scholarly journals Correlation based snapshot models of the archeomagnetic field

2020 ◽  
Vol 223 (1) ◽  
pp. 648-665
Author(s):  
S Mauerberger ◽  
M Schanner ◽  
M Korte ◽  
M Holschneider
Keyword(s):  
Model Uncertainty ◽  
Geomagnetic Field ◽  
A Priori ◽  
Field Vector ◽  
Parametric Approach ◽  
Full Field ◽  
The Past ◽  
Uncertainty Estimates ◽  
Improved Model ◽  
Field Estimate

SUMMARY For the time stationary global geomagnetic field, a new modelling concept is presented. A Bayesian non-parametric approach provides realistic location dependent uncertainty estimates. Modelling related variabilities are dealt with systematically by making little subjective a priori assumptions. Rather than parametrizing the model by Gauss coefficients, a functional analytic approach is applied. The geomagnetic potential is assumed a Gaussian process to describe a distribution over functions. A priori correlations are given by an explicit kernel function with non-informative dipole contribution. A refined modelling strategy is proposed that accommodates non-linearities of archeomagnetic observables: First, a rough field estimate is obtained considering only sites that provide full field vector records. Subsequently, this estimate supports the linearization that incorporates the remaining incomplete records. The comparison of results for the archeomagnetic field over the past 1000 yr is in general agreement with previous models while improved model uncertainty estimates are provided.

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.

Autonomous navigation algorithm based on AUKF filter about fusion of geomagnetic and sunlight directions

2018 ◽  
Vol 11 (4) ◽  
pp. 471-485 ◽  
Author(s):  
Bing Hua ◽  
Zhiwen Zhang ◽  
Yunhua Wu ◽  
Zhiming Chen
Keyword(s):  
Orbit Determination ◽  
Geomagnetic Field ◽  
Autonomous Navigation ◽  
Unscented Kalman Filter ◽  
Satellite Orbit ◽  
Field Vector ◽  
Low Earth Orbit ◽  
Fusion Algorithm ◽  
Content Type ◽  
Navigation Algorithm

Purpose The geomagnetic field vector is a function of the satellite’s position. The position and speed of the satellite can be determined by comparing the geomagnetic field vector measured by on board three-axis magnetometer with the standard value of the international geomagnetic field. The geomagnetic model has the disadvantages of uncertainty, low precision and long-term variability. Therefore, accuracy of autonomous navigation using the magnetometer is low. The purpose of this paper is to use the geomagnetic and sunlight information fusion algorithm to improve the orbit accuracy. Design/methodology/approach In this paper, an autonomous navigation method for low earth orbit satellite is studied by fusing geomagnetic and solar energy information. The algorithm selects the cosine value of the angle between the solar light vector and the geomagnetic vector, and the geomagnetic field intensity as observation. The Adaptive Unscented Kalman Filter (AUKF) filter is used to estimate the speed and position of the satellite, and the simulation research is carried out. This paper also made the same study using the UKF filter for comparison with the AUKF filter. Findings The algorithm of adding the sun direction vector information improves the positioning accuracy compared with the simple geomagnetic navigation, and the convergence and stability of the filter are better. The navigation error does not accumulate with time and has engineering application value. It also can be seen that AUKF filtering accuracy is better than UKF filtering accuracy. Research limitations/implications Geomagnetic navigation is greatly affected by the accuracy of magnetometer. This paper does not consider the spacecraft’s environmental interference with magnetic sensors. Practical implications Magnetometers and solar sensors are common sensors for micro-satellites. Near-Earth satellite orbit has abundant geomagnetic field resources. Therefore, the algorithm will have higher engineering significance in the practical application of low orbit micro-satellites orbit determination. Originality/value This paper introduces a satellite autonomous navigation algorithm. The AUKF geomagnetic filter algorithm using sunlight information can obviously improve the navigation accuracy and meet the basic requirements of low orbit small satellite orbit determination.

scholarly journals Falsifiability Is Not Optional

2017 ◽  
Author(s):  
Etienne P. LeBel ◽  
Derek Michael Berger ◽  
Lorne Campbell ◽  
Timothy Loving
Keyword(s):  
Statistical Power ◽  
A Priori ◽  
Open Science ◽  
Research Quality ◽  
Original Research ◽  
Fine Grained ◽  
Psychological Phenomena ◽  
Trade Offs ◽  
Cumulative Knowledge ◽  
Improved Model

Finkel, Eastwick, and Reis (2016; FER2016) argued the post-2011 methodological reform movement has focused narrowly on replicability, neglecting other essential goals of research. We agree multiple scientific goals are essential, but argue, however, a more fine-grained language, conceptualization, and approach to replication is needed to accomplish these goals. Replication is the general empirical mechanism for testing and falsifying theory. Sufficiently methodologically similar replications, also known as direct replications, test the basic existence of phenomena and ensure cumulative progress is possible a priori. In contrast, increasingly methodologically dissimilar replications, also known as conceptual replications, test the relevance of auxiliary hypotheses (e.g., manipulation and measurement issues, contextual factors) required to productively investigate validity and generalizability. Without prioritizing replicability, a field is not empirically falsifiable. We also disagree with FER2016’s position that “bigger samples are generally better, but … that very large samples could have the downside of commandeering resources that would have been better invested in other studies” (abstract). We identify problematic assumptions involved in FER2016’s modifications of our original research-economic model, and present an improved model that quantifies when (and whether) it is reasonable to worry that increasing statistical power will engender potential trade-offs. Sufficiently-powering studies (i.e., >80%) maximizes both research efficiency and confidence in the literature (research quality). Given we are in agreement with FER2016 on all key open science points, we are eager to start seeing the accelerated rate of cumulative knowledge development of social psychological phenomena such a sufficiently transparent, powered, and falsifiable approach will generate.

Comparing the MLC and JavaNNS Approaches in Classifying Multi-Temporal LANDSAT Satellite Imagery over an Ephemeral River Area

2015 ◽  
Vol 6 (4) ◽  
pp. 83-102 ◽  
Author(s):  
Eufemia Tarantino ◽  
Antonio Novelli ◽  
Mariella Aquilino ◽  
Benedetto Figorito ◽  
Umberto Fratino
Keyword(s):  
Land Cover ◽  
A Priori ◽  
Sensor Data ◽  
Network Simulator ◽  
Research Activity ◽  
The Past ◽  
Time Space ◽  
Multi Temporal ◽  
Study Case ◽  
Landsat Satellite

This paper analyzes two pixel-based classification approaches to support the analysis of land cover transformations based on multitemporal LANDSAT sensor data covering a time space of about 24 years. The research activity presented in this paper was carried out using Lama San Giorgio (Bari, Italy) catchment area as a study case, being this area prone to flooding as proved by its geological and hydrological characteristics and by the significant number of floods occurred in the past. Land cover classes were defined in accordance with on the CN method with the aim of characterizing land use based on attitude to generate runoff. Two different classifiers, i.e. Maximum Likelihood Classifier (MLC) and Java Neural Network Simulator (JavaNNS) models, were compared. The Artificial Neural Networks (ANN) approach was found to be the most reliable and efficient when lacking ground reference data and a priori knowledge on input data distribution.

scholarly journals Magnetic anomalies possibly linked to local low seismicity

2009 ◽  
Vol 9 (5) ◽  
pp. 1567-1572 ◽  
Author(s):  
F. Masci ◽  
P. Palangio ◽  
M. Di Persio
Keyword(s):  
Geomagnetic Field ◽  
Central Italy ◽  
Low Frequency ◽  
Magnetic Anomalies ◽  
Tectonic Activity ◽  
The Past ◽  
Tectonic Events ◽  
The City ◽  
Network Station ◽  
The Magnetic Field

Abstract. During the last twenty years a time-synchronized network of magnetometers has operated in Central Italy along the Apennine chain to monitor the magnetic field anomalies eventually related to the tectonic activity. At present time the network consists of five stations. In the past only few anomalies in the local geomagnetic field, possibly associated to earthquakes, has been observed, not least because the network area has shown a low-moderate seismic activity with the epicentres of the few events with Ml≥5 located away from the network station. During 2007 two Ml≈4 earthquakes occurred in proximity of two stations of the network. Here we report the magnetic anomalies in the geomagnetic field that could be related with these tectonic events. To better investigate these two events a study of ULF (ultra-low-frequency) emissions has been carried out on the geomagnetic field components H, D, and Z measured in L'Aquila Observatory during the period from January 2006 to December 2008. We want to stress that this paper refers to the period before the 2009 L'Aquila seismic sequence which main shock (Ml=5.8) of 6 April heavily damaged the medieval centre of the city and surroundings. At present time the analysis of the 2009 data is in progress.

Improved model predictive control for the flow field in a wind tunnel with model uncertainty

2020 ◽  
Vol 357 (12) ◽  
pp. 7439-7455
Author(s):  
Yanming Liu ◽  
Junjie Wang ◽  
Xiaotao Liu ◽  
Xiaoping Li ◽  
Bo Yao ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Model Predictive Control ◽  
Predictive Control ◽  
Model Uncertainty ◽  
Improved Model

Induction Justified (But Just Barely)

Philosophy ◽  
1983 ◽  
Vol 58 (226) ◽  
pp. 481-488
Author(s):  
Ralph W. Clark
Keyword(s):  
A Priori ◽  
Empirical Knowledge ◽  
The Past ◽  
Empirical World ◽  
Future Events

Hume's sceptical arguments regarding induction have not yet been successfully answered. However, I shall not in this paper discuss the important attempts to answer Hume since that would be too lengthy a task. On the supposition that Hume's sceptical arguments have not been met, the empirical world is a place where, as the popular metaphor goes, all the glue has been removed. For the Humean sceptic, the only empirical knowledge that we can have is given to us in immediate perception. We have no reason to believe that the patterns of future events will in any way resemble patterns of events in the present or past. We have no reason to believe even that present events not observed resemble present events that are observed, or that knowledge of past and present can be any guide in making new discoveries about what took place in the past. What we have is an ideal setting for the calculation of a priori probabilities. We have a field of distinct events having no logical or evidential ties to one another. The attempt to justify induction that I wish to present is an appeal to a priori probability.

scholarly journals Archaeointensity results spanning the past 6 kiloyears from eastern China and implications for extreme behaviors of the geomagnetic field

2016 ◽  
Vol 114 (1) ◽  
pp. 39-44 ◽  
Author(s):  
Shuhui Cai ◽  
Guiyun Jin ◽  
Lisa Tauxe ◽  
Chenglong Deng ◽  
Huafeng Qin ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Dipole Moments ◽  
Eastern China ◽  
Published Data ◽  
Reference Curve ◽  
The Holocene ◽  
The Past ◽  
Deep Interior ◽  
Archaeomagnetic Dating ◽  
Data Points

Variations of the Earth’s geomagnetic field during the Holocene are important for understanding centennial to millennial-scale processes of the Earth’s deep interior and have enormous potential implications for chronological correlations (e.g., comparisons between different sedimentary recording sequences, archaeomagnetic dating). Here, we present 21 robust archaeointensity data points from eastern China spanning the past ∼6 kyr. These results add significantly to the published data both regionally and globally. Taking together, we establish an archaeointensity reference curve for Eastern Asia, which can be used for archaeomagnetic dating in this region. Virtual axial dipole moments (VADMs) of the data range from a Holocene-wide low of ∼27 to “spike” values of ∼166 ZAm2(Z: 1021). The results, in conjunction with our recently published data, confirm the existence of a decrease in paleointensity (DIP) in China around ∼2200 BCE. These low intensities are the lowest ever found for the Holocene and have not been reported outside of China. We also report a spike intensity of 165.8 ± 6.0 ZAm2at ∼1300 BCE (±300 y), which is either a prelude to or the same event (within age uncertainties) as spikes first reported in the Levant.

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