Data Set Information
DATA_SET_NAME MGS RS: ATMOSPHERIC TEMPERATURE-PRESSURE PROFILES V1.0
DATA_SET_ID MGS-M-RSS-5-TPS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : MGS radio occultation experiments were conducted using a 3.6-cm wavelength radio signal transmitted by the spacecraft and received on Earth. In principle this 'downlink' configuration allows atmospheric structure to be sampled twice per orbit. Occultation entry and exit generally occurred in the northern and southern hemispheres, respectively, and the latitude of the measurements drifted gradually in response to changes in the observing geometry. The experiments eventually visited essentially all latitudes on Mars. However, far more experiments were performed at occultation entry than exit, owing to a problem with one of the gimbals used to point the spacecraft high-gain antenna (HGA). This resulted in particularly dense coverage at latitudes of 60-80 deg in the northern hemisphere. The coverage in longitude of the data set is fairly dense and uniform with few exceptions. Radio occultation temperature-pressure (T-p) profiles were computed with standard vertical resolution (approximately 500 m); an option to compute them at high resolution (approximately 20 m, after correction for diffraction effects) was never exercised. T-p files are stored as ASCII tables, preceded by a header record which contains supplementary information as described below. The headers from each individual file have been collected in a single occultation summary file, which may be useful for scanning the data set, identifying profiles of particular interest, and reviewing the coverage in latitude, season, and local time. David Hinson at Stanford University created all T-p profiles and the occultation summary file. For more information about these data, see [TYLERETAL1992], [HINSONETAL1999], [HINSONETAL2001], [TYLERETAL2001], and [HINSONETAL2004]. Parameters : Temperature-pressure profiles are tables of geopotential, temperature, pressure, and molecular number density versus radius from Mars' center of mass. Each profile extends from the surface to the 10-Pa pressure level with a sample spacing of about 1 km. A header record prepended to each table provides information about observing times and geometry, surface conditions, and files used in the data processing. Processing : T-p profiles are derived from raw receiver output in several steps. First, deterministic sources of frequency change are 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 leaves the carrier signal at a known frequency except for phase drift associated with passage of the radio ray through Mars' atmosphere and/or ionosphere. Drift associated with passage through solar plasma or the Earth's atmosphere or ionosphere is assumed to be negligible over the time of a Mars occultation (approximately two minutes). Second, using an accurate reconstruction of the spacecraft trajectory, the phase of the signal versus time is 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 is 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 is converted to vertical distribution of mass density. Fourth, assuming hydrostatic equilibrium and an ideal gas law, the mass density profile is converted to a profile of both temperature and pressure for the neutral atmosphere. Data : Data are stored on a single volume in the TPS directory in subdirectories in the order they were collected. Thirty-four subdirectories have been defined with names of the form yyyy_ddd where yyyy is the year and ddd is the day-of-year of the first profile in each directory. Directory boundaries have been chosen so that collections have common characteristics, such as similar Ls values, or are easily separated by periods when there was little MGS RST activity, such as solar conjunction or spacecraft anomalies when no data were collected. When these criteria allowed more than 1000 profiles in a directory, arbitrary boundaries were added so that the largest directory contains only 971 profiles. The directories and their boundaries are summarized below. Temperature-pressure profiles are stored 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 a one-character string denoting 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 sources 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'. T-p profiles from 2006 have file names in which y is set to 'G' to avoid conflict with files which might have originated in 1996. In fact, there were no occultation profiles in 1996, but other data types do have files from those years. An occultation summary file is stored in the OCS directory. Its file name is 801609AA.OCS where 801 indicates that the first occultation was from January 1998 and 609 indicates that the last occultation was from September 2006. 'AA' is a two character string which indicates that this is the first version of the file. Ancillary Data : OCCLOG.TAB in the DOCUMENT directory provides single-line summaries for each observation opportunity. Parameters listed mostly relate to settings of and quick-look results from data acquisition. See detached PDS label OCCLOG.LBL for details. Coordinate System : MGS RST SDP files use a Mars centered body-fixed coordinate system with positive east longitude. Gravity models generally use the IAU 1991 [DAVIESETAL1992B] coordinate frame. Variations are noted in the labels of specific gravity products. Software : None. Media/Format : The archival data set was written on CD-WO media using the Sun Ultra-60/PlexWriter/cdrtoaster system. The CD-WO volumes conform to ISO 9660 standards.
DATA_SET_RELEASE_DATE 2008-05-31T00:00:00.000Z
START_TIME 1998-01-28T03:38:00.000Z
STOP_TIME 2006-09-19T11:56:00.000Z
MISSION_NAME MARS GLOBAL SURVEYOR
MISSION_START_DATE 1994-10-12T12:00:00.000Z
MISSION_STOP_DATE 2007-09-30T12:00:00.000Z
TARGET_NAME MARS
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID MGS
INSTRUMENT_NAME RADIO SCIENCE SUBSYSTEM
INSTRUMENT_ID RSS
INSTRUMENT_TYPE RADIO SCIENCE
NODE_NAME Planetary Atmospheres
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Overview : Data in this archive have been reduced as part of mission data analysis activities of the MGS Radio Science Team. Products of questionable validity have been flagged or omitted. Review : This archival data set was reviewed by the MGS Radio Science Team prior to submission to the Planetary Data System (PDS). All of the profiles had been in the public domain as elements of the MGS-M-RSS-5-SDP-V1.0 data set for as much as seven years before this reorganized data set was compiled. Data Coverage : The following table describes the directories that contain the profiles. Each directory is represented by one row. The first two columns list the year and day-of-year of the first and last profiles in each directory, respectively. The first column is also the directory name. The third and fourth columns provide the same information in standard calendar format. The fifth and sixth columns give the number of the Martian year (MY, as defined by [CLANCYETAL2000]) and the approximate areocentric longitude of the Sun (Ls, in degrees) of the first and last profiles in each directory, respectively. The last column specifies the number of profiles in each directory. Blank rows denote gaps caused by solar conjunction (see below). Start End Start End Start End yyyy_ddd yyyy_ddd yyyy-mm-dd yyyy-mm-dd MY/Ls MY/Ls Number -------- -------- ---------- ---------- ------ ------ ------ 1998_028 1998_100 1998-01-28 1998-04-10 23/264 23/308 88 1998_358 1998_365 1998-12-24 1998-12-31 24/074 24/077 36 1999_068 1999_086 1999-03-09 1999-03-27 24/108 24/116 97 1999_126 1999_178 1999-05-06 1999-06-27 24/135 24/161 882 1999_350 2000_038 1999-12-16 2000-02-07 24/264 24/297 800 2000_039 2000_152 2000-02-08 2000-05-31 24/297 25/000 838 2000_214 2000_305 2000-08-01 2000-10-31 25/029 25/070 854 2000_306 2001_031 2000-11-01 2001-01-31 25/070 25/111 904 2001_032 2001_122 2001-02-01 2001-05-02 25/111 25/155 687 2001_130 2001_197 2001-05-10 2001-07-16 25/159 25/197 690 2001_347 2002_058 2001-12-13 2002-02-27 25/290 25/334 906 2002_066 2002_137 2002-03-07 2002-05-17 25/338 26/014 702 2002_138 2002_196 2002-05-18 2002-07-15 26/014 26/041 536 2002_251 2002_304 2002-09-08 2002-10-31 26/065 26/089 544 2002_305 2002_365 2002-11-01 2002-12-31 26/089 26/116 557 2003_001 2003_080 2003-01-01 2003-03-21 26/116 26/156 694 2003_081 2003_161 2003-03-22 2003-06-10 26/156 26/201 720 2003_169 2003_253 2003-06-18 2003-09-10 26/205 26/258 654 2003_254 2003_291 2003-09-11 2003-10-18 26/258 26/282 405 2003_320 2004_019 2003-11-16 2004-01-19 26/299 26/336 436 2004_061 2004_100 2004-03-01 2004-04-09 26/358 27/017 388 2004_101 2004_145 2004-04-10 2004-05-24 27/017 27/038 723 2004_146 2004_203 2004-05-25 2004-07-21 27/038 27/064 819 2004_284 2004_357 2004-10-10 2004-12-22 27/099 27/133 696 2004_361 2005_090 2004-12-26 2005-03-31 27/135 27/185 898 2005_091 2005_181 2005-04-01 2005-06-30 27/185 27/241 971 2005_182 2005_238 2005-07-01 2005-08-26 27/241 27/276 597 2005_252 2005_296 2005-09-09 2005-10-23 27/285 27/312 794 2005_297 2005_334 2005-10-24 2005-11-30 27/312 27/333 604 2005_335 2005_365 2005-12-01 2005-12-31 27/333 27/350 610 2006_001 2006_050 2006-01-01 2006-02-19 27/350 28/014 309 2006_130 2006_181 2006-05-10 2006-06-30 28/051 28/073 381 2006_182 2006_218 2006-07-01 2006-08-06 28/073 28/089 699 2006_219 2006_262 2006-08-07 2006-09-19 28/089 28/109 724 Data coverage was limited by many factors. This is particularly true during the pre-mapping phases of the mission, which extended into early 1999. Prior to the start of the mapping phase, the spacecraft frequently conducted special maneuvers for aerobraking and temperature control, and scientific observations were constrained by numerous other operational issues. The following discussion focuses on the mapping phase of the mission, when data collection was much more systematic. The most significant gaps in coverage fall into five categories. Coverage in Local Time ---------------------- These occultation measurements are geometrically constrained to occur near the terminator within a restricted range of local true solar time. With few exceptions, observations at latitudes between 60 deg N and 60 deg S are available only at local times of about 3-6 hours. Observations at local times of 9-16 hours are available only at latitudes poleward of 60 deg, and this daytime coverage is generally restricted to autumn and winter of the respective hemispheres. Solar Conjunction ------------------ The noise level of the radio occultation measurements increased dramatically near solar conjunction. This prevented retrieval of profiles in the following intervals, denoted by blank rows in the preceding table: 2000_153 - 2000_213 2002_197 - 2002_250 2004_204 - 2004_283 2006_263 - 2006_277 Beta Supplement ---------------- The range of motion of one of the gimbals that controls pointing of the spacecraft HGA was severely restricted until late in the mission, when the obstruction vanished for reasons unknown. During the extended intervals when the failed gimbal prevented normal operations, the spacecraft was configured in a 'beta supplement' mode that restored most of its functionality. This had no effect on measurements at occultation entry (northern hemisphere) but experiments could not be conducted routinely at occultation exit (southern hemisphere) when the spacecraft was in the beta supplement mode. The resulting loss of exit data was reduced slightly through use of special spacecraft maneuvers that allowed collection of radio occultation data over sequences of typically 12 consecutive orbits at intervals of about one month. The spacecraft operated in the beta supplement mode during the following periods, during which exit measurements are extremely sparse: 2000_039 - 2001_171 2002_073 - 2003_253 2004_204 - 2005_251 Spacecraft Anomalies and Emergencies -------------------------------------- The spacecraft occasionally stopped collecting scientific data for periods of several days in response to problems with flight software or hardware. This prevented occultation experiments from being conducted in the following intervals: 2001_123 - 2001_129 2002_059 - 2002_065 2002_092 - 2002_100 2003_162 - 2003_168 2004_358 - 2004_360 2005_239 - 2005_251 2005_256 - 2005_261 Broadside Orbit / Highly Grazing Geometry -------------------------------------------- In periods when the MGS orbit plane was nearly broadside as viewed from Earth, the atmospheric occultation either occurred in a highly grazing geometry or was entirely absent. For this reason no profiles are available in the following intervals: 1999_179 - 1999_349 2001_198 - 2001_346 2006_051 - 2006_129 Anomalous HGA Motion --------------------- Throughout most of its mission, MGS orbited Mars with its nadir panel facing the surface. The HGA was positioned at the end of a rotating boom that maintained pointing toward Earth. Radio occultation data were calibrated to remove effects caused by the mean motion of the HGA, but it was not possible to correct for abrupt changes in HGA pointing. The occultation data are especially vulnerable to HGA motion associated with two types of spacecraft activity: (1) repositioning of the solar arrays, performed in discrete steps several times per orbit, and (2) rewinding of the HGA, which usually occurred when the spacecraft was behind Mars. These types of HGA motion interfered with the occultation experiments and prevented retrieval of atmospheric profiles in the following periods: 2001_347 - 2002_006 (entry) 2001_352 - 2002_001 (exit) 2003_272 - 2004_100 (entry) 2003_265 - 2003_275 (exit) 2003_292 - 2003_319 (exit) 2004_020 - 2004_060 (exit) 2004_134 - 2004_171 (exit) 2005_297 - 2005_309 (entry) 2006_001 - 2006_006 (exit) 2006_012 - 2006_034 (exit) 2006_012 - 2006_050 (entry) 2006_130 - 2006_169 (entry) 2006_134 - 2006_160 (exit) Data Quality : Each profile includes uncertainties on the estimates of pressure, temperature, and number density. This is the best source of information about data quality. Some obvious trends are apparent in the error bars, such as a general increase in the noise level when the spacecraft was close to solar conjunction. Data quality can vary significantly between successive experiments, and sometimes from one DSN complex to another, and these variations are reflected in the error bars. Some error sources are difficult to quantify, and their effects are therefore not included in the formal uncertainties. As a general rule, diametric occultations yield more reliable results than grazing occultations. (The header of each profile includes several parameters, such as the 'angle from diametric', that characterize the experiment geometry.) Limitations : The limitations in this data set follow from the quality of the execution, which is described above under Data Coverage and Quality.
CITATION_DESCRIPTION Hinson, D.P., Mars Global Surveyor Radio Occultation Profiles of the Neutral Atmosphere - Reorganized, MGS-M-RSS-5-TPS-V1.0, NASA Planetary Data System, 2008.
ABSTRACT_TEXT This data set contains over 21000 temperature-pressure profiles (TPS files) of the neutral atmosphere derived from Mars Global Surveyor (MGS) radio occultation data. The profiles were previously archived in the MGS-M-RSS-5-SDP-V1.0 data set along with other reduced data products from the MGS Radio Science Team (RST). Here they have been pulled from the original 38 volumes and reorganized in chronological order on a single volume. The profiles themselves have not been modified, and the labels have been edited only to conform with the requirements of the new data set. This set of profiles is accompanied by a single occultation summary file which lists key characteristics of each experiment.
PRODUCER_FULL_NAME DAVID P. HINSON
SEARCH/ACCESS DATA
  • Atmospheres Mars Archive
  • MGS RSS Derived Volume MORS_1101
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