Fundamental Technologies

Ulysses HISCALE Pages

Guide to Scientific Use of Ulysses HISCALE Data Available Through VHO

Authors:

Thomas P. Armstrong

and

Errol J. Summerlin

Armstrong@ftecs.com

 

Errol.Summerlin@nasa.gov

Appendix: Special Circumstances That Must Be Accounted For

1. The HISCALE instrument was commanded into in-flight calibration mode on 5 occasions. Foreground measurements are not valid at these times (1990 Day 319; 1992 Day 9, Day 49; 1993 Day 8; 1994 Day 91). Full details on these occasions are provided at: http://hiscale.ftecs.com/chapter%205/coverclose.html.

2. Filtering of obviously erroneous points arising mostly from bit errors in the telemetry stream has been done and files that have names beginning with “UFA,” standing for Ulysses filtered averages, have been staged in folders by year at URL http://data.ftecs.com/VHO/VEPO/ulysses_hiscale/rates/Filtered/. The archive data available are full time resolution (12 seconds for 8 channel rates; 1024 seconds for the 25 channel data, and digitized pulse heights accompanied by timing information that allows assigning a time to every arriving event). The 8 channel rates are averaged to even 5 minute, 1 hour, and daily cadences while the 25 channel rates are averaged to 1 hour and daily cadences. The comma separated variable files are printed out with the same data item in the same column for all cadences so that a user can conveniently make judgments about odd data points and eliminate bad points and re-average the data to perfect the data set. It is the user’s responsibility to do this to their own satisfaction. Note that the regular and filtered averages should be checked before use. An artifact of the filtering program includes occasional periods of time when the instrument was turned off and data were interpreted falsely as “0” accumulated counts. These are infrequent and easy to spot as points for which the filtered rates go below the unfiltered data.

3. Observed Ulysses magnetic field vectors expressed in spacecraft coordinates have been furnished by the MAG team (Andre Balogh, PI). The HISCALE team have interpolated the MAG vectors to the 12 second cadence of 8 channel rate data so that pitch angles could be assigned to the HISCALE sensor look directions. No warranty on use of the MAG data included in the 8 channel rate files apart from pitch angle is made by the HISCALE team. Further, as with all interpolation procedures, the results are approximate and the user must examine the data and its use very carefully.

4. Observed solar wind speeds made available by the SWOOPS team (Dave McComas, PI) have been used to correct for the effect of plasma convection on the apparent energies and intensities of the low energy protons and Z>1 ions so that the 25 channel data can be expressed as background corrected fluxes in the solar wind rest frame. Any use of this data presumes that the user has read the documents furnished to describe this process and accepts the assumptions made therein.

5. The PHA event files included in the HISCALE archive are described at http://hiscale.ftecs.com/chapter%204/3-analogelectronics.html; http://hiscale.ftecs.com/chapter%202/RecHeadDef.html; http://hiscale.ftecs.com/chapter%202/PHA-block.html. The PHA event selection system was designed to achieve several purposes: a.) To identify the ion species triggering each of the W1-W8 rate channels and b.) To determine the energy spectra within species groups (W1 & W2, protons), (W3 & W4 Helium nuclei); (W5 & W6, CNO group), (W6 & W7, Iron group). A “rotating priority event selection system” was used to alternate the selection of events for downlink transmission between a rare species (if available) and the next lower priority (if available), etc. This procedure necessarily biases the selection of events so that the “Event 2” events should not be used to obtain the foreground abundance ratios. For that, the user must rely upon the simple, unselected counting rates of the W1-W8 channels—not the PHA event counts.

6. The HISCALE counting rates presented in the archive include “out-of-passband, aka background”, responses. HISCALE rate backgrounds are due to the interactions in the silicon detectors of spacecraft RTG-produced gamma rays and galactic cosmic rays penetrating the passive shielding. These two components of the background have been separately determined as described at http://hiscale.ftecs.com/chapter%204/11-RTG.html; http://hiscale.ftecs.com/chapter%204/12-galacticCR.html; http://hiscale.ftecs.com/chapter%204/15-radiation-background.html. Values of the resulting background for all HISCALE channels are tabulated for each day of the mission at http://data.ftecs.com/archive/ulysses_hiscale/background/. Converting the tabulated “*8-channel” rates into fluxes amounts to subtracting the background and dividing result by the (geometrical factor-ΔE) product.

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Last modified Sept. 7, 2010
T. Hunt-Ward
tizby@ftecs.com