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Resource ID | spase://VMO/NumericalData/THEMIS/B/FBK/PT4S | ||||||||||||||||||
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Name | THEMIS-B: Probe Electric Field Instrument and Search Coil Magnetometer Instrument, Digital Fields Board - digitally computed Filter Bank spectra and E12 peak and average in HF band. | ||||||||||||||||||
Description | The Filter Bank is part of the Digital fields board and provides band-pass filtering for EFI and SCM spectra as well as E12HF peak and average value calculations. The Filter Bank provides band-pass filtering for less computationally and power intensive spectra than the FFT would provide. The process is as follows: Signals are fed to the Filter Bank via a low-pass FIR filter with a cut-off frequency half that of the original signal maximum. The output is passed to the band-pass filters, is differenced from the original signal, then absolute value of the data is taken and averaged. The output from the low-pass filter is also sent to a second FIR filter with 2:1 decimation. This output is then fed back through the system. The process runs through 12 cascades for input at 8,192 samples/s and 13 for input at 16,384 samples/sec (EAC input only), reducing the signal and computing power by a factor 2 at each cascade. At each cascade a set of data is produced at a sampling frequency of 2^n from 2 Hz to the initial sampling frequency (frequency characteristics for each step are shown below in Table 1). The average from the Filter Bank is compressed to 8 bits with a pseudo-logarithmic encoder. The data is stored in sets of six frequency bins at 2.689 kHz, 572 Hz, 144.2 Hz, 36.2 Hz, 9.05 Hz, and 2.26 Hz. The average of the coupled E12HF signal and it's peak value are recorded over 62.5 ms windows (i.e. a 16 Hz sampling rate). Accumulation of values from signal 31.25 ms windows is performed externally. The analog signals fed into the FBK are E12DC and SCM1. Sensor and electronics design provided by UCB (J. W. Bonnell, F. S. Mozer), Digital Fields Board provided by LASP (R. Ergun), Search coil data provided by CETP (A. Roux). Table 1: Frequency Properties. Cascade | Frequency content of Input Signal | Low-pass Filter Cutoff Frequency | Freuency Content of Low-pass Output Signal | Filter Bank Frequency Band 0* 0 - 8 kHz 4 kHz 0 - 4 kHz 4 - 8 kHz 1 0 - 4 kHz 2 kHz 0 - 2 kHz 2 - 4 kHz 2 0 - 2 kHz 1 kHz 0 - 1 kHz 1 - 2 kHz 3 0 - 1 kHz 512 Hz 0 - 512 Hz 512 Hz - 1 kHz 4 0 - 512 Hz 256 Hz 0 - 256 Hz 256 - 512 Hz 5 0 - 256 Hz 128 Hz 0 - 128 Hz 128 - 256 Hz 6 0 - 128 Hz 64 Hz 0 - 64 Hz 64 - 128 Hz 7 0 - 64 Hz 32 Hz 0 - 32 Hz 32 - 64 Hz 8 0 - 32 Hz 16 Hz 0 - 16 Hz 16 - 32 Hz 9 0 - 16 Hz 8 Hz 0 - 8 Hz 8 - 16 Hz 10 0 - 8 Hz 4 Hz 0 - 4 Hz 4 - 8 Hz 11 0 - 4 Hz 2 Hz 0 - 2 Hz 2 - 4 Hz 12 0 - 2 Hz 1 Hz 0 - 1 Hz 1 - 2 Hz *Only available for 16,384 Hz sampling. | ||||||||||||||||||
Acknowledgement | NASA Contract NAS5-02099 | ||||||||||||||||||
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Release date | 2008-12-06 01:08:40 | ||||||||||||||||||
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Provider version | xxxx | ||||||||||||||||||
Instruments | THEMIS-B Electric Field Instrument THEMIS-B: Search Coil Magnetometer |
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Measurement type | Electric field Magnetic field Spectrum |
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Instrument ID | spase://SMWG/Instrument/THEMIS/B/EFI | ||||||||||||
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Name | THEMIS-B Electric Field Instrument | ||||||||||||
Alternate name | THEMIS-B EFI |
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Description | The Electric Field Instrument (EFI) on the THEMIS spacecraft measures the three components of the ambient vector electric field. Measurements are performed using four wire spin plane booms and two rigid axial booms. Waveform measurements cover DC up to 4 kHz (with AC-coupled differential measurements from ~10 Hz up to 8 kHz), with on-board spectral measurements covering the same ranges, as well as providing an estimate of integrated power in the 100- to 400-kHz band. On-board spin-fit E-field estimates are also provided for both the spin plane and axial measurements. On-board estimates of the spacecraft floating potential are also produced for use in particle moment calculations and burst trigger evaluations. Both individual (Vn, n=1..6) and differential (Emn = Vm – Vn, m,n = [(1,2), (3,4), (5,6)]) sensor potentials are measured. Booms 1 & 2 are in the spin plane and have a length from tip to tip of 49.6 meters. Booms 3 & 4 are in the spin plane and have a length from tip to tip of 40.4 meters. Booms 5 & 6 are the axial booms and have a length from tip to tip of 5.63 meters. The differential sensor potentials are used to estimate the ambient vector E-field. The individual sensor potentials are used to verify proper sensor operation, estimate the spacecraft floating potential, and measure the ambient plasma density with high (sub-spin-period) time resolution. Ground based electric field magnitude and direction measurements are provided with the Z component, with the Z component removed, and with the Z component estimated using the E.B=0 equality. The data are provided in DSL (despun spacecraft L-Z vector), GSM, and GSE coordinates. | ||||||||||||
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Acknowledgement | NASA contract NAS5-02099 and V. Angelopoulos for use of data from the THEMIS Mission. Specifically: J. W. Bonnell and F. S. Mozer for use of EFI data. | ||||||||||||
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Release date | 2008-12-05 02:24:47 | ||||||||||||
Prior ID | spase://SMWG/Instrument/THEMIS-B/EFI |
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Instrument type | Antenna DoubleSphere |
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Investigation name | THEMIS Electric Fields Instrument | ||||||||||||
Observatory | THEMIS-B | ||||||||||||
Caveats | Measurements on the axial booms(5 & 6) may have large errors due to their proximity to the spacecraft (the axial booms are much shorter than other booms). The spin plane booms for THEMIS B were not deployed until November 17, 2007 at 0600 UT, any EFI measurements before this date should not be used. |
Instrument ID | spase://SMWG/Instrument/THEMIS/B/SCM | |||||||||
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Name | THEMIS-B: Search Coil Magnetometer | |||||||||
Alternate name | THEMIS-B SCM |
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Description | THEMIS-B Search Coil Magnetometer for measuring three dimensional changes in magnetic flux between 0.1 Hz and 4 kHz; the range extending to 8 kHz under certain conditions. The instrument is mounted on a ridged, retractable boom one meter in length extending from the top corner of the spacecraft (positive y-axis, negative x-axis in SPG coordinates). The SCM boom deploys at an angle of -167.9 degrees from the x-axis (SPG) and 10.1 degrees above the spin plane. Two of the probe's sensors are aligned within the spin plane of the spacecraft, with the B_x component 12.1 degrees from the SPG x-axis, the third being parallel to the spin axis completing a right handed orthogonal system. The three sensors are composed of two windings surrounding a core with a high magnetic permeability. The main winding, used for detection, consists of 51600 turns; the secondary winding introduces a flux feedback to damped the frequency response of the sensor and keep it independent of temperature variation. Multi-Layer Insulation keeps the probe thermally insulated while electrostatic shielding reduces its sensitivity to electric fields. Low noise at slower frewencies allows for sufficient overlap with Fluxgate Magnetomer (FGM) measurements (noise less than 0.76 pT/sqrt(Hz) at 10 Hz). Data from the SCM is passed through three pre-amplifiers, one for each sensor component, before going on to the DFB and IDPU for processing and digitization. Survey modes for the SCM are listed below in Table 1. Table 1: SCM Telemetry Modes. Filter Bank (fbk)*: Mean signal value over 6 frequency bands (4-2 kHz, 1-0.5 kHz, 256-128 Hz, 64-32 Hz, 16-8 Hz, 4-2 Hz); sampling rate of 1/16 to 8 S/s. Fast Survey (scf): Waveform data for the 3 SCM components; sampling rate between 2 and 256 S/s, nominal value is 8. Particle Burst (scp): Waveform data nominally at 128 S/s. Wave Burst (scw): Waveform data nominally at 8192 S/s. Particle Burst Spectra (ffp)**: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s. Wave Burst Spectra (ffw)**: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s. *Only two available inputs between all 3 SCM and 12 EFI data signals. **Only four available inputs between 3 SCM and 16 other data signals. | |||||||||
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Acknowledgement | NASA contract NAS5-02099, V. Angelopoulos for use of data from the THEMIS Mission; also A. Roux and CETP for their work on the SCM. | |||||||||
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Release date | 2008-12-09 21:38:17 | |||||||||
Instrument type | Magnetometer SearchCoil |
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Investigation name | THEMIS Search Coil Magnetometer | |||||||||
Observatory | THEMIS-B |
Observatory ID | spase://SMWG/Observatory/THEMIS/B | |||||||||
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Name | THEMIS-B | |||||||||
Alternate names | Explorer 86 2007-004B MIDEX/THEMIS THEMIS-P1 30581 |
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Description | The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is a five-satellite Explorer mission whose primary objective is to understand the onset and macroscale evolution of magnetospheric substorms. Most importantly, THEMIS will find out which magnetotail process is responsible for substorm onset: (a) a local disruption of the plasma sheet current; or, (b) that current's interaction with the rapid influx of plasma emanating from lobe flux annihilation at ~25Re. Three inner probes at ~10Re will monitor current disruption onset, while two outer probes, at 20 and 30Re respectively, will remotely monitor plasma acceleration due to lobe flux dissipation. The five small satellites were launched together on a Delta II rocket and they carry identical sets of instruments including an electric field instrument (EFI), a flux gate magnetometer (FGM), a search coil magnetometer (SCM), a electro-static analyzer, and solid state telescopes (SST). The mission consists of several phases. In the first phase, the spacecraft will all orbit as a tight cluster in the same orbital plane with apogee at 15.4 Earth radii (RE). In the second phase, also called the Dawn Phase, the satellites will be placed in their orbits and during this time their apogees will be on the dawn side of the magnetosphere. During the third phase (also known as the Tail Science Phase) the apogees will be in the magnetotail. The fourth phase is called the Dusk Phase or Radiation Belt Science Phase, with all apogees on the dusk side. In the fifth and final phase, the apogees will shift to the sunward side (Dayside Science Phase). All five satellites will have similar perigee altitudes (1.16-1.5 Re) but varying apogee altitudes (P1: ~30 RE, P2: ~20 RE, P3 & P4: ~12 RE, P5: ~10RE) with corresponding orbital periods of ~4, 2, and 1 days, respectively. This results in multi-point magnetic conjunctions. Every four days the satellites will line up along the Earth's magnetic tail with magnetic foot points in the North American sector, allowing the tracking of disturbances through different geospace regions from tail to ground. The satellite data will be combined with observations of the aurora from a network of 20 ground observatories (all sky imagers, magnetometers) across the North American continent. In addition to its primary goal, THEMIS will answer critical questions in radiation belt physics and solar wind - magnetosphere energy coupling. THEMIS is complementary to MMS in terms of the temporal and spatial scales of the phenomena observed by these two constellation missions. THEMIS's focus is macroscale, whereas MMS will observe micro/meso scale features. | |||||||||
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Acknowledgement | National Aeronautics and Space Administration/United States | |||||||||
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Release date | 2008-11-11 22:24:55 | |||||||||
Prior ID | spase://SMWG/Observatory/THEMIS-B |
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Observatory group | THEMIS | |||||||||
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Name | Dr. Robert E. Ergun |
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Organization | University of Colorado |
Person ID | spase://SMWG/Person/Robert.E.Ergun |
Name | Dr. Alain Roux |
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Organization | CNRS Centre de Recherches en Physique de L Environ |
Person ID | spase://SMWG/Person/Alain.Roux |
Name | Dr. David G. Sibeck |
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Organization | NASA/GSFC, Code 672 |
Person ID | spase://SMWG/Person/David.G.Sibeck |
Repository ID | spase://SMWG/Repository/NASA/GSFC/SPDF/CDAWeb | ||||||
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Name | CDAWeb Data Repository FTP Interface | ||||||
Description | Coordinated Data Analysis Web (CDAWeb) supports not only interactive plotting of variables from multiple instruments on multiple investigations simultaneously on arbitrary, user-defined time-scales. It also supports data retrieval in various formats using its interactive web interface or ftp service. | ||||||
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Release date | 2008-08-26 21:14:34 | ||||||
Prior ID | spase://VMO/Repository/CDAWeb |
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