DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set includes all data from the Cassini High Rate Detector (HRD)
through Dec. 31, 2009. All data products in this data set are in tabular
format. Since HRD is mounted on the same platform as the Dust Analyzer, the
pointing is the same for both instruments.
Data file types and contents
============================
Data files in the 'raw' subdirectory contain all recorded events, including
impacts, noise events, and calibration events. The first column of each
file is a unique event number of the format Xnnnnnnnnn where X is a code for
the year (A = 2000, B = 2001, etc,) and nnnnnnnnn is a sequential number
within the year. The raw filenames are of the form hrd_yyyy_doy_doy.tab and
include data within the date range specified.
Data files in the 'calibrate' subdirectory contain calibration events
extracted from the raw files. Note that the sample rate is changed
periodically, resulting to changes in the time increments in the calibration
files. Calibration files are grouped by year, and since in-flight
calibrations were not done in all years, subdirectories do not exist for all
years of the mission. The event number corresponds to that in the raw file.
The filenames are of the form hrd_yyyy_doy_doy_cal.tab and include data
within the date range specified.
Data files in the 'processed' subdirectory have had calibration events and
noisy events removed. On 2005-248 there occurred an M4 event in the large
detector which resulted in a noisy M1 threshold. Since then, all M1 events
are considered to be noise and have been removed from the processed data
unless the M2 threshold is triggered or the small detector m1 threshold is
triggered or the large detector High Mass is set. The processed files have
filenames of the form hrd_yyyy_doy_doy_prc.tab and include data within the
date range specified.
The calibration and processed files include a quality code flag. The QC
flag indicates a discrepancy in the data line and is set if any one of the
following obtain:
1. Missing latch data.
2. Counters change with no latch data.
3. Higher threshold triggered and lower threshold did not.
The data directory 'onoff' contains files with the on-off times of the HRD,
divided by year. These have filenames of the form hrd_yyyy_on_off.tab. Note
that if the instrument was not powered on or off during the covered time
period, there will not be an on-off file for that time period.
The data directory 'pointing' contains hourly instrument pointing and
spacecraft positions generated from the SPICE kernels. The pointing data
pertains to both the CDA and HRD instruments, which are mounted on the same
platform. Gaps in the pointing and position data are due to the fact
kernels are not available for those time periods. For versions 3.0 and 4.0
of this data set, the pointing files for 2004-2006 have been regenerated
using additional kernels released since version 1.0. The pointing files for
1999-2003 are the same as in version 1.0 since no additional relevant
kernels for those years have been released. The metakernels listing the
kernels used to generate the pointing and position files are included in the
document directory.
Calibration of the HRD Detectors
================================
The HRD calibrations are similar to those for the Dust Flux Monitor
Instrument(DFMI) on the STARDUST misssion to comet Wild 2. The calibrations
of HRD detectors for the Cassini mission as well as for those for the DFMI
have done with dust particle accellerators in Heidelgerg and Munich. During
the calibration at Heidelberg iron particles in the velocity range of 1-12
km/sec were used while at Munich accelerator glass particles at similar
range were used. Please refer to Simpson and Tuzzolino (1985), Simpson and
Tuzzolino (1989), and Tuzzolino et al. (2000) for more details and
description of how these calibrations were performed.
Besides laboratory calibration, in-flight pulser calibrations were performed
periodically to ascertain the performance of the electronic system of the
HRD instrument.
References
==========
Srama, R., T.J. Ahrens, N. Altobelli, S. Auer, J.G. Bradley, and 35 others,
The Cassini Dust Analyzer, Space Science Reviews 114, 465-518, 2004.
Simpson, J.A. and Tuzzolino, A.J., Polarized Polymer Films as Electronic
Pulse Detectors of Cosmic Dust Particles, Nucl. Instrum. Methods A236,
187-202, 1985.
Simpson, J.A., D. Rabinowitz, and Tuzzolino, A.J., Cosmic Dust
Investigations, I: PVDF Detector Signal Dependence on Mass and Velocity for
Penetrating Particles, Nucl. Instrum. Methods A279, 611, 1989.
Simpson, J.A. and Tuzzolino, A.J., Cosmic Dust Investigations, II:
Instruments for measurement of particle trajectory, velocity, and mass,
Nucl. Instrum. Methods A279, 625, 1989.
Tuzzolino, A.J., R.B. McKibben, J.A. Simpson, J.A.M. McDonnell, M.J.
Burchell, and 8 others, Calibration of the Dust Flux Monitor Instrument
(DFMI) for the Stardust Mission to Comet Wild 2, in the Stardust Docushare,
Jet Propulsion Laboratory, 2000.
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CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
On-off times in 2008
====================
Although the instrument was turned back on briefly after 2008-311, no
additional data for 2008 after DOY 311 were received. The data set is
complete for the full period of 2008.
Large impact during Ring Plane Crossing
=======================================
The HRD performed well throughout the entire mission. However, after
crossing the Saturn G ring on DOY 2005_248, the #1 large HRD sensor was
hit by a large size dust particle that exceeded all mass thresholds of the
HRD instrument (the size was greater than several hundred microns). This
event probably changed the capacitance of the sensor and the HRD
instrument started to show some noise in the lowest threshold M1 of the #1
sensor in the range of several counts per mimute. It was decided not to
change the threshold level by a factor of 10 (the only possible response)
in order not to lose the data from the other three thresholds (M2, M3,
M4). So, the M1 data are not trustworthy for low count rates, but they
could be useful when the counting rate is high during the ring crossing,
or satellite flybys.
Both detectors triggered
========================
In some events in the 'raw' data, both detectors are triggered. This
implies simultaneous impacts in the two detectors. In the 'processed'
files, such events have been split into two lines, one for each impact.
Both lines have the same event number since they come from the same entry
in the corresponding events file.
Note that within a single detector, the triggering of a higher threshold
will ordinarily be accompanied by the lower thresholds being set also. If
not, the impact is suspect and the quality code is set.
Cumulative count discrepancy
============================
In some instances the cumulative counts don't agree with the individual
counts numerically. This is due to the processing time the CPU takes to
reset the latch for the next discrete event. If an event occurs during
the latch reset cycle the event will not be saved by the latch and the CPU
will read a zero value. However, the missing latched event will still be
recorded by the eight 16-bit counters.
HRD instrument reset
====================
On instrument power-on, the HRD performs a power-on reset. The reset sets
the HRD clock and all the counters to zero. Since the counters are set to
zero on reset, the counts appear to go down with time on reset. Missing
data can be determined by looking at the on-off files (described above)
which contain a list of the power on and off times.
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