Monthly averages of several products retrieved from the SSM/I sensors on board
the DMSP satellites have been produced starting in June of 1992.  Images of the
following monthly composite fields are available in this directory.

clw -> Cloud liquid water retrievals from SSM/I (Weng and Grody)
rn1 -> Rainfall retrievals from SSM/I (Hollinger et al.)
rn2 -> Rainfall retrievals from SSM/I (Ferriday and Avery)
rn3 -> Rainfall retrievals from SSM/I (Ferraro and Marks)
wvp -> Precipitable water retrievals from SSM/I (Schluessel and Emery)
mws -> Marine wind speed retrievals from SSM/I (Goodberlet)
nob -> Number of observations per month from SSM/I

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DMSP   -> Defense Meteorological Satellite Program
SSM/I  -> Special Sensor Microwave/Imager

References:

Ferraro, R.R. and G.F. Marks, 1995: The development of SSM/I rain-rate retrieval
  algorithms using ground-based radar measurements, J. Atmos. Oceanici Technol.,
  Vol 12, pp. 755.

Ferriday, J. G. and S. K. Avery, 1994: Passive microwave remote sensing of
  rainfall with SSM/I: Algorithm development and implementation, J. Appl.
  Meteor., Vol 33, pp. 1587-1596. 

Goodberlet, M. A., C. T. Swift, and J. C. Wilkerson, 1989: Remote sensing of
  surface winds with the special sensor microwave/imager, J. Geophys. Res., Vol
  94, pp. 14,547-14,555.

Hollinger, J., R. Lo, and G. Poe, 1987: Special Sensor Microwave/Imager User's
  Guide, Naval Research Laboratory, Washington D.C. 

Schluessel, P., and W. J. Emery, 1990: Atmospheric water vapour over oceans
  from SSM/I measurements, Int. J. of Remote Sensing, Vol 11, pp. 753. 

Weng, F. and N. C. Grody, 1994: Retrieval of cloud liquid water using the
  special sensor microwave imager, J. Geophys. Res., Vol 99, pp. 25,535.