Impact of Aerosol Model Selection on Water-Leaving Radiance Retrievals from Satellite Ocean Color Imagery

Sean Mccarthy,James Richman,Richard Gould,Courtney Kearney,Adam Lawson

doi:10.3390/rs4123638

Abstract

We examine the impact of atmospheric correction, specifically aerosol model selection, on retrieval of bio-optical properties from satellite ocean color imagery. Uncertainties in retrievals of bio-optical properties (such as chlorophyll, absorption, and backscattering coefficients) from satellite ocean color imagery are related to a variety of factors, including errors associated with sensor calibration, atmospheric correction, and the bio-optical inversion algorithms. In many cases, selection of an inappropriate or erroneous aerosol model during atmospheric correction can dominate the errors in the satellite estimation of the normalized water-leaving radiances (nLw), especially over turbid, coastal waters. These errors affect the downstream bio-optical properties. Here, we focus on the impact of aerosol model selection on the nLw radiance estimates by comparing Aerosol Robotic Network-Ocean Color (AERONET-OC) measurements of nLw and aerosol optical depth (AOD) to satellite-derived values from Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS). We also apply noise to the satellite top-of-atmosphere (TOA) radiance values in the two near-infrared (NIR) wavelengths used for atmospheric correction, to assess the effect on aerosol model selection and nLw retrievals. In general, for the data sets examined, we found that as little as 1% uncertainty (noise) in the NIR TOA radiances can lead to the selection of a different pair of bounding aerosol models, thus changing nLw retrievals. We also compare aerosol size fraction retrieved from AERONET and size fraction represented by aerosol models selected during atmospheric correction.

Highlights

The main challenge in ocean color atmospheric correction is the estimation and the removal of the path radiance from the TOA radiance values recorded by the satellite sensor [1]
In other words, is the same “optimal” model selected independently for each wavelength, or do different models at each wavelength yield better results? We evaluate individual normalized water-leaving radiance (nLw) retrievals for all 80 aerosol models to show there usually exists several aerosol models, and not just the one “optimal” model or bounding models chosen during standard atmospheric correction, that are capable of producing good spectral nLw Moderate Resolution Imaging Spectroradiometer (MODIS) to AERONET-OC matchups
During standard, automated atmospheric correction, selection of inappropriate or erroneous bounding aerosol models can dominate the errors in the satellite estimation of nLw

Summary

Introduction

The main challenge in ocean color atmospheric correction is the estimation and the removal of the path radiance from the TOA radiance values recorded by the satellite sensor [1]. We derive spectral nLw from the 1 kilometer resolution satellite imagery for both MODIS and SeaWiFS at the locations of AERONET-OC sites, using the aerosol models selected automatically from the standard 80-model atmospheric correction scheme [9]. We compare these satellite values to the in situ nLw measurements. We apply noise to the satellite TOA radiance values in the two NIR channels used for atmospheric correction, to determine the effect on aerosol model selection and nLw retrievals

Ocean Color Atmospheric Correction

Findings

Conclusions