Dear Christian,

There is a large professional literature on the topic of estimating the Chlorophyll A content of water from remote sensing measurements. A variety of algorithms have been developed by the major Space Agencies to perform this very task. Here are some pointers:

http://oceancolor.gsfc.nasa.gov/MEETINGS/OCBAM/docs/cannizzaro_and_carder_2006_rse.pdf

http://www.ssec.wisc.edu/meetings/ciw/Workshop_Presentations/Wednesday_6_20_2012/2_Algorithm_Approaches/ignite_algorithm_application/3_Gilerson_WI12_Chl.pdf

https://www.osapublishing.org/view_article.cfm?gotourl=https%3A%2F%2Fwww.osapublishing.org%2FDirectPDFAccess%2F29CEC100-9229-5C9E-F111D1C05E9C2585_252039%2Foe-21-7-9024.pdf%3Fda%3D1%26id%3D252039%26seq%3D0%26mobile%3Dno&org=

If you search further information, look at publications related to CZCS, SeaWiFS, and MODIS Ocean products.

Another source of useful information is provided by the various high quality reports generated by International Ocean Colour Coordinating Group (IOCCG). Visit their web site at

http://www.ioccg.org/

and look, in particular, at their publications list.

You mention a 4-band algorithm: the following paper uses this approach specifically

http://www.mdpi.com/2072-4292/6/6/5090/htm

I hope this helps. Cheers, Michel.

I agree with Michel above.

To add, here are a couple of recent articles that may be of help to you.

http://www.sciencedirect.com/science/article/pii/S1364815215301146

Article Development and application of a remote sensing-based Chloro...

Yes, there are a lot of papers on this field. You can search for them in the REMOTE SENSING OF ENVIRONMENT. Generally, there are two ways to estimate Chlorophyll from remotely sensed date, the radiative transfer model based method and empirical method using narrow bands remote sensing data.

I suggest you MODIS Chl-a. To gain more information,you can refer to the following publication:

Conference Paper Investigation the Behavior of MODIS Ocean Color Products und...