Present-day ocean color satellite and airborne sensors can monitor chlorophyll-a (chl-a), which they derive from remote sensing reflectance (Rrs). In order to retrieve accurate chl-a values, satellite and airborne Rrs must first be corrected for optical scattering and absorption caused by the atmosphere. Correcting for atmospheric interference is a complex task, and there are many correction algorithms that function in different ways. Here I conduct a sensitivity analysis of the 6SV atmospheric correction algorithm in order to gauge its performance in retrieving accurate chl-a measurements while systematically altering the algorithm’s input parameters. 6SV was run using an uncorrected (L1) AVIRIS image of Monterey Bay, for which there are spatially and temporally consistent in-situ chl-a measurements sampled at three predetermined stations (HyspIRI ST 12-14). To perform the sensitivity analysis, 6SV was run using the required input parameters, including an estimate of aerosol optical depth (AOD) from a nearby AERONET station. Corrections were performed at each chl-a sampling station using the AERONET AOD for each of the 5 6SV aerosol distribution models. AOD was altered in order to investigate its impact on chl-a retrieval error. The resulting Rrs values (511 & 555 nm) were input into the SeaWiFS OC4 chlorophyll retrieval algorithm to obtain chl-a values, which were then compared to their corresponding in-situ chl-a measurements. Results of this 6SV sensitivity analysis indicate that when retrieving chl-a values, 6SV is highly sensitive to AOD and the user-determined aerosol model. Out of the five aerosol distribution models, the coastal aerosol model produced the most accurate chl-a retrievals. Additionally, results indicate that overestimating AOD causes substantially larger errors in chl-a retrieval compared to underestimating AOD. Leveraging MODIS Terra AOD measurements markedly improved the accuracy of chl-a retrieval for HyspIRI ST 13, indicating that the inaccurate chl-a retrieval for this station can be attributed to spatial variability of AOD.

Presentation Slides: https://www.scribd.com/document/320956496/Atmospheric-Correction-Sensitivity-Analysis-for-Chlorophyll-a-Retrieval#fullscreen&from_embed