**3. Experiment and Results**

To verify the validity and real-time performance of the proposed method, the side scan and multibeam data measured in Meizhou Bay, Fujian, China in 2012 were selected for the experiment, as shown in Figure 9. The coverage of the survey area was approximately 13.5 <sup>×</sup> 2.5 km2, and the water depth ranged from 10 m to 40 m. The seabed sediments were mainly gravel and silt. According to the designed route, the measurements of the multibeam and side scan sonars were carried out successively in the same water area. In the multibeam measurement, Kongsberg EM 3002 with an operating frequency of 300 kHz, across-track beam aperture of 130◦ and maximum beam number of 131 was used. Meanwhile, in the side scan measurement, EdgeTech 4100P side scan sonar was towed at approximately 2 m underwater with an operating frequency of 500 kHz, maximum recorded slant range of 150 m (corresponding to 3751 sample numbers), vertical angular aperture of 50◦, and horizontal angular aperture of 0.5◦. The interval time between pings was 0.15 s on average. The side scan data were recorded in eXtended Triton Format (\*.xtf) files, which only contained the backscatter strengths. The raw signal levels were unavailable, and the echoes were compensated with unknown gains.

**Figure 9.** Survey track lines of both the side scan and multibeam sonars in Meizhou Bay, Fujian, China.

The experiment was divided into the following stages.

• The experiment began by sampling, training, and bottom tracking of a small side scan survey line. Small sets of samples were initially extracted from the side scan data. Then the proposed 1D-CNN network model was trained to learn the variation features of the sample set. The training

network was eventually used for bottom tracking, and the predicted value was compared with the artificially selected truth value.

	- The bottom tracking result obtained by the proposed method was compared with those obtained by the traditional method.
	- The water depth predicted by using the bottom tracking results were compared with the ground truth (depths measured by the multibeam sonar).
	- The real-time performance of the proposed method was analyzed and validated via statistical analysis.
