Diagnosing Atmospheric Correction Performance for the Santa Barbara Channel: Do We Really Know Aerosol Optical Properties for Complex Coastal Environments?
Bill
O'Hirok, UC Santa Barbara, bill@icess.ucsb.edu
Dave
Siegel, UC Santa Barbara, davey@icess.ucsb.edu
(Presenting)
Stephane
Maritorena, UC Santa Barbara, stephane@icess.ucsb.edu
It has been long known that the performance of operational satellite ocean color products is poor in many complex coastal regions. For example, comparisons between field and satellite determinations of water-leaving radiance from the Plumes and Blooms (PnB) project (Santa Barbara Channel, California) are very poor (squared correlation coefficient (r2) for LwN(412) matchups are 0.09 (N=595 for both SeaWiFS and MODIS-Aqua)). The largest discrepancies between field and satellite measurements of water-leaving radiance are found for the violet and blue wavebands, occur for both SeaWiFS and MODIS-Aqua observations and point towards an overcorrection by operational atmospheric correction procedures. We hypothesize that a misrepresentation of aerosol optical properties is the cause of these large discrepancies. To test this hypothesis, we employ an iterative closure scheme to match top-of-the-atmosphere (TOA) satellite radiance spectra with model simulations. All components of the TOA radiance spectrum are modeled using available observations except aerosol optical properties, which are selected via an iterative comparison with the TOA radiance spectrum. We find that the current aerosol model suite does not adequately account for the complex aerosol optical properties for this region. In particular, values of single scatter albedo, a measure of aerosol absorption, are often far smaller than values included in the current suite of aerosol models. We show that to achieve atmospheric correction for this site either absorbing aerosol types (cf., continental polluted, dust, etc.) or unusual aerosol optical properties (low values of SSA for marine aerosols) must be included. Last, we provide ideas for how atmospheric correction procedures can be improved for complex coastal environments.
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