1Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK
2Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK
*present address: Department of Medical Physics and Bioengineering, Christchurch Hospital, New Zealand
**present address: National Institute of Water and Atmospheric Research, Wellington, New Zealand
Received: 24 Jun 2009 – Discussion started: 14 Oct 2009
Abstract. The Global Retrieval of ATSR Cloud Parameters and Evaluation (GRAPE) project has produced a global data-set of cloud and aerosol properties from the Along Track Scanning Radiometer-2 (ATSR-2) instrument, covering the time period 1995–2001. This paper presents the validation of aerosol optical depths (AODs) over the ocean from this product against AERONET sun-photometer measurements, as well as a comparison to the Advanced Very High Resolution Radiometer (AVHRR) optical depth product produced by the Global Aerosol Climatology Project (GACP).
Revised: 22 Mar 2010 – Accepted: 11 May 2010 – Published: 26 May 2010
The GRAPE AOD over ocean is found to be in good agreement with AERONET measurements, with a Pearson's correlation coefficient of 0.79 and a best-fit slope of 1.0±0.1, but with a positive bias of 0.08±0.04. Although the GRAPE and GACP datasets show reasonable agreement, there are significant differences. These discrepancies are explored, and suggest that the downward trend in AOD reported by GACP may arise from changes in sampling due to the orbital drift of the AVHRR instruments.
Thomas, G. E., Poulsen, C. A., Siddans, R., Sayer, A. M., Carboni, E., Marsh, S. H., Dean, S. M., Grainger, R. G., and Lawrence, B. N.: Validation of the GRAPE single view aerosol retrieval for ATSR-2 and insights into the long term global AOD trend over the ocean, Atmos. Chem. Phys., 10, 4849-4866, doi:10.5194/acp-10-4849-2010, 2010.