scholarly journals Study of the Correction Method of Secular Variation in the Main Geomagnetic Field by the Field Seismogeomagnetic Survey

2021 ◽  
Author(s):  
shupeng su ◽  
ZhaoJing Wang ◽  
Deqiang Liu ◽  
Fenglong Mao
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Least Squares Method ◽  
Weighted Least Squares ◽  
Correction Method ◽  
Original Method ◽  
New Method ◽  
Field Variation ◽  
The Mean

Abstract The correction of the secular variation (SV) of the main geomagnetic field is a key link of field seismogeomagnetic data processing, and the current method relies on the observatory data for the relevant technical processing. To optimize the data products and obtain more accurate and reliable seismomagnetic information, this study adopted a new technical idea, which uses the repeated survey data from field stations to obtain the SV of the main geomagnetic field over the survey area by the weighted least-squares method, and compared the results with those of the current methods. The results were as follows: 1. The SV results of the main geomagnetic field produced by the new method are closer to those of the International Geomagnetic Reference Field (IGRF)_SV model. The mean square error (MSE) of the difference of the three elements F, D, and I between the new method and the IGRF_SV model is 10.7%, 47.0%, and 14.5% of that of the original method, respectively. 2. By applying the new SV correction method, more stable and reasonable variations in Earth’s crustal magnetic field can be obtained. The average amplitude of the Earth’s crustal magnetic field variation in the three elements F, D, and I is 28.5%, 55.4%, and 34.4 of the original results, the MSE is 59.1%, 56.5%, and 40.3% of the original results, and the mean gradient is 93.6%, 91.9%, and 97.0%, respectively. 3. In the processed results of the new method, the seismomagnetic information is clearly optimized, and the location of the epicenter is more consistent with the 0 value line of the Earth’s crustal magnetic field. The processed results of the new method are significantly better than those of the original method and have a higher application value.

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

A comparison of geomagnetic secular variation as recorded by historical, archaeomagnetic and palaeomagnetic measurements

1982 ◽  
Vol 306 (1492) ◽  
pp. 103-112 ◽  
Keyword(s):  
Magnetic Field ◽  
Lake Sediments ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Secular Change ◽  
Mathematical Approach ◽  
Geomagnetic Secular Variation ◽  
The Past ◽  
Palaeomagnetic Data ◽  
Field Behaviour

Palaeomagnetic methods can extend the documentary record of changes in the Earth’s magnetic field far into the past. Tolerable agreement is found between various methods, demonstrating the geophysical value of palaeomagnetic experiments. Combining results from the different approaches of investigating secular change can lead to a better perspective and to superior models of geomagnetic field behaviour. Lake sediments have recently been found to hold remarkably detailed signatures of past field changes. A mathematical approach to formulating an empirical description of global geomagnetic field behaviour is proposed and applied to palaeomagnetic data spanning the last 10 ka.

A Comparison of Simple Methods for Estimating the Mass Flow of Fluoride Discharged into Rivers

1987 ◽  
Vol 19 (5-6) ◽  
pp. 729-740 ◽  
Author(s):  
W. Van Craenenbroeck ◽  
J. Marivoet
Keyword(s):  
Mass Flow ◽  
Least Squares Method ◽  
Weighted Least Squares ◽  
Fluoride Concentration ◽  
Weighted Least Squares Method ◽  
Use Of Data ◽  
Natural Concentration ◽  
River Meuse ◽  
The Mean ◽  
Pollutant Discharge

In order to follow the long term evolution of the pollutant discharge pattern, and to detect changes in the situation, information about the discharge mass flow is necessary. First, the paper deals with the behaviour of the fluoride concentration in the river Meuse. Data are presented for the stretch Remilly (France) to Keizersveer (Netherlands), and the evolution over the period 1970–1984 is described. Data from waste waters and tributaries are discussed, and a dominating fluoride source is identified. In the second part, a linear first order equation is proposed for fitting the C-Q data at Liège (Belgium). Five methods for estimating the mean fluoride mass flow of the discharge are compared and discussed. The weighted least squares method is proposed for further use. It makes use of data from a routine measuring station, and gives the possibility to estimate a natural concentration which is constant over the studied period 1970–1984. The thus obtained value of 0.19 mg/l is equal to the mean fluoride concentration upstream of the discharge point. The estimated discharge mass flow is about 6 t/d, and this value remained constant since 1979.

Observations of the Earth's magnetic field made in Edinburgh from 1670 to the present day

1994 ◽  
Vol 85 (4) ◽  
pp. 239-252 ◽  
Author(s):  
D. R. Barraclough
Keyword(s):  
Magnetic Field ◽  
Mathematical Models ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Upper Atmosphere ◽  
The Difference ◽  
Time Changes ◽  
Relative Measurements ◽  
Magnetic North ◽  
Made In

AbstractMagnetic observations made at the same site give valuable information about the time changes (the secular variation) of the geomagnetic field. This paper gives details of all known measurements of the geomagnetic field in and around Edinburgh since the earliest observation of magnetic declination (the difference between true and magnetic north) by George Sinclair in 1670. Early observations of the strength of the field were only relative measurements. Approximate conversion factors are derived to enable these data to be expressed in modern absolute units (nanoteslas). Observed values of declination, inclination and the horizontal intensity of the geomagnetic field are plotted and compared with values computed from mathematical models of the field covering the interval 1690 to 1990, inclusive. The earlier observations were not corrected for the effects of the rapidly varying magnetic fields caused by electric currents in the upper atmosphere. The consequences of this are estimated.

Calculation of radioimmunoassay standard curves.

1977 ◽  
Vol 23 (9) ◽  
pp. 1624-1627 ◽  
Author(s):  
A J Naus ◽  
P S Kuppens ◽  
A Borst
Keyword(s):  
Least Squares ◽  
Calibration Curve ◽  
Least Squares Method ◽  
Weighted Least Squares ◽  
Mean Deviation ◽  
Weighted Least Squares Method ◽  
The Mean ◽  
Good Standard

Abstract A method for calculating radioimmunoassay standard curves, based on the theory of Ekins et al., is described. Because a four-parameter model is used, nonlinear standard curves are the result. The calibration curve is fitted to the measured standard points by means of a weighted least-squares method. The program based on this model can be easily processed on a desk-top calculator. For all 250 runs of six different assays, very good standard curves could be obtained. The mean deviation between the concentrations of the standard points and the corresponding calculated values was about 6%. In 26% of the cases it could be shown that the model we describe gave significantly better results than did two simpler ones.

scholarly journals Changes in cosmic ray cut-off rigidities due to secular variations of the geomagnetic field

1997 ◽  
Vol 15 (6) ◽  
pp. 734-739 ◽  
Author(s):  
A. Bhattacharyya ◽  
B. Mitra
Keyword(s):  
Secular Variation ◽  
Geomagnetic Field ◽  
Electric Circuit ◽  
Cosmic Ray ◽  
Computer Time ◽  
Transmission Factor ◽  
Field Variation ◽  
Quadrupole Field ◽  
Secular Variations ◽  
Time Required

Abstract. An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit.

The Analysis of Marine Magnetic Field Detection Influenced by the Platform Migration

2013 ◽  
Vol 347-350 ◽  
pp. 648-651
Author(s):  
Dan Wang ◽  
Chi Cheng
Keyword(s):  
Magnetic Field ◽  
Field Observation ◽  
Geomagnetic Field ◽  
Field Variation ◽  
Automatic Correction ◽  
Field Detection ◽  
Geomagnetic Field Variation ◽  
The World ◽  
Magnetic Model

Marine magnetic field detection is influenced by the environment of marine and the platform,The influence of the platform is mainly caused by platform migration.The variation of the geomagnetic field caused by different directions of the platform migration are compared by using the World Magnetic Model WMM2010.We come to the conclusion that the geomagnetic field variation is the biggest in the direction of depth.The conclusion can be used for automatic correction of the marine magnetic field observation platform .

scholarly journals Modeling Distance and Bandwidth Dependency of TOA-Based UWB Ranging Error for Positioning

2009 ◽  
Vol 2009 ◽  
pp. 1-4 ◽  
Author(s):  
Giovanni Bellusci ◽  
Gerard J. M. Janssen ◽  
Junlin Yan ◽  
Christian C. J. M. Tiberius
Keyword(s):  
Least Squares ◽  
Least Squares Method ◽  
Weighted Least Squares ◽  
Random Variable ◽  
Estimation Accuracy ◽  
Channel Measurements ◽  
Toa Estimation ◽  
Ranging Error ◽  
The Mean ◽  
Range Error

A statistical model for the range error provided by TOA estimation using UWB signals is given, based on UWB channel measurements between 3.1 and 10.6 GHz. The range error has been modeled as a Gaussian random variable for LOS and as a combination of a Gaussian and an exponential random variable for NLOS. The distance and bandwidth dependency of both the mean and the standard deviation of the range error has been analyzed, and insight is given in the different phenomena which affect the estimation accuracy. A possible application of the model to weighted least squares positioning is finally investigated. Noticeable improvements compared to the traditional least squares method have been obtained.

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