THEMIS-A: On Board Fast Fourier Transform (FFT) power spectra of Electric (EFI) and Magnetic (SCM) field measurements, for particle and wave burst survey modes.

https://doi.org/10.48322/yj87-yy65

2023-07-30 12:34:56.789

On Board Fast Fourier Transform (FFT) power spectra of Electric (EFI) and Magnetic (SCM) field measurements for particle and wave burst survey modes. Spectra are produced only in Particle Burst and Wave Burst modes; only a preselected four of the signals listed in Table 1 are input at any time. Data fed through the FFT while not in Particle or Wave Burst modes is automatically disgarded. The FFTs (Cooley-Tukey algorithm) are conducted as an integral part of the power spectrum calculation by the Field Programable Gate Arrays (FPGAs). A CORDIC algorithm is used for sine/cosine calculations. The data has raw resolution of 1024 pts for 8,192 sample/sec signals and 2048 pts for 16,384 sample/sec signals (EAC measurements only). Signals at 8,192 samples/sec are handled by 1024-point FFTs, while those at 16,384 samples/sec go through 2048-point FFTs. Past and current signal configurations for specific spacecraft are listed bellow in Table 2. The spectra are arranged into log spaced frequency bins in steps of 16, 32, or 64. Cadence is adjusted to keep packet size constant (i.e. increasing the fequency resolution by a factor of 2 decreases the sampling rate by 1/2). The frequency bins cover a range of 0 Hz to 4 kHz. Table 1: FFT Input Signals. Signal Description SCMX, SCMY, SCMZ: Three axis magnetic fiend from SCM V1 through V6: Probe-spacecraft voltage for all six EFI sensors E12DC, E34DC, E56DC: DC-coupled electric field measured from opposing EFI sensors E12AC, E34AV, E56AC: AC-coupled electric field measured from opposing EFI sensors E12HF: High frequency electric field from EFI Table 2: Spacecraft specific configurations. All probes were initially set to use EDC34, EDC56, SCM2, and SCM3 signals for both particle and wave burst modes. Output was set to 16 frequency bins at 4 Hz. Configuration Changes: 9 June 2008: Particle burst spectra resolution increased from 16 to 64 bins and cadence slowed from 4 Hz to 1 Hz for closer analysis of spectral features. N/A: Particle burst spectra on all probes reconfigured to 64 bins at 1 Hz. 15 Aug 2008: E34DC and E56DC inputs switched to E34AC and E56AC to reduce impact of wake fields on FFT spectral measurements. 15 Oct 2008: Particle burst spectra resolution reduced from 64 to 32 bins and the rate increased from 1 Hz to 2 Hz; a response to noise from plasma wake fields in the 64 bin spectra. Table 3: Instrument-Spacecraft Physical Configuration Instrument Alignment in Spacecraft Geometric coordinates (SPG). See THEMIS website for coordinate system details and mechanical drawings. EFI boom 1: Along positive X-axis EFI boom 2: Along negative X-axis EFI boom 3: Along positive Y-axis EFI boom 4: Along negative Y-axis EFI boom 5: Along positive Z-axis EFI boom 6: Along negative Z-axis SCM *The SCM uses an instrument specific set of axes; an orthogonal system centered instrument with the X-axis 12.1 degrees from the SPG X-axis.

NASA Contract NAS5-02099, V. Angelopoulos for use of data from the THEMIS Mission, also John Bonnell, Michael Cully, Bob Ergun, and Alain Roux for their work on the FFT and related systems.

spase://VMO/NumericalData/THEMIS/A/FFT/PT0.0556S

spase://VSPO/NumericalData/THEMIS/A/FFT/PT0.0556S

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PT0.0556S

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tha_ffp_16_dbpara

FFT Power Spectrum in Particle Burst mode, 16 frequencies for SCM delta-B (parallel to B)

(nT)^2/Hz

1e-18>T^2/Hz

Plots, CDF files, and listings from CDAWeb

tha_ffp_16_dbperp

FFT Power Spectrum in Particle Burst, 16 frequencies for SCM delta-B (perp to B)

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_16_eac12

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field AC Component, Sensors 1 and 2 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_eac34

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field AC Component, Sensors 3 and 4 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_eac56

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field AC Component, Sensors 5 and 6 (axial)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_edc12

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field DC Component, Sensors 1 and 2 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_edc34

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field DC Component, Sensors 3 and 4 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_edc56

FFT Power Spectrum in Particle Burst, 16 frequencies for E Field DC Component, Sensors 5 and 6 (axial)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_epara

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI E (parallel to B)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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FFT Power Spectrum in Particle Burst, 16 frequencies for EFI E (perp to B)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_16_scm1

FFT Power Spectrum in Particle Burst, 16 frequenci es for SCM, Axis 1

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_16_scm2

FFT Power Spectrum in Particle Burst, 16 frequencies for SCM, Axis 1

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_16_scm3

FFT Power Spectrum in Particle Burst, 16 frequencies for SCM, Axis 1

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_16_v1

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 1

V^2/Hz

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tha_ffp_16_v2

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 2

V^2/Hz

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tha_ffp_16_v3

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 3

V^2/Hz

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tha_ffp_16_v4

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 4

V^2/Hz

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tha_ffp_16_v5

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 5

V^2/Hz

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tha_ffp_16_v6

FFT Power Spectrum in Particle Burst, 16 frequencies for EFI Potential, Sensor 6

V^2/Hz

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tha_ffp_16_yaxis

tha_ffp_16_yaxis

Hz

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tha_ffp_16_time, UTC, in seconds since 01-Jan-1970 00:00:00

Unleaped seconds

sec

0.0

5.0E9

NaN

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tha_ffp_16_epoch0

EPOCH0 of THEMIS time base

EPOCH of 01-Jan-1970 00:00:00

msec

1e-3>sec

31-Dec-1899 15:33:20.000

01-Jan-2101 00:00:00.000

31-Dec-9999 23:59:59.999

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tha_ffp_16_epoch

tha_ffp_16_epoch

31-Dec-1899 15:33:20.000

01-Jan-2101 00:00:00.000

31-Dec-9999 23:59:59.999

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tha_ffp_32_dbpara

FFT Power Spectr um in Particle Burst, 32 frequencies for SCM delta-B (parallel to B)

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_32_dbperp

FFT Power Spectrum in Particle Burst, 32 frequencies for SCM delta-B (perp to B)

(nT)^2/Hz

1e-18>T^2/Hz

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tha_ffp_32_eac12

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field AC Component, Sensors 1 and 2 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_eac34

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field AC Component, Sensors 3 and 4 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_eac56

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field AC Component, Sensors 5 and 6 (axial)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_edc12

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field DC Component, Sensors 1 and 2 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_edc34

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field DC Component, Sensors 3 and 4 (spin plane)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_edc56

FFT Power Spectrum in Particle Burst, 32 frequencies for E Field DC Component, Sensors 5 and 6 (axial)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz

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tha_ffp_32_epara

FFT Power Spectrum in Particle Burst, 32 frequencies for EFI E (parallel to B)

(mV/m)^2/Hz

1e-6>(V/m)^2/Hz