Document title: Voldesc.sfd for NDADS DE LANG_ASCII datatype Project: DE NDADS Datatype: LANG_ASCII Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: LANG_VOLDESC_DE.SFD TRF entry: B46554.txt in NSSDC's controlled digital document library, Feb. 1998. Document text follows: ---------------------- CCSDXZLM0001SMARK001CCSDXVNM0002SMRK0001 LOG_VOL_IDENT: USANASANSSDDEB9_0001 LOG_VOL_CLOSING_DATE: 1989-10-31 LOG_VOL_FILE_STRUCTURE: FILES-11 TAPE_DENSITY=6250 BPI TAPE_TRACKS=9 TAPE_LENGTH=2400 INCHES COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: MICROVMS 4.7 COMPUTER_SYSTEM: MICRO VAX II TECHNICAL_CONTACT: DR. W. R. HOEGY CODE 614 NASA/GSFC GREENBELT, MD 20771 PHONE: 301-286-3837 SPAN: DE614::, DEIO::HOEGY, PACF::HOEGY PREV_VOL_IDENT: NONE CCSDXVNM0002EMRK0001CCSDXKNM0002SMRK0003 DATA_SET_NAME: LANG ELECTRON DENSITY AND TEMPERATURE DATA_SOURCES: DYNAMICS EXPLORER B, LANGMUIR PROBE (LANG) INVESTIGATOR_CONTACT: MR. LARRY H. BRACE CODE 614 NASA/GSFC GREENBELT, MD 20771 PHONE: 303-286-8575 SPAN: DE614::HOEGY 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 mag- netosphere, 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 tem- perature spectrometer, Fabry-Perot interferometer, 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, all- owing 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 original- ly targeted at 30%. The lifetime of the spacecraft was shorter than anti- cipated because of the less than nominal performance of the launch vehicle. The launch was on Aug. 3, 1981 and the DE-2 satellite reentered the atmosphere on Feb. 19, 1983, with the last contact the day before. TIME_SPAN_OF_THE_DATA: 8-AUG-81 TO 15-JAN-83 INVESTIGATION_OBJECTIVES: The LANG objective was to provide electron temperature, plasma density, and spacecraft potential at high resolution of 0.5 seconds to study energetics of the thermal plasma and density structure of the ionosphere including large scale structures, traveling ionospheric disturbances, and plasma waves. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT: The Dynamics Explorer Langmuir Probe Instrument (LANG) performs in-situ measurements of electron temperature and ion density. Two independent sensors are connected to individual adaptive sweep voltage circuits which continuously track the changing electron temperature and spacecraft potential while autoranging electrometers adjust their gain in response to the changing plasma density. Each voltage sweep takes place in 0.5 seconds. The control signals used to achieve this automatic tracking provide a continuous monitoring of the ionospheric parameters (at 0.5 second resolution) without telemetering each volt-ampere curve. The volt-ampere curves are transmitted twice every 8 seconds (50 samples during one 0.5 second sweep) using digital (10 bit accuracy) stored data. Analog data is digitized by the spacecraft at 8 bit resolution and provides volt-ampere data at 64 samples/second. During much of the mission probe 1 was in the ion hold mode providing 64 samples/second resolution ion density data via the analog data channel. (See Space Science Instrumentation, Vol 5, 493, 1981). B. OPERATION_MODE: Inflight electron temperature, ion and electron density, and satellite potential are detected every 0.5 second. Two stored volt-ampere curves are detected every 8 seconds. analog volt-ampere curves every 0.5 second at a rate of 64 samples/second. Normal operating mode is: probe 2 in adaptive mode to give electron temperature and ion density; probe 1 in ion hold mode to give high resolution ion density at 64 samples/second. C. MEASURED_PARAMETERS: Electrometer gain and applied voltage (start and slope) settings for every 0.5 second framed volt-ampere sweep are directly sensed. These telemetered engineering parameters are used to derive the inflight values of ion density, electron density, electron temperature, and satellite potential based on calibration with the raw volt-ampere data. Electrometer gain and applied voltage of volt-ampere curves for stored and analog data channels are telemetered for ground analysis. The geophysical parameters, electron temperature, ion density, satellite potential, and electron density, are derived from this raw volt-ampere data. 64 sample/second ion density is derived from the analog volt-ampere data when probe 1 is in ion hold mode. D. PERFORMANCE_OF_THE_INSTRUMENT: The LANG instrument returned usable data from shortly after launch until reentry. During some spinning orbits the instrument was placed in a special stepping mode to calibrate the accelerated electron current. Probe 2 was successfully cleaned and provided accurate electron temperatures throughout the mission. Probe 1 was contaminated and therefore could not provide accurate temperatures; it did provide accurate, high resolution ion densities. Probe 2 was used for the inflight temperature, density, and satellite potential. E. RESOLUTION: Each LANG record contains 0.5 second resolution engineering parameters from which the inflight electron temperature, electron and ion density, and satellite potential are derived using simple computer code. PARAMETERS: The geophysical parameters derived from the Langmuir probe are electron temperature (Te), plasma density (either ion density Ni from the ion acceleration region of the probe volt-ampere characteristic when the probe is negative with respect to the plasma and measures ion, and electron density Ne from the electron acceleration region when the probe is positive and retards the ions and accelerates the electrons) and satellite potential, Vs which is the potential difference between the probe and the undisturbed ionosphere plasma. These geophysical parameters are derived every 0.5 seconds from a voltage sweep of the probe which generates an internal volt-ampere curve. The curve is framed by adjusting the gain decade and vernier settings so that the accelerated ion current produces an electrometer output voltage of -3.3 volts, the voltage sweep is adjusted so that the electron current produces an electrometer output voltage of 9.5 volts after a voltage difference of 8kTe from the starting voltage. This frames the volt-ampere curve to maxamize the resolution of the temperature and density. The inflight engineering parameters from which Te Ni Ne and Vs are derived are telemetered every 0.5 seconds. The detailed engineering parameters described as follows: IMODE(1:2) 2 bits, mode of each of the two probes = 0 adapt = 1 step = 2 ion hold = 3 electron hold IDED 2 bits, which probe is dedicated IBIAS 2 bits, indicates the extra bias potential applied to the sweep, negative,positive, none. ICMD 1 bit, command, not used IANA 2 bits, which probe is analog ION 1 bit, probe on switch V(1:2) 8 bits, VA start of sweep potential DV(1:2) 10 bits, VA slope for this sweep, Te of last sweep NI(1:2) 10 bits, Current detector range used in this sweep, 2 bits for decade range, 8 bits for vernier range NE(1:2) 10 bits, decade range (2 bits) and curve amplitude (8 bits) giving electron current These engineering parameters are converted to the geophysical electron temperature, ion and electron density, and satellite potential using the subroutines contained in the file LANGSUBROUTINES.FOR on tape LANGDESC. Each file contains a functional description clarifying usage. DATA_SET_QUALITY: The electron temperature and ion and electron density are accurate to about 10% at all altitudes. The subroutine supplied in LANGSUBROUTINES.FOR which converts the engineering parameters to geophysical Te Ni Ne and Vs, has built in limits which only produces Te when the density is greater than 1.E4, and which returns Ni when density is above 2.E4 and Ne when density is below 2.E4. The range of Te is from about 800 K to about 10,000 K, the range of Ni and Ne is: 1.E3 to 1.E6 for Ne and 1.E4 to 1.E7 for Ni; Vs has a possible range of about -10 volts to +7 volts, but is typically at -1.5 to -0.5 volts. DATA_PROCESSING_OVERVIEW: A. DATA_PROCESSING_CYCLE: The raw telemetry data were routinely converted I-files containing the 0.5 second inflight engineering parameters which are converted by the software in LANGSUBROUTINES.FOR into geophysical parameters Te, Ne and Ni. There is one I-file for each day for which data was taken. Each daily I-file contains the telemetry segments listed on the catelog file LANGTAPELIST.DAT. The start and stop times of the telemetry segments are those of the raw telemetry segments. The files LANGSUBROUTINES.FOR and LANGTAPELIST.DAT are supplied on the LANG document file LANGDESC. B. HISTORY: The I-files were produced routinely as telemetry became available. Telemetry was rescanned for missing passes at later times. Duplicate passes or parts of passes should have been eliminated and separate segments joined. The extreme segmentation or length of some telemetry passes resulted in the inability of the Sigma 9 to bring all the data on line within the alloted processing time and results in some passes still being incomplete. All files have been updated to final values and written on VAX formatted tapes. DATA_USAGE: Data are used to obtain the ambient electron temperature, ion density, electron density, and satellite potential. Lists of times when data is bad due to orbit problems or times when the spacecraft was spinning are listed in the files BADLANG.DAT for the bad data and SPINNERSLANG.DAT for the spinning orbits. These files are on the LANG document tape LANGDESC. DATA_ORGANIZATION: LANGMUIR PROBE INFLIGHT DATA ********************************************************************** Stored on 7 tapes labeled Iyyddd where ddd is a multiple of 100 (000,100,200,300) and the tape contains all inflight files from yyddd to yyddd+99. (i.e. 81200-81299) ****************************************************************** <<<<<<>>>>>>>> Some LANG supplied software: To promote data from a tape use PROTAP.COM To promote all data from the tape answer '1ST DAY TO BE PROMOTED' with the yyddd of the tape label and 'LAST DAY TO BE PROMOTED' with the same yyddd+99 (i.e. 82000 and 82099 for tape I82000 and even 82300 and 82399 for tape I82300) To promote less than the entire tape answer '1ST DAY...' and 'LAST DAY...' as per required data (i.e. 82342 and 82345 for days 82342-82345) Once online, to read inflight data into a formatted file use EXAMLANG.EXE which uses subroutines from LANGSUBROUTINES.OBJ (INFL_READ,INFL_CONVER,INF_VGET,FNE,FNI,FNENI) EXAMLANG is the driver which, interactively, gathers the request parameters (date, start time,...) and formats the output (to file or screen). INFL_READ opens the appropriate data file, reads the packed integer data, and places the unpacked (real & integer) data in an array for the calling program (i.e. EXAMLANG) INFL_CONVER unpacks the integer data and applies INF_VGET INFL_VGET transforms the integer data (as stored in TM) into the real and integer temperatures, densities, etc. that it represents using the functions FNE and FNI for Ne and Ni calculations Thus programs needed are: PROTAP.COM and EXAMLANG.EXE or EXAMLANG.FOR, and LANGSUBROUTINES.FOR to be compiled and linked appropriately. Once linked EXAMLANG.EXE looks for the I-file(s) in SYS$MAF and tries to write out any saved data file in SYS$PROC therefore the two following assignments need to be made prior to running EXAMLANG or using PROTAP.COM ASSIGN SYS$MAF ASSIGN SYS$PROC Now you are ready to run. ****************************************************************** The data files themselves: File names are of the form Iyyddd where yy is 81, 82, or 83 and 0=SOME_UT (both times being in msec). Subsequent READ statements can read sequentially by removing the phrase KEYGE=SOME_UT, possibly adding END=label3. The 3rd through 35th words of the record comprise the data. The 3rd word (IDATA(1) above) is satellite specific data (IMODE(1-2), IDED, IBIAS, ICMD, IANA, and ION) packed as follows (((((IMODE(1)*4+IMODE(2))*4+IDED)*4+IBIAS)*2+ICMD)*4+IANA)*2+ION As implied, these seven data are 1 or 2 bit fields. IMODE(1:2) 2 bits, mode of each of the two probes = 0 adapt = 1 step = 2 ion hold = 3 electron hold IDED 2 bits, which probe is dedicated IBIAS 2 bits, indicates the extra bias potential applied to the sweep is not used (SHOULD BE!!!!!!!) ICMD 1 bit, command not used IANA 2 bits, which probe is analog ION 1 bit, probe on? The 4th through 35th words of the record are paired up (i.e. IDATA(2) and IDATA(3), IDATA(4) and IDATA(5), ..., IDATA(32) and IDATA(33)) so that the 16 pairs cover the 16 half-seconds of data in the 8-second interval. These pairs are packed as follows IDATA(2i)=((DV(1)*1024)+DV(2))*1024+NI(1) +1 {if NI(1) is negative} +1024 {if DV(2) is negative} +1024**2 {if DV(1) is negative} where i=1,2,3,...,16 IDATA(2i+1)=((NI(2)*256)+IV)*1024+N +1 {if N=max(NE(1),NE(2)) is negative} +1024 {if IV=max(V(1),V(2)) is negative} +1024*256 {if NI(2) is negative} where i=1,2,3,...,16 These are 8 or 10 bit data fields V(1:2) 8 bits, VA start of sweep potential DV(1:2) 10 bits, VA slope for this sweep, Te of last sweep NI(1:2) 10 bits, Current detector range used in this sweep, 2 bits for decade range, 8 bits for vernier range NE(1:2) 10 bits, decade range (2 bits) and curve amplitude (8 bits) giving electron current The aforementioned subroutines INFL_CONVER and INF_VGET are THE algorithms for, respectively, the unpacking and translation of this array (DATA) of packed integers. CCSDXKNM0002EMRK0003CCSDXKNM0002SMRK0005 LOG_VOL_TIME_COVERAGE: YYYY-MM-DD TO YYYY-MM-DD NAMING_CONVENTION: File names are of the form Iyyddd where yy is 81, 82, or 83 and 0