Data Set Information
DATA_SET_NAME VG2 NEP PWS RAW EXPERIMENT WAVEFORM 60MS V1.0
DATA_SET_ID VG2-N-PWS-1-EDR-WFRM-60MS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview ================= This data set consists of electric field waveform samples from the Voyager 2 Plasma Wave Receiver waveform receiver obtained during the Neptune encounter. The waveforms are collections of 4-bit samples of the electric field measured by the dipole electric antenna at a rate of 28,800 samples per second. 1600 samples are collected in 55.56 msec followed by a 4.44-msec gap. Each 60-msec interval constitutes a line of waveform samples. The data set includes about 271 frames of waveform samples consisting of up to 800 lines, each. The telemetry format for the waveform data is identical to that for images, hence the use of line and frame as constructs in describing the form of the data. The waveform is sampled through a bandpass filter with a passband of 40 Hz to 12 kHz. The 4-bit samples provide sixteen digital values of the electric field with a linear amplitude scale, but the amplitude scale is arbitrary because of the automatic gain control used in the waveform receiver. The instantaneous dynamic range afforded by the 4 bit samples is about 23 db, but the automatic gain control allows the dominant signal in the passband to be set at the optimum level to fit within the instantaneous dynamic range. With the gain control, the overall dynamic range of the waveform receiver is about 100 db. The automatic gain control gain setting is not returned to the ground, hence, there is no absolute calibration for the data. However, by comparing the waveform spectrum derived by Fourier transforming the waveform to the spectrum provided by the spectrum analyzer data, an absolute calibration may be obtained in most cases. The data may be plotted in raw form to show the actual waveform; this is useful for studying events such as dust impacts on the spacecraft. But the normal method of analyzing the waveform data is by Fourier transforming the samples from each line to arrive at an amplitude versus frequency spectrum. By stacking the spectra side-by-side in time order, a frequency- time spectrogram can be produced. Additional information about this dataset and the instrument which produced it can be found elsewhere in this catalog. An overview of the data in this data set can be found in Gurnett et al. [1989] and a complete instrument description can be found in Scarf and Gurnett [1977]. Parameters ========== Derived Parameters ------------------ Sampling Parameter Name : time Sampling Parameter Resolution : 0.000034722 seconds Minimum Sampling Parameter : n/a Maximum Sampling Parameter : n/a Sampling Parameter Interval : 0.000034722 seconds Minimum Available Sampling Interval : 0.000034722 seconds Data Set Parameter Name : plasma wave waveform Noise Level : 0.000005 Data Set Parameter Unit : volt/meter (Data not absolutely calibrated) Plasma wave waveform: A plasma wave waveform is a time series of measurements of the electric or magnetic field component of the wave spectrum taken through a broadband filter. The temporal sample rate is normally such that samples are made at more than twice the analysis filter bandwidth. A typical waveform will consist of the order of 1000 contiguous samples of between 4 and 12 bits each. For a 10-kHz analysis bandwidth, the sample rate would normally be approximately 25 kHz or 25,000 samples/second. Once received, the waveforms are typically Fourier transformed in order to provide an amplitude versus frequency spectrum across the analysis bandwidth. The sample rate, then, is required to be at least a factor of two greater than the filter bandwidth in order to avoid aliasing in the transformed spectrum. The spectra can be stacked side-by-side in time to build a frequency-time spectrogram (that is, amplitude as a function of time and frequency) in order to identify the temporal and spectral variations in the wave spectrum. Alternately, the untransformed time series can be used to study the details of the waveform. This has been useful for measuring small-scale structures in the plasma and for identifying the signature of micron-sized dust impact on the spacecraft. Measured Parameters ------------------- Electric field component: A measured parameter equaling the electric field strength (e.g. in milli-volts per meter) along a particular axis direction. Wave magnetic field intensity: A measured parameter equaling the magnetic field strength in a specific frequency passband (in MKS unit: volts/meter) measured in a single sensor or antenna. Wave electric field intensity: A measured parameter equaling the electric field strength in a specific frequency passband (in MKS unit: volts/meter) measured in a single sensor or antenna. Processing ========== The data files in this data set were created using the 'CDREF' software. CDREF ----- Node ID : IMAGING Software Release Date : 1990-04-07 Cognizant Full Name : MR. JASON J. HYON CDREF is primarily a data format translation routine which is used to convert Voyager PWS EDR tape files to CD-ROM files. CDREF is written in FORTRAN and is not available for public use. The EDR, or Engineering Data Records, are produced at Multi-mission Image Processing Laboratory at JPL as the uncalibrated, full-resolution PWS spectrum analyzer data set. The CD files contain uncalibrated, full-resolution PWS data with minimal ancillary data in a simplified format which may be used in CDROM production.
DATA_SET_RELEASE_DATE 1990-09-01T00:00:00.000Z
START_TIME 1989-06-06T02:16:56.000Z
STOP_TIME 1989-09-27T05:52:43.000Z
MISSION_NAME VOYAGER
MISSION_START_DATE 1972-07-01T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME NEPTUNE
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID VG2
INSTRUMENT_NAME RADIO AND PLASMA WAVE SCIENCE
PLASMA WAVE RECEIVER
INSTRUMENT_ID PWS
INSTRUMENT_TYPE PLASMA WAVE SPECTROMETER
NODE_NAME planetary plasma interactions
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview ========================= This data set includes all available waveform receiver data obtained during the Neptune encounter. There has been no attempt to clean various interference signals from the data. Most of these can normally be easily seen in frequency-time spectrograms as narrowband, fixed-frequency tones. The most common include narrow- band tones at 2.4 and 4.8 kHz which are power supply harmonics. There is sometimes a tone near 1.7 kHz which is associated with the operation of the spacecraft gyros. The spacecraft tape recorder results in a rather intense band in the frequency range of a few hundred Hz. There are few times when the data in this frequency range can be used. However, there are times when the real signals in this frequency range can exceed the intensity of the interference sufficiently so that the frequency range near a few hundred Hz can be used. Use of the spectrum analyzer data can be of use to determine when these time periods occur. The stepper motor of the LECP instrument also interferes in the frequency range of a few hundred Hz, but for periods of a few seconds. The LECP interference is very intense and captures the automatic gain control so that real signals, even where there is no interference, will appear to decrease in amplitude until the LECP interference fades in amplitude. The PLS instrument periodically interferes at 400 Hz and odd harmonics because of a 400-Hz square wave used to modulate a grid in the detector. The PLS interference lasts for several seconds and ends abruptly. Telemetry errors result in a fairly graceful degradation of the waveform data. Assuming the telemetry errors are randomly occurring bursts, they typically appear as an enhanced background level in the spectrum. Since the bursts are short, their Fourier transform is a broadband spectrum. When looking for relatively narrowband features or features with distinct frequency-time characteristics, the result of the bursts simply reduce the signal-to-noise in the spectrum. One way of reducing the effect of burst telemetry errors is to pass the waveform data through a low-pass filter to despike it, prior to running the Fourier transform. The waveform data is not subject to the negative effects of the failure in the Voyager 2 Flight Data System which reduces the sensitivity of the spectrum analyzer and affects the calibration above 1 kHz. In fact, use of the 1 - 12 kHz waveform data is an effective way of avoiding the problems with the spectrum analyzer data in this frequency range. Data Quality and Coverage ========================= -------------------------------------------------------------------- Table 1. Data Quality ID Descriptions -------------------------------------------------------------------- ID Description -------------------------------------------------------------------- -1 no attempt has been made to specify a data quality for this time range 1 Contamination removed by deleting measurements which are affected. Some contamination may still be present to avoid deleting too many data points. Remaining LECP contamination will appear as periodic bursts of noise in one or more channels in the range 100 Hertz to about 1 kiloHertz. -------------------------------------------------------------------- Table 2. Data Contamination ID Descriptions -------------------------------------------------------------------- ID Description -------------------------------------------------------------------- -1 no evaluation of possible contamination has been made 1 Contamination code 01 refers to contamination by the LECP stepper motor and PLS grid modulation which causes periodic spikes in the spectrum analyzer data particularly in the frequency range 100 Hertz to about 1 kiloHertz.
CITATION_DESCRIPTION Kurth, W.S., VG2-N-PWS-1-EDR-WFRM-60MS-V1.0, VG2 NEP PWS RAW EXPERIMENT WAVEFORM 60MS V1.0, NASA Planetary Data System, 1990.
ABSTRACT_TEXT This data set consists of electric field waveform samples from the Voyager 2 Plasma Wave Receiver waveform receiver obtained during the Neptune encounter. The waveforms are collections of 4-bit samples of the electric field measured by the dipole electric antenna at a rate of 28,800 samples per second. 1600 samples are collected in 55.56 msec followed by a 4.44-msec gap. Each 60-msec interval constitutes a line of waveform samples. The data set includes about 271 frames of waveform samples consisting of up to 800 lines, each.
PRODUCER_FULL_NAME DR. WILLIAM S. KURTH
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