Atmospheric Measurement Techniques www.atmos-meas-tech.net 1867-1381 1867-8548 2 2 2009 10.5194/amt-2-533-2009 http://www.atmos-meas-tech.net/2/533/2009/ http://www.atmos-meas-tech.net/2/533/2009/amt-2-533-2009.html http://www.atmos-meas-tech.net/2/533/2009/amt-2-533-2009.pdf 533 547 2009-09-18 Cloud detection for MIPAS using singular vector decomposition J. Hurley hurley@atm.ox.ac.uk A. Dudhia R. G. Grainger Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Department of Physics, Parks Road, Oxford, UK Satellite-borne high-spectral-resolution limb sounders, such as the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT, provide information on clouds, especially optically thin clouds, which have been difficult to observe in the past. The aim of this work is to develop, implement and test a reliable cloud detection method for infrared spectra measured by MIPAS. <br><br> Current MIPAS cloud detection methods used operationally have been developed to detect cloud effective filling more than 30% of the measurement field-of-view (FOV), under geometric and optical considerations – and hence are limited to detecting fairly thick cloud, or large physical extents of thin cloud. In order to resolve thin clouds, a new detection method using Singular Vector Decomposition (SVD) is formulated and tested. This new SVD detection method has been applied to a year's worth of MIPAS data, and qualitatively appears to be more sensitive to thin cloud than the current operational method. Barton, I.: Upper-level cloud climatology from an orbiting satellite, J. Atmos. Sci., 40, 435–447, 1983. Dudhia, A.: The Reference Forward Model (RFM), Software User's Manual (SUM), http://www.atm.ox.ac.uk/RFM/sum/ (last access: September 2009), 2005. ESA ENVISAT website: http://envisat.esa.int/instruments/images/MIPAS_Interferometer.gif (last access: June 2006), 2005. Ewen, G.: Infrared Limb Observations of Cloud, DPhil thesis in Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK, 2005. Hurley, J.: Detection and Retrieval of Clouds from MIPAS, thesis in partial fulfillment of DPhil in Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK, 2008. ISCCP website: http://isccp.giss.nasa.gov/index.html (last access: September 2008), 2008. Mantovani, R.: ENVISAT MIPAS Report: Mar 2004–Feb 2005, ENVI-SPPA-EOPG-TN-05-0006, 2005. Murtagh, F. and Heck, A.: Multivariate Data Analysis, D. Reidel Publishing Company, Dordrecht, Holland, 1987. Prabhakara, C., Fraser, R., Dalu, G., Wu, M., Curran, R., and Styles, T.: Thin cirrus clouds: Seasonal distribution over oceans deduced from NIMBUS-4 IRIS, J. Appl. Meteor., 27, 379–399, 1988. Press, W., Teukolsky, S., Vettering, W., and Flannery, B.: Numerical Recipes: The Art of Scientific Computing, Cambridge University Press, 3, 65–74, 2007. Remedios, J.: Profiles for MIPAS, EOS, Space Research Centre, Leicester, UK, January 2001. Sayer, A., Campmany, E., Dean, S., Ewen, G., Poulsen, C. A., Arnold, C., Thomas, G. E., Grainger, R. G., Siddans, R., Lawrence, B., and Watts, P.: Validation of GRAPE ORAC ATSR-2 cloud products, in preparation, 2009. Spang, R., Remedios, J., and Barkley, M.: Colour Indices for the Detection and Differentiation of Cloud Types in Infra-red Limb Emission Spectra, Adv. Space Res., 33, 1041–1047, 2004. SAGE III ATBD Team: SAGE III Algorithm Theoretical Basis Document (ATBD) Cloud Data Products, LaRC 475-00-106, 1.2, 2002. Spang, R., Griessbach, S., Hopfner, M., Dudhia, A., Hurley, J., Siddans, R., Waterfall, A., Remedios, J., and Sembhi, H.: Technical Note: Retrievability of MIPAS cloud parameter, ESA-ITT AO/1-5255/06/I-OL, 2008. Warren, S., Hahn, C., and London, J.: Simultaneous occurrence of different cloud types, J. Clim. Appl. Meteot., 24, 658–667, 1985. Woodbury, G. and McCormick, M.: Global Distributions of Cirrus Clouds Determined from SAGE Data, Geophys. Res. Lett., 10, 1180–1183, 1983. Wylie, D. and Menzel, W.: Two years of cloud cover statistics using VAS, J. Clim. Appl. Meteor., 2, 380–392, 1989. Wylie, D., Menzel, W., Woolf, H., and Strabala, K.: Four Years of Global Cirrus Cloud Statistics Using HIRS, J. Climate, 7, 1972–1986, 1994. Wylie, D., Jackson, D., Menzel, W., and Bates, J.: Trends in Global Cloud Cover in Two Decades of HIRS Observations, J. Climate, 130, 18, 3021–3033, 2005.