A suggestion on determining field gravity in sea through satellite altimetry observations, Case study; field gravity in Oman Sea



Measuring field gravity in sea due to the accelerations introduced via waves and movements to the gravity measuring systems has a low accuracy since according to Einstein's equalent principle, gravimeter isn't able to separate the gravity acceleration from another acceleration. Ship borne Gravimetery observations by means of like oscillations and accelerations of the ship motion, and also more equipments errors in sea, indicating less accuracy ,and also concerning the extent of seas and low ship velocity, perfectly covering all Shipborne area seas takes up much time and it is perhaps economically impossible. One of the key points in measurement gravity is the apparatus consistency within time intervals. The gravity measurement is done over a moving pad; thus it becomes a source of error into measurement observations. These errors are mostly: (a) errors apparatus,(b) error drift,(c) error in Eotvos correction ,(d) error in correction vertical acceleration, (e) error in horizontal acceleration. Thus much effort has been made by the researchers in the field to increase observations regarding sea gravity and to find other possible solution in order to provide the required. Since the beginning of Satellite altimetry techniques, taking this advantage has been paid much attention to produce gravity data. The usual method in this regard is the Stocks Integral or Veining Meinesz and also the reverse of their solutions in order to produce gravity anomalies. In this article a different method has been presented to produce gravity anomaly in sea from satellite altimetry. The case study below evaluated in Oman Sea contains the following stages:
1. Computation of Mean Sea level (MSL) from satellite altimetry observations.
2. determining the Sea Surface Topography (SST) obtained via oceanographic studies.
3. Conversion of the MSL level to geoidal undulations by difference SST and MSL.
3. Converting the geoidal undulations into potential value at the surface of the reference ellipsoid using inverse Brun's formula.
4. Removal of the effect of ellipsoidal harmonic expansion to 360 degree and order computational point.
5. Upward continuation of the incremental gravity potential obtained from the removal steps to gravity intensity at the point of interest by using gradient ellipsoidal Abel-Poisson integral.
6. Restoring the removed effect at the fourth step at computational point of step 5.