The history and future of the Secchi disk

Oliver Zielinski

Springer Palermo 2020.


A standardized method to determine water clarity (transparency) was adopted at the end of the nineteenth century. This method, lowering a 30 cm diameter white painted disc into the water until it disappeared out of sight, was extensively investigated by Alessandra Cialdi and Angelo Secchi and published 1865 in the journal “Il Nuovo Cimento Giornale di Fisica, Chimica e Storia Naturale”. It is now universally recognized as the Secchi disk method. The Secchi disk method and its corresponding parameter, the Secchi disk depth, today continues to be a subject of scientific investigation and theoretical considerations. It is even available in a smartphone App ( and its data can be visualized in a global historic dataset ( Algorithms are available and operationally used to convert ocean color satellite data into Secchi disk depth. Combining historical and ongoing Secchi disk observations with satellite products, standardized water clarity products are at hand enabling researchers to assess long term changes in water clarity in global seas and freshwater environments.

Letter-Zielinski_(004).pdf (pdf, 95 KB )

Deutsches Forschungszentrum für Künstliche Intelligenz
German Research Center for Artificial Intelligence