Iberia-Azores Gravity Model (IAGRM) using multi-source gravity data

J Catalao

doi:10.1186/bf03351924

Abstract

Abstract A consistent high precision and high resolution gravity model in the north-east Atlantic off Iberia peninsula using multi-source gravity data, ship-borne and satellite derived gravity anomalies, is presented. A solution strategy based on least squares optimal interpolation was used to assimilate into a coherent gravity model, gravity data with different spectral and spatial resolutions. Satellite derived gravity anomalies from KMS02 model, with an error covariance of 25 mGal2, and marine data carefully edited and validated by bias crossover error adjustment, were used in this study. The observation error variance was determined from ship-borne track adjustment and assigned an independent value for each track determined from error variance propagation. Unbiased ship-borne gravity observations were assimilated into the satellite derived gravity KMS02 model by the least squares optimal interpolation algorithm (OI) with bias removed by applying a regional bias to all ship tracks (OI-b) and alternatively by constraining all ship tracks to KMS02 using bias and tilt (OI-t). External error of the model was determined by comparing with recent surveys and it was verified that OI-t approach improved the final gravity model to an accuracy of about 3 mGal. The effect of different merging approaches on geoid solution was also evaluated and it was verified that the merging process can contribute to improve the geoid accuracy up to 4 cm with the OI-t approach.

Highlights

New methods and tools to support gravity data collection were developed worldwide in the last ten years (Childers et al, 2001; Forsberg and Brozena, 1992; Forsberg et al, 1997; Schwarz and Li, 1996; Kearsley et al, 1998)
Marine gravity data are mixed using least squares collocation. These authors present two different merging techniques, both based on collocation, that combines airborne gravity observations with either geoid observations derived from satellite altimetry or gravity derived from satellite altimetry
It was shown that combined gravity data improves the precision of the derived geoid undulation and the fit to precise shipborne gravity data

Summary

Introduction

New methods and tools to support gravity data collection were developed worldwide in the last ten years (Childers et al, 2001; Forsberg and Brozena, 1992; Forsberg et al, 1997; Schwarz and Li, 1996; Kearsley et al, 1998). The proposed method was an n-step process that maps less quality anomalies into better precision gravity anomalies data set, through the use of a residual surface computed from the difference between the first and the second model In this method, a global precision is attributed for each data set discarding the possibility of local or regional variations in the precision given by different tracks surveyed in different epochs. CATALAO: IBERIA-AZORES GRAVITY MODEL USING MULTI-SOURCE GRAVITY DATA and marine gravity data are mixed using least squares collocation These authors present two different merging techniques, both based on collocation, that combines airborne gravity observations with either geoid observations derived from satellite altimetry or gravity derived from satellite altimetry. The geoid for this area was computed and its accuracy evaluated on sea by comparison with 10 year of Topex data and on land with GPS/levelling data

Mathematical Background

Merging by Optimal Interpolation

Findings

Conclusions