PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "R. SIMPSON, 2000-02-09" RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 72 OBJECT = DATA_SET DATA_SET_ID = "MGS-M-RSS-5-SDP-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "MGS RADIO SCIENCE -- SCIENCE DATA PRODUCTS V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = TABLE START_TIME = 1998-10-01T00:00:00Z STOP_TIME = 1999-11-08T14:00:00Z DATA_SET_RELEASE_DATE = 2000-02-10 PRODUCER_FULL_NAME = "RICHARD A. SIMPSON" DETAILED_CATALOG_FLAG = "N" DATA_SET_DESC = " Data Set Overview ================= The Mars Global Surveyor (MGS) Radio Science (RS) Archive Data Collection (ADC) of Science Data Products (SDP) includes data from radio occultation, gravity, and surface reflection investigations conducted by members of the MGS Radio Science Team (RST). The archive includes both Standard Data Products (STDPs) and Special Data Products (SPDPs). STDPs were defined prior to Launch and were produced routinely during the mission. SPDPs were defined after Launch and/or were produced on an irregular basis. Radio occultation STDPs include temperature-pressure (T-p) profiles, occultation summary files, and intensity power spectra. T-p profiles were computed with both standard vertical resolution (approximately 200 m) and, after correction for diffraction effects, at high resolution (approximately 20 m). Gravity STDPs include spherical harmonic models, maps or images of those models, and line-of-sight acceleration profiles. For more information on STDPs, see [TYLERETAL1992]. The surface reflection investigation was developed only after the spacecraft was in Mars orbit. SPDPs include summary tables of observing geometry, summary tables of signal characteristics, and images of signals in time-frequency space. Parameters ========== Temperature-pressure profiles are tables of atmospheric temperature, pressure, and molecular number density versus radius from Mars' center of mass. A header record prepended to each table provides information on observing times and geometry and on files used in the data processing. 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 include covariance terms. Each file contains up to three 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 coefficients table (degree m, order n, coefficients Cmn and Smn, and their uncertainties); and 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. Surface Reflection Tables list carrier frequency and power and the estimated frequency and power in the surface echo. Surface Reflection Images are series of power spectra showing the progression of signal characteristics as a function of time. Surface Reflection Geometry tables summarize the observing geometry at and near occultations at (typically) 1-10 s intervals. Quantities include Earth receive time; the transit time (receive time corrected for one-way light time); vectors to the spacecraft, Earth receiving station, and several points on the surface; angles; and sensitivities of some quantities to changes in assumed Mars radius. The surface points include the specular point, the backscatter point (the intersection of a line from the receiver through the spacecraft to the surface), the raypath closest approach point (the point where a line from the Earth to the spacecraft is closest to the surface), and a user-defined 'target' on the surface. The backscatter point and the raypath closest approach point do not both exist at the same time; the 'target' point may or may not be meaningful. Processing ========== T-p profiles and ionosphere profiles were derived from raw receiver output in several steps. First, deterministic sources of frequency change were identified and removed coherently. These included motion of the spacecraft, motion of the Earth receiving station, drift of the UltraStable Oscillator (USO), and relativistic effects associated with gravity fields of solar system bodies. This left the carrier signal at a known frequency except for phase drift associated with passage of the radio ray through the atmosphere. Second, using an accurate reconstruction of the spacecraft trajectory, the phase of the signal versus time was converted into a measure of refraction angle versus impact parameter -- the perpendicular distance between the incoming raypath and the center of curvature of the atmosphere. Third, the index of refraction versus radius was obtained using an Abel inversion [FJELDBOETAL1971]. From knowledge of the composition of the atmosphere and laboratory measurements of refractive index for major constituents, index of refraction versus radius for the neutral atmosphere was converted to vertical distribution of mass density. Fourth, assuming hydrostatic equilibrium and an ideal gas law, the mass density profile was converted to a profile of both temperature and pressure for the neutral atmosphere. For the ionosphere, refractive index versus radius was converted to density of free electrons versus radius using a method described by [YEH&LIU1972]. Spherical harmonic models, maps, and line-of-sight acceleration profiles were derived from raw radio tracking data in several steps. The gravity field coefficients were obtained by solving systems of equations with thousands of unknowns. Radio tracking data in long arcs delimited by propulsive maneuvers, occultations, etc. were used in solutions which were obtained iteratively and by least squares. Maps of free air gravity and other quantities were generated from the spherical harmonic model(s) evaluated at regular grid points. Line-of-sight acceleration profiles were derived from single arcs of radio tracking data. Doppler residuals with respect to specific spherical harmonic models were spline-fitted and the splines were then differentiated analytically to obtain the accelerations. See [TYLERETAL1992] and references therein for additional details on processing in the products listed above. Surface Reflection Geometry tables are summaries of observing geometry, typically at 1 or 10 second intervals. The spacecraft-surface-Earth geometry was derived from an SPK (NAIF spacecraft and planetary ephemeris) file. The Surface Reflection Table data are derived as follows. (1) The occultation is located in time and its sense (ingress or egress) is determined by searching for a sudden change in output from the receiver. If ingress (egress), the receiver output would decrease (increase). (2) Raw 12-bit unsigned integer samples are passed through a digital 'equalizing' filter which flattens the output spectral response over the central 80 percent of the passband. The output is a string of double-precision complex floating point time samples at 2500 per second. (3) 512-point power spectra (0.2 s each) are computed around the transition point (1); approximately 30 spectra are saved on the occulted side of the transition and 270 are saved when the carrier was clearly visible (total of 300 spectra, spaced by 0.2 s and having 5 Hz frequency bins). (4) A search within each spectrum for the bin with maximum signal locates the carrier (when it is present). (5) A second search for the strongest signal above (below) the carrier if ingress (egress) locates the surface echo. The surface echo is transient, however, so not all results from the second search are valid. A predicted frequency curve (straight line) is fitted to the DIFFERENCE between the peak echo bin and the carrier bin; half of the points are thrown out (the worst residuals). A new straight line is fitted to the remaining points, and the single point with the worst residual is thrown out. The process is repeated until there are 10 points left. The final straight line is taken to be the actual drift of the surface echo with respect to the carrier. (6) An estimate of the noise power is made by averaging 64 frequency bins from 300 spectra on the side OPPOSITE the surface echo and comparing the average with a system temperature estimate provided by the DSN Monitor data. The noise pedestal is removed and the remaining values are scaled to units of watts. (7) Five bins centered on the carrier are summed to obtain the carrier power. (8) Seven bins centered on the fitted straight line are summed to obtain the echo power. (9) The results are tabulated for each of the 300 spectra and stored in the SRT file. (10) The array of 300 512-point spectra is saved as the SRI file. Data ==== Data are stored on CD-WO volumes approximately chronologically. A CD volume was usually created for delivery of data to PDS every six months, though volumes were adjusted to accommodate variable numbers and sizes of files. Standard resolution temperature-pressure profiles are stored in the TPS directory with file names of the form ydddhmmC.TPS where y is the least significant digit of the year, ddd is the three-digit day number, h is one-character which denotes the hour, and mm is a two-character string denoting the minute in which data acquisition began. h is 'A' if the hour was 00, 'B' if the hour was 01, ... and 'X' if the hour was 23. In most cases mm is the two-digit minute; but when data were collected from two antennas and the start time was in the same minute, the second digit in mm was changed to a letter in the second file name (minute 00 becomes 0A, 01 becomes 0B, etc.). C is a single character indicating the version of the file, starting with 'A'. High-resolution temperature-pressure profiles are stored in the TPH directory with file names of the form ydddhmmC.TPH where components in the name are the same as for TPS files. Occultation summary files are stored in the OCS directory if derived from TPS data and in the OCH directory if derived from TPH files. File names are of the form YMMymmCC.OCS and YMMymmCC.OCH, respectively, where Y is the one-digit year of the first entry in the file, MM is the two-digit month of the first entry, y is the one-digit year of the last entry, and mm is the two-digit month of the last entry. CC is a two-character string indicating the version of the file. ASCII spherical harmonic models are stored in the SHA directory with file names of the form GTnnnnvv.SHA where G denotes the generating institution J for Jet Propulsion Laboratory G for Goddard Space Flight Center C for Centre National d'Etudes Spatiales T denotes the type of data represented G for gravity field T for topography M for magnetic field nnnn is a 4-character modifier specified by the data producer vv is a decimal version number, initialized to '01' and SHA denotes that this is an ASCII file of spherical harmonic coefficients. Binary spherical harmonic models are stored in the SHB directory with file names of the form GTnnnnvv.SHB where individual name components are as defined above except for the SHB suffix. Radio Science Digital Map products are stored in the IMG directory with file names of the form GTnnnnvv.IMG where G denotes the generating institution J for Jet Propulsion Laboratory G for Goddard Space Flight Center C for Centre National d'Etudes Spatiales S for Stanford University T denotes the type of data represented G for free air gravity field O for geoid B for Bouguer anomaly I for isostatic anomaly T for topography M for magnetic field nnnn is a 4-character modifier specified by the data producer vv is a decimal version number, initialized to '01' and IMG denotes that this is a PDS image object. Line-of-sight acceleration profiles are stored in the LOS directory with file names of the form MOnnnnnC.LOS where nnnnn is the 5-digit orbit number and C is a character indicating the version (starting from 'A'). Ancillary Data ============== The file OCCLOGM1.TAB in the DOCUMENT directory of the archival volume lists parameters for each radio occultation data acquisition opportunity during the first occultation season of Mapping. Its detached label OCCLOGM1.LBL describes the format and contents of the file. Coordinate System ================= MGS RST SDP files use a Mars centered body-fixed coordinate system with positive east longitude. The gravity model uses the IAU 1991 [DAVIESETAL1992B] coordinate frame. Software ======== None. Media/Format ============ The archival data set was written on CD-WO media using the Sun Ultra-5/Yamaha/GEAR CD authoring subsystem provided by the MGS Project. The CD-WO volumes conform to ISO 9660 standards." CONFIDENCE_LEVEL_NOTE = " Overview ======== Data in this archive have been reduced as part of mission data analysis activities of the MGS Radio Science Team. Profiles and intensity power spectra of questionable validity have been omitted. Review ====== This archival data set was reviewed by the MGS Radio Science Team prior to submission to the Planetary Data System (PDS). The MGS Science Data Validation Team (SDVT) monitored the submissions. 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 ========================= MORS_1001 --------- T-p profiles included in this volume were derived from data acquired between 24 January 1998 and 28 April 1998. The spacecraft was at nearly maximum Earth-Mars range and the observations ended just a few days before solar conjunction. 88 profiles are included in the volume. Significant events during this period were: YY/DDD Start Stop Comments ------ -------- -------- ---------------- 98/024 19:15:36 19:32:15 First occultation recording 98/076 13:19:18 (ET) Close Phobos approach (380 km) 98/087 02:44:09 First SPO-1 periapsis gravity 98/088 01:51:00 02:15:00 First egress recording (LGA) 98/107 23:01:28 23:18:00 Last good ingress recording 98/118 15:52:00 16:33:00 Last occultation recording Quality of data was affected by anomalous conditions during data acquisition. Specifics are given in the OCCLOGA1.TAB file in the DOCUMENT directory of MORS_1001; five general types of problems dominated: a) 2-6 dB lower carrier-to-noise level at Madrid antennas throughout the occultation period (98/024-98/118), later found to be from a weak oscillator in the front end of the radio science receiver b) 'Sawtooth' frequency residuals in approximately 10 percent of the data (all stations), later found to be from an intermittent synchronization error in merging two data streams at the DSN station c) Amplitude baseline variations more than +/-0.1 dB (various) d) Spurs (occasional, no consistent pattern) e) Unreliable local oscillator tuning (wrong controller software) (Madrid antennas, 98/084-98/106) Gravity models and maps included in this volume were generated from Mariner 9 and Viking data. They do not contain any data from the Mars Global Surveyor mission; they do, however, serve as the baseline models from which the MGS models will evolve. Over time, the MGS data will come to dominate the solutions. Labels for each of the gravity products provide more information on how the models were derived. JGM50C01.SHA is the pre-MGS Mars gravity model produced at the Jet Propulsion Laboratory under supervision of Bill Sjogren. JGM50C01.IMG is the free-air gravity map corresponding to this model. It is defined in IAU 1994 coordinates [DAVIESETAL1995]. GGM50A01.SHA is the pre-MGS Mars gravity model produced at Goddard Space Flight Center under supervision of David Smith. It is defined in IAU 1994 coordinates [DAVIESETAL1995]. GGM50A02.SHA is a slight variation on this model (a coordinate transformation to IAU 1991 coordinates [DAVIESETAL1992B]) used by David Hinson in reduction of radio occultation data acquired during January-April 1998 and included in this volume. MORS_1002 --------- This volume contains gravity models and maps generated from Mariner 9, Viking Orbiter, and MGS data collected through mid-September 1998. The MGS data included tracking results from Orbit Insertion subphases Aerobraking 1, Science Phasing Orbit 1, and Science Phasing Orbit 2. Orbit periapsis passed near Mars' north pole during the summer of 1998, so the data are particularly good in defining the gravity field of the north polar region. GGM0890A.SHA is an ASCII file of coefficients for a 70x70 degree and order field produced at Goddard Space Flight Center. GGM0890A.IMG is a gridded representation of the field. Derivation of the model is described by a paper in both PostScript and LaTeX formats in the DOCUMENT directory (see DOCUMENT/AAS99147.LBL for details). JGM75A01.SHA is an ASCII file of coefficients for a 75x75 degree and order field produced at the Jet Propulsion Laboratory. JGM75A01.SHB is a binary file of covariances. MORS_1003 --------- This volume contains gravity models and maps generated from Viking Orbiter and MGS data collected through March 1999. The MGS data included tracking results from Orbit Insertion subphases Aerobraking 1, Science Phasing Orbit 1, Science Phasing Orbit 2, and the Gravity Calibration Orbit. It also included data from approximately the first month of MGS Mapping operations, while the high-gain antenna was still not deployed. Noise produced by the HGA control system after deployment corrupts those data to an extent that is still being evaluated. GGM0964A.SHA is an ASCII file of coefficients for a 70x70 degree and order field produced at Goddard Space Flight Center. GGM0890A.IMG is a gridded representation of gravity anomalies with respect to an evaluation of the Goddard model to degree and order 50. Derivation of the model is described by a paper in both PostScript and LaTeX formats in the DOCUMENT directory (see DOCUMENT/AAS99328.LBL for details). The Goddard group argues that the MGS data are of sufficient quality that historic data (Mariner 9 and Viking Orbiter) can be omitted. Their solution is based solely on MGS data. JGM75B01.SHA is an ASCII file of coefficients for a 75x75 degree and order field produced at the Jet Propulsion Laboratory. JGM75B01.SHB is a binary file of coefficients and covariances. JGD75B50.IMG is a gridded representation of gravity anomalies with respect to an evaluation of the JPL model to degree and order 50. The JPL solution continues to include Viking Orbiter data. The Goddard group has also provided a map of uncertainties in their gravity anomalies; the JPL group has provided a map of geoid height above a reference ellipsoid. The BRO directory is new with this volume; it contains PostScript representations of selected gravity results. For a discussion of the major conclusions resulting from study of the gravity field to this point, see [SMITHETAL1999]. MORS_1003 also contains 36 radio occultation profiles of neutral atmosphere temperature and pressure derived from data collected in late December 1998. These observations were made while there was no telemetry modulation on the spacecraft carrier, providing some of the highest signal-to-noise prior to circularization of the orbit (February 1999). Latitudes at the occultation point were between 64.2N and 67.3N. MORS_1004 --------- This volume contains a gravity model and maps generated at JPL from MGS tracking data collected through early November 1999. The MGS data included tracking results from the following phases/subphases of the mission: Science Phasing Orbit 1, Science Phasing Orbit 2, Gravity Calibration Orbit, Fixed High-Gain Antenna Mapping, and the first seven months of nominal Mapping. JGM75C01.SHA is an ASCII file of coefficients for a 75x75 degree and order field produced at the Jet Propulsion Laboratory. JGM75C01.SHB is a binary file of coefficients and covariances. JGD75C60.IMG is a gridded representation of gravity anomalies with respect to an evaluation of the JPL model to degree and order 60. JOD75C60.IMG is a gridded representation of geoid height with respect to a reference ellipsoid. MORS_1004 also contains example files from the Surface Reflection investigation. 9133H43A.SRG is a summary table of observing geometry for an occultation starting 1999-133T07:43:00. 9133H43A.SRT is a tabulation of carrier and surface echo signal characteristics. 9133H43A.SRI is a two-dimensional array showing signal strength as a function of both frequency and time around the occultation. Surface echo was visible while the specular point moved from about (69S, 91W) to about (68S, 83W). Limitations =========== The limitations in this data set follow from the quality of the execution, which is described above under Data Coverage and Quality." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = MARS END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = MGS INSTRUMENT_ID = RSS END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "DAVIESETAL1992B" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "DAVIESETAL1995" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "FJELDBOETAL1971" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITHETAL1999" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "TYLERETAL1992" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "YEH&LIU1972" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END