New Chicago IMP 8 Data Set Arrives at NSSDC

Volume 12, Number 4, December 1996
By Joseph King

Over the years the University of Chicago cosmic ray group led by Prof. John Simpson has participated in many NASA spacecraft missions and has contributed many significant advances to the understanding of cosmic ray phenomena.

The Chicago instruments have mostly been cylindrical multisensor "telescopes" wherein count rates of all incident cosmic rays that trigger various coincidences of the sensors along the telescope axis are captured, as well as "pulse height" data, corresponding to the energy deposited in multiple sensors, for a sampling of the particles.

Most science analyses require the folding together of the coincidence mode count rate data with the pulse height data to determine fluxes of cosmic rays of well identified species (and, in many cases, isotopes) and energy range. However, this folding together of the rate and pulse height data to yield fluxes is difficult and involves some assumptions and irreversible transformations of the basic data.

IMP 8 and the CD-ROM from the Chicago IMP team

The Chicago team has been very conscientious in its archiving of its basic count rate and pulse height data. However, at least in part because such data are difficult to use, the data have been little accessed from the archive. To facilitate use of the Chicago Interplanetary Monitoring Platform (IMP) 8 data, which started in October 1973 and continues to accumulate today, the IMP 8 project funded Chicago to generate maximally time-continuous fluxes of well identified species in well identified energy ranges.

The Chicago IMP team, now led by Dr. Clifford Lopate, has just provided to NSSDC one CD-ROM with much more readily usable IMP 8 data at 15-min resolution. The data consist of the coincidence mode rates and "box counts" determined from the pulse height data; these two data types are easily combined to give fluxes. The "boxes" correspond to electrons in three energy bins from .7-2 to 12-50 MeV, protons in nine energy bins from 11.24-12.62 to 74.50-94.78 MeV, helium nuclei in ten energy bins from 10.90-12.89 to 84.32-94.81 Mev/nucleon, and one 25-250 CNO channel.

The CD-ROM has extensive on-disk documentation and labels adhering to the Standard Formatted Data Unit (SFDU) of the international Consultative Committee for Space Data Systems. NSSDC expects to make these data electronically accessible in the very near future.

It is of interest that the space science community continues to ponder the relative values (in resource expenditure) of archiving low-processing-level, harder-to-use data sets (and typically extensive documentation, often including software which itself must be maintainable) and generating and archiving higher-processing-level, easier-to-use data sets (and typically less daunting documentation) that usually involve some informed but irreversible transformations. For the Chicago IMP-8 data, NSSDC now has data sets of both types. We will be watching closely as to whether the new data set significantly increases the use of and science extracted from the unique Chicago data.

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Miranda Beall,, (301) 286-0162
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.

Erin D. Gardner,, (301) 286-0163
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.

NASA home page GSFC home page GSFC organizational page

Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 10 JAN 1997 [EDG]