S2 MCI Algorithm Specification |

### S2 MCI

The maximum chlorophyll index (MCI) algorithms exploits the height of the measurement in a certain spectral band above a baseline, which passes through two other spectral bands.
The band combination, provided as preset, B4 (665 nm), B5 (705 nm), B6 (740 nm) (see figure 2) is best suited to compute the MCI on Sentinel-2 MSI data. The MCI can indicate red tides or other aquatic vegetation for example.

Figure 1

The general form of a baseline algorithm is:

where the indices 1 and 3 indicate the baseline bands (B4 and B6) and index 2 the peak wavelength (B5). This algorithm is taken from the following publication: Interpretation of the 685 nm peak in water-leaving radiance spectra in terms of fluorescence, absorption and scattering, and its observation by MERIS" J. F. R. Gower, R. Doerffer, G. A. Borstad, Int. J. Remote Sensing, 1999, vol. 20, no. 9, 1771-1786

The algorithm implemented in this S2 MCI processor contains an additional factor to correct the influence of thin clouds. This factor was introduced according to personal communications with J.F.R. Gower in February 2003.

Figure 2

'If we use k=1, then MCI increases as radiance rises in thin cloud. We correct this using k=1.005. This is what I mean by "reducing the effect of thin cloud." We then find a mask at band 7 level 1 at about 50 radiance units gives a good picture. Using the same formula on level 2 reflectance data requires a mask at about .017 reflectance in band 7.' , J.F.R. Gower.

Figure 3