Data Set Overview
  =================
    All ALTITUDE data are packaged by periapsis number for each
    aerobraking orbit.  ALTITUDE data are provided in a table labeled
    Pyyyy.tab where 'yyyy' is the four digit periapsis number.
 
 
  Parameters
  ==========
    Altitude:               Units = km
    Latitude:               Units = degrees
    Longitude:              Units = degrees
    Local Solar Time:       Units = N/A
    Longitude of the Sun:   Units = degrees
    Solar Zenith Angle:     Units = degrees
    Density:                Units = kg/km**3
    Sigma Density:          Units = kg/km**3
    Scale Height:           Units = km
    Sigma Scale Height:     Units = km
 
 
  Data
  ====
    For each orbit, ALTITUDE data consist of an 11 by 10 array in the
    file folder Pyyyy.  Each row gives atmospheric characteristics at
    a constant altitude.  When applicable, inbound and outbound legs
    are in separate rows.  The altitude levels going from row 1 to
    row 11 are: periapsis, 1.26 nbar inbound, 1.26 nbar outbound, 130
    km inbound, 130 km outbound, 140 km inbound, 140 km outbound, 150
    km inbound, 150 km outbound, 160 km inbound, 160 km outbound.
    The columns from one to ten are separated as follows: altitude,
    latitude, longitude, local solar time, longitude of the sun,
    solar zenith angle, density, sigma density, scale height, and
    sigma scale height.
 
 
  Processing
  ==========
    Density and density scale heights are provided at reference
    altitudes of periapsis, 1.26 nbar, 130, 140, 150, and 160 km.
    The latter 4 are obtained by a least squares fit to the 40 point
    running mean data sets that span 5 km on either side of a
    reference altitude for both the inbound and outbound portions of
    the orbit.  The values at periapsis are obtained by a similar fit
    to all data within 10km of the periapsis altitude.  See
    [TOLSONETAL1999B].
 
 
  Coordinate System
  =================
    Latitude and longitude are in the IAU Mars Centered Mars
    Equatorial System.  Altitude is above the IAU reference
    ellipsoid, with a=3393.4 km and f=0.0052083 and including
    corrections for (4,4) gravitational potential.

Confidence Level Overview
  =========================
    Standard deviations on density and scale height are based on the
    formal covariance matrix for the linear regression of log density
    and altitude.  Data noise is assumed to be the standard deviation
    of the fit.
 
 
  Review
  ======
    Comparisons were made with operational data sets.  Deviations
    were within expectations founded on archiving analysis that is
    based on (4,4) gravitational potential and numerically integrated
    precision trajectories that were not included in operational
    software.
 
  Data Coverage and Quality
  =========================
    Data coverage during an aerobraking pass has varied throughout
    the mission.  Early in the mission, data were received for 500
    seconds on either side of periapsis.  Later, the data started
    between 200 and 250 seconds before periapsis.  This change was
    made to reduce propulsion usage.  Though this change somewhat
    reduced the accuracy of determining the accelerometer bias, it
    had the advantage of reducing the corruption of the data set with
    thruster firings while still inside the detectable atmosphere.
 
    Not all orbits have yet been included in current archiving data
    sets.  Omitted orbits include orbits where automatic data
    processing procedures did not produce realistic answers.  If
    required, many of these orbits can be recovered by manual
    manipulation of data and data analysis procedures.