Magellan Global Reflectivity Data Record (GREDR) Description

Extracted from the PDS Data Set Catalog File.

  Data Set Description 
  ==================== 

   Global Reflectivity Data Record (GREDR). The power reflection coefficients
   are derived by fitting altimeter echoes from the fan- beam altimetry antenna
   as a function of time to Hagfors' radar backscatter model templates. The
   values are then corrected for the presence of multiple echo peaks and further
   corrected for diffuse scattering using backscatter data obtained by the side-
   looking mode of the Magellan radar. The reflectivities are then filtered to
   remove low-frequency instrument calibration errors, and re-sampled into
   sinusoidal, Mercator, and north and south polar stereographic projections at
   a resolution of about 5x5 kilometers per pixel.
                                                                              
   Each GREDR image pixel is represented by a 8-bit unsigned integer. In
   sinusoidal images, pixels lying outside the domain of the projection are set
   to zero. In all images, pixels with unknown or unmeasured values are also set
   to zero. The remaining values are related to the reflectivity by the
   following equation:
                                                                              
       DN = (REFLECTIVITY * 200) + 1                                          
                                                                              
   See:  Software Interface Specification Document (Peter G. Ford, 1991, Global
   Altimetry and Radiometry Data Records, MIT-MGN-GxDR SIS Version 2.3, 40 p.)
   that is included on GxDR CD-ROMs.
                                                                              
   Note:  There exist photoproducts that are identified as GxDRP (where x is E
   (Emissivity), S (Slope), RE (Reflectivity), or T (Topography)) however, they
   are not generated from the digital GxDR products. They are instead produced
   from the Magellan ARCDR (Altimetry and Radiometry Composite Data Record) data
   files.
                                            
  References
  ==========
  
    Ford, P. G., Global Altimetry and Radiometry Data Record, Project Magellan
    Software Interface Specification Document MIT-MGN- GxDR, 1991 Version 2.3,
    40p."

    Ford, P.G. and G.H. Pettengill, Venus Topography and Kilometer-Scale Slopes,
    JGR, V. 97, pp. 13103-13114, 1992.

    Saunders, R.S., G.H. Pettengill, R.E. Arvidson, W.L. Sjogren, W.T.K.
    Johnson, L. Pieri, The Magellan Venus Radar Mapping Mission, JGR, V. 95, pp.
    8339-8355, 1990.