This review is pertinent for the following sensors with which we had experience with in-line systems: Transmissometers: WETLabs CStar Sequoia LISST WETLabs ac-9 and ac-s. Spectrophotometers: WETLabs ac-9 and ac-s. Backscattering meters: WETLabs Eco series. HobiLabs Hydroscat sensors. Fluorometers: WETLabs WETStar Chlorophyll/CDOM fluorometers WETLabs ALFA spectrofluorometer Seapoint Chlorophyll/CDOM fluorometers (with cap for flowthrough applications). It