Underwater robots with sonar and smart tether for underground cistern mapping and exploration

Abstract

This paper describes the application of using a submersible remotely operated vehicle (ROV) to map and explore
\nunderground water cisterns during a series of expeditions to Malta and Gozo. The purpose of this project was to
\ncreate maps of ancient cisterns located under private homes, churches, and fortresses where passageways leading
\nto the cisterns are too narrow and dangerous for humans to enter. These cisterns were used as water storage
\nsystems for hundreds of years, and many still contained water. The small ROV that was lowered into these cisterns
\nwas equipped with a sonar module to enable the creation of maps, two cameras to record live video, a grabber-arm
\nfor interacting with objects in the environment, and a Smart Tether to record additional positioning data of the ROV.
\nEach of these components are discussed in terms of functionality and appropriateness for use by archaeologists
\nwishing to explore and extract mapping information from narrow water-filled caverns. Additionally, three different
\nmapping and localization techniques are presented including 1) Sonar image mosaics using stationary sonar
\nscans, 2) Sonar image mosaics using stationary sonar scans with Smart Tether position data, and 3) Simultaneous
\nLocalization and Mapping (SLAM) using stationary sonar scans. Each of the algorithms used in this project have
\nbenefits in certain applications. During two expeditions in Malta and Gozo, 2-dimensional maps of 32 cisterns
\nwere successfully constructed.