Abstract
Abstract. The Medium Resolution Imaging Spectrometer (MERIS) launched in February 2002 on-board the ENVISAT spacecraft is making global observations of top-of-atmosphere (TOA) radiances. Aerosol optical properties are retrieved over land using Look-Up Table (LUT) based algorithm and surface reflectances in the blue and the red spectral regions. We compared instantaneous aerosol optical thicknesses retrieved by MERIS in the blue and the red at locations containing sites within the Aerosol Robotic Network (AERONET). Between 2002 and 2005, a set of 500 MERIS images were used in this study. The result shows that, over land, MERIS aerosol optical thicknesses are well retrieved in the blue and poorly retrieved in the red, leading to an underestimation of the Angstrom coefficient. Correlations are improved by applying a simple criterion to avoid scenes probably contaminated by thin clouds. To investigate the weakness of the MERIS algorithm, ground-based radiometer measurements have been used in order to retrieve new aerosol models, based on their Inherent Optical Properties (IOP). These new aerosol models slightly improve the correlation, but the main problem of the MERIS aerosol product over land can be attributed to the surface reflectance model in the red.
Highlights
There is a clearly need for an accurate representation of the distribution of aerosols over the globe because of their direct and indirect radiative impacts on climate (IPCC, 2007), and because of their health impact on population (Wilson and Sprengler, 1996)
In order to take into account both the spatial and temporal variability of aerosol distribution, the Medium Resolution Imaging Spectrometer (MERIS) level-2 aerosol product at 1.2 km pixel resolution and the Aerosol Robotic Network (AERONET) direct Sun measurements need to be collocated in space and time
An extensive data set of CIMEL AERONET measurements was used in the evaluation of the MERIS aerosol product over land
Summary
The Medium Resolution Imaging Spectrometer (MERIS) instrument can assume an integral role in the effort of obtaining a global picture of aerosols due to its frequent global measurements of aerosol amount and type over a wide variety of surface types. The primary goal of MERIS is the ocean color observation, while the secondary purpose is the observation of the atmosphere and the terrestrial surface. MERIS is one of the instruments of the ENVISAT satellite launched in 2002. ENVISAT is a sun-synchronous orbit with an equator crossing time of 10:00 a.m. local time.
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