Document title: Voldesc.sfd for NDADS DE LAPI datatype Project: DE NDADS Datatype: LAPI Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: LAPI_VOLDESC.SFD TRF entry B46550.txt in NSSDC's controlled digital document library. Feb. 1998. Document text follows: ---------------------- CCSD3ZF0000100000001CCSD3VS00002MRK**001 LOG_VOL_IDENT: USANASANSSDDEB8-0001D LOG_VOL_INITIATION_DATE: 1992-05-31 LOG_VOL_CLOSING_DATE: YYYY-MM-DD LOG_VOL_CAPACITY: 1 GB/LOGICAL_VOL LOG_VOL_FILE_STRUCTURE: FILES-11 VOLUME_DIAMETER: 12 INCHES VOLUME_DRIVE_MFGR_AND_MODEL: OPTIMUM 1000 WITH 1.6 CONTROLLER COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: MICROVMS 5.4 COMPUTER_SYSTEM: MICRO VAX II TRANSFER_SOFTWARE: SOAR 4.2 TECHNICAL_CONTACTS: ROBERT M. CANDEY NASA/GSFC CODE 632 GREENBELT, MD 20771 PHONE: 1-301-286-6707 SPAN: NCF::CANDEY INTERNET: ROBERT.M.CANDEY.1@GSFC.NASA.GOV PREV_LOG_VOLS: USANASANSSDDEB8-0001A USANASANSSDDEB8-0001B USANASANSSDDEB8-0001C CCSD$$MARKERMRK**001CCSD3SS00002MRK**002 DATA_SET_NAME: LAPI SATM file. (SATM = Stand Alone Telemetry) DATA_SOURCES: DYNAMICS EXPLORER B, LOW ALTITUDE PLASMA INSTRUMENT (LAPI) SCIENTIFIC_CONTACTS: DR. J. D. WINNINGHAM / DR. R. A. HOFFMAN SOUTHWEST RESEARCH INST. CODE 696 P.O. DRAWER 28510 NASA/GSFC SAN ANTONIO, TX 78284 GREENBELT, MD 20771 PHONE: 512-522-3075 PHONE: 301-286-7386 SPAN: NSSDCA::PEM::DAVID SPAN: DE696::U6RAH 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 interferometer, ion drift meter, retarding potential analyzer, low altitude plasma instrument, and Langmuir probe. B. ORBIT_INFORMATION: The initial orbit was 1012 by 309 km, with an inclination of 89.9 degrees. 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 with the spin axis perpendicular to the orbital plane, so that one axis of the satellite always was aligned with the center of the earth. Occasionally the spacecraft was spun at 1 RPM. C. PERFORMANCE: The launch was on Aug. 3, 1981 and the satellite reentered the atmosphere on Feb. 19, 1983, with the last contact the day before. 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. INVESTIGATION_OBJECTIVES: The LAPI objective was to provide high resolution velocity space measurements of positive ions and electrons from 5 eV to 32 keV and from 0 to 180 degrees in pitch angle, as well as to provide measurements of E > 35 keV electrons at two angles separated by 90 degrees. Analysis of data from this instrument along with supporting measurements are concerned with: (1) the identification and determination of intensities of Birkeland currents, (2) auroral particle source regions and acceleration mechanisms, (3) the existence and role of the electric field parallel to the magnetic field, (4) sources and effects of polar cap particle fluxes, (5) transport of plasma within and through the magnetospheric clefts, (6) loss cone effects of wave-particle interactions, (7) hot-cold plasma interactions, and (8) ionospheric effects of particle precipitation. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT: The Low-Altitude Plasma Instrument (LAPI) consisted of an array of 15 parabolic electrostatic analyzers, spanning 180 degrees in angle, and two Geiger-Mueller counters, all mounted on a one-degree of freedom scan platform. The platform was controlled by a magnetometer that allowed placement of the array to selected angles with respect to the magnetic field. Each parabolic analyzer was followed by two channel electron multipliers to measure simultaneously electrons and positive ions. The basic mode of operation provided a 32-point energy spectrum every second between 5 eV and 32 keV by stepping through 32 sets of voltages on the analyzer plates on a logarithmic scale each second. The telemetry sampled a selectable set of 16 of the 30 sensor outputs. The set of detectors sampled, sampling rate, voltages, sequencing, etc. could be changed by ground command. All sensor outputs were gated to the accumulators simultaneously. The field of view of the electrostatic analyzer was 5 degrees by 20 degrees, except for the two pair at the 0 degree and 180 degree ends of the array, each offset by +/- 5 degrees out of the plane of the array, which were 5 degrees by 5 degrees. The full-width, half-maximum of the analyzers (delta E/E) was 32%. In addition, measurements of electrons with energies above about 35keV were made at two angles separated by 90 degrees by two Geiger-Mueller counters. Refer to [Winningham, J. D., et al., The Low Altitude Plasma Instrument, Space Science Instrumentation, Vol 5 No. 4 (1981), D. Reidel Publishing Company, pp 465-476] for a detailed description of the LAPI instrument. B. OPERATIONAL_MODE: The nominal mode of operation provided one 32-point energy spectrum per second for each ion and each electron sensor sampled. Though the energy sequence could be changed, this mode was used until a failure on November 23, 1981 (81327) halved the number of steps to 16. The scan platform normally positioned the array to provide pitch angle coverage from 0 degrees to 180 degrees, where 0 degrees is defined as parallel to the magnetic field in the northern hemisphere, and anti-parallel in the southern hemisphere. Thus, in crossing the equator, the array was slewed 180 degrees. Usually the array provided measurements at approximately the pitch angles of 0 , 7, 15, 30, 45, 60, 97, 105, 112, 135, 165, 172, and 180 degrees. One Geiger-Mueller counter measured trapped electrons, the other precipitating electrons, both at one measurement per second. C. MEASURED_PARAMETERS: Outputs from pulse amplifiers in the detector modules were converted into an 8- bit compressed telemetry word using a quasi-logarithmic compression scheme. A decompression algorithm is used to calculate a decimal count rate, and with appropriate geometric factors, accumulation times and detector efficiencies, various types of fluxes can be derived as a function of energy. These fluxes are described in the file FORMAT.SFD and include the calculations via software provided of the differential number flux, the differential energy flux, and the phase space density. The distribution function can be derived from the phase space density data by contouring the density in velocity space. Software is not provided for this last calculation. Integral number fluxes can be calculated from the Geiger- Muller tube data via software provided and is documented in the file FORMAT.SFD. PERFORMANCE_OF_THE_INSTRUMENT: The LAPI instrument returned usable data from shortly after launch until the spacecraft reentered the atmosphere (Feb. 19, 83). This was occasionally interrupted by very brief periods in which the spacecraft was placed in a spinning mode. Data during these periods are difficult to use and should be generally avoided. A failure in the telemetry system on Nov. 23, 1981 (81327) resulted in the reduction of the energy step measurements from 32 to 16 (still covering the full energy range). Also, one data word was lost (i.e., only 15 remained). Modifications allowed the continued production of energy spectra which were essentially the same as spectra prior to the failure except that the energy resolution was degraded. Output from half of the detectors was lost after Dec. 21, 1981 (81355) when one of the two (PPS2) high voltage power supplies failed. Pitch angle resolution was lessened because of the smaller number of detectors still operating. There was a complete loss of data from March 16, 1982 to April 4, 1982 (82075 to 82094) during which the instrument was turned off for analysis of the problems. E. RESOLUTION: Each SATM record contains one DE-2 major telemetry frame (8 seconds) of data. The typical resolution of the LAPI data is 32 energy steps per second before 81327, and 16 energy steps per second after 81327. Energy steps range from 5 eV to 32 keV logarithmically. The Geiger-Mueller tubes measure electrons above about 35 keV, and have a resolution of 1 second. PARAMETERS: The SATM files contain: The date and time of each record, the number of sensors which were operating, each sensor's ID number, the energy step rate, selected orbit/attitude components in spacecraft coordinates (once per second), the scan platform shaft encoder angle, magnetic field data, counts from the sensors, energy step numbers, and Geiger-Mueller tube data. See the file FORMAT.SFD for a detailed list of the various parameters. It should be noted that the SATM files do not contain geophysically meaningful parameters from the LAPI instrument. Such parameters, as described in (C. MEASURED PARAMETERS), are obtained via the software provided which reads the SATM files and calculates the parameters. The magnetic field parameters are only used for the calculation of the pitch angles of the detectors. DATA_SET_QUALITY: There is a problem with the calibration of the 0 and 180 degree field-aligned detectors. Caution should be taken when comparing the fluxes from these detectors with other detectors. The 15 degree detector also seems to have calibration problems, but of considerably less magnitude. Contact the Scientific Contacts for guidance. DATA_PROCESSING_OVERVIEW: A. DATA_PROCESSING_CYCLE: The Stand Alone Telemetry (SATM) files were generated directly from DE-2 Telemetry files stored on optical disks and merged with orbit data from the DE Orbit/Attitude database. B. HISTORY: The original LAPI Stand Alone Telemetry (SATM) file database was generated on the DE Sigma-9 computer. The Sigma-9 software had problems dealing with time gaps and telemetry errors, and produced fragmented files (several files per pass). The SATM records had to be split into three records due to a limitation on the maximum record size. Mission Analysis Files (MAFs) were also generated on the Sigma-9 and used for analysis and plotting. Between 1990 and 1992, the LAPI SATM database was regenerated on a microVax computer from the telemetry data which had been written to optical disks, to correct these problems. Only a few of the old Sigma-9 SATM files are still in use where new SATM files could not be generated. Old Sigma-9 SATM files from the same DE orbit pass have been combined into single SATM files. These are marked by the letter D in the SATM file name. (See NAMING_CONVENTION.) These SATM D files may be incomplete. The rest of the old Sigma-9 SATM files, as well as MAFs are no longer in use. There is now only one SATM file per DE orbit pass. A new, more efficient file structure was used allowing easier access and reducing file size. See the file FORMAT.SFD for information concerning the LAPI SATM files. DATA_SET_NAME: LAPI STAND-ALONE TELEMETRY FILES (SATM) DATA_USAGE: DATA_ORGANIZATION: Are described in FORMAT.SFD. TIME_SPAN_OF_THE_DATA: 04-Sep-1981 to 18-Feb-1983 TYPE_OF_FILE_RELATIONSHIP: All the LAPI instrument data are contained in SATM files. TIME_GAPS: There are occasionally time gaps between major frames. This is due to the fact that bad major frames were not written to the SATM files. Care should be taken in checking for time gaps when analyzing the data. The FLAG variable in the file will indicate when there is a major frame time gap. See also PROCESSING_SOFTWARE, below. PROCESSING_SOFTWARE: The processing software REDUCE_SATM.PRO will also sometimes throw out bad sweeps, leaving a time gap in the flux and count arrays which are generated. One should check for time gaps when doing any kind of analysis which requires consecutive times. PROCESSING_TELEMETRY_ERRORS: Occasionally glitches in the telemetry occur. 1. Sensor ID and/or counts = 84. The REDUCE_SATM.PRO program ignores this data. 2. PPS start, stop, step, or skip values are wrong. In this case they have to be manually set by modifying the PROCESS_SATM_C program (included in REDUCE_SATM.PRO) to set the values. 3. Sensor IDs switch during a pass. 4. PPS step value gets stuck at a particular number. The REDUCE_SATM.PRO program ignores this data. SOFTWARE_TO_UNPACK_THE_DATA: The utility is included in HLAPI_SOFTWARE.TAR-GZ that must be uncompressed and untarred (zcat hlapi_software.tar-gz | tar xvf -) and stored in your local directory. Instructions on how to use the software can be found in the file HOW_TO_USE_REDUCE_SATM.TXT in the LAPI directory. SOFTWARE_APPLICATION_SCOPE: This utility applies to all the data files, i.e. those that can be named (using wildcards, and "/" to denote directory levels) /LAPI/8*/*.SATM . CCSD$$MARKERMRK**002CCSD3KS00002MRK**003 LOG_VOL_COVERAGE: 1982-09-06 TO 1983-02-18 General Note: Inspecting the names of the directories that are subordinate to the LAPI directory will directly indicate the dates of the data covered in the given volume. For example, on the first side (LAPI01) one of the directories is named: 81247_81275 This means that the data covered in the directory is "from 1981, 247th day through 1981, 275th day, inclusive." The four platter-sides are named LAPI01, LAPI02, LAPI03, and LAPI04. The directories on the four platter-sides are: (LAPI01) (LAPI02) (LAPI03) (LAPI04) 81247_81275 81334_81362 82123_82143 82249_82273 81276_81295 81363_82020 82144_82164 82274_82291 81296_81314 82021_82046 82165_82184 82292_82313 81315_81333 82047_82098 82185_82209 82314_82334 82099_82122 82210_82248 82335_82359 82360_83022 83023_83049 There are two files that list the names/time-coverages/directories of the data files (*.SATM). One of these files lists this information for the "current" platter-side, and the other file lists this for all four platter sides. The format of these two lists is the same, and is described in the file LISTFORM.SFD . TYPES_OF_DATA_FILES_INCLUDED: LAPI SATM FILES ONLY SATM_TIME_COVERAGE: 1982-09-06T00:29:47 1983-02-18T16:42:20 NAMING_CONVENTION: The start day and time are encoded in the LAPI SATM filename. Each LAPI SATM filename is in the following format: LyrdayhhmmC.SATM' L - indicates a LAPI file (all files in this data set are L) yr - the last two digits of the year, i.e., 81 for 1981 day - the Julian day (Jan 1 = 001) hh - the starting hour of the file mm - the starting minute of the file C - the production version of the file (most files in this data set are C, the few files from the Sigma-9 are D - see B. HISTORY) SATM - the extension, indicating it is a Stand Alone Telemetry File For example: L812471037C.SATM would be a LAPI SATM file which started at 10:37 on Julian day 247 in 1981. FILE_TIME_COVERAGE: See LOG_VOL_COVERAGE, above, and See NAMING_CONVENTION, above, and See file THIS_SIDE.DATA_FILE_LIST, and See file ALL_4_SIDES.DATA_FILE_LIST. OTHER_LOG_VOL_COVERAGE: 1981-09-04 TO 1981-11-29 1981-11-30 TO 1982-05-02 1982-05-03 TO 1982-09-05 CCSD$$MARKERMRK**003CCSD3RF0000300000001 REFERENCETYPE=$CCSDS2; LABEL=ATTACHED; REFERENCE="/LAPI/FORMAT.SFD"; REFERENCE="/LAPI/LISTFORM.SFD"; LABEL=CCSD3SF0000200000001; REFERENCE="/LAPI/HLAPI_SOFTWARE.TAR-GZ-*"; REFERENCE="/LAPI/HOW_TO_USE_REDUCE_SATM.TXT-*"; LABEL=NSSD3IF0013000000001; REFERENCE="/LAPI/82249_82273/*.SATM-*"; REFERENCE="/LAPI/82274_82291/*.SATM-*"; REFERENCE="/LAPI/82292_82313/*.SATM-*"; REFERENCE="/LAPI/82314_82334/*.SATM-*"; REFERENCE="/LAPI/82335_82359/*.SATM-*"; REFERENCE="/LAPI/82360_83022/*.SATM-*"; REFERENCE="/LAPI/83023_83049/*.SATM-*"; LABEL=NSSD3KF0012900000001; REFERENCE="/LAPI/THIS_SIDE.DATA_FILE_LIST-*"; REFERENCE="/LAPI/ALL_4_SIDES.DATA_FILE_LIST-*"; /* (EOF) */