Evaluating satellite estimates of particulate backscatter in the global open ocean using autonomous profiling floats

Satellite retrievals of particulate backscattering (b_bp) 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 b_bp using observations from autonomous floats (n = 2,486 total matchups across three satellites), which provide b_bp at 700 nm. With these data, we quantify how well the three inversion products currently distributed by NASA ocean color retrieve b_bp. We find that the median ratio of satellite derived b_bp to float b_bp 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.