POSITIONING AND NAVIGATION

The Positioning system NAVPRO V5.6 by Communication Technology (Cesena, Italy) was used. The instrumental offsets are presented in Fig. 6 and in Tab. 3. The integrated system used a Microtecnica Gyrocompasse and a Trimble 4000 Differential Locator, with a DGPS Satellite link by FUGRO. The datum was WGS84 and the Direct Mercator projection on 38.00'N and UTM 33 were chosen for navigation and display. Timing was set to UTC. The SBP-CHIRP workstation received the 'VESSEL(0,0)' positions by the NAVPRO serial output. These positions were therefore recorded on the SEGY trace headers. The speed of Sound for DEPTH 1 and 2 was set to 1500m/sec, with a transducer immersion of 3.5m. CTD measurements were made with the ship's Sea Bird Probe (Fig.7).

Table 3: Instrumental Offsets on Ship Urania. Point (VESSEL,(0,0)) is located on the axis of the mast just behind the Command Bridge. The main GPS antenna (primary positioning system) is located on point POS1.

WHERE	ALONG	ACROSS	RANGE	BEARING
POS 1	4.80	1.40	5.0	16.26
VESSEL (POS 2)	0	0	0	0
ECHO SOUNDER 12	5.50	-1.85
CHIRP	-5.50	-0.95	5.58	189.80
STERN	-46.6	-1.40	46.62	189.80
GI-GUN	-65.0	5.0
FIRST ACTIVE	-177.5	0.0
MAG	-230.0	-5.0

figure

Figure 6: Instrumental Offsets on R/V Urania

Figure 7: The SEA BIRD SBE CTD probe.