## 2 Methodology
### Satellite Imagery and Matching  
Ocean color satellite imagery from SeaWiFS, MODIS-Aqua, and MODIS-Terra that matched the field observations were selected and processed for further analysis. Scripted calls to the NASA GSFC Ocean Color browser ([[http://oceancolor.gsfc.nasa.gov/cgi/browse.pl](http://oceancolor.gsfc.nasa.gov/cgi/browse.pl)]([http://oceancolor.gsfc.nasa.gov/cgi/browse.pl](http://oceancolor.gsfc.nasa.gov/cgi/browse.pl))) after the 2012.0 MODIS-Aqua reprocessing ([[http://oceancolor.gsfc.nasa.gov/WIKI/OCRepproc20120](http://oceancolor.gsfc.nasa.gov/WIKI/OCRepproc20120) MA.html]([http://oceancolor.gsfc.nasa.gov/WIKI/OCRepproc20120](http://oceancolor.gsfc.nasa.gov/WIKI/OCRepproc20120) MA.html)) were used to identify and download 1 km nominal nadir resolution L2 SeaWiFS, Aqua, and Terra satellite scenes within 0.05 degrees of field observations on the same day. These were spatially extracted for a 5 \(\times\) 5 pixel array around the station location. In <1% of stations, high resolution SeaWiFS imagery was not available, and Global Area Coverage (GAC; nominally 4.4 km spacing) scenes were substituted. By default, data were masked based on standard L2 flags using the criteria described in [55]: land, high solar or satellite zenith angle, clouds, sea ice, high light, stray light, glint, low water leaving radiance, and atmospheric correction failure. Extracted satellite data were then evaluated for coincidence with field sampling stations. Criteria were principally based on those of [PERSON] and [PERSON] (2006). Specifically, extracted satellite pixel arrays were retained in the database if the overpass occurred within 8 h of field sampling. For each waveband of \(R_{rs}\), negative and outlier pixels within each array (>1.5 standard deviations from the mean) were set to null values. Data were only retained in each waveband if greater than 50% of non-land pixels were still valid, with no fewer than five valid pixels in total. Finally, the mean \(R_{rs}\) values for each array were calculated and retained in the database only if those pixels had a coefficient of variation (CV) < 0.25 (rather than <0.15 applied in [PERSON] and [PERSON] (2006)). Of the 50,127 field stations with spatially gridded, depth binned and quality controlled CDOM data, 8252 stations had matching quality controlled Aqua imagery, 11,156 matched Terra imagery, and 11,818 matched SeaWiFS imagery.  
For the purpose of further quality assurance, several match-up metrics were retained in the final database, including the time difference, CV, the number of matched satellite pixel arrays for eachchannel, the areal extent of the matched pixels (nominally \(\sim\)25 km\({}^{2}\)), and the distance between the field sampling location and the central pixel (nominally \(<\) \(\sim\)1 km). Sensor viewing angle, which can significantly increase error in estimates of satellite \(R_{rs}\) due to increased uncertainties in the atmospheric correction, is not available on a pixel-by-pixel basis in standard L2 products. On the other hand, ground sample area, which can be approximated from the geographic coordinates of pixel arrays, is a good proxy for sensor viewing angle, with larger areas representing larger viewing angles. Area is also a reasonable metric for accuracy of the geographic collocation, wherein \(R_{rs}\) averaged over larger areas of the ocean may not be representative of those measured at the sampling location, depending on the degree of spatial variability of ocean color within the sampled region. These match-up metrics were described in greater detail in [56].