| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The Ulysses spacecraft was occulted by the Io Plasma Torus
(IPT) during its Jupiter encounter on 8 February 1992. The
Ulysses dual-frequency radio subsystem used by the Ulysses
Solar Corona Experiment (SCE) was utilized to measure the
electron content (column density) of the IPT [BIRDETAL1992B].
In the nominal mode for radio-sounding observations
[BIRDETAL1992A], both downlinks (S-band: f_s = 2.3 GHz;
X-band: f_x = 8.4 GHz) are phase coherent with the uplink
(S-band: f_u = 2.1 GHz). The dual-frequency radio-sounding
technique exploits the dispersive nature of ionized media on
the propagation of the two downlinks. The tiny Doppler shift
due to plasma moving in and out of the ray path is greater
at S-band than at the higher frequency X-band.
The SCE data are obtained from the Radio Science Support group
at JPL. There are basically two types of data: Ranging and
Doppler (Frequency), recorded as a function of UT Ground
Received Time. The raw data are delivered in special binary
files called ATDFs (Archival Tracking Data Files), containing
Ranging and Doppler data from the standard DSN tracking
receivers. There are high-time resolution Doppler data from
special radio science receivers (so-called 'open loop' data)
as well. These are in files called ODRs (Original Data
Records).
ATDFs are files of radiometric data produced by the Network
Operations Control Center (NOCC) Navigation Subsystem (NAV).
They are derived from Intermediate Data Records by NAV and
contain all radiometric measurements received from the DSN
station including signal levels (`AGC' = automatic gain
control in dBm), antenna pointing angles, frequency (often
referred to simply as 'Doppler'), range, and residuals.
Doppler data are often used to infer spacecraft radial motion
relative to the tracking antenna. Data values in ATDFs are
reported at rates no higher than 10 per second. For the
Ulysses Jupiter encounter the received frequencies at S-Band
and X-band were recorded at a sample time of one per second.
Each ATDF data record contains 117 parameters, stored in
records of 288 bytes. The ATDF is described in section
TRK-2-25 of the JPL Document 820-13 [DSN820-13].
The ATDFs have been analyzed for the Jupiter encounter and a
detailed report has been published [BIRDETAL1993]. Data files
have been generated which contain the Ranging and Doppler data
at various stages of processing. Stage #1 is generally just
stripping the Ranging/Doppler data from the ATDFs. Stage #2 is
to 'clean' the data files by weeding out obviously bad data.
Stage #3 is to produce a 'final data set', a table of the
measured data plus physically relevant quantities as function
of time.
For the Doppler data, getting to stage #3 involves
manipulating the frequency data to extract the changes in
electron column density. An additional complication is the
compensation for the Earth's ionosphere to separate its
contribution from that of the Io Plasma Torus. This requires
obtaining ionospheric calibration data from the DSN for the
days of the Jupiter encounter. Details of the calibration
procedure can be found in section TRK-2-23 of JPL document
820-13 [DSN820-13]. Because the processing to stage #3 can be
done in a variety of ways, it is best to leave the frequency
measurements in their stage #2 form for the archiving process.
In contrast to the modest volume of ranging data, the much
higher sample rate increases the Doppler data volume to
Megabyte proportions.
Data
====
The following tables give an idea about the size and coverage
of the data set:
Ulysses SCE Doppler data at Jupiter (complete set):
Stage# start stop ascii size
doy:hh:mm doy:hh:mm (MB)
1 36:15:45 41:15:44 72
2 36:20:30 40:19:18 21
The size of the data set has been reduced by providing only
the Doppler data from the tracking passes at DSS 43/42 on
Jupiter encounter day, when the spacecraft was occulted by the
Io Plasma Torus. In this case the table of data becomes:
Ulysses SCE Doppler data at Jupiter (encounter day only):
Stage# start stop ascii size
doy:hh:mm doy:hh:mm (MB)
1 39:03:15 40:00:00 16
2 39:11:00 39:20:45 2
Here are a few lines of the ASCII file at stage #2:
ULS IPT OCCULTATION: 8 FEB 1992 (DOY 39)
DSS 42/43: S/X-BAND COHERENT
10.25000 21.41667 0.7528 -2.5346 5.6032 3.4620 -1.4765 -2.5889
time (hrs) S-band phase S-3/11X AGC
10.99999992 1566823818.441 -0.075 -150.9
11.00027784 1567875175.345 -0.071 -150.9
11.00055552 1568926527.281 -0.067 -151.3
11.00083344 1569977874.261 -0.043 -151.1
11.00111112 1571029216.279 -0.054 -151.6
11.00138880 1572080553.284 -0.090 -151.3
11.00166672 1573131885.437 0.010 -151.6
where:
time (hours) = time in hours on 8 FEB 1992 (DOY 39)
S-Band phase = running S-band Doppler count (cycles)
S-3/11X = differential frequency (Hz)
AGC = S-band received signal level (dBm)
and the row of numbers preceding the table gives the necessary
parameters for the ionospheric calibration according to
TRK-2-23 [DSN820-13] during this pass:
tstart tstop c_0 c_1 c_2 c_3 c_4 c_5
10.25000 21.41667 0.7528 -2.5346 5.6032 3.4620 -1.4765 -2.5889
with
tstart = start time for the interval of ionospheric
calibration
tstop = stop time for the interval of ionospheric
calibration
c_i, i=0,5 = polynomial coefficients for ionospheric
calibration
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