Data Set Overview
    =================
    The Mars Reconnaisance Orbiter (MRO) Gravity Archive Data Collection
    of Science Data Products (SDP) includes data products generated from
    radio occultation, gravity, and surface reflection investigations
    conducted by members of the MRO Gravity Team.

    Gravity SDPs include spherical harmonic models, maps or images
    of those models, and possibly line-of-sight acceleration profiles.
    Groups at the Goddard Space Flight Center (GSFC) under the
    direction of David Smith and at JPL under the direction of
    William Sjogren produced spherical harmonic models, maps, and images.

    The models are derived from a mix of data, including data from
    the missions of Mars Global Surveyor, Mars Odyssey, and Mars
    Reconnaissance Orbiter. These spacecraft have different
    orbit characteristics (primarily mean periapse and apoapsis
    altitudes for these near-polar and near circular orbits)
    which determine their sensitivity to the Mars gravity field.

    The Mars Reconnaissance Orbiter was in an orbit with
    a periapse near 250 km and an apoapsis near 320 km. As with the
    other Mars mapping missions (Mars Global Surveyor
    and Mars Odyssey), periapsis was frozen over the South Pole.
    Aerobraking data are not including in these solutions since
    (a) There is usually no radio tracking of the spacecraft
    available through periapsis, and (b) the frequent firing
    of thrusters during the periapsis passes and the strong
    drag signal will mask any signal from Mars gravity.

    The Mars Global Surveyor spacecraft remained operational
    from 1997 through 2005, spending the bulk of its time
    (after March 1999) in a low-altitude mapping orbit whose
    mean periapsis was 370 km and mean apoapsis was 420 to 430
    km. The Mars Odyssey spacecraft was in a similar orbit
    albeit with slightly higher altitude. An approximately
    two week segment of Mars Odyssey tracking data was
    obtained from the 'transition orbit', an orbit intermediate
    in orbit altitude mean the aerobraking altitude and
    the mapping orbit altitude, with a periapsis near 200 km
    and an apoapsis near 500 km.


    Parameters
    ==========
      Spherical harmonic models are tables of coefficients GM, Cmn,
      and Smn -- as in equation (1) of [TYLERETAL1992].  These can
      be used to represent gravitational potential of Mars, for
      example.  Both ASCII (data type SHA) and binary (data type
      SHB) formats are defined, with the latter being preferred for
      large files which also include covariance terms.  Each file
      contains up to four tables: a header table containing general
      parameters for the model (gravitational constant, its
      uncertainty, degree and order of the field, normalization
      state, reference longitude, and reference latitude); a names
      table, giving the order in which coefficients appear; a
      coefficients table (degree m, order n, coefficients Cmn and
      Smn, and their uncertainties); and a covariances table giving
      the covariances of CijCmn, SijSmn, CijSmn, and SijCmn.

      Radio Science Digital Map files are image representations
      of gravity and other parameters.  Free air gravity, geoid,
      Bouguer anomaly, isostatic anomaly, and topographic values
      may be displayed using this data type.  Data are formatted
      as PDS image objects.

      The Line-of-Sight Acceleration Profile Data Record is a pair
      of PDS tables.  The first table contains header information
      such as time and observing geometry, parameters used in
      deriving acceleration from radio tracking measurements, and
      first-order Keplerian orbit elements.  The second table gives
      spacecraft acceleration versus time.  Also included at each
      time is the spacecraft position in planetocentric coordinates.

    Processing
    ==========
      Spherical harmonic models, maps, and line-of-sight acceleration
      profiles are derived from raw radio tracking data in several
      steps.

     The tracking data are processed in large orbit determination
     programs that integrate the equations of motion (DPODP at JPL
     [MOYER1971], and GEODYN at NASA GSFC [PAVLISETAL2007]), and
     model mathematically the radio science observables (ramped
     Doppler and range data).
     The observations are related to the geophysical parameters
     through the numerical integration and the detailed
     mathematical modeling of the radio science observables, and of
     all forces acting on the spacecraft trajectory, including
     planetary and third body gravity, solar radiation pressure,
     planetary radiation pressure, atmospheric drag, solid body tides,
     and relativity.

     The gravity field coefficients are obtained by accumulating
     normal equations from often hundreds of data arcs, and
     solving these systems of linear equations with thousands of unknowns.
     The unknowns include arc parameters, particular to one data arc (such
     as the spacecraft state, radiation pressure scale factors,
     atmospheric drag scale factors, etc.) and common parameters
     (such as the gravity coefficients, the planetary gravitational
     constant or GM, the Phobos and Deimos gravitational constants,
     and the Mars K2 Love number).
     Radio tracking data are processed in arcs delimited by
     propulsive maneuvers, occultations, etc.

     The Mars orbiting spacecraft perform regular
     angular momentum desaturation (AMD) maneuvers to remove the angular
     momentum that has accumulated in the spacecraft momentum
     wheels. On MRO, these AMD maneuvers occur usually every
     2-3 days, and arcs may be delimited by these maneuvers. AMD
     maneuvers on MGS and Mars Odyssey were much more frequent
     up to several times per day in some cases. In those circumstances
     the AMD's must be modeled in the orbit determination solution
     and solved for empirically along with the other orbital arc
     parameters. The times of the AMD's are specified in the
     small forces files (SFF) that are part of the MRO raw data
     archive.

      Maps of free air gravity and other quantities are generated from
      the spherical harmonic model(s) evaluated at regular grid
      points.

      Line-of-sight acceleration profiles are derived from single arcs
      of radio tracking data.  Doppler residuals with respect to a
      specific spherical harmonic model are spline-fitted; the splines
      are then differentiated analytically to obtain accelerations.

     Useful references which describe the procedures applied in
     general to processing Mars orbiter tracking data include
     [YUANETAL2001], [LEMOINEETAL2001], [KONOPLIVETAL2006].
     [THORNTON&BORDER2003] is a general reference for Orbit Determination.

    Data
    ====
      Data are available online through the Planetary Data System
      (http://pds.nasa.gov). A volume of reduced data was prepared for
      the MRO primary mission and it is expected that a volume will be
      prepared for the extended mission.

      ASCII spherical harmonic models are stored in the SHA directory
      with file names of the form GTsss_nnnnvv_SHA.TAB where

      'G'   denotes the generating institution
                      'J'       for the Jet Propulsion Laboratory
                      'G'       for Goddard Space Flight Center
                      'C'       for Centre National d'Etudes Spatiales
                      'M'       for Massachusetts Institute of Technology
      'T'         indicates the type of data represented
                      'G'       for gravity field
                      'T'       for topography
                      'M'       for magnetic field
      'sss'    is a 3-character modifier specified by the data producer.
               This modifier is used to indicate the source spacecraft or
               project, such as MRO for the Mars Reconnaisance Orbiter.
      '_'      the underscore character is used to delimit modifiers in
               the file name for clarity.

      'nnnnvv'  is a 4- to 6-character modifier specified by the data
               producer.  Among other things, this modifier may be used to
               indicate the target body, whether the SHADR contains primary
               data values as specified by 'T' or uncertainties/errors,
               and/or the version number.  For MRO, this modifier indicates
               the degree and order of the solution for the gravity field,
               topography or magnetic field.
       '_'     the underscore character is used to delimit information in
               the file name for clarity.
       'SHA'   denotes that this is an ASCII file of Spherical Harmonic
               coefficients
       '.TAB'  indicates the data is stored in tabular form.

      Each SHADR file is accompanied by a detached PDS label; that label is
      a file in its own right, having the name GTsss_nnnnvv_SHA.LBL.


      Binary spherical harmonic models are stored in the SHB
      directory with file names of the form GTsss_nnnnvv_SHB.DAT where

      'G'     denotes the generating institution
                      'J'  for the Jet Propulsion Laboratory
                      'G' or Goddard Space Flight Center
                      'C' or Centre National d'Etudes Spatiales
                      'M' for Massachusetts Institute of Technology
      'T'    indicates the type of data represented
                      'G' for gravity field
                      'T' for topography
                      'M' for magnetic field
      'sss'   is a 3-character modifier specified by the data producer.  This
              modifier is used to indicate the source spacecraft or Project,
              such as MRO for the Mars Reconnaissance Orbiter.
      '_'     the underscore character is used to delimit modifiers in the
              file name for clarity.
      'nnnnvv' is a 4- to 6-character modifier specified by the data
              producer.  Among other things, this modifier may be
              used to indicate the target body, whether the SHBDR
              contains primary data values as specified by 'T' or
              uncertainties/errors, and/or the version number. For MRO, this
              modifier indicates the degree and order of the solution for the
              gravity field, topography or magnetic field.
      '_'     the underscore character is used to delimit modifiers in the
              file name for clarity.
      'SHB'   denotes that this is a Binary file of Spherical
              Harmonic coefficients and error covariance information
      '.DAT'  indicates the data is stored in binary format.

      Each SHBDR file is accompanied by a detached PDS label; that
      label is a file in its own right, having the name  GTsss_nnnnvv_SHB.LBL.


      Radio Science Digital Map products are stored in the RADMAP
      directory with file names of the form  GTsss_ffff_nnnn_cccc.IMG where

      'G'       denotes the generating institution
                      'A'      for Arizona State University
                      'J'      for the Jet Propulsion Laboratory
                      'G'      for Goddard Space Flight Center
                      'C'      for Centre National d'Etudes Spatiales
                      'S'      for Stanford University
      'T'       indicates the type of mission data represented
                      'G' for gravity field
                      'T' for topography
                      'M' for magnetic field
      'sss'     is a 3-character modifier specified by the data
                producer. This modifier is used to indicate the source
                spacecraft or project, such as MRO for the Mars
                Reconnaisance Orbiter.
      '_'       the underscore character is used to delimit information
                in the file name for clarity.
      'ffff'    is a 4-character modifier specified by the data
                producer to indicate the degree and order of the
                solution for the gravity field, topography or magnetic
                field.
      '_'       the underscore character is used to delimit information
                in the file name for clarity.
      'nnnn'    is a 4- to 8-character modifier indicating the type
                of data represented
                      'ANOM'      for free air gravity anomalies
                      'ANOMERR'   for free air gravity anomaly
                                  errors (1)
                      'GEOID'     for geoid
                      'GEOIDERR'  for geoid errors (1)
                      'BOUG'      for Bouguer anomaly
                      'ISOS'      for isostatic anomaly
                      'TOPO'      for topography
                      'MAGF'      for magnetic field

               (1) Geoid and gravity anomaly errors are computed
                   from a mapping of the error covariance matrix
                   of the gravity field solution.

        '_'     the underscore character is used to delimit information
                in the file name for clarity.

        'cccc'  is a 4-character modifier specified by the data producer
                to indicate the degree and order to which the potential
                solution (gravity, topography or magnetic field) has
                been evaluated. In the case of the error maps for the
                gravity anomalies or geoid error, this field indicates to
                which maximum degree and order the error covariance was
                used to propagate the spatial errors

        '.IMG'  indicates the data is stored as an image.


      Each RSDMAP file is accompanied by a detached PDS label; that label is a
      file in its own right with name GTsss_ffff_nnnn_cccc.LBL

    Coordinate System
    =================
   MRO Gravity SDP files use a Mars centered body-fixed coordinate
   system with positive east longitude.

   Gravity models are defined in the Mars coordinate system defined
   by [KONOPLIVETAL2006]. This coordinate system supersedes the
   IAU 1991 and IAU 2000 coordinate systems used for most previous
   Mars gravity models.

   See labels of specific gravity products for details.

    Software
    ========
      None.


    Media/Format
    ============
      This data set is stored online at the Planetary Data System
      (http://pds.nasa.gov/) and may be downloaded using a web browser
      or FTP software. A copy may be requested on physical media if
      downloading is not possible. The Planetary Data System maintains
      backup copies of this data set on various media.

Overview
    ========
      Data in this archive have been reduced as part of mission data
      analysis activities of the MRO Gravity Team.  Products of questionable
      validity have been flagged or omitted.


    Review
    ======
      This archival data set was reviewed by the MRO Gravity
      Team prior to submission to the Planetary Data System (PDS).
      Data set design, documentation, and sample products have passed
      a PDS peer review.

      Prior to creation of the final version of the archival data
      set, key elements of the archive were distributed for
      preliminary review.  These included electronic versions of
      example PDS labels, example data files, CATALOG files, and
      Software Interface Specifications.  These materials were
      distributed to PDS personnel, the experiment investigator,
      and others, as appropriate.


    Data Coverage and Quality
    =========================

      This volume contains gravity models and maps generated from Viking 1
      Lander, Pathfinder, MGS, Odyssey, and MRO data collected through
      the end of October 2008.  The Viking and Mariner 9 orbiter data were
      not included in this delivery as this data did not seem to any more
      information for the gravity field. The MRO data included tracking
      results from Transition Orbit and Mapping Orbit phases.  All useful
      MGS tracking data collected prior to the loss of the spacecraft in
      Nov. 2006 was used. Odyssey data included tracking data from
      Transition Orbit and Mapping Orbit phases.

      JGMRO_095A_SHA.TAB is an ASCII file of coefficients and related data
      for a 95th degree and order Mars static gravity field produced at the
      Jet Propulsion Laboratory.  The model used is described in the file's
      detached label.

      JGMRO_095A_SHB.DAT is a binary file of covariances and related data
      for a 95th degree and order Mars static gravity field produced at the
      Jet Propulsion Laboratory.  The model used is described in the file's
      detached label.

      JGMRO_O95A_GEOIDERR_085.IMG is a digital map of the Mars geoid formal
      uncertainty derived from the covariance matrix for the spherical
      harmonic coefficients of the JPL MRO95A Mars gravity field. The
      JGMRO_O95A_GEOIDERR_085 geoid error is computed from a truncated
      MRO95A covariance (from degree 2 up to degree 85). The map is
      produced by Alex Konopliv at JPL for the MRO Gravity Science Team.

      JGMRO_O95A_GEOID_085.IMG is a digital map of the Mars geoid derived
      from the JPL MRO95A spherical harmonic model of the Mars gravity
      field. Each point is the Mars geoid height in meters above a
      reference ellipsoid (semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3,
      and rotation rate = 7.088218081e-5 rad/s). The JGMRO_095A_GEOID85
      geoid is computed from a truncated MRO95A solution (from degree 2 up
      to degree 85). The map is produced by Alex Konopliv at JPL
      for the MRO Gravity Science Team.

      JGMRO_095A_ANOM_085.IMG is a digital map of the gravity anomaly
      derived from the JPL MRO95A model of the Mars gravity field.  Each
      point gives the Mars gravity anomaly in milligals, which is the
      difference of the model gravity on the geoid from the normal gravity
      on a reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_095A_ANOM85 gravity
      anomaly is computed from a truncated MRO95A solution (from degree 2
      up to degree 85). The map is produced by Alex Konopliv at JPL for the
      MRO Gravity Science Team.

      JGMRO_095A_ANOMERR_085.IMG is a digital map of the Mars gravity
      anomaly formal uncertainty derived from the covariance matrix for
      the spherical harmonic coefficients of the JPL MRO95A Mars gravity
      field. Each point gives the Mars gravity anomaly error in milligals,
      which is the error of the model gravity on the geoid defined by the
      reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_095A_ANOM85_ERR
      gravity anomaly is computed from a truncated MRO95A solution
      (from degree 2 up to degree 85). The map is produced by Alex Konopliv
      at JPL for the MRO Gravity Science Team.

      JGMRO_110B2_GEOIDERR_095.IMG is a digital map of the Mars geoid formal
      uncertainty derived from the covariance matrix for the spherical
      harmonic coefficients of the JPL MR110B2 Mars gravity field. The
      JGMRO_110B2_GEOIDERR_095 geoid error is computed from a truncated
      MR110B2 covariance (from degree 2 up to degree 95). The map is
      produced by Alex Konopliv at JPL for the MRO Gravity Science Team.

      JGMRO_110B2_GEOID_095.IMG is a digital map of the Mars geoid derived
      from the JPL MR110B2 spherical harmonic model of the Mars gravity
      field. Each point is the Mars geoid height in meters above a
      reference ellipsoid (semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3,
      and rotation rate = 7.088218081e-5 rad/s). The JGMRO_110B2_GEOID_095
      geoid is computed from a truncated MR110B2 solution (from degree 2 up
      to degree 95). The map is produced by Alex Konopliv at JPL
      for the MRO Gravity Science Team.

      JGMRO_110B_GEOIDERR_095.IMG is a digital map of the Mars geoid formal
      uncertainty derived from the covariance matrix for the spherical
      harmonic coefficients of the JPL MR110B Mars gravity field. The
      JGMRO_110B_GEOIDERR_095 geoid error is computed from a truncated
      MR110B covariance (from degree 2 up to degree 95). The map is
      produced by Alex Konopliv at JPL for the MRO Gravity Science Team.

      JGMRO_110B_GEOID_095.IMG is a digital map of the Mars geoid derived
      from the JPL MR110B spherical harmonic model of the Mars gravity
      field. Each point is the Mars geoid height in meters above a
      reference ellipsoid (semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3,
      and rotation rate = 7.088218081e-5 rad/s). The JGMRO_110B_GEOID_095
      geoid is computed from a truncated MR110B solution (from degree 2 up
      to degree 95). The map is produced by Alex Konopliv at JPL
      for the MRO Gravity Science Team.

      JGMRO_110B2_ANOM_095.IMG is a digital map of the gravity anomaly
      derived from the JPL MRO110B2 model of the Mars gravity field.  Each
      point gives the Mars gravity anomaly in milligals, which is the
      difference of the model gravity on the geoid from the normal gravity
      on a reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_110B2_ANOM_095 gravity
      anomaly is computed from a truncated MRO110B2 solution (from degree 2
      up to degree 95). The map is produced by Alex Konopliv at JPL for the
      MRO Gravity Science Team.

      JGMRO_110B2_ANOMERR_095.IMG is a digital map of the Mars gravity
      anomaly formal uncertainty derived from the covariance matrix for
      the spherical harmonic coefficients of the JPL MRO110B2 Mars gravity
      field. Each point gives the Mars gravity anomaly error in milligals,
      which is the error of the model gravity on the geoid defined by the
      reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_110B2_ANOMERR_095
      gravity anomaly is computed from a truncated MRO110B2 solution
      (from degree 2 up to degree 95). The map is produced by Alex Konopliv
      at JPL for the MRO Gravity Science Team.

      JGMRO_110B_ANOM_095.IMG is a digital map of the gravity anomaly
      derived from the JPL MRO110B model of the Mars gravity field.  Each
      point gives the Mars gravity anomaly in milligals, which is the
      difference of the model gravity on the geoid from the normal gravity
      on a reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_110B_ANOM_095 gravity
      anomaly is computed from a truncated MRO110B solution (from degree 2
      up to degree 95). The map is produced by Alex Konopliv at JPL for the
      MRO Gravity Science Team.

      JGMRO_110B_ANOMERR_095.IMG is a digital map of the Mars gravity
      anomaly formal uncertainty derived from the covariance matrix for
      the spherical harmonic coefficients of the JPL MRO110B Mars gravity
      field. Each point gives the Mars gravity anomaly error in milligals,
      which is the error of the model gravity on the geoid defined by the
      reference ellipsoid with semi-major-axis = 3397.0 km,
      GM = 42828.35796 km**3/s**2, flattening = 5.079304192e-3, and
      rotation rate = 7.088218081e-5 rad/s. The JGMRO_110B_ANOMERR_095
      gravity anomaly is computed from a truncated MRO110B solution
      (from degree 2 up to degree 95). The map is produced by Alex Konopliv
      at JPL for the MRO Gravity Science Team.

    Limitations
    ===========
      The limitations in this data set follow from the quality of
      the execution, which is described above under Data Coverage
      and Quality.