Roger Hipkin

Combining altimetric/gravimetric and ocean model mean dynamic topography models in the GOCINA region

Initially, existing mean dynamic topography (MDT) models were collected and reviewed. The models were corrected for the differences in averaging period using the annual anomalies computed from satellite altimetry. Then a composite MDT was derived as the mean value in each grid node together with a standard deviation to represent its error. A new synthetic MDT was obtained from the new mean sea surface (MSS) KMS04 combined with a regional geoid updated using GRACE gravity and gravimetric data from a recent airborne survey. Compared with the composite MDT the synthetic MDT showed very similar results.

Combined Use of Altimetry and In Situ Gravity Data for Coastal Dynamics Studies

Accurate local geoids derived from in situ gravity data will be valuable in the validation of GOCE results. In addition it will be a challenge to use GOCE data in an optimal way, in combination with in situ gravity, to produce better local geoid solutions. This paper discusses the derivation of a new geoid over the NW European shelf, and its comparison with both tide gauge and altimetric sea level data, and with data from ocean models. It is hoped that over the next few years local geoid methods such as these can be extended to cover larger areas and to incorporate both in situ and satellite measured gravity data.

How Close are we to a Centimetric Geoid

This paper deals with the accuracy of a geoid computed using local gravity data supplemented by a global potential model. Local gravity can only correct the global model for wavelengths less than about one third of the dimension of local data, so any longer wavelength errors in the global geoid remain in the local model. This paper examines a geoid model for a 40 km square area refined from the 1000 km square area of the British geoid EDIN891 and demonstrates that the accuracy of the geoid components in the wavelength range correctable by local data (here up to 300 km) is now better than 1 cm.

Testing Newton’s Law in the Megget Water Reservoir

Gravity was measured at seven levels inside a submerged tower in Megget Water Reservoir, Scotland, in an experiment to test the inverse square law of gravitation over length scales from decimetres to tens of kilometres. The effects of Earth rotation, the global mass distribution, natural topography and man-made structures must be predicted at points outside the solid Earth, in order that that part of the measured attraction which is due to water in the reservoir can be separately identified. This attraction can be related to the Newtonian gravitational constant because, unlike natural rock masses, the density of water can be reliably predicted. This paper describes techniques aiming to determine all necessary corrections with a differential accuracy of 5 nm.s-2 over a 50 m vertical interval in order to exploit the 10 nm.s-2 accuracy available from LaCoste & Romberg gravity meters.

British and French Gravity Datums Connected via the Channel Tunnel

This Report describes a project to determine absolute gravity values along a continuous profile within the Channel Tunnel service tunnel. The work was carried out in close collaboration with the Ordnance Survey of Great Britain (who were simultaneously undertaking a reciprocal heighting traverse) and with the Institute Geographique National (who undertook first order geodetic levelling).