Abstract
Satellite retrievals of particulate backscattering (bbp) are widely used in studies of ocean ecology and biogeochemistry, but have been historically difficult to validate due to the paucity of available ship-based comparative field measurements. Here we present a comparison of satellite and in situ bbp using observations from autonomous floats (n = 2,486 total matchups across three satellites), which provide bbp at 700 nm. With these data, we quantify how well the three inversion products currently distributed by NASA ocean color retrieve bbp. We find that the median ratio of satellite derived bbp to float bbp ranges from 0.77 to 1.60 and Spearman's rank correlations vary from r = 0.06 to r = 0.79, depending on which algorithm and sensor is used. Model skill degrades with increased spatial variability in remote sensing reflectance, which suggests that more rigorous matchup criteria and factors contributing to sensor noisiness may be useful to address in future work, and/or that we have built in biases in the current widely distributed inversion algorithms.
Highlights
Satellite observations of particulate backscattering have advanced our understanding of ocean biology over the last few decades by using bbp_sat as a proxy for particulate organic carbon [1], phytoplankton biomass [2], and particle size [3]
No matter which algorithm is used, we found that bbp_sat correlations are highest in open ocean waters with MODIS (r = 0.60 to 0.79) compared to VIIRS (r = 0.21 to 0.38) and OLCI (r = 0.32 to 0.47) because Rrs observations are noisiest using either VIIRS or OLCI, on the basis of their coefficient of variations within the 5 × 5-pixel box, and on their relatively higher Median Percent Error (MPE)
The original Bailey and Werdell criteria stipulate that the median coefficient of variation in Rrs around a 5 × 5-pixel box be less than 15%
Summary
Satellite observations of particulate backscattering (bbp_sat) have advanced our understanding of ocean biology over the last few decades by using bbp_sat as a proxy for particulate organic carbon [1], phytoplankton biomass [2], and particle size [3]. There are three algorithms for which NASA’s Ocean Biology Processing Group distributes bbp_sat products While they are widely used, it remains a challenge to compare satellite and in situ observations of bbp at global scales. Autonomous profiling floats (of the Bio-geochemical Argo program, [4]) have recently become the backbone of a global array for biogeochemical monitoring. These float measurements have since been used for a variety of applications [5,6,7,8], including regional assessments of ocean color products [9].
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