Geomagnetic Map Research Articles

Study on the Influence of Downward Continuation on Matching Suitability in Underwater Geomagnetic Navigation

Geomagnetic matching is to utilize the geomagnetic field for positioning, and the matching suitability of candidate matching areas (CMAs) is a key factor of affecting matching precision. In underwater geomagnetic navigation, the underwater geomagnetic map is usually obtained by downward continuation, and therefore the influence of downward continuation on matching suitability is studied in this article. Firstly, the downward continuation algorithm is briefly introduced. Then the comparison analysis of matching suitability before and after downward continuation is made from an experimental point of view. Results show that the CMAs that own excellent matching suitability can still keep the well matching suitability, and moreover, for the CMAs whose matching suitability is normal or bad, the matching suitability may be improved after downward continuation. The conclusions of this article may provide helpful lessons for matching suitability analysis in underwater geomagnetic navigation.

The Study of Degaussing Technology for Underwater Vehicle

The underwater vehicle is mainly made of ferromagnetic material, the sensor measured except magnetic field, besides magnetic field that the vehicle of the inherent hard magnetic and soft magnetic materials produce and vehicle magnetic fields produced in mechanical and electrical equipment. At the same time, the precision of the geomagnetic measurements will be affected by sensor manufacturing error and installation error factors. Therefore, how to extract the magnetic field from complex environment is a real time measurement of a difficult problem. In this paper, it is based on soft compensation. The magnetic survey experiment that underwater carrier rotates 360 degrees underwater has been done on this basis, and the effect of underwater carrier on cesium magnetometer in different heading is analyzed. The degaussing algorithm for own magnetic field of carrier is obtained and the real value of underwater magnetic field can be restored. It is the solid foundation of high precision underwater geomagnetic navigation and establishing the underwater geomagnetic map.

Guidance and control of a cruise missile flying along a geomagnetic isoline

This paper presents a new guidance method for cruise missiles, which makes use of geomagnetic isolines. The isolines are extracted by using bilinear interpolation in the geomagnetic contour map. Path tracking is implemented in the geomagnetic map and takes into account the dynamics of the missile and its constraints. For this, the dynamic equations for the missile during its cruise phase are established. Using an inverse dynamics guidance law to implement the simulation experiments, the simulation results show that missile flight along a geomagnetic isoline is theoretically feasible. As the path made up of isoline points is determined, the missile can follow the isoline with a path tracking controller.

Positioning performance evaluation of magnetic contour matching under different accuracy of sensor

The accuracy of geomagnetic reference map, geomagnetic sensor, and inertial navigation system is the key factor which affects the reliability of magnetic contour matching (MAGCOM) system. In order to improve the reliability of MAGCOM, the influence of the sensor's accuracy on the matching success rate has been studied. For different geomagnetic reference maps, the factors and their physical mechanism affecting matching success rate have been analyzed, the factors are geomagnetic sensor error, velocity error, and heading angle error. The error range of sensors was determined by the simulation computing which was based on a practical system and a simulation experimentation was implemented by using the geomagnetic reference map. The simulation results show that MAGCOM can allow the velocity error 0.14 m/s, the heading angle error 0.6 and the standard deviation of geomagnetic sensor noise 11 nT, when the matching success rate is 90%.

Animal Orientation Strategies for Movement in Flows

For organisms that fly or swim, movement results from the combined effects of the moving medium - air or water - and the organism's own locomotion. For larger organisms, propulsion contributes significantly to progress but the flow usually still provides significant opposition or assistance, or produces lateral displacement ('drift'). Animals show a range of responses to flows, depending on the direction of the flow relative to their preferred direction, the speed of the flow relative to their own self-propelled speed, the incidence of flows in different directions and the proportion of the journey remaining. We here present a classification of responses based on the direction of the resulting movement relative to flow and preferred direction, which is applicable to a range of taxa and environments. The responses adopted in particular circumstances are related to the organisms' locomotory and sensory capacities and the environmental cues available. Advances in biologging technologies and particle tracking models are now providing a wealth of data, which often demonstrate a striking level of convergence in the strategies that very different animals living in very different environments employ when moving in a flow.

Geomagnetic Matching Algorithm Based on the Probabilistic Neural Network

In order to realize geomagnetism-aided navigation in the regions with insignificant geomagnetic characteristic, inspired by the pattern recognition idea, the geomagnetic matching problem was transformed into statistical pattern recognition and was analysed from the aspect of pattern recognition. A matching algorithm based on the probabilistic neural network (PNN) was proposed. The selection of training sample for the PNN, the relation between the parameter of the PNN, and the geomagnetic roughness were studied. Then a PNN was constructed for geomagnetic matching. Simulation results show that the proposed method can greatly improve the efficiency and achieve better performance than ordinary correlative matching algorithm. The accuracy of the matching method is less than the unit cell size of the geomagnetic map.

Underwater Navigation for Long-Range Autonomous Underwater Vehicles Using Geomagnetic and Bathymetric Information

This paper evaluates methods for the long-range navigation of autonomous underwater vehicles (AUVs) at a middle depth of deep water from the viewpoint of spatial fields-aided navigation. Motivated by experimental works on the geomagnetic field-aided navigation of aquatic animals, we focus on the application of inertia systems with reference to maps of geomagnetic and bathymetric fields of the Earth to the navigation of AUVs. The Inertia Navigation System (INS) in combination with acoustic transponders, the Doppler velocity log, normally used for navigation systems of AUVs near the sea floor, cannot be used for long-range navigation of an AUV at a middle depth of deep water. We first carried out experiments to obtain geomagnetic and bathymetric data in the Harima Sea with a gentle slope of the sea floor and geomagnetic field. At Suruga Bay, which has a steep seabed slope, however, we used a bathymetric map and digital geomagnetic map published by the Japan Coast Guard. We performed a simulation to evaluate the performance of these navigation methods, and found that the precision of navigation of an AUV in water current by the method using the geomagnetic map and bathymetric map without INS is better than by the method using INS alone or by the method using INS with a positional correction by geomagnetic and bathymetric information.

Geomagnetic field modeling from satellite attitude control magnetometer measurements

To demonstrate the utility of satellite attitude control magnetometer measurements for mapping main field variations, we analyzed the three‐axis magnetometer (TAM) measurements that provide attitude control for the KOMPSAT‐1 satellite. Initial processing involved transforming the TAM's magnetic measurements from the Earth‐Centered Inertial coordinates (ECI) to the Earth‐Centered Earth‐Fixed coordinates (ECEF) and then to spherical coordinates. The magnetic field of the satellite body produces symmetric signatures in the ascending and descending orbital measurements and thus can be readily removed. Spectral correlation filtering of the orbital observations helped to eliminate the dynamic external field and solar activity noise components. The ascending and descending data were then spectrally reconstructed to estimate the total magnetic field with minimum track line noise. Correlation coefficients of 0.97 and 0.96 mark the correlation of the KOMPSAT‐1 total geomagnetic intensity map with the Ørsted and IGRF2000 core magnetic field models, respectively. Power spectra from Gauss coefficients of KOMPSAT‐1 model showed closeness with the models from Ørsted data and IGRF2000 model. The spherical harmonic coefficients calculated from the KOMPSAT‐1 model by conjugate gradient inversion are strongly coherent with the Ørsted and IGRF2000 coefficients through degree 9.

Contour Constraint Based Geomagnetic Matching Method

地磁辅助导航是组合导航技术研究的新方向.简要介绍了地磁辅助导航的基本原理和发展现状,并重点对地磁匹配方法进行了研究.地磁匹配是利用地磁图进行定位的方法,位置输出可用于限制惯性导航系统的误差积累.提出了一种改进的基于等值线约束的相关匹配算法,能够有效消除导航系统的初始位置误差并能限制匹配过程中惯性导航系统的积累误差.仿真实验证明,该算法能有效提高相关匹配的实时性,并能把定位精度控制在地磁数据网格间距以内.该算法对航向误差具有一定的适应性.

Oceanic Long-distance Navigation: Do Experienced Migrants use the Earth's Magnetic Field?

Albatrosses and sea turtles are known to perform extremely long-distance journeys between disparate feeding areas and breeding sites located on small, isolated, oceanic islands or at specific coastal sites. These oceanic journeys, performed mainly over or through apparently featureless mediums, indicate impressive navigational abilities, and the sensory mechanisms used are still largely unknown. This research used three different approaches to investigate whether bi-coordinate navigation based on magnetic field gradients is likely to explain the navigational performance of wandering albatrosses in the South Atlantic and Indian Oceans and of green turtles breeding on Ascension Island in the South Atlantic Ocean. The possibility that magnetic field parameters can potentially be used in a bi-coordinate magnetic map by wandering albatrosses in their foraging area was investigated by analysing satellite telemetry data published in the literature. The possibilities for using bi-coordinate magnetic navigation varied widely between different areas of the Southern Oceans, indicating that a common mechanism, based on a bi-coordinate geomagnetic map alone, was unlikely for navigation in these areas. In the second approach, satellite telemetry was used to investigate whether Ascension Island green turtles use magnetic information for navigation during migration from their breeding island to foraging areas in Brazilian coastal waters. Disturbing magnets were applied to the heads and carapaces of the turtles, but these appeared to have little effect on their ability to navigate. The only possible effect observed was that some of the turtles with magnets attached were heading for foraging areas slightly south of the control turtles along the Brazilian coast. In the third approach, breeding female green turtles were deliberately displaced in the waters around Ascension Island to investigate which cues these turtles might use to locate and return to the island; the results suggested that cues transported by wind might be involved in the final stages of navigation.

Geomagnetic Basement Relief of the Northern Taiwan Area

A detailed magnetic survey has been carried out in the northern Taiwan area in order to determine the topographic surface of the magnetic basement. This survey covers an area of about 900 km2, and totally the observation point is 269. After geomagnetic corrections of the observed data, the magnetic anomaly map was obtained. For the purpose of resolving the deeper (relative to the shallow effects) magnetic basement, a low-pass filter was applied to the magnetic anomaly to obtain a smoothed magnetic anomaly. Thirteen profiles were designed to cross and cover evenly the smoothed geomagnetic anomaly in the study area. These geomagnetic anomaly profiles were inverted to obtain the magnetic basement profiles by trial and error method. Compiling these 1-D magnetic basement profiles, we outlined the 2-D magnetic basement relief. The pattern of the relief of the geomagnetic basement shows that the depth is ranged from 2.6 to 6 km. There exists a basement high under the Tatun volcano area. Compiling with the topographic relief, we can find that they correlate to each other well, except for a contravention in the mountainous area surrounding the Taipei basin. This converse can be explained by supposing that tectonic forces lifted the mountainous area after the basement was formed. In order to verify the “truth” of the solution, we calculated the theoretical geomagnetic anomaly using the model we have inverted. Comparing the result with the observed geomagnetic anomaly map, we can find that they are quite similar to each other, with only a small variance.

Open-sea migration of magnetically disturbed sea turtles.

Green turtles (Chelonia mydas) that shuttle between their Brazilian feeding grounds and nesting beaches at Ascension Island in the middle of the Atlantic Ocean are a paradigmatic case of long-distance oceanic migrants. It has been suggested that they calculate their position and the direction of their target areas by using the inclination and intensity of the earth's magnetic field. To test this hypothesis, we tracked, by satellite, green turtles during their postnesting migration from Ascension Island to the Brazilian coast more than 2000 km away. Seven turtles were each fitted with six powerful static magnets attached in such a way as to produce variable artificial fields around the turtle that made reliance on a geomagnetic map impossible. The reconstructed courses were very similar to those of eight turtles without magnets that were tracked over the same period and in the previous year, and no differences between magnetically disrupted and untreated turtles were found as regards navigational performance and course straightness. These findings show that magnetic cues are not essential to turtles making the return trip to the Brazilian coast. The navigational mechanisms used by these turtles remain enigmatic.

Geomagnetic map used for long-distance navigation?

We used stable isotopes (δ15N and δ13C) and compared prey provided to chicks by each sex to evaluate seasonal and sex-specific diets in Rhinoceros Auklets (Cerorhinca monocerata) in the central California Current system during 2012–2013. Mixing models indicated northern anchovy (Engraulis mordax) were important prey for adults during fall/winter and juvenile rockfishes (Sebastes spp.) were important prey during incubation both years. Adult trophic level increased between incubation and chick-rearing periods in both years. During 2012, δ15N and δ13C of chick-rearing males and females differed significantly; mixing models indicated that females ate more Pacific saury (Cololabis saira) and less market squid (Doryteuthis opalescens) than males. Likewise, females delivered significantly more Pacific saury and less market squid to chicks than males during 2012. Chick growth (g d− 1) and chick survival to fledging were significantly lower during 2012 than 2013, likely because chicks were fed lesser quality prey or fed less frequently in 2012. Lesser body mass of females during incubation in 2012 indicated sex-specific diet differences may have been related to female energetic constraints. The observed variability in Rhinoceros Auklet diet underscores the importance of managing multiple prey populations in this system so that generalist predators have sufficient resources through changing conditions.

Aeromagnetic Anomalies over the Area of Unzendake Volcano.

An aeromagnetic survey flight over the area of Unzendake volcano was conducted in August, 1991, after the commencement of this time eruption, and a geomagnetic anomaly map was derived from collected data. The comparison of magnetic anomalies with the ones in 1981 by the New Energy Development Organization was attempted in order to judge whether there was a significant change of magnetic anomaly pattern for these ten years. However, no large variations with wavelengths more than 6 km were detected. The magnetic anomalies of the area revealed a close correlation with the topography. Average magnetization of normally magnetized terrain was estimated to 2.9 A/m from statistical analysis, and the effect of topographic relief was removed. The residuals were interpreted in terms of a graben structure filled with magnetic volcanics and shallower lateral inhomogeneity of magnetization. And the possibility was pointed out that an old volcanic unit unknown around Sarubayama might have considerable extension under the surface.

Geomagnetic anomaly maps of Central Victoria Land (East Antarctica) from ground measurements

The results of an extensive ground geomagnetic survey over the Central Victoria Land (East Antarctica) between the Transantarctic Mountains and the Ross Sea are used to plot the residual field map of the area under consideration. The data indicate that intense positive anomalies occur along two corridors, one near Mt. Nansen and the other near Mt. Melbourne. Further elaboration of our measurements has produced three other geomagnetic maps: (1) a high-pass filter (cut-off wavelength of 20 km) map; (2) a low-pass filter (cut-off wavelength of 80 km) map; and (3) an upward continuation of the geomagnetic field up to 12000 ft (3660 m) map. The residual field map and the high-pass filter geomagnetic map indicate that all the intense anomalies (both positive and negative) are of shallow origin. The low pass filter map and the upward continuation map show that the land mass of the Central Victoria Land is characterized-by a weak, negative geomagnetic anomaly whereas the near-shore area, close to Terra Nova Bay, displays a weak positive anomaly. Our measurements indicate that all rock types characterized by high susceptibility produce geomagnetic anomalies, even if their outcrop is not extensive. These rocks belong to the Mt. Melbourne volcanics, Jurassic dolerites and Granite Harbour plutons. None of the formations of the metamorphic complex are responsible for intense magnetic signals.

Marine magnetic anomalies over the Lord Howe Rise and the Tasman Sea: Implications for the magnetization of the lower continental crust

Marine geophysical and geological data provide evidence for a continental origin of the Lord Howe Rise, a submarine plateau east of Australia. Our marine geomagnetic data reveal a long-wavelength anomaly associated with the western margin of the rise. Forward and inverse modeling shows that the anomalies can be best explained by strong magnetization of the lower crust of the Lord Howe Rise. A geomagnetic map of the northern Tasman Sea that includes Dampier Ridge, another elongated piece of presumably continental crust, shows positive anomalies over areas of continental origin and negative ones over the deep sea basin. This indicates higher values of the product of magnetization times thickness for the continental crust than for the oceanic crust. Three-dimensional model calculations show that the high magnetization in the lower crust of eastern Australia is limited to a maximum depth of 15–20 km. This is in accordance with geothermal results that indicate the Curie isotherm is at a shallow depth there. The anomalies of the Tasman Sea are negative due to the negative part of the edge anomaly on the seaward side of the continental margin. It is not necessary to hypothesize strong reversed magnetization in the lower oceanic crust and upper mantle.

Low‐energy particle layer outside of the plasma sheet boundary

The ISEE spacecraft in the geomagnetic tail frequently crossed the high‐latitude boundary of the plasma sheet. On a number of these crossings on the morningside (between 15 RE and 22 RE) the ISEE instruments detected an enhanced population of low‐energy electrons and ions immediately adjacent to the plasma sheet boundary layer (PSBL). The electrons in this low‐energy layer (LEL) have energies less than a few hundred eV, and they are aligned along the magnetic field direction propagating in the tailward direction. The ions have energies less than 100 eV and are also streaming along the magnetic field direction but in the earthward direction. These particles are clearly distinguished from the bulk of the particles in the plasma sheet and the PSBL. These observations may help clarify where the various particle features in the geomagnetic tail map to in the ionosphere. It is suggested that the LEL maps to the soft (<1 keV) electron precipitation region poleward of the plasma sheet boundary.