A study of the gas seep Istok in the Selenga shoal using active acoustic, passive acoustic and optical methods

Abstract Surveys to locate and monitor bubble gas seeps in Lake Baikal have been conducted mainly using the active echolocation methods since the 2000s. This paper compares the active acoustic method with a newly developed optical and passive acoustic methods using the example of the shallow-water gas seep Istok in the Selenga shoal. The optical method is based on processing of underwater video records of ascending bubbles while the passive acoustic uses spectral analysis of gas jet noise recorded using a hydrophone. Optical and passive acoustic methods enables estimation of the bubble size distribution function, which is necessary for the calculation of the bubble gas flux. The latter can be evaluated from active echolocation or optical data. By applying these methods, their possibilities and limitations are revealed as well as benefits of their combined use and ways to improve their accuracy in future.