  Cooperative localization is an important technique in environments devoid of
GPS-based localization, more so in underwater scenarios, where none of the
terrestrial localization techniques based on radio frequency or optics are
suitable due to severe attenuation. Given the large swaths of oceans and seas
where autonomous underwater vehicles (AUVs) operate, traditional acoustic
positioning systems fall short on many counts. Cooperative localization (CL),
which involves sharing mutual information amongst the vehicles, has thus
emerged as a viable option in the past decade. This paper assimilates the
research carried out in AUV cooperative localization and presents a qualitative
overview. The cooperative localization approaches are categorized by their
cooperation and localization strategies, while the algorithms employed are
reviewed on the various challenges posed by the underwater acoustic channel and
environment. Furthermore, existing problems and future scope in the domain of
underwater cooperative localization are discussed.
