AUREOL-3 SAMPLE DATA ON PARTICLES AND FIELDS I N T R O D U C T I O N The main scientific objectives of the Soviet-French ARCAD-3 Project on the AUREOL-3 near-Earth satellite (1981-1986) were to study magnetospheric plasma processes including measurements of auroral particles, electromagnetic fields, thermal plasma variations, auroral field-aligned currents and related auroral emissions. The satellite measurements were often coordinated with ground-based measurements of magnetospheric phenomena, which helped in the analysis of the time/space development of the observed phenomena. The set of complementary plasma detectors flown on the AUREOL-3 satellite was developed partly in the USSR, partly in France, and partly together. This set is unique by its instruments' sensitivity and precision, and by its coverage of the near-Earth plasma characteristics during this period of intensive magnetosphere-ionosphere plasma research by several simultaneously operating satallites including Dynamics Explorers 1 and 2, Intercosmos-Bulgaria-1300, topside ionosphere sounder Intercosmos-19, etc., together with several high altitude magnetosphere/solar wind research satellites such as IMP-8, ISEE-1,2 and 3, VIKING, etc. The full description of the ARCAD-3 Project, the AUREOL-3 satellite, the onboard instrument set, together with the first scientific results obtained, was published in the special number of the Annales de Geophysique, v.38, N 5 (Numero Special), pp.543 - 723, 1982. Since then, more than a hundred scientific publications and scientific reports based on the data of the ARCAD-3 Project have been published in refereed scientific journals and presented at international scientific symposia. The analysis of the AUREOL-3 data is still ongoing. This is due to the high quality of the data and their uniqueness in certain aspects, such as the high sensitivity of the 4 channel fixed energy particle detector which usually allows measurement of the weak ion and electron precipitation above the polar caps, wave-form data on 5 components of the electromagnetic field in parallel in the 0.01-1.6 kHz range, uniquely high precision (deltaN/N ~ 10^-4) at time resolution (1 msec) in electron density measurements, etc. New insights into magnetospheric and ionospheric physical processes may be obtained from comparisons of AUREOL-3 data with simultaneous data from other spacecraft during that period, combined with progress from theory and recent experiments. Sample data are archived and accessible for time periods ranging from October, 1981 to April, 1985 (93% of the data are for October 1981 to June 1982). The data are from three Aureol-3 instruments and have been initially prepared for writing onto a pair of CD-ROMs. The data and their locations on CD-ROM are: a) low-energy electron and proton fluxes and pitch angles (4 constant energy channels of high sensitivity, plus the locations of specific particle precipitation boundaries determined by these and other particle detectors onboard, file PRECBORD.TXT) located in the Directory PARTICLE; b) electromagnetic emissions in the VLF frequency band (10 narrow-band filters) located in the Directory VLF; c) magnetic field disturbance data located in the Directory MAGNET. These magnetic disturbances are mostly induced by field-aligned electric currents of magnetospheric origin. All three data sets have their values given in physical units and include geographic location and selected geophysical parameters (invariant coordinates, magnetic local time, solar zenith angle). Descriptions of the data on the CD ROM are contained in the directories PARTICLE, VLF, and MAGNET (file extension - .TXT and .TAB). These files contain the time intervals of the measured data, respective data files, formats and meanings of individual parameters. The filename of a particular data file contains the number of the memory readout telemetry sequence (sometimes referred to as "seance" below) and the instrument indication: the letters "a3k" for particles data, "a3a" for the VLF data, and "tr" for the magnetic data. In the latter filenames, the last digit (after "tr") indicates the number of the recording time interval within the memory readout sequence for which the data are presented. THE SOVIET-FRENCH SCIENTIFIC ARCAD-3 PROJECT, AUREOL-3 SATELLITE 1. SATELLITE NAME: AUREOL-3 (AURora and EOLe) SATELLITE TYPE: AUOS-Z (Automatic Universal Orbital Station). Total mass: 1200 kg, payload ~ 250 kg. Velocity - oriented, gravity-gradient stabilized. LAUNCH : September 21, 1981, Plesetsk, Russia. ORBIT : ha = 2012 km, hp = 408 km, i = 82.5 degrees. AIM : Magnetosphere-ionosphere research. PROJECT SCIENTIST: Yuri I.Galperin, Space Research Institute (IKI) of Russian Academy of Sciences, Profsouznaya str., 84/32, Moscow, 117810, Russia; PROJECT SCIENTIST: Henri Reme, Centre d'Etudes Spatiales des Rayonnements (CESR), Toulouse, France; PRINCIPAL INVESTIGATORS AND SCIENTIFIC INSTITUTES: Christian Beghin, LPCE, Orleans, France, -the PI of the experiment ISOPROBE - Double Mutual Impedance Interferometric Probe (high precision/high time resolution electron density and temperature). Jean-Jacques Berthelier, CRPE, Saint-Maur, France, -the PI of the DYCTION experiment (multi-window thermal ion mass-spectrometer, ion densities and ion temperature); -the PI of the quasi-DC electric field experiment; -the CoPI of the TBF-ONCH multi-component wave experiment; -the CoPI of the magnetometer-TRAC experiment. Jean-Michel Bosqued, CESR, Toulouse, France, -the PI of the experiment SPECTRO - multi-detector low energy particle measurements (energy, angle and ion mass spectra); Yuri I. Galperin, IKI of Russian Academy of Sciences, Moscow, Russia, -the PI of the low energy particle experiment (4 parallel fixed energy channels). Vladimir A. Gladyshev, IKI, Moscow, Russia, -the CoPI of the magnetometer-TRAC experiment. Rostislav A. Kovrazhkin, IKI, Moscow, Russia, -the PI of the high energy particle experiment (4 channel electron and 4 channel proton solid-state spectrometer). Alexander K. Kuzmin, IKI, Moscow, Russia, -the PI of the auroral photometry experiment (3 photometers for visible auroral lines and a stellar photometer). Francois Lefeuvre, CRPE, Orleans-la-Source, France, -the CoPI of the TBF-ONCH multi-component wave experiment. Oleg A. Molchanov, IZMIRAN of Russian Academy of Sciences, Troitsk near Moscow, Russia; -the CoPI of the TBF-ONCH multi-component wave experiment. For a full description of the project, scientific instruments, the satellite, data treatment, etc., see papers in Annales de Geophysique, 38, N 5 (Numero Special), 543-723, 1982. TELEMETRY: memory modes named ZAP1 (10 ms per second per channel), ZAP2 (80 ms), ZAP3 (320 ms) and ZAP4 (2.56 s). Sample data from three instruments were prepared for archiving in 1996, were provided to NSSDC, and are discussed in detail below. Please, NOTE: Often within a seance there were switches from one to another telemetry mode, and/or temporary interruptions of data flow according to a particular measurement program chosen by the Scientific Control Group of the Project. The data files for each experiment have a complex structure: the header records and the data records have different formats; segments of different time resolution may be found within the same file. Therefore we have provided a program (ARCAD.EXE) which displays the segments of each file and enables the user to select and output the desired segment. The format of this output file corresponds to the data format for a given experiment (see description), but the date (YY MM DD) is added at the beginning of each record. 2. SHORT DESCRIPTIONS OF INSTRUMENTS, DATA TREATMENT AND PRESENTATION 2.1. LOW ENERGY PARTICLES Particle detector RIEP-2802 was developed and built in Russia. It is a large geometric factor 4-channel electrostatic spectrometer with spectral resolution (deltaE)/E ~ 0.2. For a detailed description see Galperin et al., Annales de Geophysique, v.38, N 5, p. 583, 1982. Two detector channels were for electrons, two channels for ions, all working in parallel. Among 8 energy steps possible only four were used in the seances presented below. They are identified in the heading of respective data column in each data file by the particles' central energy for each of the 4 deectors (NSTEP ranging from 0 to 3, see Table 2.1). The Table 2.1. gives the respective central energies for these energy steps: Table 2.1. ----------------------------------------------------------------- NSTEP: Low energy : Low energy : Medium energy : Medium energy :electrons (eV): ions (eV) : electrons(keV) : ions (keV) ----------------------------------------------------------------- 0 <10 <10 <0.01 <0.01 1 40 40 0.76 0.76 2 60 60 1.20 1.20 3 100 100 1.80 1.80 ----------------------------------------------------------------- In the data files the values of the particle number flux is given in the data columns in units: particles per square cm per second per steradian per keV. Also given are the NSTEP code (in most of the seances, but not always, unchanged during a telemetry mode within a seance), and pitch-angles (angles of the local magnetic field direction with the particle velocity along a particular detector axis) for the electrons (ae) and ions (ie) in degrees. These angles are evaluated from the onboard magnetometer data. Please, note that in a data file the first 1-7 rows usually give spurious data due to telemetry and instrument switched and decoding programs adjustments, AND THUS MUST BE DISCARDED. Besides, the locations of the typical particle precipitation boundaries deduced from the above channels and other particle detectors onboard, together with their INVARIANT LATITUDE/MAGNETIC LOCAL TIME, and definitions of the boundaries, are given in the separate file PRECBORD.TXT. 2.2. VLF FILTER-BANK The combined Soviet-French ONCH-TBF onboard instrument (for a full description see Berthelier et al., Ann. Geophys., v.38, N 5, p.643, 1982) had in memory modes the data only from several filter-banks in the range from 10 Hz to 16 kHz (while in the real-time telemetry modes, not presented here, the measurements included 5-component wave-form data in the range 10 Hz - 1.5 kHz for 3 magnetic and 2 electric field components, or a wide-band mode in the range 10 Hz - 15 kHz, and several filter banks). The components of electromagnetic field are named by their direction in the SATELLITE FRAME or, the S/C FRAME. Thus the BZ (magnetic), and EZ (electric) components are along the satellite's Z-axis, BX is along the X-axis, BX45 is in the XY-plane at 45 degrees between the X- and Y-axis, EH is in a plane making an angle of 18 degrees with the YZ plane and at an angle of 11.5 degrees with the XY plane. This distribution of the measurement axes was partly due to constraints implied by the satellite construction. The data presented here are from the ACP filter bank which included 5 pairs of narrow band (~10%) filters (ACP1-ACP10). Their center frequencies are given in the Table 2.2. Table 2.2. ------------------------------------------------------------------- Filter : ACP1 and : ACP2 and : ACP3 and :ACP4 and : ACP5 and : ACP6 : ACP7 : ACP8 : ACP9 : ACP10 ------------------------------------------------------------------- Center Frequency 140 450 800 4.500 15000 (Hz) ------------------------------------------------------------------- The name of the electric and/or magnetic field component sampled by a filter is given by the code F/S. The Table 2.3. gives the coding (which is repeated in a data file in each data line. During a seance it can be fixed (regime "STOP"), or cycling, changing each 4 seconds in the 16 seconds period in one of the following sequences: (1,3,2,5) or (1,4,2,5). Table 2.3. ------------------------------------------------------------------ Code F/S : Field component for : Field component for : ACP1-ACP5 : ACP6-ACP10 ------------------------------------------------------------------ 1 EZ BX 2 EH EZ 3 EH BZ 4 EH BX45 5 BZ BX ------------------------------------------------------------------ For the instrument switched off, the F/S = 0. The data in a file (for a seance) contain the UT time (hh-mm-ss-mss), the code F/S, the component name, 10 columns for ELF/VLF wave intensities in the ACP1-ACP10 filters (in physical units). They are accompanied by the geographic coordinates (3 columns) and geophysical parameters (invariant coordinates, etc. - 5 columns). Please, note that in a data file, the first 1-7 rows usualy give spurious data due to telemetry and instrument switches and decoding programs adjustments, AND THUS MUST BE DISCARDED. 2.3. MAGNETIC FIELD The combined Soviet-French TRAC experiment was aimed to measure magnetic field variations due to auroral field-aligned currents. The signals ofthe onboard magnetic field detector for attitude restitution were read and treated by the TRAC device in a way of a "zoom". Each of the three magnetic components measured, once in 43 seconds, was digitized to 12 bits, and these values, together with the difference analog signal (currently measured value minus the last digitized) were given to telemetry. (For a full description see Berthelier et al., Annales de Geophysique, v.38, N 5, p.635, 1982). One of the main difficulties in the treatment of the vector magnetic measurements from a satellite is the account of the satellite attitude. The gravity-gradient oriented satellite of about 1200 kG mass slowly oscillated around the nominal ORBITAL PLANE ORIENTATION (one axis along the local vertical, another axis along the velocity vector, the third axis to form a right- hand frame). The angular amplitude from the nominal orbital plane can reach sometimes 15 degrees. Another attitude problem with this satellite is that after a crossing of the solar terminator, the satellite oscillated during several minutes with a period of about 40 seconds due to thermal shock on the 17 meter boom carrying a floating magnet for damping of the satellite's oscillations. Besides that, during intervals where at least one of the magnetic field components changed rather fast, the damping magnet rotated non-homogeneously inducing additional oscillations. In such cases this component could change more than 1420 nT during 43 seconds driving the TRAC signal off scale, and a constant scale limit was given to the output. After the measured vector rotation from the magnetometer axis frame to the S/C FRAME these off scale constant values lead to false deviations in all three components ending just before the end of 43-seconds interval. These satellite's motions around its center of mass, and off-scalings, when they occur, make the problem of automated attitude restitution quite difficult. Thus, in the data presentation below a simplifying assumption about the satellite attitude was adopted for the mass data treatment as described below. However, the auxiliary data columns are provided in a data file which allow an experienced user to determine, and then use, a more precise attitude from the same magnetometer, or from more precise TRAC data. The onboard standard magnetometer was mounted on a short boom, and its output was digitized to 8 bit word giving about 300 nT/bit. These original data are also given in the files below with the title MAGNX, MAGNY, MAGNZ in units nT. These standard data were originally aimed to only technological purposes of the satellite's attitude restitution. When looked through the TRAC "zoom", this magnetometer had a noise up to about 13-26 nT, a magnetic deviation and zero shifts. These factors became noticeable when the magnetometer outputs were digitized to 12 bits by the "zoom" provided by the TRAC device. Thus these magnetic data are obviously not of a quality of a typical scientific satellite magnetometer. But still, after some averaging, they may be used for evaluation of medium-scale (~ 50 - 500 km) field-aligned current direction and approximate magnitude. 2.3.1. TRAC DATA - TELEMETRY OUTPUT The TRAC device digitized the magnetometer detector outputs (3 components of the magnetic field) once in 43 seconds to 12 bit words (about 13 nT/bit). These data were readout through an additional telemetry channel. Then for each magnetic component the output signal (currently measured minus the last digitized) was zeroed, and the difference signal was given to the telemetry during the next 43 seconds, till the new 12 bit digitization, and so on. It produced for each magnetic component an analog saw-tooth shape output signal, and periodic 12 bit digital base values, which are the basis for the further data treatment. 2.3.2. TRAC DATA - TREATMENT First of all, the times of 12 bit digitalisation/zeroing are determined for each component, spurios points removed, the base values are smoothed. The resulting base values (in nT) measured once in 43 seconds, are given in the columns with the names BXSAT, BYSAT, BZSAT in the S/C FRAME of reference. These base values are qualified by the NOISE CODE for each component (a column in a data file, see below). The coding is: 0 is an unchanged measured value; 1 - a digital zeroing point (unchanged); 2 - a value that was interpolated, or otherwise modified during the treatment. Using these data (the base values and the saw-tooth TRAC signal between them in the satellite frame), a continuous sequence of the measured values was determined for each component. It is given in the respective columns, in the S/C FRAME, under the names BXSATF, BYSATF and BZSATF. These data are considered as final measured (though in a not convenient frame of reference). They are given in the physical units (in nT). An indirect quality control of the measured magnetic field vector is provided by comparisons of the module of the measured magnetic field with the module of the IGRF80 model field calculated for the measurement date, time and location. The difference between the modules (MEASURED - MODEL) as given in the column BMODIGRF. (Such a control is justified because the local field-aligned current mainly rotates the magnetic field, but nearly does not change its module, while effects of other currents are small and may be neglected). Usually the difference BMODIGRF is less than 500 nT, but occasionally may be larger. If the difference is smooth, this corresponds mainly to a zero shift in one or more components. These zero shifts are not too important for the determination of characteristics of the field-aligned currents because the time/space derivative of a magnetic signal carries the most important information. But if the difference between measured and model modules jumps, this most probably means a spurious noise, or another error, in one or more components, and such a measurement interval must be considred with care. To reduce the quantity of such jumps, a special filtering procedures were applied to the signals, so that when the difference between two sequential points was more than ~ 50 - 100 nT, an interpolation between neighbouring points was applied. If real, such jumps would imply abnormally large field-aligned current densities (which, however, cannot be absolutely excuded). Such a smoothing technique is somewhat similar to a sliding average procedure but applied locally. The large-scale signal trends are present in the these data due to large-scale geomagnetic field gradients along the satellite trajectory. To remove these trends by subtracting the model IGRF80 magnetic field, the rotation must be performed of the magnetic vector from the S/C FRAME, to the ORBITAL FRAME. It needs the knowledge of the precise satellite attitude in respect to its ORBITAL FRAME. However, while for parts of some orbits the time-dependent transformation for the magnetic vector rotation from the S/C FRAME to the ORBITAL FRAME was determined, its availability and precision are inadequate for the majority of the data given here. In view of this, here it was adopted for simplicity, as an approximation, that the S/C FRAME of reference is coincident with the ORBITAL FRAME. (ORBITAL FRAME of reference is the frame with the Z-axis vertically upward, X-axis along the satellite's velocity vector, and Y-axis forming the right-hand frame). The IGRF80 model magnetic field vector is rotated to the ORBITAL FRAME. Its components are given in the data files in the columns BXIGRF, BYIGRF, BZIGRF in the ORBITAL FRAME. These values then were subtracted from the respective full field measured components BXSATF, BYSATF, BZSATF to get the components of the disturbance magnetic field vector, again in the ORBITAL FRAME. Now, this vector is rotated to the GEOMAGNETIC FRAME, This is the output disturbance vector with the components DBXGM, DBYGM, and DBZGM in the GEOMAGNETIC FRAME, which is given in the first data columns just after the UT time. These results of the TRAC magnetic field data treatment allow to analyse short-term variations of the magnetic field due to field-aligned currents. These signal variations are superimposed with the variations due to the satellite's motions around its center of mass which were described above, to zero shifts of the magnetometer-TRAC system, and to not-precise attitude. Due to the simplification adopted concering the satellite's attitude (see above), a given X- and/or Y-component's value can reach 10 000 nT or sometimes even more. Besides that, the effects of the neglected satellite's motions around the center of mass are still present in the output components DBXGM, DBYGM, and DBZGM. It may be noted that only the time/space derivative of a component value is significant for evaluation of the field-aligned current direction. Differentiation of the signal with respect to time/space removes the rest of the slow trend and zero shifts from the data. Thus even a large but slowly varying shift of a component due to a not-precise satellite attitude and magnetometer zero shift is not very important for the scientific aims of the TRAC experiment. However, if an experienced user would like to determine the satellite attitude more precisely, the auxiliary information given in the data files allows to do that. Indeed, the same magnetometer signals, or more precise TRAC signals in the satellite frame, are to be used together with the information on the IGRF80 field components given in other columns of the data files. The last 8 columns of the data file give characteristics of the point in space of the measurement: In the 3 columns named ALT, LAT, LONG, the location of the AUREOL-3 satellite at the particular moment of time is given: ALT - geographic altitude, LAT - geographic latitude, and LONG - geographic longitude, calculated with the CADR4 program for geophysical reference data along the orbit. In the next columns the following geophysical characteristics of a measurement point in the near-Earth's space are given: The 3 columns give the invariant coordinates: L is the McIlwain's parameter of the magnetic drift shell (in Earth's radii), LO - invariant latitude in degrees, LO=arc cos (SQRT(1/L)), BMAG - module of the IGRF80 magnetic field in units milligauss (1 milligauss=100 nT), The last 2 columns give: MLT - magnetic local time in hours.decimal part of hour (calcu- lated for the centered dipole magnetic coordinates), and ZSUN - solar zenith angle ( from the local zenith to the direction to the Sun center) in degrees. --------------------------------------------------------------- Project definition: Prof. Yuri I. Galperin, IKI, Russia. Dr. Joseph H. King, NASA/National Space Science Data Center Dr. Vladimir O. Papitashvili University of Michigan Data processing : Dr. Nikolai V. Jorjio, IKI, Russia. Dr. Mikhail V. Veselov, IKI , Russia. Dr. Leonid V. Zinin, Kaliningrad State University, Russia Mr. Dmitriy Chugunin, IKI,Russia. Ms. Ludmila I. Masuk, IKI,Russia. ---------------------------------------------------------- The ARCAD-3 SAMPLE DATA CD-ROM has been created at the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A. by: Prof. Yuri I. Galperin ARCAD-3 Progect Scientist, IKI, RUSSIA Dr. Joseph H. King Head, NASA/National Space Science Data Center Dr. Natalia E. Papitashvili NASA/National Space Science Data Center ------------------------------------------------------------------------- The ARCAD-3 CD-ROM can be ordered from the Coordinated Request and User Support Office (CRUSO) at NSSDC, which will also respond to any questions about the CD-ROM. ------------------------------------------------------------------------- ------------------------------------------------------------------ Related data and directories: SPDF Data and Orbits Services ------------------------------------------------------------------- SPDF Contact: Natalia Papitashvili ------------------------------------------------------------- Please acknowledge NASA's Space Physics Data Facility and and relevant scientists identified above for data usage. -------------------------------------------------------- Authorizing NASA Official: Dr. R.E. McGuire, Head, SPDF, NASA Goddard Space Flight Center 301-286-7794, e-mail: Robert.E.McGuire@nasa.gov ------------------------------------------------------------------------- ----------------------------------------------------------------------------------