statistical modelling of ecological data suggests that prediction accuracy is usually overestimated by traditional CV methods when the data are spatially auto-correlated. This issue can be mitigated by splitting the data along spatial blocks rather than randomly. We conducted experiments on synthetic gravity data to investigate the use of traditional and blocked CV methods in equivalent-source interpolation. We found that the overestimation problem also occurs and that more conservative accuracy estimates are obtained when applying blocked versions of random permutations and k-fold. Further studies need to be conducted to generalize these findings to upward-continuation, reduction-to-the-pole, and derivative calculation.</p><p>Open-source software implementations of the equivalent-source and blocked cross-validation (in progress) methods are available in the Python libraries Harmonica and Verde, which are part of the Fatiando a Terra project (www.fatiando.org).</p>

Downward continuation of potential field is a useful tool in the processing and interpretation of magnetic and gravity data, but its direct calculation in space or spectral domain is unstable even in the presence of a small level of the noise and consequently restricts its practical application. This paper introduces a new method that combines upward continuation, vertical gradient via smoothing filters (Tikhonov regularization or Gaussian filters) and an iterative method into a single scheme to improve the stability and accuracy of the downward continuation. The optimal interval of iteration numbers for our developed approach is estimated by analysing the correlation coefficient curve between consecutive iterations. Applications to synthetic and real magnetic data show that this method can yield a more stable downward continuation of potential field data.

In the search for hydrocarbons, geologists, geochemists and geophysicists work together on the scale of a sedimentary basin. They seek to identify a petroleum system in order to maximise the chances of finding an accumulation of hydrocarbons in a specific part of the subsoil. The exploration campaign in the Cuvette Centrale began in the 1950s with geological, geophysical, geochemical and drilling campaigns carried out by several foreign organisations, including the Belgian firm Remina. These campaigns provided key information about the petroleum systems. These include the presence of hydrocarbon showings and geological structures that may favour the formation, migration and trapping of hydrocarbons. The main aim of this work is to highlight the geological structures of major petroleum interest, while identifying the geological structures found in our study area, particularly in Blocks 1 and 24 in the central basin of the Democratic Republic of Congo, and their petroleum interest, based on the processing and interpretation of magnetic and gravity data. To better study our sedimentary basin, we used the method of regional-residual separation and variation of the Magnetic Field, we had to highlight the faults in different directions North-West towards the South-East, the collapse trenches localised in the North-East, the zones of uplift of Socle which today constitute the top of Inongo. As never done before, this study develops a structural reference model by integrating the analysis of Bouguer and magnetic anomalies. It aims to locate zones of source rock maturation, identify possible hydrocarbon migration paths and pinpoint geological structures conducive to hydrocarbon accumulation. The results, presented in map form, are a strategic tool for petroleum exploration and the analysis of regional tectonic dynamics. In particular, it provides an unprecedented and detailed geophysical record for Blocks 1 and 24 of the Cuvette Centrale, enabling a targeted and efficient assessment of petroleum potential.

The possibility of applying the continuous wavelet analysis on the basis of a Poissonian core for the processing and interpretation of gravity and magnetic survey data is considered. Based on the wavelet spectrum, W(x,h), reconstruction of the initial signal, g(x), is possible. Additionally, based on this wavelet spectrum, the equivalent distributions of mass and magnetization that produce the initial field, g(x), can be reconstructed. These possibilities allow the wavelet transform to be used for solving such classical problems as the filtering of initial signals, continuation of the field, calculation of higher field derivatives in the upper and lower half-spaces, and reduction of magnetic anomalies to the pole.

The magnetic data and gravity data have been recovered from magnetic tapes and earlier paper maps for Iraq. The magnetic data belonging to the State Company of Geology and Mining of Iraq (GEOSURV) were recovered by Frontier Processing Company and the U.S. Geological Survey (USGS) from the tapes originally flown by the French firm Compagnie General de Geophysique (CGG) in 1974. GETECH reprocessed the magnetic data using Geosoft and GETECH in‐house micro‐levelling software to its full glory which displays as a comprehensive and high quality dataset and shows fine detail along the profiles. GETECH recovered the legacy gravity data from the original field data sheets archived by IPC (Iraq Petroleum Company). These gravity data have been compiled with more recent GEOSURV sponsored surveys thus allowing for the first time a comprehensive digital and unified national gravity database to be constructed with full principal facts. Figure 1 shows the final aeromagnetic and gravity data coverage of Iraq. The only part of Iraq lacking gravity and aeromagnetic data coverage is the mountainous areas of the Kurdish Region of northeastern Iraq. Joint interpretation of the magnetic and gravity data will help to guide future geophysical investigations by GEOSURV, whose ultimate aim is to discover economical mineral and energy resources.

<p>The nature of the Estonian crust was studied using global topography, magnetic data, and gravity data to estimate its tectonic regime. The Estonian Precambrian crystalline basement, composed of Paleo- to MesoProterozoic metamorphic and igneous rocks, is covered by a Paleozoic sedimentary rock deposit 100–780 m thick. To visualize crustal sources of the Estonian basement, we employed spectrum analysis of magnetic and gravity data, as well as two-dimensional (2D) forward modeling of gravity data. The gravimetric data was also evaluated to identify the depth of the Moho and Conrad discontinuities in Estonia. The magnetic data has also been evaluated to calculate the Curie point depth, which was then utilized to predict heat flow values inside the research zone. The subsurface of Estonia is divided into six petrological-structural zones: Tallinn, Alutaguse, Johvi, West-Estonian, Tapa and South-Estonian. To assess the structural variations of the crust at these locations, profiles of topographic, gravity, magnetic and heat flow data were constructed in each of the petrological-structural zones. The spectrum analysis and 2D gravity forward models yielded residual and regional gravity anomaly maps that show a significant amplitude potential maximum across the precambrian Rapakivi granitoid plutons and the Paldiski-Pskov tectonic zone. The Curie point depth reveals values ranging from 7 to 26 km, whereas the Moho depth suggests values ranging from 48 to 72 km and the Conrad depth values ranging from 14 to 20 km.</p>

Sander Geophysics has now operated its AIRGrav airborne gravity system for over ten years. More than 2,500,000 lkm of AIRGrav surveys have been flown, predominantly for hydrocarbon exploration. Recent advances in SGL's gravity data processing, involving advanced analysis of system dynamics and improved filtering, help to further reduce system noise and allow for the generation of high quality, low noise gravity data through a wider range of survey conditions than was previously possible. In the past year, a number of AIRGrav projects with innovative survey design parameters have been successfully completed. Mineral exploration projects have been flown using a helicopter at extremely slow acquisition speed (30 knots) combined with tight (50 m) line spacing to produce data sets with higher resolution and higher accuracy. On the other end of the spectrum, the AIRGrav system produced excellent results when installed in a NASA DC 8 flown from 500 to 11000 m altitude at 300 knots, covering approximately 9,000 km in 12 hour flights, with differential GPS baselines as long as 3,000 km. New data processing techniques have allowed the extraction of the horizontal gravity components of the airborne gravity data in addition to the traditionally used scalar gravity measurement.

Sub-ice geology inland of the Transantarctic Mountains in light of new aerogeophysical data

Understanding the structural framework controlling the sedimentary basins from the integration of gravity and magnetic data: A case study from the east of the Qattara Depression area, Egypt

Continues magnetic measurements at the IKIR FEB RAS obser-vatories Magadan (MGD), Paratunka (PET), Yuzhno-Sakhalinsk (YSS), Cape Schmidt (CPS) and Khabarovsk (KHB) and CSIR-NGRI observatories Hyder-abad (HYB) and Choutuppal (CPL) have been started almost since their formation. A significant part of the results obtained is presented in the WDC and INTERMAGNET databases. However, a large amount of raw data remains un-processed and unavailable for using by scientific community. In the past few years, institutes has been making efforts to process and reprocess old magnetic data. Digital images of analog magnetograms of the Observatory Paratunka since 1967 were obtained and the possibility of their use for calculation hourly and minute values of magnetic field elements was evaluated. Old digital data that was available during the conversion from analog to digital magnetometers is processed. The main problem of processing or re-processing archived data is the lack of information (metadata) about the measurement conditions. First of all, these are the results of absolute observations, which are necessary to obtain the values of the elements of the total field vector. In this paper, some technologies are proposed that allow to use the data obtained during processing of analog magnetograms to adjust the digital magnetometers records. A signif-icant problem is the lack or inaccuracy of information about the temperature conditions in the variation pavilion, about magnetometers or support equipment maintenance or about works in and near the pavilions. As we accumulate the experience during the processing of old magnetic data, a “catalog” of noise and its typical images is formed. This makes it more reliable and efficient to identify and remove this noise from records.

The Qingdong area, located in Bohai bay basin, was suspected good exploration prospects. In order to study tectonic features and find out favourable petroleum prospects in the area, the gravity data at a scale of 1:50,000 were interpreted. This paper, through data processing and synthetic interpretation of the high-precision gravity data in the area, discusses characteristics of the gravity field and their geological implications, determines the fault system, analyses features of the main strata, divides structure units and predicts favourable petroleum zones. The results showed that the faults controlled the development of the Mesozoic and Cenozoic strata and the distribution of local structures in this area. The study revealed that the Qingtuozi uplift and the Kendong uplift in the north were formed in Mesozoic, and the Qingdong depression in the middle was the rift basin in Mesozoic and Cenozoic. Thicker strata in Mesozoic and Cenozoic developed in the Dongying depression and the Qingdong depression, so there is abundant hydrocarbon in these two depressions, and then the Guangligang rise-in-sag and the Qingdong rise-in-sag developed in the center in these two depressions are also favorable places for prospecting

Imaging Pleistocene volcanic edifices along the Egyptian Red Sea margin: Insights from reflection seismics and 3D constrained inversion of gravity and magnetic data

It is known to all that the wide monitoring of geomagnetic anomalies requires geomagnetic detection equipment to be of low cost, low power, and high stability. On the basis of the weak magnetic signal detection technology, a weak magnetic signal acquisition system with low-cost magnetic data acquisition, data processing, and data analysis is established by using a three-dimensional SEN-R65 magnetic sensor, magnetic signal acquisition chip PNI 11096, and P89C668 chips. Firstly, the hardware of a low-cost geomagnetic data acquisition system is designed, and the corresponding data processing and analysis programs are written. Based on the designed hardware circuit and data processing for functions such as acquisition, transmission, storage, and real-time display of geomagnetic signals, it is found that the developed instrument meets the expectations of the low-cost geomagnetic data acquisition system designed in this paper, indicating that the system is applicable.