Figure 1

Schematic diagram of the depth and range (diagonal distance) from the camera plane to the objects"

Figure 2

Sample RGB and depth images captured within the water tank"

Figure 3

(a) Illustration of the sonar sensor positioned at 0° horizontally, with the transducer head aligned along the $x$-axis. The expected vertical and horizontal coverage of the transmitted pulse is depicted, along with the scan area (represented by the blue rectangular box) in a hypothetical tank[18]; (b) Raw sonar data from a 102° scan of an empty tank, with a boundary detected at approximately 1.50 meters. The left axis represents intensity values ($I$) ranging from 0 to 255, displayed in a polar coordinate system; (c) Converted polar representation of the raw data in (b), where the tank boundary is clearly visible at 1.50 meters. This format is typically used by the sonar interface software and is commonly employed in AI-driven research for analysing sonar data. All figures are provided for demonstration purposes."

Figure 4

General framework of the proposed methodology using SAM[27]"

Figure 5

Framework of the proposed refinement strategy[29]"

Figure 6

Framework of the depth refinement strategy using BasNet"

Figure 7

Schematic diagrams of the testing environments"

Figure 8

Target objects used for the experiments along with their corresponding dimensions (The uniform pipe on the left is galvanized, while the bent pipe is made of PVC fabric)"

Figure 9

Sonar images obtained with low, medium, and high gain settings for a bent pipe placed at distances of 50, 70, 90, and 110 cm (The generated mask image is based on SAM, with the medium gain image as input)"

Table 1

Distance measurement results for the bent pipe at different distances"

Table 2

Distance measurement results for the uniform pipe at different distances"

Figure 10

RGB, RealSense depth, and relative depth images captured under five different experimental settings with objects placed at varying distances"

Table 3

Distance measurement results for objects in various experiments"

Figure 11

Diagrams showing the relative and absolute depth measurement error"