PDS_VERSION_ID = PDS3
RECORD_TYPE = STREAM
OBJECT = TEXT
PUBLICATION_DATE = 2006-10-03
NOTE = "
DATATIPS.TXT provides quick-start help for anyone wanting to write
software to make use of the Voyager PWS full-resolution uncalibrated
data on this volume."
END_OBJECT = TEXT
END
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DATA FILE OVERVIEW
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The binary files containing the Voyager PWS full-resolution uncalibrated
data are found under directories named
DATA/FULLv/Tyymm_mm
where v is 1 for Voyager 1 and 2 for Voyager 2, yy is the two-digit year,
and mm_mm indicates an inclusive range of four months. The data files
are named
Tyymmdd.DAT
where yymmdd represents the year, month, and day (SCET) of data
contained in the file. Each file record is 48 bytes in length,
consisting of 24 low-byte-first (little-endian) 16-bit integer fields.
The detailed description of these fields is contained in the file
VGRPWSEL.FMT
found in each data directory. This file along with corresponding
Tyymmdd.LBL label files and the information in the CATALOG and DOCUMENT
directories provide full details.
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DATA PROCESSING OVERVIEW
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The uncalibrated integer data numbers contained in these files are
roughly proportional to the log of the voltage detected by the PWS
instrument in each of 16 frequency channels ranging from 10 Hz to 56.2
kHz, logarithmically spaced, four per decade:
Voyager 1 Voyager 2
Channel Center Frequency Bandwidth Bandwidth
1 10.0 Hz 2.99 Hz 2.16 Hz
2 17.8 Hz 3.77 Hz 3.58 Hz
3 31.1 Hz 7.50 Hz 4.50 Hz
4 56.2 Hz 10.06 Hz 10.7 Hz
5 100. Hz 13.3 Hz 13.8 Hz
6 178. Hz 29.8 Hz 28.8 Hz
7 311. Hz 59.5 Hz 39.8 Hz
8 562. Hz 106 Hz 75.9 Hz
9 1.00 kHz 133 Hz 75.9 Hz
10 1.78 kHz 211 Hz 151. Hz
11 3.11 kHz 298 Hz 324. Hz
12 5.62 kHz 421 Hz 513. Hz
13 10.0 kHz 943 Hz 832. Hz
14 17.8 kHz 2110 Hz 1260 Hz
15 31.1 kHz 4210 Hz 2400 Hz
16 56.2 kHz 5950 Hz 3800 Hz
Of the 24 16-bit LSB integer items in each record, the most useful are:
Item Byte offset Description
1 0 SCET years past 1900 (2001 = 101)
2 2 SCET hour of year plus 24
3 4 SCET second of hour
4 6 SCET millisecond of second
9 16 data number from PWS channel 1
10 18 data number from PWS channel 2
. . . . . . . . .
24 46 data number from PWS channel 16
An ASCII text file included in each data directory contains a
calibration table mapping each 8-bit instrument sample to a calibrated
voltage. This file,
VG1PWSCL.TAB, described in VGRPWSCL.FMT,
may be read and further manipulated to produce a look-up table for other
scientifically interesting units, such as:
Electric field, V/m, calculated by dividing the values in VG1PWSCL.TAB
by the effective electrical length of the PWS antenna, 7.07 meters;
Spectral density, V**2/m**2/Hz, calculated by squaring the electric
field and dividing by the noise bandwidth of the corresponding channel
as given in the table above;
Power flux, W/m**2/Hz, calculated by dividing the spectral density
by the impedance of free space, 376.73 ohms.
Special caveats include:
1. Voyager 2 data for the upper 8 channels of the instrument must be
adjusted to compensate for a degradation in sensitivity that
occured early in the mission.
2. Only units proportional to power (or volts squared) are
appropriate for averaging.
3. Some data numbers have been multiplied by -1 to indicate the
presence of interference.
4. Data numbers for some telemetry modes are actually 10-bit sums
of 4 instrument samples.
5. Zero data numbers indicate missing samples.
Typical ways of graphing these data for analysis include:
1. An amplitude vs. frequency spectrum taken either from a single
data record or averaged over a larger period of time.
2. An amplitude vs. time plot of the time evolution of the signal
detected in a single frequency channel.
3. Combined amplitude vs. time plots from several or all channels,
resulting in a representation of the time evolution of the
spectrum across a range of frequencies. This is often presented
as a "stacked histogram" or sometimes as a "spectrogram" with
amplitude represented as color or shades of gray.
See the example code in EXTRAS/SOFTWARE/C for details on how to extract
calibrated values from these data.
The application in EXTRAS/SOFTWARE/JAVA provides all of the analysis
capabilities routinely used by the PWS team.
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