MAGNETICS

GEM Mod. GSM-19MD Overhauser Effect Magnetometer was used (the instrument was kindly provided by PNRA). The sensor was towed at a constant offset of 185 m from ship's stern. Data were recorded at the rate of about 0.1 Hz by the NAVPRO navigation system. During the cruise we received by e-mail the data from the Observatory operated by the IIV-CNR of Catania (courtesy of Dr. Del Negro and Dr. Napoli) in the proximity of the M.Etna (located at 37 50.9N, 14 44.5E, 1340m), that were used for preliminary clean-up to eliminate possible abnormal magnetic activity and to prepare the algorithms for the final processing.

The instrument performed well for the totality of the cruise, when it was towed at the speed of 10-10.5 Kn constantly, except when the ship was in contrasting seas. We were forced to change the bronze shackle and nut at the nose of the fish after 45 days cruise. Some 12 H data were lost at the end of the cruise for problems at the connectors on the fish.

The magnetic data of the 1999 survey were collected by the NAVPRO navigation computer, along with date, time (+1GMT), DGPS antenna latitude and longitude, gyrocompass, bathymetry (central beam of EM12). A procedure was set to make a first display of the data, by means of:

1. positioning of the sensor according to the offset and gyro;
2. computing of the IGRF-95 anomaly
3. display of magnetics and bathymetry along the line;

This served primarily for data inspection. An example can be seen in Fig. 19.

Figure 19: TIR99: example of unfiltered magnetic data (GEM GSM 19D).

Thank to Istituto Nazionale di Geofisica and to Istituto Internazionale di Vulcanologia we have been provided the data of the Observatories of L'Aquila and od Catania for the entire cruise period. The data of the two observatories are presented in Fig. 20.

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Figure 20: TIR99: magnetic observatories data (Aquila and Catania). Courtesy of ING of Rome (Dr. DeSantis)and IIV of Catania (Dr. DelNegro and Dr. Napoli)