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Status of Edinburgh WDC Global Survey Data

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  1. Status of Edinburgh WDC Global Survey Data T J G Shanahan and S Macmillan June 2009 MagNetE Workshop Helsinki, Finland

  2. 2009 MagNetE Workshop – Helsinki, 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)

  3. 2009 MagNetE Workshop – Helsinki, Finland Rate of Submission to WDC World World Europe Europe One-off Survey Repeat Survey 2009 Total Records: 126,380 (126,376) 2009 Total Records: 21,167 (21,038) Receipt of data can vary greatly year on year Some repeat occupation periods > 15 yrs

  4. 2009 MagNetE Workshop – Helsinki, Finland World Survey and Repeat Data Origins (1900 onwards) Repeat Survey Locations One-off Survey Locations

  5. 2009 MagNetE Workshop – Helsinki, Finland European Survey and Repeat Data (1900 onwards) One-off Survey Data Repeat Station Data

  6. 2009 MagNetE Workshop – Helsinki, Finland Data Residuals (F) RMS residual: 405 nT RMS residual: 204 nT FIGRF– FSTATION (All World Data) FIGRF– FSTATION (All Europe Data) • Repeat data include the crustal field • Submitted data compared against IGRF

  7. 2009 MagNetE Workshop – Helsinki, Finland 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?

  8. 2009 MagNetE Workshop – Helsinki, Finland Evidence of Induced Field? All Repeat Station and One-off Data Since 1900 Using data since 1900 Using data since 1960 Full analysis requires vector (repeat) data to determine the mean magnetisation susceptibility matrix

  9. 2009 MagNetE Workshop – Helsinki, Finland 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: wdcgeomag@bgs.ac.uk or myself: tjgs@bgs.ac.uk

  10. 2009 MagNetE Workshop – Helsinki, Finland 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

  11. 2009 MagNetE Workshop – Helsinki, Finland Questions?