Document title: VOLDESC.SFD for NDADS DE IDM_ASCII datatype Project: DE NDADS Datatype: IDM_ASCII Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: IDM_VOLDESC_DE.SFD TRF entry: B46560.txt in NSSDC's controlled digital document library, Feb. 1998. Document text follows: ---------------------- CCSDXZLM0001SMARK001CCSDXVNM0002SMARK002 LOG_VOL_IDENT: USANASANSSDDEB6_0001A LOG_VOL_INITIATION_DATE: 1992-09-15 LOG_VOL_CLOSING_DATE: 1992-09-15 LOG_VOL_CAPACITY: 2.2GB LOG_VOL_FILE_STRUCTURE: VAX FILES-11 STRUCTURE LEVEL 2 Written with backup utility as a save set with name DEB601.BCK TAPE_LENGTH: 106 METERS VOLUME_DRIVE_MFGR_AND_MODEL: AVIV, model ACT850 COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: VMS, VERSION 5.5 COMPUTER_SYSTEM: VAX 4000/500 TECHNICAL_CONTACT: Robert A. Power and/or Dr. William R. Coley Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-690-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::POWER PREV_LOG_VOLS: NONE CCSDXVNM0002EMARK002CCSDXKNM0002SMARK003 DATA_SET_NAME: ION DRIFT METER FILES (IDM) DATA_SOURCES: DYNAMICS EXPLORER 2, ION DRIFT METER (IDM) SCIENTIFIC_CONTACTS: Dr. William B. Hanson and/or Dr. R. A. Heelis Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-690-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::HEELIS SOURCE_CHARACTERISTICS: A. DESCRIPTION_OF_SPACECRAFT: The Dynamics Explorer 2 spacecraft was one of two satellites launched for the Dynamics Explorer program. The two spacecraft were launched together into coplanar polar orbits for the purpose of studying coupling between the magnetosphere, ionosphere, and the atmosphere. The DE-2 spacecraft was placed in a low elliptical orbit whereas the DE-1 orbit was highly elliptical. Instruments aboard the DE-2 spacecraft were: magnetometer, vector electric field instrument, neutral atmosphere composition spectrometer, wind and temperature spectrometer, Fabry-Perot intereferometer, ion drift meter, retarding potential analyzer, low altitude plasma instrument, and Langmuir probe. B. ORBIT_INFORMATION: Because the Delta launch vehicle did not complete a full burn the DE-2 satellite was placed in a lower than anticipated polar orbit, initially 1012 by 309 km. The orbital period was 98 min. The DE-1 and DE-2 satellites were launched by the same vehicle so that their orbits would be coplanar, allowing occasional two-point measurements along magnetic field lines. The DE-2 spacecraft spun once per orbit and the spin axis was perpendicular to the orbital plane so that one axis of the satellite always was aligned with the center of the earth. C. PERFORMANCE: The DE-2 spacecraft performed well through its lifetime. Power limitations forced the duty cycle to be limited to an average which was originally targeted at 30%. The lifetime of the spacecraft was shorter than anticipated because of the less than nominal performance of the launch vehicle. The launch was on August 3, 1981 and the DE-2 satellite reentered the atmosphere on February 19, 1983, with the last contact the day before. INVESTIGATION_OBJECTIVES: Among the science objectives for the DE program was the study of the electrodynamics of the ionosphere and its application to ionosphere- magnetosphere interactions. The IDM objective was to provide a measure of the cross-drift ion velocity in the ionosphere. This data is used in studies of the ionospheric electric field and ionosphere-thermosphere interactions. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT The Ion Drift Meter (IDM) consists of two sensors that view approximately along the spacecraft velocity vector. Each sensor has a square entrance aperture to a gridded region in front of a collector with four quadrant sectors. By comparison of the ion currents to each sector it is possible to measure the angle of arrival of the ions in two mutually perpendicular directions perpendicular to the look direction of the sensor. From this angular information, knowledge of the ion velocity along the sensor look direction from the RPA and knowledge of the spacecraft attitude, it is possible to derive the ambient ion drift along the two mutually perpendicular directions. ( See Heelis et al., Space Sci. Instrum., 5, 511, 1981) B. OPERATIONAL_MODES: The IDM provides absolute measures of the ion arrival angle 4 times per second and measurements of the angle relative to an absolute value, established every 8 seconds, at the rate of 32 samples per second. C. MEASURED_PARAMETERS: Using the velocity of the spacecraft relative to the ambient plasma, it is possible to use the angular information provided by the IDM to compute the ion velocity along the mutually perpendicular directions (nominally horizontal, perpendicular to the spacecraft's orbital plane, and vertical ). D. PERFORMANCE_OF_THE_INSTRUMENT: The IDM provided data on the ion arrival angle for the entire duration of the DE-2 lifetime. Interpretation of this data in terms of ion drifts requires the assumption of zero ram drift during the period of failure (81317 06:26:40 UT to 82057 13:16:00 UT) of the Retarding Potential Analyzer (RPA). This is usually not a serious limitation (see DATA_SET_QUALITY). E. RESOLUTION: IDM geophysical data files provide absolute measurements of the cross track ion drift velocity 4 times per second PARAMETERS: IDM data files contain geophysical data in 8 second blocks corresponding to the standard segment of data on the DE spacecraft. Each 8 second block of IDM data containing 32 pairs of mutually perpendicular ion drift velocities in spacecraft coordinates, is accompanied by some orbit position information. DATA_SET_QUALITY: IDM data is of high quality since only absolute ion drift velocities have been retained in the data files. This higher resolution data has not been corrected for the presence of ion drifts along the sensor look direction. If such a drift Vx exists then the value in the file should be corrected by the factor (Vs +Vx)/Vs, where Vs is the spacecraft velocity along the sensor look direction. This correction factor can be as high as 20%. Values of Vx are available from the Retarding Potential Analyzer (RPA) files. DATA_PROCESSING OVERVIEW: A. DATA_PROCESSING CYCLE: Raw telemetry segments were reduced to IDM mission analysis files (MAF's) utilizing production processing on the project computer. The cpu commitment to IDM analysis could not be retained during the periods when the TM was initially available. Thus a situation in which TM file promotion was required for IDM analysis evolved. This quickly resulted in a backlog of unprocessed TM which still exists. Though data files for most data segments exists some files do not exist at all and others require complete reprocessing due to inadequate least-squares analysis. B. HISTORY All data was originally reduced on project computers at GSFC. More recently an attempt to transfer telemetry files to local computers at the investigators site has been undertaken. Some data files originate from reduction of telemetry on local computers. This data is usually of higher quality and higher temporal resolution owing to the resources that can be applied to it. It is not identified in any way as originating from this source. DATA_USAGE: Usage of the geophysical data is not formally restricted. Users are urged to be cautious in interpretation of structure and discontinuities in the IDM data. In many cases such structure is real, but it may also be caused by instrumental noise or telemetry problems. Use of the data quality flags is encouraged to to ensure that the data is used correctly. DATA_ORGANIZATION: Geophysical data files exist for each DE2 telemetry segment. These data files may be identified by orbit number or by approximate UT start time. CCSDXKNM0002EMARK003CCSDXKNM0002SMARK005 LOG_VOL_TIME_COVERAGE: 1981-08-15 TO 1983-02-16 TYPE_OF_FILE_TIME_COVERAGE: IDM 1981-08-15T03:44:38 1983-02-16T19:54:45 NAMING_CONVENTION: IDM files are named according to the U.T. starting date and time of the data in the file. Example: IDM821141206.DAT indicates that this is an IDM file for the year (19)82, day 114, hour 12, minute 06. PREV_LOG_VOL_TIME_COVERAGE: NONE CCSDXKNM0002EMARK005CCSDXRNM0003SMARK006 NESTING=L REF=IDMFORMAT.SFD CCSDXRNM0003EMARK006CCSDXRLM0003SMARK007 ADI=NSSD0055 CLASS=I NESTING=N SCOPE=EACH REF=[IDM]IDM*.dat;* CCSDXRLM0003EMARK007CCSDXZLM0001EMARK001