"Salinity matched" does not make any sense, and the article said nothing of the sort.
It said "make them appear ... as part of the natural background — something that required adapting to the specific salinity of the water". Making something invisible to sonar could depend on the acoustic impedance (which varies with salinity) of the surrounding water and might involve adapting the object accordingly.
It said "make them appear ... as part of the natural background — something that required adapting to the specific salinity of the water". Making something invisible to sonar could depend on the acoustic impedance (which varies with salinity) of the surrounding water and might involve adapting the object accordingly.