1. Assessment of Satellite Ocean Color Products of the Coast of Martha’s Vineyard using AERONET-Ocean Color Measurements Hui Feng1, Heidi Sosik2 , and Tim Moore1 1: University of New Hampshire ; 2 : Woods Hole Oceanographic Institution
Abstract
Optical complexity of both waters and atmospheres in coastal environments may lead to significant issues in the quality of satellite-retrieved ocean color products. Validation of satellite ocean color products requires high-quality in-situ measurements.
A coastal ocean color validation project has been funded by the NASA Ocean Biology and Biogeochemistry (OBB) program, focusing on the coastal region near the Martha’s Vineyard Coastal Observatory (MVCO) in Massachusetts. One key field component of the project is the monitoring of multi-spectral water-leaving radiances and aerosol optical properties using an above-water automatic sun-photometer (AERONET-Ocean Color, i.e. SeaPRISM ) deployed at the MVCO tower since 2004.
Earlier studies showed that 12 candidate aerosol models (Gordon and Wang, ) used for the atmospheric correction do not adequately represent observed aerosol properties in the coastal region. The significantly improved atmospheric correction scheme has been implemented in SeaDAS version 6 (Ahmad et al., 2010; Bailey et al., 2010).
This poster presents an updated assessment of the MODIS-Aqua and SeaWiFS ocean color products in reprocessing versions 5 & 6.
Project objectives
Establish a high-quality observational long time series dedicated to satellite ocean color product validation at a Northwest Atlantic coastal site (MVCO)
Extend and analyze the existing AERONET-OC times series at MVCO for coastal ocean color validation
Quantify major uncertainty sources in satellite ocean color retrievals, and understand temporal and spatial variability of these uncertainties
Explore (and possibly adapt) published approaches to retrieve phytoplankton functional groups and/or size classes from AEROENT-OC / MODIS normalized water-leaving radiance on the basis of comparison with the in situ time series.
Location and Platform
The Air-Sea Interaction Tower (ASIT) is located about 3 km offshore at 15.6 m water depth. The ASIT was built specifically to support measurements in the ocean and atmosphere to investigate ocean processes that include air-sea interactions, ocean mixing, gas exchange, bio-optics, and sediment transport.
SeaWiFS Chla image
MODIS-Aqua Normalized water leaving radiance nLw and aerosol properties
SeaWiFS nLw and aerosol properties
Version 6
Version 6
Version 5 vs. Version 6
Scatter plots of MODIS-retrieved nLw412nm version 6 vs. Version 5 at MVCO site.
Scatter plots of MODIS-retrieved vs. AERONET-OC (SeaPRISM) measured nLw at 412, 443, 488, 531, 547, and 667 nm from top left to bottom right. Vertical bars show one standard deviation for 2-by-3 pixels with the upper center at MVCO; horizontal bars indicate the SeaPRISM uncertainties. N =185 is the number of match-ups, and uncertainty measures of δ(%), |δ|(%) and r2 are indicated. Products are from AERONET-OC Level-2 data and MODIS-Aqua SeaDAS version 6 for
Scatter plots of SeaWiFS-retrieved vs. AERONET-OC (SeaPRISM) measured nLw at 412, 443, 490,510, 555 and 670 nm from top left to bottom right. Vertical bars show one standard deviation for 2-by-3 pixels with the upper center at MVCO; horizontal bars indicate the SeaPRISM uncertainties. N =92 is the number of match-ups, and uncertainty measures of δ(%), |δ|(%) and r2 are indicated. Products are from AERONET-OC Level-2 data and SeaWiFS SeaDAS v6.
Mean spectra of MODIS-retrieved and AERONET-OC measured nLw based on all available match-up pairs at MVCO for version 5 (left) vs. version 6 (right). Vertical bars display the range of one standard deviation.
Scatter plots of SeaWiFS-retrieved vs. AERONET-OC (SeaPRISM) measured aot at 870nm (left), Angstrum exponent (870nm) (middle), and chla-OC2 ( right), based on the match-up analysis. Products are from AERONET-OC Level-2 data and SeaWiFS SeaDAS version 6 for
Scatter plots of MODIS-retrieved vs. AERONET-OC (SeaPRISM) measured aot at 870nm (left), Angstrum exponent (870nm) (middle), and chla-OC2 ( right), based on the match-up analysis. Products are from AERONET-OC Level-2 data and MODIS-Aqua SeaDAS version 6 for
Summary and future work
The AERONET-OC instrument deployed at MVCO has provided a valuable long time series of in-situ measured ocean color and aerosol properties for coastal ocean color validation efforts.
The cross assessment of the MODIS-Aqua ocean color products of Reprocessing Versions 5 and 6 ( V5 and V6) shows that V6 MODIS-Aqua ocean color products have an improvement
over the V5 ones. Particularly, MODIS-retrieved nLw at 412nm, nLw(412), is improved in terms of 1) that the number of negative values decreases and 2) the mean increases.
The AERONET-OC data at MVCO and other sites (LISCO and COVE) will be used to quantify uncertainties in satellite ocean color retrievals in the northeast US coastal region.
Acknowledgements
This work has been sponsored supported by 1) NASA OBB program (NNX11AF07G ) and 2) NASA NIP program (NNX08AV24G). The GSFC DAAC are also acknowledged for providing the MODIS –Aqua ocean color data.
NASA Ocean Color Research Team Meeting, Seattle, WA, April 23-25, 2012