F. Levinsen, Joanna

Herceg, Matija

Tscherning, Carl Christian

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 21, 2017Greenland mass variation from GOCE gradients as changes in reduced point massesHerceg, Matija; Tscherning, Carl Christian; Fredenslund Levinsen, JoannaPublication date:2013Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Herceg, M., Tscherning, C. C., & F. Levinsen, J. (2013). Greenland mass variation from GOCE gradients aschanges in reduced point masses [Sound/Visual production (digital)]. European Geosciences Union GeneralAssembly 2013, Vienna, Austria, 07/04/201301/22/14European Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Greenland mass variation from GOCE gradients as changes in reduced point massesMatija Herceg1, Carl Christian Tscherning2, Joanna F. Levinsen31IGN, University of Copenhagen, Denmark2Niels Bohr Institute, University of Copenhagen, Denmark3DTU Space, Technical University of Denmark, DenmarkGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 201/22/14Motivation• The GOCE gradients may potentially be used for determination of residual masses in local regions, by the use of Reduced Point Mass (RPM) method• Reduced Point Masses can not be interpreted directly in the term of mass changes but may aid in localizing the areas where (positive or negative) changes takes place.• Is it possible to track rapid mass change of glacier in Greenland by GOCE gradients?Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 301/22/14EGM2008 gravity anomalyEGM2008 truncated gravity anomaly (contribution up to spherical harmonic degree and order 36 is subtracted)EGM2008 gravity anomalyGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 401/22/14GOCE TZZ gravity gradients from 11.2009. - 06.2010.GOCE Tzz gravity gradients GOCE Tzz truncated gravity gradients (contribution up to spherical harmonic degree and order 36 is subtracted)Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 501/22/14Monthly GOCE TZZ gravity gradientsGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 601/22/14Empirical covariance function based onGOCE Tzz gradientsGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 701/22/14Comparison of gravity anomaly prediction with GOCE TZZ gravity gradients (Dec 2009.)Collocation Reduced point massGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 801/22/14Comparison of gravity anomaly prediction with GOCE TZZ gravity gradients (Dec 2009.)Difference (Collocation - Reduced point mass)Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 901/22/14Gravity anomaly change from November 2009. to June 2010. calculated by GOCE Tzz gradientsGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1001/22/14Prediction of mass change by GOCE Tzz gradients and RPM from November 2009. to June 2010.Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1101/22/14Test region - Jakobshavn Isbræ glacier• Rapidly changing outlet glacier in Greenland– NASA Earth Observatory’s IceBridge program indicates that Greenland's Jakobshavn Isbræ glacier has the potential to influence sea level rise more than any other single feature in the Northern Hemisphere– Lowering at rates of 30-35 m/yr (Levinsen et al., 2013.)Figure credit: NASA Earth ObservatoryGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1201/22/14Test region - Jakobshavn Isbræ glacier• High-resolution (~100 m) surface elevations and elevations changes over rapidly changing outlet glaciers in Greenland– Derived from combination of the complimentary characteristics of laser altimeter data and stereoscopic Digital Elevation Models (Levinsen et al., 2013.)Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1301/22/14Calculation of gravity anomaly change• Method used1.) Gravity anomaly coming from changes in topography can be approximated by simple Bouguer correction2.) Gravity anomaly calculated by GRAVSOFT TC program• Calculation of direct topographic effect of all masses above reference level, assuming the density to be constant (0.92 g/cm^3).Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1401/22/14Gravity anomaly change calculated from change in Greenland ice massGravity change from height change by BouguerGravity change from height change by TCChange in height of 50m corresponds to the gravity change of 2 mGal.Change in height of Jakobshavn Glacier ice from 2007-2008  (Levinsen et al., 2013.)Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1501/22/14Jakobshavn Glacier Tzz gravity gradient at satellite altitude calculated by GRAVSOFT TC programTzz for 08.2007. Tzz for 08.2008.Greenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1601/22/14Jakobshavn Glacier Tzz gravity gradient change resulting from change in ice mass calculated by RPM• The maximal vertical gradient change at satellite altitude for the Jakobshavn area (2007 - 2008) is only 0.2mE • The gradients observed by GOCE has a minimum error of 3mE for the along track componentGreenland mass variation by GOCE gradients and reduced point mass methodEuropean Geosciences Union, General Assembly 2013, Vienna | Austria | 07 – 12 April 2013Slide 1701/22/14Conclusion and future work• The estimated gravity anomalies are very similar for the two methods used • The maximal gravity changes at the ground are between 2 and 4mGal for the period considered. The error of estimation of gravity anomalies from the GOCE gradient data using only Tzz with an associated error of 20mE is 11mGal• Using more gradient components in the GRF would certainly reduce this error, probably down to 5-6mGal• The maximal vertical gradient change at satellite altitude for the Jakobshavn area (2007 - 2008) is only 0.2mE. The gradients observed by GOCE has a minimum error of 3mE for the along track component• combination of all 4 components could lower error to 1mE• With a period of 5 years it could be possible to to observe this small signal (4 years of observations to be available at the end of 2013)

Greenland mass variation from GOCE gradients as changes in reduced point masses

http://orbit.dtu.dk/ws/files/117703933/EGU2013_HercegGOCEgreenland.pdf

Greenland mass variation from GOCE gradients as changes in reduced point masses

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