status of edinburgh wdc global survey data

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Status of Edinburgh WDC Global Survey Data

T J G Shanahan and S Macmillan

June 2009 MagNetE WorkshopHelsinki, Finland


What We Do With Survey Data

• Letters/Emails sent every year to organisations operating observatories requesting repeat/survey data

• Data received in wide variety of formats and reformatted into common format (Project Magnet)

• Data compared with previous data and IGRF for gross errors/anomalies

• Checked data is published on Edinburgh WDC website: http://geomag.nmh.ac.uk/gifs/surveydata.html

(unfortunately misses out countries do not operate magnetic observatories)

2009 MagNetE Workshop – Helsinki, Finland


Rate of Submission to WDC2009 MagNetE Workshop – Helsinki, Finland

One-off Survey Repeat Survey

World

Europe

Receipt of data can vary greatly year on yearSome repeat occupation periods > 15 yrs

2009 Total Records: 21,167 (21,038)2009 Total Records: 126,380 (126,376)

World

Europe


World Survey and Repeat Data Origins (1900 onwards)


Repeat Survey LocationsOne-off Survey Locations


European Survey and Repeat Data (1900 onwards)

One-off Survey Data Repeat Station Data



Data Residuals (F)2009 MagNetE Workshop – Helsinki, Finland

FIGRF – FSTATION (All World Data)

• Repeat data include the crustal field• Submitted data compared against IGRF

RMS residual: 405 nT

FIGRF – FSTATION (All Europe Data)

RMS residual: 204 nT


The Dominant Crustal Source?

• Remnant magnetisation – static with time

• Induced magnetisation – changes with main field

• Is continental crust dominated by induced or remnant magnetisation? (Koenigsberger ratio)

• Repeat station vector data could provide information on the source of the crustal field by solving for the susceptibility

• Does correlation of total field anomalies with main field strength imply dominant effect of induced field?



Evidence of Induced Field?

Using data since 1900

Using data since 1960

All Repeat Station and One-off Data Since 1900


Full analysis requires vector (repeat) data to determine the mean magnetisation susceptibility matrix


Submitting Data to WDC

• All data welcomed!

• Data currently received in many ‘formats’

• WDC data stored in PMF but closely resembles MagNetE format (via Gerald Duma’s RS-Enter software) so this format is particularly welcome

• Will soon make the component scatter fields used in MagNetE format available on WDC

• Send to WDC at: [email protected] or myself: [email protected]



Good and Bad Things About WDC Global Survey Dataset

• Data held in one place in homogeneous format

• Global coverage

• > 100 years time span

• Available on-line

• Actively maintained

• Some (earlier) observations entered twice: for date of occupation and for date of reduction

• Information on method of reduction (sometimes) minimal and not reliable

• Manual intervention often required



Questions?2009 MagNetE Workshop – Helsinki, Finland

status of edinburgh wdc global survey data

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