Emily Eidam, Kelsey Bisson, Chao Wang, Catherine Walker, Aimee Gibbons

ICESat-2’s Advanced Topographic Laser Altimeter System (ATLAS) has emerged as useful tool for calculating attenuation signals in natural surface waters, thus improving our understanding of particulates from open-ocean plankton to nearshore suspended terrigenous sediments. While several studies have employed methods based on Beer’s Law to derive attenuation coefficients (including through a machine-learning approach), a rigorous sensitivity test on specific tuning parameters and processing choices has not yet been performed. Here we present comprehensive sensitivity tests of solar background removal, noise removal, choice of bin sizes, surface-peak exclusion, and beam pairing across four contrasting marine environments as well as two contrasting daytime/nighttime examples to quantify the impact of these processing choices on the derived photon-based attenuation coefficient Kdph. Horizontal and vertical bin sizes caused 6-13% variation in results, and adjusting the starting depth for calculations (i.e., the exclusion depth for the noisy sea-surface peak) caused 17% variation in results. Pairing data from strong and weak beams caused ~6-11% variation in results. In some environments, daytime data could be reasonably salvaged, but in others the results were not reliable. Detailed information about processing choices and a suggested workflow for ocean applications are provided. The sensitivity test results and suggested workflow pave the way for expanded Kdph analyses of global datasets (including turbid coastal waters) as well as interdisciplinary applications, such as evaluating nearshore ecological processes related to sediment dynamics and light attenuation.