I am comparing two methods for estimating Chl-a using Sentinel-2 data
1- Chlorophyll a concentration (µg/l) using the red edge algorithm by Gons et al.
2- Chlorophyll a using C2CRR method
I am observing that Chl-a concentration output in one area is similar using both methods. However on other area its reverse, where Chl-a is high using Gons et al.(2002) (First image) there chl-a is low using C2CRR (red color shows low values and Blue corresponds to high Chl-a) (second image)
A chlorophyll-retrieval algorithm for satellite imagery (medium resolution imaging spectrometer)
of inland and coastal waters. Journal of Plankton Research 24 (9), 947–951
Description of algorithm included in Acolite: chl_re_gons, chl_re_gons740: Chlorophyll a concentration (µg=l) using the red edge algorithm by Gons et al.(2002) with published coefficients and a mass specific chlorophyll a absorption of 0.015. By default 780 nm(band 6) is used as a reference, but the chl_re_gons740 product uses 740 nm (band 5) on MSI. Output products are by default only produced for waters where ρs664 > 0.005 and ρs704/ρs664 > 0.63 (thresholds defined by Héloïse Lavigne). Sensors: S2A/MSI, S2B/MSI
I think results will depend very much on the type of water you have. Acolite is designed for high turbid scattering waters, while the range in the C2RCC (normal net) is more limited. You have the possibility to use the “extreme” C2RCC net in SNAP and re-check. But it really looks as if the colour palettes are reversed…