change depth scale in reefmaster sonar viewer

The image above shows a typical sonar return. Information about the bottom type is extracted from several places in each sonar return, each of which provides a different value and each of which can be shown separately as different layers within the bottom composition module. It is important to note that the values that ReefMaster calculates for bottom hardness are unit-less and provide only an indication of relative changes in bottom type across the mapped area. By calculating and averaging a range of values, ReefMaster is able to determine to relative hardness and roughness of areas within the map project. Our study also shows that low-cost commercially available technology can be used for rapid scientific investigations in shallow water areas.Bottom composition is determined by analysing the data within sonar log files and looking at signal returns at various positions within the returned 'ping'. Subsidence and northward tilting of sedimentary rocks north of the island, probably caused by collapse of abandoned subsea mine workings, created an extensional regime south of the island that led to the formation of steep cliffs and collapse of the southern side of the island. We showed that the partial submergence of the island could be interpreted as a result of subsidence. Two low-cost techniques were used to view underwater structures: a commercial drone fitted with a video camera in waters shallower than 5 m and an echo sounder and side-scan sonar system designed for amateur fishers in waters deeper than 5 m.

We analyzed the geology of the island and surrounding seafloor to investigate how it became submerged. The island lies about 1 km off the coast of Nagasaki and was mined for coal during the late 19th and early 20th centuries.

Between 19, about half of Yokoshima Island disappeared beneath the East China Sea.

Change depth scale in reefmaster sonar viewer