Low Magnetic Latitude Research Articles

Difference in the Sporadic E Layer Occurrence Ratio Between the Southern and Northern Low Magnetic Latitude Regions as Observed by COSMIC Radio Occultation Data

AbstractIn this study, the difference in the sporadic E layer occurrence ratio between two low‐magnetic‐latitude (±5° to ±15°) regions is analyzed by using COSMIC scintillation observations covering the period from 2007.001 to 2017.365. Obvious longitudinal, seasonal, and LT dependencies of this phenomenon are found. Most features of the differences between two hemispheres could be explained by the difference in zonal vertical wind shear between the two hemispheres induced by the difference between the magnetic and geographic latitudes of the studied regions. This result also indicates that the wind shear mechanism still dominates sporadic E layer formation in low‐magnetic‐latitude regions.

Low-latitude reduction-to-the-pole and upward continuation between arbitrary surfaces based on the partial differential equation framework

SUMMARY Magnetic surveys conducted in complex conditions, such as low magnetic latitudes, uneven observation surfaces, or above high-susceptibility sources, pose significant challenges for obtaining stable solutions for reduction-to-the-pole (RTP) and upward-continuation processing on arbitrary surfaces. To tackle these challenges, in this study, we propose constructing an equivalent-susceptibility model based on the partial differential equation (PDE) framework in the space domain. A multilayer equivalent-susceptibility method was used for RTP and upward-continuation operations, thus allowing for application on undulating observation surfaces and strong self-demagnetization effect in a non-uniform mesh. A novel positivity constraint is introduced to improve the accuracy and efficiency of the inversion. We analysed the effect of the depth-weighting function in the inversion of equivalent susceptibility for RTP and upward-continuation reproduction. Iterative and direct solvers were utilized and compared in solving the large, sparse, non-symmetric and ill-conditioned system of linear equations produced by PDE-based equivalent-source construction. Two synthetic models were used to illustrate the efficiency and accuracy of the proposed method in processing both ground and airborne magnetic data. Aeromagnetic and ground data collected in Brazil at a low magnetic latitude region were used to validate the proposed method for processing RTP and upward-continuation operations on magnetic data sets with strong self-demagnetization.

Suprathermal electron moments in the ionosphere

The ionospheric electron population is divided into two groups. The ambient electrons are thermalized. Their energy is usually smaller than one electron volt. Their densities and temperatures are the usual ones measured by incoherent scatter radars, or modeled by international codes such as International Reference Ionosphere (IRI). There is however a second population called the suprathermal electrons. This one is either due to photoionization or to electron impact between the thermosphere and the precipitation in the high latitude zone. In the frame of space weather, it may be the source of scintillations, plasma bulks and other physical phenomena. The suprathermal electron population can only indirectly be measured through the plasmaline and had never been modeled. Its modeling requires the computation of the electron stationary flux by solving the Boltzmann transport equation. This flux is multiplied by various powers of the velocity v and integrated to obtain the different order moments. By integrating f over v0dv, one deduces the suprathermal electron density. An integration of v1fdv allows the computation of their mean velocity. Higher moments give access to their temperature and finally to their heat flux. In this work, we demonstrate for the first time the full and rigorous calculation of the ionospheric electron moments up to three. As two case studies, we focus on high latitude in the auroral oval and low magnetic latitude over Algiers for different solar and geophysical conditions. We compare the suprathermal densities and temperatures to the thermal electron parameters. Our results highlight that – as expected – the suprathermal density is small compared to the thermal one. Although it is close to 3 × 103 m−3 at 180 km during the day, it drops drastically at night, to hardly reach 3 m−3. Contrarily to the density, the velocity is about 10 times more important during the nighttime when precipitation occurs than during the daytime under the electromagnetic solar flux. At 400 km, it varies during the day between 700,000 m s−1 (active solar conditions) and 900,000 m s−1 (quiet Sun). At night, the velocity varies between 3 × 106 m s−1 (low mean energy precipitation) and 3 × 107 m s−1 (high mean energy precipitation) at 400 km. The suprathermal temperature increases as the solar activity decreases or as the mean energy of the electron precipitation increases. It may reach values close to 3 × 108 K. The heat flux may be fully oriented downward or experiences a reversal with some flux going up depending on the forcing.

Edge detection and magnetic basement depth of Danko area, northwestern Nigeria, from low-latitude aeromagnetic anomaly data

This study aims at estimating depths and boundaries of magnetic source bodies, in order to provide an indirect insight into subsurface geologic features within Danko area of Kebbi state. The study area is located within low magnetic latitude. Hence, the total magnetic intensity anomaly map was reduced to the magnetic equator. This is to center magnetic anomalies over their respective magnetic source bodies, which equally makes the interpretation of sources easier. Matched filtering of the reduced-to-equator (RTE) magnetic anomaly map indicates that the anomalies could be represented by two equivalent layers with some additional noise. The estimated mean depths of burial for the regional and residual sources are 1000 m and 500 m, respectively. Horizontal gradient magnitude and tilt derivative methods carried out on the RTE aeromagnetic anomaly map facilitated the identification of two distinct geologic trends bounded by a prominent fault suspected to be the documented Yelwa fault. Furthermore, the analytic signal map showed magnetic basement depth values between 50 and 900 m with an average value of 475 m, indicating a compelling alignment of results with the 500 m depth value for the residual matched filter layer. Several mineral occurrences have been found within the outcropping basement rocks of the study area. Hence, the combined appraisal of source edge locations and magnetic basement depth estimates offers useful information of the underlying basement configuration, which is highly essential for mineral exploration targets that are mostly obscured by regolith cover.

ScintPi: A Low‐Cost, Easy‐to‐Build GPS Ionospheric Scintillation Monitor for DASI Studies of Space Weather, Education, and Citizen Science Initiatives

AbstractWe report the proposal and results of a low‐cost, easy‐to‐build GPS‐based sensor for detection and monitoring ionospheric irregularities through the detection of amplitude scintillation. The system is based on the Raspberry Pi single‐board computer combined with an Adafruit Ultimate GPS peripheral, which is capable of measuring (at 10‐Hz rate) the intensity of the L1 signals transmitted by GPS satellites. We introduce and discuss results of short‐ and long‐term observations obtained with a prototype of this system deployed in Presidente Prudente, a low magnetic latitude site in Brazil. The deployment and observations were carried out to test the ability of the system to detect ionospheric scintillations and, therefore, monitor the occurrence of ionospheric irregularities associated with equatorial spread F. Our results show that this low‐cost sensor is indeed capable of detecting scintillation events associated with equatorial spread F. Comparison with simultaneous, collocated measurements made by a commercial scintillation monitor are also presented. The joint observations allowed us to quantify the performance of the low‐cost monitor and to identify sources of potential limitations. While the sensor cannot (and it was not intended to) substitute commercial scintillation monitors, the low cost allows its use in studies of ionospheric irregularities (space weather) that require observations made by distributed arrays of small instruments (DASI). Furthermore, the simplicity of the sensor design stimulates its use in educational and citizen science initiatives.

Predictive lithological mapping through machine learning methods: a case study in the Cinzento Lineament, Carajás Province, Brazil

The Cinzento Lineament (Carajas Mineral Province) represents a complex deformational system with great associated mineral potential, mainly for IOCG deposits. However, the tropical vegetation of the Amazon rainforest considerably limits the number of outcrops available for systematic geological mapping. Therefore, the use of remote data such as airborne geophysics and remote sensing is essential to provide a reliable geological map. The airborne magnetometric data to define lithological units and its boundaries is a challenge, especially in regions with low magnetic latitude and/or remanent magnetization. In this work, we proposed an approach using Magnetization Vector Inversion (MVI) to map the distribution of the magnetic susceptibility, in order to replace techniques such as pole reduction and total gradient. We applied the Random Forest algorithm (supervised Machine Learning algorithm) to recognize patterns in remote data and improve the current mapped lithological units. With 1400 training samples (2.5% of the total samples), we produced two Predictive lithological maps: a first with remote data only and a second with remote data and spatial coordinates. We evaluate the advantages and disadvantages of each Predictive map, and we conclude that both maps need to be analyzed together for the refinement of the current geological map. These predictive maps represent a powerful tool to combine remote data to improve current geological maps, or even generate the first-pass geological map for regions with scarce geological knowledge.

Integrated geophysical methods and techniques for siting productive boreholes in basement complex terrain of southwestern Nigeria

Electrical resistivity survey involving 2D Dipole-Dipole subsurface imaging and 1D Vertical Electrical Sounding (VES) and an integrated magnetic and electrical resistivity survey involving magnetic profiling and 1D VES/2D electrical imaging techniques were carried out at two sites underlain by grey gneiss and pegmatised schist, respectively, within the Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. The surveys were carried out with a view to delineating the subsurface layers and determining the geoelectrical characteristics; identify geological structures such as faults, fractured, jointed and sheared basement zones that are favourable to groundwater accumulation and transmission and estimate hydrogeologically significant borehole drill depth in an area with previous experience of failed borehole drilling attempts. At the two sites (A&B) investigated, the 2D resistivity images identified suspected fractured basement zones as low resistivity vertical discontinuities within high resistivity fresh basement host rock. The magnetic profiles at site B displayed typical magnetic anomaly of a thick dyke (two magnetic lows with central high in low magnetic latitude) over each vertical resistivity discontinuity. The follow-up VES delineated maximum of five subsurface layers which include the topsoil/laterite, weathered layer, partly weathered/fresh basement, fractured basement and the fresh basement. The weathered/fractured basement constitutes the main aquifer unit with thicknesses varying from 17.7 - 125 m. Two boreholes, one per site, were drilled to 80 m at site A and 70 m at site B. Both boreholes encountered the predicted fractured basement zones and the borehole logs correlated well with the interpretation models of the drilled VES locations. The boreholes were very productive (yields of about 1.5 l/s and 2.2 l/s at sites A & B respectively). The study demonstrated the effectiveness of integrated geophysical methods and techniques in providing information on the subsurface sequence and the structural disposition required for a successful groundwater development through borehole drilling, in a borehole-failure-prone basement complex terrain.Keywords: Integrated Geophysical Methods, Geophysical Techniques, Productive Borehole, Basement Complex Terrain

Recurrent geomagnetic storms and equinoctial ionospheric F-region in the low magnetic latitude: a case study

This paper analyses a case study of 27-day recurrent geomagnetic storms (RGSs) and the ionospheric F-region over Peruvian, Ascension Island, and Port Stanley during vernal equinox in 2006. The RGSs are categorized into High-Intensity Long-Duration Continuous AE Activity (HILDCAA) and non-HILDCAA cases. The solar wind plasma, Ionosonde, and magnetometer data are used. The results reveal that in both cases prompt penetration electric field and disturbance dynamo electric field (DDEF) control the ionospheric plasma and affect night time spread F (SF) that disturbs the HF-radio communications in equatorial and southern crest of equatorial ionization anomaly (EIA). The SF at magnetic equator is delayed, more predominant, and last longer than at the southern EIA. DDEFs and thermospheric winds persist in the recovery phase of storm with stronger ones can inhibit the SF.

Sporadic auroras near the geomagnetic equator: in the Philippines, on 27 October 1856

Abstract. While low-latitude auroral displays are normally considered to be a manifestation of magnetic storms of considerable size, Silverman (2003, JGR, 108, A4) reported numerous “sporadic auroras” which appear locally at relatively low magnetic latitude during times of just moderate magnetic activity. Here, a case study is presented of an aurora near the geomagnetic equator based on a report from the Philippine islands on 27 October 1856. An analysis of this report shows it to be consistent with the known cases of sporadic auroras, except for its appearance at considerably low magnetic latitude. The record also suggests that an extremely low-latitude aurora is not always accompanied by large magnetic storms. The description of its brief appearance leads to a possible physical explanation based on an ephemeral magnetospheric disturbance provoking this sporadic aurora.

Coordinated Satellite Observations of the Very Low Frequency Transmission Through the Ionospheric D Layer at Low Latitudes, Using Broadband Radio Emissions From Lightning

AbstractBoth ray theory and full‐wave models of very low frequency transmission through the ionospheric D layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low‐inclination Communication/Navigation Outage Forecast System satellite to test this semiquantitatively, for broadband very low frequency emissions from lightning. Approximate ground‐truthing of the incident wavefields in the Earth‐ionosphere waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes <26°. Thus, our conclusions, too, must be limited to the near‐equatorial region and are not necessarily predictive of midlatitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of very low frequency lightning emissions through the D layer, at a level exceeding model predictions by at least an order of magnitude. We show that kilometric‐scale D‐layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D‐layer transmission for transmission from powerful man‐made radio beacons.

Ionospheric delay gradient model for GBAS in the Asia-Pacific region

We investigated characteristics of anomalous spatial gradients in ionospheric delay on GNSS signals in the Asia-Pacific (APAC) low-magnetic latitude region in the context of the ground-based augmentation system (GBAS). The ionospheric studies task force established under the Communications, Navigation, and Surveillance subgroup of International Civil Aviation Organization (ICAO) Asia-Pacific Air Navigation Planning and Implementation Regional Group, analyzed GNSS observation data from the Asia-Pacific region to establish a regionally specified ionospheric threat model for GBAS. The largest ionospheric delay gradient value in the analyzed data was 518 mm/km at the L1 frequency (1.57542 GHz), observed at Ishigaki, Japan in April 2008. The upper bound on the ionospheric delay gradient for a common ionospheric threat model for GBAS in the ICAO APAC region was determined to be 600 mm/km, irrespective of satellite elevation angle.

GBAS Availability Assessment and Modeling of Ionospheric Scintillation Effects

The Japan Aerospace Exploration Agency (JAXA) is promoting a research and development program named DREAMS (Distributed and Revolutionary Efficient Air-safety Management System) to contribute to the realization of next-generation air transportation systems. One of the most important targets of this program is a reliable, high-precision navigation system. This paper describes an investigation into the effects of ionospheric plasma bubbles on the availability of Ground-based Augmentation Systems (GBAS). Although the effects of ionospheric anomalies on GBAS integrity have been well researched, their effects on GBAS availability have not received much attention. Since ionospheric plasma bubbles occur much more frequently than the Storm-enhanced Density (SED) phenomenon in regions at low magnetic latitude, their effects on availability as well as on integrity should be investigated. Copyright © 2016 Institute of Navigation

Application of 3D magnetic amplitude inversion to iron oxide-copper-gold deposits at low magnetic latitudes: A case study from Carajás Mineral Province, Brazil

Strong hydrothermal alteration modifies rock physical properties in iron oxide-copper-gold deposits (IOCGs) and may result in characteristic signatures detectable in geophysical surveys. Magnetic data are commonly used in characterizing orebodies, and 3D inversions are often used to assist in interpretations. In areas with strong remanence and self-demagnetization, the total magnetization can have directions different from the inducing field direction. This deviation precludes the use of traditional inversion methods. Magnetic amplitude inversion offers one solution to this challenge because the amplitude data are weakly dependent on the magnetization direction. In addition, the low magnetic latitude also imposes difficulty in amplitude data calculation due to the instability in the component conversion in the wavenumber domain. To formulate a practical approach, we present a case study on applying the magnetic amplitude inversion to the Furnas southeast IOCG deposit at the low magnetic latitude in Carajás Mineral Province, Brazil, and demonstrate that the approach can reliably recover an interpretable distribution of effective magnetic susceptibility and identify massive magnetite from hydrothermal alterations associated with the high-grade ore.

Forward modeling of total magnetic anomaly over a pseudo-2D underground ferromagnetic pipeline

Magnetic anomalies are formed by the superposition of earth's magnetic field and the induced field of an underground ferromagnetic pipeline. To analyze the influence of all factors on the detected magnetic anomalies, a forward model is established in this paper. A numerical integration method, magnetic dipole reconstruction (MDR), for magnetic anomaly forward modeling is proposed, and a series of calculations is performed between model parameters of the pipeline, the geomagnetic field, the measuring trace, and total magnetic anomaly (TMA). The influence of model parameters on the shape, amplitude, and magnetic width is then analyzed. Results show that the shape of TMA curve is primarily influenced by the magnetic inclination and relative azimuth of the pipeline. The amplitude is linearly related to geomagnetic intensity and pipeline parameters including diameter, thickness, and susceptibility, and decreases in inverse proportion to increase in distance between the pipeline's axis and measurement plane; it decreases in a cosine manner with decrease in inclination and relative azimuth. The magnetic width is less affected by the geomagnetic intensity and pipeline parameters, but does increase with increase in distance between the pipeline's axis and measurement plane, and decreases with decreasing inclination and relative azimuth. The MDR method effectively simulates the distributions of TMA caused by various models of pseudo-2D underground ferrous pipeline. Magnetic anomaly detection (MAD) does not effectively estimate existence or orientation of pipeline that are deeply-buried, slender or with axes parallel to the earth's magnetic field in the low magnetic latitude area. Rough measurement of magnetic anomaly is necessary before the orientation of the underground pipeline is identified, followed by exact measurements along the perpendicular direction of the axis of pipeline to accurately locate underground pipeline.

Ionospheric response to 2009 sudden stratospheric warming in the Northern Hemisphere

AbstractWe study the behavior of the F region ionosphere in the Northern Hemisphere during the sudden stratospheric warming period of 19–30 January 2009 by using FORMOSAT‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) ionosphere data (NmF2, hmF2, and height profile). We concentrated our study in the longitude bands 30°E–30°W, as well as 150°E–150°W, where no detailed study has been reported so far. At low magnetic latitude, the NmF2 decreases except during 09–12 LT: in the latitude zone of 20–40° NmF2 shows an increase of 30% during 09–12 LT. At higher magnetic latitude the NmF2 shows an increase during daytime and a reduction in the evening (21–03 LT). There is a latitude zone where NmF2 does not change. The latitude seems to correspond to the latitude where atmospheric temperature does not change. The behavior of the NmF2 seems to suggest a reduction of neutral density in low latitude and increase of neutral density in higher latitude. During the period of day of year (DOY) 25–31, the NmF2 shows a drastic reduction only during 06–09 LT in low latitudes, which is slightly away from geomagnetic equator. This special feature which occurred during declining phase of the sudden stratospheric warming (SSW) might be explained as due to enhanced dynamo electric field. The study suggests global change of the thermosphere including dynamo region, in spite of the fact that SSW is a high‐latitude phenomenon which occurred much below the height region of thermosphere.

An Improved Model of the Jovian Magnetosphere

The Jovian magnetosphere is modulated by the solar wind and centrifugal force. The configuration of the magnetic field in the previous model of the magnetosphere including the centrifugal force is consistent with the observations at low magnetic latitude (Λ < 50°), while there is a substantial difference between the results of the model and the observations at high magnetic latitude (Λ ≥ 50°), especially in the distant magnetotail. Based on the previous model, a new configuration of the Jovian magnetosphere in the night side is suggested by a three-step transformation in this study. The new magnetosphere obtained by the transformation method is flattened in the z-direction and stretched in the x-direction in distant magnetotail, which agree with general knowledge.

A New Technique for Low Magnetic Latitude Transformation: Synthetic Model Results and Examples

SUMMARY Traditional methods for processing low magnetic latitude data below ±25° magnetic latitude do not fully resolve anomaly location and may distort the anomaly shape leading to misinterpretation of the data, as well as loss of certain directional anomalies. The principal objective of our research was to develop a new filter that would better position anomalies, reduce anomaly distortion and provide good anomaly shape while attempting to recover structures parallel to the declination direction. The MTC-LML Filter (Modulus of Total Component at low magnetic latitudes) is based on the calculation of the Modulus of the three magnetic components of the main field (one vertical and two orthogonal horizontal). To test the MTC-LML Filter, a set of synthetic models were constructed composed of complicated magnetic bodies each with different strike directions and depths. Each model was designed to address a specific aspect of the low magnetic latitude problem. The results of synthetic modelling for the MTC-LML Filter were compared with synthetic models of standard transformations and techniques for dealing with low magnetic latitude data. Practical applications of the MTC-LML Filter were then made using survey data. The filter results for synthetic model and survey data, show better location and shape of model source bodies when compared to the existing standard transformations and techniques. The MTC-LML Filter provides an improved transformation of the data with reliable location and shape of the anomalies above the source, reduced anomaly distortion and better recovery of structure parallel to the declination direction.

EVALUATION OF ENHANCEMENT TECHNIQUES OF MAGNETIC ANOMALIES APPLIED TO STRUCTURAL INTERPRETATION OF THE ITAITUBA REGION, STATE OF PARÁ – BRAZIL

The purpose of this article is to describe the work carried out for evaluating enhancement techniques of magnetic anomalies applying the reduction-to-the-pole method and its implications for structural interpretation of a region located in low magnetic latitude. With this objective, the answer given by several data enhancement methods with and without reduction-to-the-pole was analyzed. These methods were applied to synthetic prisms located at low magnetic latitudes similar to the area of analysis and the resulting anomalies were compared to those calculated at the magnetic pole. The synthetic data has been generated from a program that calculates the anomalies from prisms with arbitrary dimensions, susceptibilities and depths. The enhancement methods were also applied to magnetic data of rocks from the Amazon Basin and the Amazonian Craton, in the Itaituba region, Par´a state, northern Brazil. The reduction-to-the-pole algorithm applied to synthetic data during this work improved the performance of the enhancement methods, once, after its application, the maximum amplitude of the transformed anomalies were positioned over the edges of the sources, facilitating magnetic-structural interpretation. Good correlation among magnetic lineaments – particularly those inferred by the recently proposed tilt derivative of the total horizontal gradient method – and the already interpreted geologic structures back up the reduction to the pole indicating it may be applied even when data is collected in low magnetic latitudes.

An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005

In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15–16 May 2005. The geomagnetic storm reached a minimum Dst of −263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Belém, Brasília, Presidente Prudente, and Porto Alegre, Brazil, during the period 14–17 May 2005. Also, we present ionospheric parameters h’F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas and São José dos Campos, Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14–15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.

3D magnetic interpretation of the Regis kimberlite pipe, Minas Gerais, Brazil

ABSTRACTIn the present work, high‐resolution ground magnetic data are used to unveil the structure of the Regis kimberlite pipe, which is located in a well‐known diamondiferous province in the central portion of Brazil. The main tectonic feature of the area is a NW‐SE major crustal fracture zone, extending for more than 3000 km within Brazil, along which Regis and several other kimberlite pipes have intruded. The area is located at low magnetic latitude (inclination approximately 27o south) and the ground magnetic anomaly associated with the Regis pipe appears as an isolated asymmetric dipole‐like source caused by magnetization primarily in the direction of the Earth’s magnetic field. We inverted this high‐resolution magnetic data set in order to recover the 3D effective susceptibility model of the studied pipe. We obtained an asymmetric conical‐shaped strongly magnetized body (35 × 10‐3 SI units) extending from 50–720 m depth. Prior to the inversion, the data were upward continued to 30 m above the surface to attenuate high‐frequency noise and mitigate inversion artefacts. Our results were used to better define the subsequent drilling positions to thoroughly evaluate the economic potential of the Regis pipe. One available borehole drilled approximately in the centre of the structure corroborates our interpretation.