Abstract
In 2014, the Jeddah Municipality made a call for an estimate of a centimetric precision geoid model to be used for engineering and surveying applications, because the regional geoid model available at that time did not reach a sufficient precision. A project was set up to this end and dedicated sets of gravity and Global Positioning System (GPS)/levelling data were acquired in the framework of this project. In this paper, a thorough analysis of these newly acquired data and of the last available Global Gravity Field Models (GGMs) has been done in order to obtain a geoid undulation estimate with the prescribed precision. In the framework of the Remove–Compute–Restore (RCR) approach, the collocation method was used to obtain the height anomaly estimation that was then converted to geoid undulation. The remove and restore steps of the RCR approach were based on GGMs, derived from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and Gravity Recovery and Climate Experiment (GRACE) dedicated gravity satellite missions, which were used to improve the long wavelength components of the Earth’s gravity field. Furthermore, two different quasi-geoid collocation estimates were computed, based on gravity data only and on gravity plus GPS/levelling data (the so-called hybrid estimate). The best solutions were obtained with the hybrid geoid estimate. This was tested by comparison with an independent set of GPS/levelling geoid undulations that were not included in the computed solutions. By these tests, the precision of the hybrid geoid is estimated to be 3.7 cm. This precision proved to be better, by a factor of two, than the corresponding one estimated from the pure gravimetric geoid. This project has been also useful to verify the importance and reliability of GGMs developed from the last satellite gravity missions (GOCE and GRACE) that have significantly improved our knowledge of the long wavelength components of the Earth’s gravity field, especially in areas with poor coverage of terrestrial gravity data. In fact, the geoid models based on satellite-only GGMs proved to have a better performance, despite the lower spatial resolution with respect to high-resolution models (i.e., Earth Gravitational Model 2008 (EGM2008)).
Highlights
Since the available regional model for Saudi Arabia did not achieve the required centimetric precision [1], in 2014 the Municipality of Jeddah (Saudi Arabia) set up a project for the estimation of a geoid undulation model that is appropriate for promoting the use of Global Navigation Satellite System (GNSS) techniques in positioning and surveying applications
The geodetic community has had the opportunity of reprocessing the entire data span of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission [2] and combining these new satellite data with other types of data, like the satellite gravity data provided by the Gravity Recovery and Climate Experiment (GRACE, [3,4]), the Satellite Laser Ranging information from different satellites and terrestrial gravity observations
This has been done in order to check how effective new satellite-only Global Gravity Models (GGMs), based on the GRACE and GOCE satellite missions, are in representing the low-frequency components of the gravity field, while comparing them to the high-degree GGMs that are based on the combination of satellite and ground data
Summary
Since the available regional model for Saudi Arabia did not achieve the required centimetric precision [1], in 2014 the Municipality of Jeddah (Saudi Arabia) set up a project for the estimation of a geoid undulation model that is appropriate for promoting the use of Global Navigation Satellite System (GNSS) techniques in positioning and surveying applications. Gravity data have been integrated with geoid undulation values derived by GPS and leveling measures on the same benchmarks to obtain a hybrid model, according to the approach in ([9,10]) These new local geoid undulation models computed for the Jeddah Region improved the previous estimate, matching the required precision. This result was achieved due to the use of the satellite-only global geopotential models that proved to be effective in recovering/modeling the long wavelength of the Earth’s gravity field.
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