Data Set Overview
  =================
 
  This data set includes all data from the Cassini High Rate Detector (HRD)
  through Dec. 31, 2008.  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.

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 through the end 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.