Data Set Overview :  This data set includes all data from the Cassini High Rate Detector (HRD) through Aug. 16, 2007. 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 version 2.0 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 version 1.0 and 2.0 pointing and position files is 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 : 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.