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New Zealand Region Gravity Grids

Bouguer, free air and topography corrected gravity anomaly grids for the New Zealand region between 25°S to 60°S and 160°E to 170°W (McCubbine et al. submitted). The grids were determined from existing terrestrial, marine and satellite altimetry gravity data enhanced with new airborne gravimetry data that was acquired for determination of the New Zealand vertical datum (available from LINZ data service). 

All data were corrected for the gravitational effect of the GRS80 reference ellipsoid and tied to the I.G.S.N.71 gravity datum. The gravity anomaly data from all sources were combined using the method of least squares collocation with a three dimensional logarithmic covariance function. An error grid is provided that gives the estimated residual gravity noise determined during the least squares collocation process. Terrain corrections for gravity anomaly grids were calculated using a one arc-minute block averaged elevation model derived from an 8 m digital elevation model for topography above sea level (available from LINZ data service) and a 250 m seafloor topography model (Mitchel et al. 2012, Weatherall et al.2015). 

Terrestrial gravity data are from the GNS Science database of terrestrial gravity observations from approximately 40,000 locations across New Zealand that were made by several different institutions with various gravimeters. Most of the observations have been made with Lacoste and Romberg D and G relative gravity metres.

Airborne gravity survey data were collected between September 2013 and June 2014 from a twin engine Piper Chieftain aircraft and a LaCoste and Romberg dynamic gravimeter (model number S-80). Data are available from LINZ data service.

Marine gravity observation data are from publically available sources at GNS Science, US National Oceanic and Atmospheric Administration (NOAA) geophysical data centre and Geoscience Australia (GA). These data are reduced to free air anomalies and cross-over adjusted to remove potential offsets between separate gravity surveys (Amos et al. 2005).

Satellite marine gravity anomaly grid data are from Sandwell et al. (2014) released in 2014 (at one arc minute) obtained from http://topex.ucsd.edu/marine_grav/mar_grav.html (accessed September 2015).

Gravity grids are in Arc-ascii format:

Amos MJ, Featherstone WE, Brett J 2005. Crossover adjustment of New Zealand marine gravity data, and comparisons with satellite altimetry and global geopotential models. In; Gravity, Geoid and Space Missions, Volume 129, pp. 266271. IAG Symposia Series, Springer, Berlin, Germany.

McCubbine JC, Stagpoole V, Caratori Tontini F, Amos M, Smith E, Winefield R, (submitted). Gravity Anomaly Grids for the New Zealand Region. New Zealand Journal of Geology and Geophysics. 

Mitchell JS, Mackay KA, Neil HL, Mackay EJ, Pallentin A, Notman P 2012. Undersea New Zealand, 1:5,000,000. NIWA Chart, Miscellaneous Series No. 92. National Institute of Water and Atmospheric Research, Wellington.

Sandwell DT, Miller RD, Smith WHF, Garcia E, Francis R 2014. New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure 2014, Science 346(6205): 65-67, doi: 10.1126/science.1258213, 2014.

Weatherall P, Marks KM, Jakobsson M, Schmitt T, Tani S, Arndt JE, RovereM, Chayes D, Ferrini V, Wigley R 2015. A new digital bathymetric model of the world's oceans, Earth and Space Science, 2, 331–345, doi:10.1002/2015EA000107.