This dataset contains the TIROS Operational Vertical Sounder (TOVS)
                                    level 3 geophysical parameters derived using the physical retrieval
                                    method of Susskind et al. (1984) and processed by the Satellite Data
                                    Utilization Office of the Goddard Laboratory for Atmospheres at
                                    NASA/GSFC. This method, which is hydrodynamic model- and a priori
                                    data-dependent, is designated as the so-called Path A scheme by the
                                    TOVS Pathfinder Science Working Group. The 20 channel High resolution
                                    Infrared Radiation Sounder 2 (HIRS2) and the 4 channel Microwave
                                    Sounding Unit (MSU) aboard the NOAA-xx series of Polar Orbiting
                                    Satellites are used to produce global fields of the 3-dimensional
                                    temperature-moisture structure of the atmosphere. In addition to
                                    profiles of temperature and moisture, the HIRS2/MSU data are used to
                                    derive important quantities such as land and sea surface temperature,
                                    outgoing longwave radiation, cloud fraction, cloudtop height, total
                                    ozone overburden and precipitation estimates.
                                    
                                    The Path A system steps through an interactive
                                    forecast-retrieval-analysis cycle. In each 6 hour synoptic period, a
                                    2nd order General Circulation Model (Takacs et al., 1994) is used to
                                    generate the 6 hour forecast fields of temperature and humidity. These
                                    global fields are used as the first guess for all soundings occuring
                                    within a 6 hour time window centered upon the forecast time. These
                                    retrievals are then assimilated with all available insitu measurements
                                    (such as radiosonde and ship reports) in the 6 hour interval using an
                                    Optimal Interpolation (OI) analysis scheme developed by the Data
                                    Assimilation Office of the Goddard Laboratory for Atmospheres. This
                                    analysis is then used to specify the initial conditions for the next 6
                                    hour forecast, thus completing the cycle.
                                    
                                    The retrieval algorithm itself is a physical method based on the
                                    iterative relaxation technique originally proposed by Chahine
                                    (1968). The basic approach consists of modifying the temperature
                                    profile from the previous iteration by an amount proportional to the
                                    difference between the observed brightness temperatures and the
                                    brightness temperatures computed from the trial parameters using the
                                    full radiative transfer equation applied at the observed satellite
                                    zenith angle. For the case of the temperature profile, the updated
                                    layer mean temperatures are given as a linear combination of
                                    multichannel brightness temperature differences with the coefficients
                                    given by the channel weighting functions. Constraints are imposed upon
                                    the solution in order to ensure stability and convergence of...