Validation of the GRAPE single view aerosol retrieval for ATSR-2 and insights into the long term global AOD trend over the ocean

Thomas, G. E.; Poulsen, C. A.; Siddans, R.; Sayer, A. M.; Carboni, E.; Marsh, S. H.; Dean, S. M.; Grainger, R. G.; Lawrence, B. N.

doi:https://doi.org/10.5194/acp-10-4849-2010

Articles | Volume 10, issue 10

Atmos. Chem. Phys., 10, 4849–4866, 2010

https://doi.org/10.5194/acp-10-4849-2010

© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Atmos. Chem. Phys., 10, 4849–4866, 2010

https://doi.org/10.5194/acp-10-4849-2010

© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 10, issue 10

26 May 2010

Validation of the GRAPE single view aerosol retrieval for ATSR-2 and insights into the long term global AOD trend over the ocean

G. E. Thomas¹, C. A. Poulsen², R. Siddans², A. M. Sayer¹, E. Carboni¹, S. H. Marsh^1,*, S. M. Dean^1,**, R. G. Grainger¹, and B. N. Lawrence² G. E. Thomas et al.

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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 – Revised: 22 Mar 2010 – Accepted: 11 May 2010 – Published: 26 May 2010

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).

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.