14 November, 2013 – Seminar
When: 4pm on Thursday November 14th, 2013
Where: DIAS 10 Burlington Road
Speaker: Dr. Alan D. Chave (Woods Hole Oceanographic Institution, Woods Hole, MA, USA)
Title: Magnetotelluric Data, Stable Distributions and Impropriety: An Existential Combination
Description:
The author has long noted that the residuals from a robust or bounded influence estimate of the magnetotelluric (MT) response function are systematically long-tailed rather than being consistent with the fundamental robust model of a Gaussian core contaminated by a fraction of outlying data that are removed through processing. Recent investigation has shown that the actual distribution of magnetotelluric residuals is alpha stable. Alpha stable distributions are a family characterized by four parameters, one of which determines the tail thickness. Its upper end member is Gaussian, but for all other stable distributions, the variance is infinite and the distribution tails fall off algebraically rather than exponentially. It will be shown that a stable model for MT data is pervasive, and hence a maximum likelihood estimator (MLE) based on the stable model can be implemented through nonlinear minimization of an objective function. In parallel, it has been observed that MT responses are pervasively improper complex numbers, meaning that they are correlated with their complex conjugate. This has implications for the asymptotic complex Gaussian distribution of the MLE, and if accounted for, results in more realistic error estimates for the MT response function. These issues will be illustrated with data.
Finally, the implications of persistent infinite variance distributions for MT data will be discussed, including the need to abandon a nonstationary model for geomagnetic fluctuations and their origin in fractional derivative processes in the magnetosphere and ionosphere.
Leave a Comment
Last Updated: 22nd March 2016 by Anna
2013-11-14 – Seminar: Dr Alan Chave
14 November, 2013 – Seminar
When: 4pm on Thursday November 14th, 2013
Where: DIAS 10 Burlington Road
Speaker: Dr. Alan D. Chave (Woods Hole Oceanographic Institution, Woods Hole, MA, USA)
Title: Magnetotelluric Data, Stable Distributions and Impropriety: An Existential Combination
Description:
The author has long noted that the residuals from a robust or bounded influence estimate of the magnetotelluric (MT) response function are systematically long-tailed rather than being consistent with the fundamental robust model of a Gaussian core contaminated by a fraction of outlying data that are removed through processing. Recent investigation has shown that the actual distribution of magnetotelluric residuals is alpha stable. Alpha stable distributions are a family characterized by four parameters, one of which determines the tail thickness. Its upper end member is Gaussian, but for all other stable distributions, the variance is infinite and the distribution tails fall off algebraically rather than exponentially. It will be shown that a stable model for MT data is pervasive, and hence a maximum likelihood estimator (MLE) based on the stable model can be implemented through nonlinear minimization of an objective function. In parallel, it has been observed that MT responses are pervasively improper complex numbers, meaning that they are correlated with their complex conjugate. This has implications for the asymptotic complex Gaussian distribution of the MLE, and if accounted for, results in more realistic error estimates for the MT response function. These issues will be illustrated with data.
Finally, the implications of persistent infinite variance distributions for MT data will be discussed, including the need to abandon a nonstationary model for geomagnetic fluctuations and their origin in fractional derivative processes in the magnetosphere and ionosphere.
Category: Geophysics Section News & Events
Available to buy on the DIAS bookshop: books.dias.ie/index.php?main… (5/5) #DIASdiscovers #celtic #studies #twopatricks
"In the lives of St. Patrick, the two saints are invariably fused into one", said Prof. O'Rahilly in his lecture. The lecture was a condensation from O’Rahilly’s book “The two Patricks: a lecture on the history of Christianity in fifth-century Ireland”. (4/5)
He was known by his first name Patricius, which in later times would lead to confusion as he was succeeded by another apostle of the same name (Saint Patrick or Patricius in Latin). (3/5)
He spoke on "Palladius and Patrick". Palladius was the first bishop of the Christians of Ireland. (2/5)
Date: 21st March 1942 Paper: The Irish Press Headline: Palladius and Patrick | School Of Celtic Studies Lecture Synopsis: The first public lecture under the auspices of the School of Celtic Studies was delivered in Trinity College by Professor T. F. O'Rahilly in 1942. (1/5)
As part of our ongoing participation in the @HistFest we decided to take a look into the Irish Newspaper Archives and see where DIAS made it into print over the last 80 years. There were so many articles, the hardest part was selecting what we would post. We hope you enjoy!
@AReillyFailte @CultureNight @VisitDublin Thanks Antoinette! Glad you enjoyed 😊
Big thank you to @MartinaPQuinn of @helloalicepr for moderating the discussion, and of course to our panel @NeasaMcG @CormacORafferty and @laoneill111
@CormacORafferty "to cut yourself off from fundamental research means you could miss out on some of the biggest ideas"
@laoneill "it's our job as researchers to keep reminding governments how important basic research is" "For Dev basic research being carried out in Ireland was a badge of pride"
@NeasaMcG Schrödinger's work in causality was not well received by the religious authorities at the time At the same time DIAS did have Catholic priests working on research projects in the early days, so there was not the conflict you might think between science and religion
@laoneill111 Schrödinger was very popular in social circles in Dublin, a bit of a renaissance man
@CormacORafferty Schrödinger was gifted at explaining difficult concepts
@CormacORafferty on how unsuccessful work, in Schrödinger's case, unified field theory, is just as important part of science. And no one has managed to crack it yet! And not forgetting the cat
@laoneill111 how Schrödinger's book inspired scientists to change fields and result in the finding of the double helix.
@NeasaMcG explaining how DIAS came about and how Schrödinger was attracted to Ireland #DIASdiscovers
Panel Discussion getting underway! @laoneill111 @CormacORafferty @NeasaMcG @MartinaPQuinn
We're half way through the documentary... Join us for the rest and the fascinating discussion to follow DM for link