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

2. © NERC All rights reserved 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 http://geomag.nmh.ac.uk/gifs/surveydata.html (unfortunately misses out countries do not operate magnetic observatories) 2009 MagNetE Workshop – Helsinki, Finland

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

4. © NERC All rights reserved World Survey and Repeat Data Origins (1900 onwards) 2009 MagNetE Workshop – Helsinki, Finland Repeat Survey LocationsOne-off Survey Locations

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

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

7. © NERC All rights reserved 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? 2009 MagNetE Workshop – Helsinki, Finland

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

9. © NERC All rights reserved 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.ukwdcgeomag@bgs.ac.uk tjgs@bgs.ac.uk 2009 MagNetE Workshop – Helsinki, Finland

10. © NERC All rights reserved 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 2009 MagNetE Workshop – Helsinki, Finland

11. © NERC All rights reserved Questions? 2009 MagNetE Workshop – Helsinki, Finland