The Malta cistern mapping project : underwater robot mapping and localization within ancient tunnel systems

Abstract

This paper documents the development of an underwater robot system enabled with several mapping and localization techniques applied to a particular archaeological expedition. The goal of the expedition was to explore and map ancient cisterns located on the islands of Malta and Gozo. The cisterns of interest acted

as water storage systems for fortresses, private homes, and churches. Such cisterns often consisted of sev- eral connected chambers, still containing water. A sonar-equipped remotely operated vehicle (ROV) was de- ployed into these cisterns to obtain both video footage and sonar range measurements. Six different mapping

and localization techniques were employed, including (1) sonar image mosaics using stationary sonar scans,

(2) sonar image mosaics using stationary sonar scans with Smart Tether position data, (3) simultaneous lo- calization and mapping (SLAM) while the vehicle was in motion, (4) SLAM using stationary sonar scans,

(5) localization using previously created maps, and (6) SLAM while the vehicle was in motion with Smart Tether position data. Top-down-view maps of 22 different cisterns were successfully constructed. It is estimated that the cisterns were built as far back as 300 B.C., and few records of their size, shape, and connectivity existed before the expedition.