The data were logged on a PC. The record consisted of PC SYSTEM TIME (corrected by data from NAVPRO navigation system), gravimetric band (turns of the main spring, 0 to 16), mV. The field data were tranformed from mV to mgal with the following formula:
where G is the gravimetric anomaly (mGal), V is the voltage drop reading, and C is a numerical constant wich is related to the gravimetric band (Table 9). These coefficients were calculated during the zero drift calibration in Civitavecchia 3-apr-1999. This tranformation will be recalculated basing on a new theoretical, non-linear approach.
G was then corrected (a) for ship's speed and for response time of the system (typically 300 seconds) using a moving average filter at 300 seconds. A (b) classical Eotvos correction was then applied according to Dehlinger (1978)(p.150). A better correction will be evaluated and applied during final processing of the data, due to the high frequency of turning of ships' heading; (c) Normal Gravity field correction (1970 formula of International Geodesy Association, Dehlinger, 1978)) was finally applied, and the Free Air anomaly data were obtained. No drift correction was applied yet.
A crossing line was performed in order to check the drift of the sensors and to make an estimate of the errors. This analysis will be used for the final processing of the Free Air Gravity anomaly.
By using a 1km grid of the surveyed area the Bouguer Gravity Anomaly will then be computed at a constant density of 2.67 gr/cm3.
