In order to carry out this bathymetric survey, ESTEIO made use of an ODOM SDH-13A bathymeter, which uses ultrasonic waves for the determination of depth. According to the technical specifications of the equipment, depth measures in the range of 0.5 to 120 meters can be obtained.
The data collected are recorded graphically in digital ways by Digitrace. This equipment allows the insertion of data regarding the sound propagation speed in the water and the Transdutor depth (sounder which sends and receives sound, being this the way for the determination of the depth).
Before starting the gathering of data activities, a daily calibration of the bathymeter was performed, by means of introducing into the water a scaled rope with a weight tied to its edge. Such procedure allowed the readings from the bathymeter to be compared with the reading from the rope, and it allowed the corrections to be made at the sound propagation speed in the water. In this case, due to the water characteristics, the 1,500m/s speed was chosen. It is important to notice that the boat speed by the time of the gathering of data was always inferior to 3 knots.
For the planimetric positioning of the boat (2D), GPS receivers from TRIMBLE were used, receiving then differential corrections (DGPS). The GPS antenna was installed centered in relation to the sounder, minimizing in this way the positioning error of the boat due to its inclination angle.
The service was carried out according to the planning above, in which the positioning of the sections was obtained through the HYPACH software, developed by Coastal Oceanographics Inc. The survey itself was carried out after the sections were defined. Such survey consists of collecting and putting together the data from the GPS (NMEA format, with GGA and VTG messages) and from the bathymeter (depth), using an on board microcomputer as the interface. These data were collected in WGS-84 coordinates in instantaneous time with the depth register being performed by the bathymeter every 20-30 centimeters run in the section. The boat had to cover each of the sections planned for the carrying out of the survey.