Dawn Ceres Gravity Science Derived Data Bundle Description
==========================================================

References
==========

- Asmar, S.W., R.G. Herrera, and T. Priest, Radio Science Handbook, 
JPL D-7938 Vol. 6, Jet Propulsion Laboratory, Pasadena, CA, 1995.

- Asmar, S.W., and N.A. Renzetti, The Deep Space Network as an 
Instrument for Radio Science Research, Jet Propulsion Laboratory 
Publication 80-93, Rev. 1, 1993.

- Deep Space Network Telecommunications Link Design Handbook, 
JPL-E-810-005 Jet Propulsion Laboratory, Pasadena, CA, 2013.

- H.&B.S. Jeffreys, Methods of Mathematical Physics, Third Edition. 
Cambridge University Press, 1962, 269 p.

- Konopliv, A.S., Asmar, S.W., Bills, B.G., Mastrodemos, N., Park, R.S., 
Raymond, C.A., Smith D.E., and M.T. Zuber, The Dawn Gravity Investigation 
at Vesta and Ceres, Space Science Reviews, 163, 461-486, 2011.

- Konopliv, A.S., S.W. Asmar, R.S. Park, B.G. Bills, F. Centinello, 
A.B. Chamberlin, A. Ermakov, R.W. Gaskell, N. Rambaux, C.A. Raymond, 
C.T. Russel, D.E. Smith, P. Tricarico, and M.T. Zuber, The Vesta gravity 
field, spin pole and rotation period, landmark positions, and ephemeris 
from the Dawn tracking and optical data, Icarus, 
doi:10.1016/j.icarus.2013.09.005, 2014.

- Moyer, T.D., Mathematical Formulation of the Double-Precision Orbit
Determination Program (DPODP), TR 32-1527, Jet Propulsion Laboratory,
Pasadena, CA, 1971.

- Park, R.S., A.S. Konopliv, B.G. Bills, N. Rambaux, J.C. Castillo-Rogez,
C.A. Raymond, A.T. Vaughan, A.I. Ermakov, M.T. Zuber, R.R. Fu, M.J.
Toplis, C.T. Russell, A. Nathues and F. Preusker, A partially
differentiated interior for (1) Ceres deduced from its gravity field
and shape, Nature 537, 515-517, doi:10.1038/nature18955, 2016.

- Park, R.S., A.T. Vaughan, A.S. Konopliv, A.I. Ermakov, N. Mastrodemos, 
J.C. Castillo-Rogez, S.P. Joy, A. Nathues, C.A. Polanskey, M.D. Rayman, 
J.E. Riedel, C.A. Raymond, C.T. Russell, and M.T. Zuber, High-resolution 
shape model of Ceres from stereophotoclinometry using Dawn Imaging Data,
Icarus, Volume 319, 812-827, doi:10.1016/j.icarus.2018.10.024, 2019.

- Park, R.S., A.S. Konopliv, A.I. Ermakov, J.C. Castillo-Rogez, R.R. Fu, 
K.H.G. Hughson, T.H. Prettyman, C.A. Raymond, J.E.C. Scully, H.G. Sizemore, 
M.M. Sori, A.T. Vaughan, G. Mitri, B.E. Schmidt, and C.T. Russell, Evidence 
of non-uniform crust of Ceres from Dawn's high-resolution gravity data. 
Nature Astronomy 4, 748-755 (2020). https://doi.org/10.1038/s41550-020-1019-1

- Russell, C.T., and C.A. Raymond, The Dawn Mission to Vesta and Ceres, 
Space Science Reviews, 163, 3-23, 2011.

- Thornton, C.L. and J.S. Border, Radiometric Tracking Techniques for 
Deep Space Navigation, John Wiley and Sons, Hoboken, NY, 2003.

- Tyler, G.L., G. Balmino, D.P. Hinson, W.L. Sjogren, D.E. Smith, R. Woo, 
S.W. Asmar, M.J. Connally, C.L. Hamilton, and R.A. Simpson, Radio Science
Investigations with Mars Observer, Journal of Geophysical Research, 97, 
7759-7779, 1992.

Collections Overview
====================

The Dawn Ceres Gravity Archive Data Collection of Science Data Products (SDP)
includes data products generated from gravity investigations
conducted by members of the Dawn Gravity Team while the spacecraft
was in orbit around the asteroid Ceres. Radio measurements were made
using the Dawn spacecraft and Earth-based stations of the NASA Deep
Space Network (DSN).

Gravity SDPs include spherical harmonic models of Ceres' gravity field, 
maps or images of those models, and possibly line-of-sight acceleration 
profiles. A group at the Jet Propulsion Laboratory JPL under the direction 
of Ryan Park produced spherical harmonic models and maps. These results 
were derived from raw radio tracking data.

At Ceres, the mission was divided into different science orbits.
All the orbits were polar. The RC3 orbit was conducted at an alitutde
of 13500 km, The Survey orbit was performed at a nominal altitude of
4400 km. The High Altitude Mapping Orbit, or HAMO, was performed
at a nominal altitude of 1450 km. The Low Altitude Mapping Orbit,
or LAMO, was performed at a nominal altitude of 375 km. An extended
mission phase XMO1 was conducted at the same altitude as LAMO.
Additional extended mission phases of XMO2, XMO3 and XMO4 were
conducted at altitudes of 1480 km, 7520-9350 km, and 20000 km.

Between these science orbits, the spacecraft as in a transfer phase
using the electric ion engines (Russell & Raymond, 2011).

Parameters
==========

Spherical harmonic models are tables of coefficients GM, Cmn,
and Smn -- as in equation (1) of (Tyler et al., 1992). These can
be used to represent gravitational potential of Ceres, for
example. ASCII (data type SHA) formatted spherical harmonics
are defined. 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).

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.

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
(Moyer, 1971)), 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, where applicable.

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). Radio tracking data are processed in arcs delimited by 
propulsive maneuvers, occultations, etc. 

The spacecraft periodically performed angular momentum
desaturation maneuvers. These maneuvers allowed the reaction
wheels to spin down to avoid damage, but they had be countered
the use of thrusters. Arcs may be delimited by these maneuvers.
The details of each of these maneuvers specified in the small forces
file of the Dawn Ceres Gravity Science Raw Data Archive.

Useful references which describe the procedures applied in
general to processing Ceres orbiter tracking data include
(Park et al., 2016).

(Thornton & Border, 2003) is a general reference for Orbit Determination.

Data
====
Data are available online through the Planetary Data System
(http://pds.nasa.gov).

ASCII spherical harmonic models are stored in the data-shadr collection
with file names of the form GTsss_nnnnvv_SHA.TAB where:

  'G'       denotes the generating institution
                  'J' for the Jet Propulsion Laboratory
  'T'          indicates the type of data represented
                  'G' for gravity field
  'DWN'    all products use this.
  '_'       the underscore character is used to delimit modifiers in
            the file name for clarity.
  'nnnvvv'  is a 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 Dawn, this specifies the
            degree and version of the 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.xml.

Binary spherical harmonic models are stored in the data-shbdr/ directory,
with file names of the form GTsss_nnnnvv_SHB.DAT where:

  'G'       denotes the generating institution
                  'J' for the Jet Propulsion Laboratory
  'T'          indicates the type of data represented
                  'G' for gravity field
  'DWN'    all products use this.
  '_'       the underscore character is used to delimit modifiers in
            the file name for clarity.
  'nnnvvv'  is a 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 Dawn, this specifies the
            degree and version of the field.
   '_'      the underscore character is used to delimit information in
            the file name for clarity.
   'SHB'    denotes that this is an Binary file of Spherical Harmonic
            coefficients and covariance
   '.DAT'   indicates the data is stored in a binary data file.

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.xml.

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

  'G'       denotes the generating institution
                  'J' for the Jet Propulsion Laboratory
  'T'       indicates the type of mission data represented
                  'G' for gravity field
  'DWN'    all products use this.
  '_'       the underscore character is used to delimit information
            in the file name for clarity.
  'ffff'    is a 4- to 6-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)
                  'BOU'      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.xml.



SHADR Files Descriptions
------------------------


# SHADR Header Table Description

The SHADR header includes descriptive information about the 
spherical harmonic coefficients which follow in SHADR Coefficients 
Table. The header consists of a single record of eight (delimited)
data columns requiring 137 bytes, a pad of 105 unspecified ASCII 
characters, an ASCII carriage-return, and an ASCII line-feed.


# SHADR Coefficients Table Description

The SHADR coefficients table contains the coefficients for the 
spherical harmonic model. Each row in the table contains the 
degree index m, the order index n, the coefficients Cmn and Smn, 
and the uncertainties in Cmn and Smn.  The (delimited) data
require 107 ASCII characters; these are followed by a pad of 13 
unspecified ASCII characters, an ASCII carriage-return, and an 
ASCII line-feed.



# CERES70E SHADR File Description

This file contains coefficients and related data for the                      
CERES70E spherical harmonic gravity model of Ceres.                           
                                                                              
CERES70E is a 70th degree and order model obtained from radiometric           
tracking (Doppler and range data) and optical landmarks of the                
Dawn spacecraft in orbit about Ceres. The gravity model includes              
Prime Mission data from the Approach phase to the end of the LAMO             
orbit. The data span is Feb 2, 2015 to Sept 2, 2016. Optical                  
landmark tracking is included for LAMO and HAMO phases. The Doppler           
and landmark tracking is also included for the Extended Mission-2             
phase from June 6, 2018 to October 31, 2018. This gravity field is            
consistent with the final SPC shape model of Ceres (Park et al.               
High resolution shape model of Ceres from stereophotoclinometry               
using Dawn imaging data, Icarus, 2019). More details can be found in          
Park, R.S., Konopliv, A.S., Ermakov, A.I. et al.                              
Evidence of non-uniform crust of Ceres from Dawn's                            
high-resolution gravity data. Nat Astron 4, 748-755 (2020).                   
https://doi.org/10.1038/s41550-020-1019-1                                     
                                                                              
Some details describing this model are:                                       
   The spherical harmonic coefficients are fully normalized.                  
   The associated GM = 62.628896902 km^3/s^2                                  
   The reference radius = 470.0 km                                            
   The Ceres-fixed reference frame prime meridian and pole                    
      location in IAU coordinates are fixed to CERES18D values:               
         Right ascension = 291.42763 degrees                                  
         RA rate         =   0.0 degrees/cty                                  
         Declination     =  66.76033 degrees                                  
         Dec rate        =   0.0 degrees/cty                                  
         Prime Meridian  = 170.309 degrees                                    
         Rotation rate   = 952.1532635 degrees/day                            
   The pole location, W0 and spin rate were determined in the CERES18D        
   gravity field by fixing the y-value of the Kait landmark to zero.          
   The uncertainties of the pole for CERES18D solution are                    
         Right ascension = 0.0002 degrees                                     
         Declination     = 0.0002 degrees                                     
   The gravity field is constrained using a variable surface                  
   acceleration constraint based upon the degree strength of the              
   gravity field for each longitude and latitude location.                    
                                                                              
Observations for the gravity field consist of Doppler and                     
range measurements from Deep Space Network (DSN) tracking.                    
                                                                              
The count time for the Doppler observations is 60 seconds.                    
The typical accuracy for the Doppler is 0.02-0.03 mm/s for the                
60 second sample time. The range accuracy is about 1-2 meters                 
and is limited by the station calibration accuracy. The actual                
rms scatter is less than 0.3 meters in spacecraft position.                   
                                                                              
This product is a set of two ASCII tables: a header table and                 
a coefficients table with 5037 coefficients and a GM value.                   
Definitions of the tables follow.                                             
                                                                              
The CERES70E gravity model is delivered as a Spherical Harmonics              
Gravity ASCII Data Record (SHADR) and is produced by the JPL                 
Dawn Gravity Science Team (Alex Konopliv, Ryan Park, Sami Asmar). 



# CERES70E_ISOSIG SHADR File Description

This file contains coefficients and related data for the
CERES70E spherical harmonic gravity model of Ceres.

CERES70E is a 70th degree and order model obtained from radiometric
tracking (Doppler and range data) and optical landmarks of the
Dawn spacecraft in orbit about Ceres. The gravity model includes
Prime Mission data from the Approach phase to the end of the LAMO
orbit. The data span is Feb 2, 2015 to Sept 2, 2016. Optical
landmark tracking is included for LAMO and HAMO phases. The Doppler
and landmark tracking is also included for the Extended Mission-2
phase from June 6, 2018 to October 31, 2018. This gravity field is
consistent with the final SPC shape model of Ceres (Park et al.
High resolution shape model of Ceres from stereophotoclinometry
using Dawn imaging data, Icarus, 2019). More details can be found in
Park, R.S., Konopliv, A.S., Ermakov, A.I. et al.
Evidence of non-uniform crust of Ceres from Dawn's
high-resolution gravity data. Nat Astron 4, 748-755 (2020).
https://doi.org/10.1038/s41550-020-1019-1

Some details describing this model are:
   The spherical harmonic coefficients are fully normalized.
   The associated GM = 62.628896902 km^3/s^2
   The reference radius = 470.0 km
   The Ceres-fixed reference frame prime meridian and pole
      location in IAU coordinates are fixed to CERES18D values:
         Right ascension = 291.42763 degrees
         RA rate         =   0.0 degrees/cty
         Declination     =  66.76033 degrees
         Dec rate        =   0.0 degrees/cty
         Prime Meridian  = 170.309 degrees
         Rotation rate   = 952.1532635 degrees/day
   The pole location, W0 and spin rate were determined in the CERES18D
   gravity field by fixing the y-value of the Kait landmark to zero.
   The uncertainties of the pole for CERES18D solution are
         Right ascension = 0.0002 degrees
         Declination     = 0.0002 degrees
   The gravity field is constrained using a variable surface
   acceleration constraint based upon the degree strength of the
   gravity field for each longitude and latitude location.

Observations for the gravity field consist of Doppler and
range measurements from Deep Space Network (DSN) tracking.

The count time for the Doppler observations is 60 seconds.
The typical accuracy for the Doppler is 0.02-0.03 mm/s for the
60 second sample time. The range accuracy is about 1-2 meters
and is limited by the station calibration accuracy. The actual
rms scatter is less than 0.3 meters in spacecraft position.

This product is a set of two ASCII tables: a header table and
a coefficients table with 5037 coefficients and a GM value.
Definitions of the tables follow.

The CERES70E gravity model is delivered as a Spherical Harmonics
Gravity ASCII Data Record (SHADR) and is produced by the JPL
Dawn Gravity Science Team (Alex Konopliv, Ryan Park, Sami Asmar).



# CERES70E_KAULA SHADR File Description

This file contains coefficients and related data for the                      
CERES70E_KAULA spherical harmonic gravity model of Ceres.                     
                                                                              
CERES70E_KAULA is a 70th degree and order model obtained from radiometric     
tracking (Doppler and range data) and optical landmarks of the                
Dawn spacecraft in orbit about Ceres. The gravity model includes              
Prime Mission data from the Approach phase to the end of the LAMO             
orbit. The data span is Feb 2, 2015 to Sept 2, 2016. Optical                  
landmark tracking is included for LAMO and HAMO phases. The Doppler           
and landmark tracking is also included for the Extended Mission-2             
phase from June 6, 2018 to October 31, 2018. This gravity field is            
consistent with the final SPC shape model of Ceres (Park et al.               
High resolution shape model of Ceres from stereophotoclinometry               
using Dawn imaging data, Icarus, 2019). More details can be found in          
Park, R.S., Konopliv, A.S., Ermakov, A.I. et al.                              
Evidence of non-uniform crust of Ceres from Dawn's                            
high-resolution gravity data. Nat Astron 4, 748-755 (2020).                   
https://doi.org/10.1038/s41550-020-1019-1                                     
                                                                              
Some details describing this model are:                                       
   The spherical harmonic coefficients are fully normalized.                  
   The associated GM = 62.6289111207 km^3/s^2                                 
   The reference radius = 470.0 km                                            
   The Ceres-fixed reference frame prime meridian and pole                    
      location in IAU coordinates are fixed to CERES18D values:               
         Right ascension = 291.42763 degrees                                  
         RA rate         =   0.0 degrees/cty                                  
         Declination     =  66.76033 degrees                                  
         Dec rate        =   0.0 degrees/cty                                  
         Prime Meridian  = 170.309 degrees                                    
         Rotation rate   = 952.1532635 degrees/day                            
   The pole location, W0 and spin rate were determined in the CERES18D        
   gravity field by fixing the y-value of the Kait landmark to zero.          
   The uncertainties of the pole for CERES18D solution are                    
         Right ascension = 0.0002 degrees                                     
         Declination     = 0.0002 degrees                                     
   The gravity field is constrained using a Kaula power law                   
   constraint of 0.0012/n^2.                                                  
                                                                              
Observations for the gravity field consist of Doppler and                     
range measurements from Deep Space Network (DSN) tracking.                    
                                                                              
The count time for the Doppler observations is 60 seconds.                    
The typical accuracy for the Doppler is 0.02-0.03 mm/s for the                
60 second sample time. The range accuracy is about 1-2 meters                 
and is limited by the station calibration accuracy. The actual                
rms scatter is less than 0.3 meters in spacecraft position.                   
                                                                              
This product is a set of two ASCII tables: a header table and                 
a coefficients table with 5037 coefficients and a GM value.                   
Definitions of the tables follow.                                             
                                                                              
The CERES70E_KAULA gravity model is delivered as a Spherical Harmonics        
Gravity ASCII Data Record (SHADR) and is produced by the JPL                 
Dawn Gravity Science Team (Alex Konopliv, Ryan Park, Sami Asmar).

# CERES18D Description

This file contains coefficients and related data for the                      
CERES18D spherical harmonic gravity model of Ceres.                           
                                                                              
CERES18D is a 18th degree and order model obtained from radiometric           
tracking (Doppler and range data) and optical landmarks of the                
Dawn spacecraft in orbit about Ceres. The gravity model includes              
data from the Approach phase to the end of the LAMO orbit.                    
The data span is Feb 2, 2015 to Sept 2, 2016. Optical landmark                
tracking is included for all phases. This gravity field is                    
consistent with the final SPC shape model of Ceres (Park et al.               
High resolution shape model of Ceres from stereophotoclinometry               
using Dawn imaging data, submitted to Icarus, 2018).                          
                                                                              
Some details describing this model are:                                       
   The spherical harmonic coefficients are fully normalized.                  
   The associated GM = 62.6290536121 km^3/s^2                                 
   The reference radius = 470.0 km                                            
   The Ceres-fixed reference frame prime meridian and pole                    
      location in IAU coordinates is given by                                 
         Right ascension = 291.42763 degrees (estimated)                      
         RA rate         =   0.0 degrees/cty (fixed)                          
         Declination     =  66.76033 degrees (estimated)                      
         Dec rate        =   0.0 degrees/cty (fixed)                          
         Prime Meridian  = 170.309 degrees (estimated)                        
         Rotation rate   = 952.1532635 degrees/day (estimated)                
   The pole location, W0 and spin rate are estimated jointly with the         
   gravity field by fixing the y-value of the Kait landmark to zero.          
   The uncertainties of the pole for this solution are                        
         Right ascension = 0.0002 degrees                                     
         Declination     = 0.0002 degrees                                     
   Note ceres18d is similar to ceres18c version 2 of the gravity field        
   which has the corrected location of the kait crater. This is a             
   rotation of -0.064074 deg about the z-axis versus the previous             
   version of the gravity field.                                              
                                                                              
Observations for the gravity field consist of Doppler and                     
range measurements from Deep Space Network (DSN) tracking.                    
                                                                              
The count time for the Doppler observations is 60 seconds.                    
The typical accuracy for the Doppler is 0.02-0.03 mm/s for the                
60 second sample time. The range accuracy is about 1-2 meters                 
and is limited by the station calibration accuracy. The actual                
rms scatter is less than 0.3 meters in spacecraft position.                   
                                                                              
This product is a set of two ASCII tables: a header table and                 
a coefficients table with 357 coefficients and a GM value.                    
Definitions of the tables follow.                                             
                                                                              
Note: the defined constant uncertainty (in this case, the                     
gravitational constant GM) is 1-sigma definition and is rounded.              
The additional zeros at the end are data formatting to be                     
consistent with SHADR files in other gravity field archives. The              
SHBDR file contains a GM uncertainty that is not rounded.                     
                                                                              
The CERES18D gravity model is delivered as a Spherical Harmonics              
Gravity ASCII Data Record (SHADR) and is produced by the JPL                 
Dawn Gravity Science Team (Alex Konopliv, Ryan Park, Sami Asmar).



SHBDR Files Descriptions
------------------------


# SHBDR Header Table Description

The SHBDR Header includes                     
descriptive information about the spherical harmonic   
coefficients which follow in SHBDR_COEFFICIENTS_TABLE. 
The header consists of a single record of nine data    
columns requiring 56 bytes.  The Header is followed by 
a pad of binary integer zeroes to ensure alignment     
with RECORD_BYTES.


# SHBDR Names Table

The SHBDR Names Table                           
contains names for the solution parameters (including    
gravity field coefficients) which will follow in         
SHBDR_COEFFICIENTS_TABLE.  The order of the names        
in SHBDR_NAMES_TABLE corresponds identically to the      
order of the parameters in SHBDR_COEFFICIENTS_TABLE.     
Each coefficient  name is of the form  Cij  or  Sij      
where  i  is the degree of the coefficient and  j  is    
the order of the coefficient.  Both indices are three-   
digit zero-filled right-justified ASCII character strings
(for example,  C010005  for the 10th degree 5th order C  
coefficient, or  S002001  for the 2nd degree 1st order   
S  coefficient).  The eighth byte in the table is an     
ASCII blank used to ensure that the row length           
is equal to RECORD_BYTES.  Names of other solution       
parameters are limited to 8 ASCII characters; if less    
than 8, they will be left-justified and padded with      
ASCII blanks.  The Names Table itself will be padded     
with ASCII blanks, if necessary, so that its length is   
an integral multiple of RECORD_BYTES.


# SHBDR Coefficients Table

The SHBDR Coefficients Table                    
contains the coefficients and other solution parameters 
for the spherical harmonic model.  The order of the     
coefficients in this table corresponds exactly to the   
order of the coefficient and parameter names in         
SHBDR_NAMES_TABLE.  The SHBDR Coefficients Table will be
padded with double precision DATA_TYPE zeroes so that   
its total length is an integral multiple of RECORD_BYTES.


# SHBDR Covariance Table

The SHBDR Covariance Table                      
contains the covariances for the spherical harmonic model
coefficients and other solution parameters.  The order of
the covariances in this table is defined as columnwise   
vector storage of the upper triangular matrix formed by  
the product of the SHBDR Names Table with its transpose. 
For example, if the Names Table has four entries  A, B,  
C, and D,  then the covariances are given by the column  
vectors in the upper triangular matrix of                

| A | [ A B C D ] = | AA AB AC AD |
| B |               | BA BB BC BD |
| C |               | CA CB CC CD |
| D |               | DA DB DC DD |

That is, the covariance table will list (in this order)
AA, AB, BB, AC, BC, CC, AD, BD, CD, and DD.            
The SHBDR Covariance Table will be padded with double  
precision DATA_TYPE zeroes so that its total length is 
an integral multiple of RECORD_BYTES.



# JGDWN_CER18D_SHB SHBDR File Description

This file contains the covariance and related data for the JPL Dawn
Ceres gravity soluttion CERES18D, a 18th degree and order spherical
harmonic model and covariance.

Some details describing this model are:
   The spherical harmonic coefficients are fully normalized.
   The associated GM = 62.6290536121 km^3/s^2
   The reference radius = 470.0 km
   The Ceres-fixed reference frame prime meridian and pole
      location in IAU coordinates is given by
         Right ascension = 291.42763 degrees (estimated)
         RA rate         =   0.0 degrees/cty (fixed)
         Declination     =  66.76033 degrees (estimated)
         Dec rate        =   0.0 degrees/cty (fixed)
         Prime Meridian  = 170.309 degrees (estimated)
         Rotation rate   = 952.1532635 degrees/day (estimated)
   The pole location, W0 and spin rate are estimated jointly with the
   gravity field by fixing the y-value of the Kait landmark to zero.
   The uncertainties of the pole for this solution are
         Right ascension = 0.0002 degrees
         Declination     = 0.0002 degrees
   Note ceres18d is similar to ceres18c version 2 of the gravity field
   which has the corrected location of the kait crater. This is a
   rotation of -0.064074 deg about the z-axis versus the previous
   version of the gravity field.

 For a description of the solution, see the ascii pds file
 for the CERES18D spherical harmonic gravity coefficients.

 The error covariance of CERES18D is delivered in the Spherical
 Harmonics Gravity Binary Data Record (SHBDR) and is produced by the
 Dawn Gravity Science Team at JPL.



Map Projection Descriptions
---------------------------


Note on value-added metadata: The PDS4 map products use updated projection 
values for upperleft_corner_x, upperleft_corner_y, pixel_resolution_x, and 
pixel_resolution_y. These values are based on proper cartographic parameters 
for equirectangular (simple cylindrical) projection. These values were 
provided by Trent Hare (PDS Imaging Node) and are documented in the figure 
equirectangular_map_projection_PDS4.pdf in the document collection; they 
supersede the values in the original PDS3 labels.


# Description of the Digital Map of the Radial Gravity

This file contains a digital map of the radial gravity derived from
the JPL CERES18D model of the Ceres gravity field.  Each point gives the
Ceres gravity radial acceleration in milligals on a 482.0-km x 445.9-km
ellipsoid of revolution, which is close to the  surface of Ceres.
The hydrostatic coefficients J2 and J4 are not included.
The JGDWN_CER18D_ACCEL_0018 gravity acceleration is computed from the full
CERES18D solution (from degree 2 up to degree 18).

The map is produced at JPL by the Dawn Radio Science Team (Alex Konopliv,
Ryan Park, Sami Asmar).



# Description of the Digital Map of the Radial Gravity Error

This file contains a digital map of the radial gravity error derived 
from the JPL CERES18D model of the Ceres gravity field.  Each point 
gives the Ceres gravity radial acceleration error in milligals on a 
482.0-km x 445.9-km ellipsoid of revolution, which is close to the 
surface of Ceres. The hydrostatic coefficients J2 and J4 are included.
The JGDWN_CER18D_ACCERR gravity acceleration error is computed from the 
full CERES18D solution covariance (from degree 2 up to degree 18).

The map is produced at JPL by the Dawn Radio Science Team (Alex Konopliv, 
Ryan Park, Sami Asmar).



#  Description of the Digital Map of the Bouguer

This file contains a digital map of the Bouguer gravity derived from
the JPL CERES18D model of the Ceres gravity field.  Each point gives the
Ceres gravity radial acceleration minus the gravity derived from
integration Ceres shape assuming uniform density in milligals on a
482.0-km x 445.9-km ellipsoid of revolution, which is close to the
surface of Ceres. The hydrostatic coefficients J2 and J4 are not included.
The JGDWN_CER18D_BOU_0018 gravity acceleration is computed from the full
CERES18D solution (from degree 2 up to degree 18).

The map is produced at JPL by the Dawn Radio Science Team (Alex Konopliv,
Ryan Park, Sami Asmar).



# Description of the Digital Map of the Ceres GEOID

This file contains a digital map of the Ceres geoid derived from
the JPL CERES18D spherical harmonic model of the Ceres gravity field.
Each point is the Ceres geoid height in meters above a reference
ellipsoid (semi-major-axis = 482.0 km, GM = 62.6273588067 km**3/s**2,
flattening = 0.074896, and rotation rate = 0.000192340387006239 rad/s).

The JGDWN_CER18D_GEOID_0018 is computed from the CERES18D
solution (from degree 2 up to degree 18).

The map is produced by Dawn Gravity Team (Alex Konopliv, Ryan Park,
Sami Asmar) at JPL.




# Description of the Digital Map of the Vesta GEOID Error

This file contains a digital map of the Ceres geoid uncertainty
derived Cfrom the covariance matrix for the spherical harmonic coefficients
of the JPL CERES18D Ceres gravity field. Each point is the Ceres geoid
height error in meters above a reference ellipsoid
(semi-major-axis = 482.0 km, GM = 62.6273588067 km**3/s**2,
flattening = 0.074896, and rotation rate = 0.000192340387006239 rad/s).

The JGDWN_CER18D_GEOIDERR_0018 is computed from the CERES18D
solution (from degree 2 up to degree 18).

The map is produced by Dawn Gravity Team (Alex Konopliv, Ryan Park,
Sami Asmar) at JPL.



Coordinate System
=================

Dawn Gravity SDP files use a Ceres centered body-fixed coordinate system
similar to the IAU coordinate system. The values differ slightly
because the the orientation of Ceres is estimated in the orbit
determination process.

See the coordinate system document in the Dawn Mission Bundle:

- dawn-mission/document-rss/CERES_COORD_SYS_180628.PDF

and the labels of specific gravity products for details.

Software
========

None.

CONFIDENCE LEVEL NOTE
=====================

Overview
========

Data in this collection have been reduced as part of mission data
analysis activities of the Dawn Gravity Team.

Review
======

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

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

This collection contains gravity models and maps generated from Dawn
data collected between January 2015 and August 2016.
