Data Set Information
DATA_SET_NAME MGS PROFILE DATA RECORDS V1.2
DATA_SET_ID MGS-M-ACCEL-5-PROFILE-V1.2
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : All PROFILE accelerometer data are packaged by periapsis number for each aerobraking orbit. Each orbit is identified by a folder with name Pyyyy where 'yyyy' is the four digit periapsis number. PROFILE data are provided in a table labeled Pyyyy.tab located in its respective orbit folder. PROFILE data are provided at one second resolution. Parameters : Time From Periapsis: Units : seconds Latitude: Units : degrees Longitude: Units : degrees Local Solar Time: Units : N/A Solar Zenith Angle: Units : degrees Altitude: Units : km 7 Second Density: Units : kg/km**3 Sigma 7 Second Density: Units : kg/km**3 40 Second Density Units : kg/km**3 Sigma 40 Second Density: Units : kg/km**3 Data : For each orbit, PROFILE data consist of an n-by-1 array in the file folder Pyyyy, where n is the number of seconds of data received during the aerobraking pass. Column 1 contains the time from periapsis. Columns 2 through 10 contain Latitude, Longitude, Local Solar Time, Solar Zenith Angle, Altitude, 6.7 Second Density, Sigma 6.7 Second Density, 40 second density, and Sigma 40 Second Density. Processing : Accelerometer data were processed in the PROFILE stage through several steps and the entire process with examples is given in [TOLSONETAL1999B]. First, traditional Euler terms were removed using low pass rates and low pass shifted rates. The shifted rates are utilized to eliminate erroneous acceleration due to thruster induced, nearly instantaneous changes in rates. Next, high frequency terms due to SAM vibration were removed using a linear regression on both high pass angular rates and angular acceleration. Third, accelerometer data at the time of thruster firings are replaced with a local exponential fit or with a constant equal to the bias. A seven point running mean is then performed to remove any remnants of the SAM vibration. The 7 second averaged counts are converted into density values. Because of considerable wave structure in data which do not represent the 'mean' thermosphere, a second data set is also archived. A 40 point running mean of the 7 second running mean density is the final data product. Density averaging was conducted in two forms. The first form, seven-second running averages, are included in the data files for only those instances following the final negative density inbound, and prior to the first negative density value outbound. (These negative count values arise due to the offsets and biases of the system at very small decelerations). These seven second running mean values account for all instantaneous measurements during this seven second window. Thus, seconds 1-7, seconds 2-8, seconds 3-9, etc., are included in consecutive average values. The second averaging is a running forty 7-second average mean. Here, the individual 7-second average density values are accumulated for 40 consecutive points (seconds 1-7, 2-8, 3-9,....33-39, 34-40). These 40- point averages DO include all 7-second points (including those which covered negative count values; recall, the individual 7-second average values included in the data tables are set to zero for all instances where a negative count value existed in the seven-second accumulation prior to averaging). Thus, in the data table, the 40-point mean values commence in the first record, while the 7-second average values are zero at the beginning of and the end of the table. These averaging procedures, and their motivation, are described more completely in [TOLSONETAL1999B]. Coordinate System : Latitude and longitude are in the IAU Mars Centered Mars Equatorial System. Altitude is above the IAU reference ellipsoid, with a:3393.4 km and f:0.0052083 and including corrections for (4,4) gravitational potential.
DATA_SET_RELEASE_DATE 2000-08-09T00:00:00.000Z
START_TIME 1997-11-13T12:58:24.680Z
STOP_TIME 1999-02-04T09:12:48.010Z
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 ACCELEROMETER
INSTRUMENT_ID ACCEL
INSTRUMENT_TYPE ACCELEROMETER
NODE_NAME Planetary Atmospheres
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : Standard deviations for the 7 second and 40 second running means are sample standard deviations and include both natural variability and data noise. Review : Comparisons were made with operational data sets. Deviations were within expectations founded on archiving analysis that is based on (4,4) gravitational potential and numerically integrated precision trajectories that were not included in operational software. Data Coverage and Quality : Data coverage during an aerobraking pass has varied throughout the mission. Early in the mission, data were received for 500 seconds on either side of periapsis. Later, the data started between 200 and 250 seconds before periapsis. This change was made to reduce propulsion usage. Though this change somewhat reduced the accuracy of determining the accelerometer bias, it Had the advantage of reducing the corruption of the data set with thruster firings while still inside the detectable atmosphere. Not all orbits have yet been included in current archiving data sets. Omitted orbits include orbits where automatic data processing procedures did not produce realistic answers. If required, many of these orbits can be recovered by manual manipulation of data and data analysis procedures.
CITATION_DESCRIPTION Citation TBD
ABSTRACT_TEXT All PROFILE accelerometer data are packaged by periapsis number for each aerobraking orbit. Each orbit is identified by a folder with name Pyyyy where 'yyyy' is the four digit periapsis number. PROFILE data are provided in a table labeled Pyyyy.tab located in its respective orbit folder. PROFILE data are provided at one second resolution.
PRODUCER_FULL_NAME GERALD M. KEATING
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