## 2 Data and Methods  
### Datasets and Study Sites  
The datasets used in this study can be broadly classified into six different categories: (a) phytoplankton absorption coefficients (\(a_{\rm ph}(\lambda)\)) from the global oceans; (b) simultaneously collected \(a_{\rm ph}(\lambda)\) and HPLC; (c) simultaneously measured \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\) and/or HPLC; (d) HPLC time series; (e) \(R_{\rm rs}(\lambda)\) from MERIS imagery; and (f) HydroLight simulated \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\), particulate backscattering coefficients (\(b_{\rm bp}(\lambda)\)) and absorption coefficients of colored dissolved and detrital matters (\(a_{\rm dg}(\lambda)\)) (International Ocean-Color Coordinating Group (IOCCG) dataset [50]). Table 1 provides an overview of the different datasets, time, size, variables, [Chl-a] range, and the main usage. The description of each dataset and the data measurements are included in the following paragraphsA series of \(a_{\rm ph}(\lambda)\) spectra measured with the quantitative filter technique (QFT [67]) were used to find the globally optimized Gaussian parameters and the relationships among them. This dataset was obtained by searching the SeaWiFS Bio-optical Archive and Storage System (SeaBASS), which covers 1619 stations across the global oceans observed during 2001-2011. A set of 430 observations that had \(a_{\rm ph}(\lambda)\) and HPLC measurements coincidently observed were obtained from this dataset and were further randomly separated into two equal subsets (N = 215). The Subset_1 was used for regression analysis between Gaussian peak height (\(a_{\rm Gau}(\lambda)\)) and pigment concentrations (Cpigs) to obtain the relationships among them; and the Subset_2 together with the \(a_{\rm ph}(\lambda)\) and HPLC from Tara Oceans, BIOSOPE, and VIIRS cal/val cruises were used to validate the relationships obtained from Subset_1. The Tara Oceans expedition contains 23 match-ups of \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\) and HPLC around the global ocean. The BIOSOPE dataset includes 31 match-ups of \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\) and HPLC which were collected in the southeastern Pacific Ocean (obtained from: [[http://www.obs-vlfr.fr/proof/vt/op/ec/biosope/bio.htm](http://www.obs-vlfr.fr/proof/vt/op/ec/biosope/bio.htm)]([http://www.obs-vlfr.fr/proof/vt/op/ec/biosope/bio.htm](http://www.obs-vlfr.fr/proof/vt/op/ec/biosope/bio.htm))). The VIIRS cal/val dataset is composed of 21 \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\) and HPLC measurements obtained from cruises covering the coastal oceans in North Atlantic Ocean off the United States east coast. The BATS (Bermuda Atlantic Time-Series Study) dataset is composed of HPLC time series from 2002 to 2012 and was obtained from the Bermuda Atlantic Time-Series Study (near Bermuda) ([[http://bats.bios.edu/bats_measurements.html](http://bats.bios.edu/bats_measurements.html)]([http://bats.bios.edu/bats_measurements.html](http://bats.bios.edu/bats_measurements.html))). All of the in situ measurements used are from the surface, defined as a depth \(\leq\)5 m. The sampling locations of all these measurements are shown in Figure 1.  
The IOCCG dataset was simulated using HydroLight software version 5.1 [68]. It was designed to cover the dynamic range observed across the global ocean but is biased to coastal waters ([[http://www.ioccg.org/data/synthetic.html](http://www.ioccg.org/data/synthetic.html)]([http://www.ioccg.org/data/synthetic.html](http://www.ioccg.org/data/synthetic.html))). The \(R_{\rm rs}(\lambda)\), \(a_{\rm ph}(\lambda)\), \(a_{\rm dg}(\lambda)\) and \(b_{\rm bp}(\lambda)\) obtained from this dataset were used to validate the MuPI retrievals.