Planetary Radio Astronomy (PRA) data from the Voyager Neptune encounter were cleaned and reformatted in a variety of formats. Most of these formats are new and have been specifically designed to provide easy access and use of the data without the need to understand esoteric characteristics of the PRA instrument or the Voyager spacecraft. Several data sets were submitted to the Planetary Data System (PDS) and have either appeared already on peer reviewed CDROM's or are in the process of being reviewed for inclusion in forthcoming CD-ROM's. Many of the data sets are also available online electronically through computer networks; it is anticipated that as time permits, the PDS will make all the data sets that were a part of this contract available both online and on CD-ROM's

Evans, David R.

English

NASA Technical Reports Server

NASA-CR-193261
CONTRACT NASW 4699 FINAL REPORT
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User Friendly Database for Neptune
Planetary Radio Astronomy Observations
Dr. David R. Evans
Radiophysics, inc.
5475 Western Avenue
Boulder, CO 80301
Telephone: (303) 447-9524
(NASA-CR-193261) USER FRIENDLY
DATABASE FOR NEPTUNE PLANETARY
RADIO ASTRONOMY OBSERVATIONS Final
Report (Radiophysics) 13 p
N93-32324
Unclas
G3/89 0175333
https://ntrs.nasa.gov/search.jsp?R=19930023135 2020-03-17T05:14:02+00:00Z
Page 2
ABSTRACT
Planetary Radio Astronomy ("PEA") data from the Voyager Neptune
encounter have been cleaned and reformatted in a variety of
formats. Most of these formats are new and have been
specifically designed to provide easy access and use of the
data without the need to understand esoteric characteristics
of the PRAinstrument or the Voyager spacecraft. Several
datasets have been submitted to the Planetary Data System
("PDS") and have either appeared already on peer reviewed CD-
ROMs or are in the process of being reviewed for inclusion in
forthcoming CD-ROMs. Many of the datasets are also available
online electronically through computer networks; it is
anticipated that as time permits, the PDS will make all the
datasets that were a part of this contract available both
online and on CD-ROMs.
Page 3
I. HISTORY
During the course of the Voyager mission to the outer planets,
PRAdata have been sent from the Voyager Project at JPL to the
PRAProject Office in Boulder in a wide variety of formats, on
the medium of half inch magnetic tape. Unfortunately, the
correct reading of the data frequently required detailed
knowledge not only of the data format used on a given tape (and
how to circumvent the frequent errors and lack of adhesion to
the published data format specifications) but also a detailed
knowledge of the working of both the PRA instrument and the
Voyager Flight Data System ("FDS"). Although many of the data
are archived with the National Space Science Data Center
("NSSDC"), the use of these data by third parties is often
difficult or impossible. The following are typical problems
that a third party investigator might find when trying to use
PRAdata from NSSDC:
i) The physical medium on which data are supplied (I/2 inch
magnetic tape) may be formatted in a density unreadable by
the investigator;
2) The printed description of the layout of the data on the
physical tape may be difficult to understand, obscure, or
lacking in precision;
3) The data may contain binary floating point numbers in a
format which is not compatible with the investigator's
computing equipment;
4) Binary integer numbers may be packed differently from
the way that the investigator's computing equipment
expects;
5) EBCDIC may be used;
6) The data may be one of:
a) Too"raw" for use by an investigator who has no
detailed knowledge of the instrument concerned;
b) Uncalibrated;
c) Of insufficient resolution;
d) Incomplete;
e) Missing necessary ancillary information (e.g.
frequency settings);
f) Contain unflagged bad or suspect data.
Under the terms of this contract, the author has made
Page 4
available a number of datasets that reduce or eliminate
entirely these difficulties. In particular:
I) The data are available electronically and on standard,
state of the art, media; i.e. CD-ROMs;
2) The description of the data format is both simple and
precise;
3) The data contain no floating point numbers, all numbers
are provided as integers, with the byte order clearly
specified;
4) Binary integer numbers may still be packed differently
from the way that an investigator's computing equipment
naturally operates. However, the datasets have been
provided in both binary and ASCII format, so that, as a last
larger butresort, an investigator can use the (slower,
universal) ASCII formatted data;
5)
6)
EBCDIC is never used;
With regard to the data themselves:
a) The data are well documented, with spacecraft and
instrument idiosynchracies removed insofar as is
possible;
b) The data are calibrated;
c) Data at both browse and full resolution are
available;
d) The data are as complete as the original raw dataset
downlinked from the spacecraft;
e) Ancillary information needed to interpret the data
are now contained within the datasets themselves;
f) All bad data are clearly marked.
Before it will make data sets available to the public, sets
submitted to the PDS must undergo rigourous peer review.
This process includes requirements that the data set be
fully documented and usable by third parties, as well as
complete documentation of the instrument characteristics
and modes of operation. Such documentation for the PRA
instrument and the submitted datasets described herein has
been submitted to the PDS and is available from their online
catalogue.
Page 5
2. DATA SETS
Four data sets have been produced.
2.1. BROWSE
The browse data set confines itself to scanning mode data, in
the lower frequency band of the PRA instrument only, and
limiting itself to 48 second "averages"of the fundamental six
second cycle of the instrument. (The term"averages"needs to be
more clearly defined: a given record on a tape contains eight
six second scans, four in each of two senses of circular
polarisation. Browse data records comprise the calibrated mean
of each set of four scans, separated out into the distinct
polarisation states.) Any data that are suspect have been
removed prior to inclusion in this dataset, so that the user of
this set is guaranteed that no signal seen in the set is an
artifact of the downlink or computer processing. It is intended
that this data set be used for the study of gross polarisation
and frequency characteristics of the neptunian radio emission.
The browse data set has undergone the usual peer review process
at the PDS, and has already been published on CD-ROM. It is also
available for direct electronic access in the particles and
fields catalogue of the PDS.
Figure 1 shows a typical plot obtained from PDS browse data.
2.2. ModifiedEDR
Low rate data are provided to the PRAproject office in a format
known as Experimenter Data Record, or"EDR". Unfortunately,
these EDRs, apart from being impossible to interpret without
access to a several-inch-thick document from JPL, frequently
contain corrupt data, errors in timing and other, similar
hurdles to their correct interpretation. We have produced a
data set at the same resolution as the original EDR data, but
containing much simpler headers and from which the obvious
contamination and corruption has been removed.
This data set is useful for the detailed examination of the
various radio emissions detected by PRAat Neptune. In
particular, the bursty radio emissions are present and
recognisable in this dataset (see Figure 2) .
Page 6
2.3. Fixed frequency
Throughout the Neptune encounter, the PRAinstrument was
placed periodically into a fixed frequency mode. This mode is
incompatible with the more common scanning mode which is
contained in the Browse data set. There is insufficient
information in the original EDR records to determine the
characteristics of this mode, although its presence can be
clearly detected. We have produced a data set containing only
the fixed frequency data and with all the information required
to extract the data correctly contained within the dataset.
Figure 3 is an example of a plot from this dataset.
2.4. High rate
During the encounter, a number of 48 second frames were
acquired when the instrument was in a mode of rapid data
acquisition. These frames are in a format completely unlike the
low rate data. Additionally, because the permitted error rate
in these frames is much higher than for lower rate data,
several copies of each frame were returned to Earth. We have
almagamated all the copies of each frame to produce a single,
combined"best" frame which in most cases is realtively noise
free.
The original format of the frames is, like that of EDRs, arcane
and incomplete (for example, the frequency being sampled is
nowhere contained in the dataset). We have produced a simpler
format which contains within it sufficient information to
extract the high rate data correctly. The data set we have
produced contains calibrated data organised simply in terms of
frequency and polarisation. This data set is most useful for
examining the dynamics of dust impacts on the spacecraft during
the encounter period. These data have been reviewed and made
public by the PDS and are available both online and on CD-ROM.
Figures 4 and 5 are examples of data obtained from this data
set.
Page 7
3. Hard copy
PoStScript format files of the entire encounter data have been
produced. These are available at the author's institution and
will be submitted to PDS. The Figures contained herein are
examples of these files.
,
Although it formed no part of this contract, software written
by the author and which is capable of manipulating the data
formats produced under this contract will shortly be made
available to the PDS. This will further reduce the necessity
for understanding instrument and spacecraft operation before
the data can be usefully used by third parties.
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Radiophysics, inc.
5475 Western Avenue
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("PRA") data from the Voyager Neptune
encounter have been cleaned and reformatted in a variety of
formats. Most of these formats are new and have been
specifically designed to provide easy access and use of the
data without the need to understand esoteric characteristics
of the PRAinstrument or the Voyager spacecraft. Several
,datasets have been submitted to the Planetary Data System
_"PDS") and have either appeared already on peer reviewed CD-
ROMs or are in the process of being reviewed for inclusion in
forthcoNing CD-ROMs. Many of the datase£s arealso available
online electronically through computer networks; it is
anticipated that as time permits, the PDS will make all the
datasets that were a part of this contract available both
online and on CD-ROMs.
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User friendly database for Neptune planetary radio astronomy observations

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