Data Products of the IMP-8 GME

H, He & Ion Differential Fluxes


 

  • These data should be considered a "high-resolution" research data product
  • Two specific data products now exist, as shown in the following table:
H and He Fluxes at 30 Minute Resolution
H, He, Ion fluxes at 6 hour resolution

The data consist of 71 bins including

  • 30 H differential fluxes 0.5-500 MeV
  • 21 He differential fluxes 1.2-80 MeV/nuc
  • a relativistic electron "flux" and "background" approximately 3-18 MeV
  • 18 event-type and singles rates.

The data consist of 96 bins including

  • 30 H differential fluxes 0.5-500 MeV
  • 29 He differential fluxes 1.2-500 MeV/nuc
  • 17 Ion differential fluxes 1.5-40 MeV/nuc
  • a relativistic electron "flux" and "background" approximately 3-18 MeV
  • 18 event-type and singles rates.

A detailed listing of all energy bands and rates in the 30 minute product

A detailed listing of all energy bands and rates in the 6 hour product

  • The flux bands in these data are defined for optimal measurements of solar and interplanetary particles. More tightly defined flux bands are more appropriate for quiet-time galactic and anomalous cosmic ray studies and are planned shortly.
  • Flux data run from the first GME data in Oct 1973 to "the present"
    • There is a typical time delay in posting new data of 3-6 months. This delay is due both to the schedule on which IMP-8 telemetry data is collected and shipped, and to time necessary for data reduction steps (including determination of gain shifts, which requires extended time spans).
  • Flux data will be shortly available in binary form. Flux data are also being converted to ISTP/IACG standard CDF format and will then be made available for graphic, ASCII and CDF output via the Space Physics Data Facility's CDAWeb system now supporting access to ISTP Key Parameters and other data.

 

1. Data Content and Usage (Fluxes)

Units of flux are counts/sec-cm2-ster-MeV/nuc and of rates are counts/second. Statistical uncertainties are included with all fluxes and rates. Data are at a time resolution optimal for many solar and interplanetary studies (including H and sometimes He spectra) given the statistics usually possible with the GME telemetry rates and GME geometry factors. The flux bands in these data are defined for optimal measurements of solar and interplanetary particles. More tightly defined flux bands are more appropriate for quiet-time galactic and anomalous cosmic ray studies.

Various issues in using these data are included in the instrument description, including definition of the various rates. Users of this data must bear in mind that

  • these are higher-resolution data (for this kind of instrument)
  • these are specifically higher-resolution energetic particle data

and from both these factors, there are UNAVOIDABLE complexities and detailed considerations in the correct and appropriate use of this data. Several specific points of particular importance:

 

  • Even "flux" data can be subject to contamination by particles and energies beyond the nominal defined bands. GME flux data bands (particular particles, particular energies) are defined to optimize the flux to background ratio, but this kind of data nonetheless always includes some measure of background. The fraction of background can be dependent on ambient conditions (spectral slopes, composition). Specific examples include flare-event onsets (very flat spectra or spectra with fluxes actually increasing with increasing energy) and some shock-spike events (very steep spectra).

 

  • The MED telescope (fluxes of protons and alphas >20 MeV/nuc, event-type rates such as DE-F-G) is a scintillation detector system using phototubes to measure pulse heights. The gain of the phototubes is known to change with time. One major reason for the delay in producing these flux data products from the original receipt of data is the need to accumulate enough data to understand the trends and define appropriate "gain shift" factors. The correction procedures are believed to be highly reliable in general. Under extreme flux conditions however (the largest flares), the phototubes will gradually saturate and the correction factors will become uncertain. The list of events where the detectors are known to have saturated is known and listed in the instrument description.

 

  • The LED telescope (fluxes of protons and alphas 1-20 MeV/nuc, event type rates such AB-C) is designed with a combination of passive collimation/shielding anti-coincidence protection and active scintillation anti-coincidence. From an initial short period in July 1983 and more serious intermittent symptoms starting in April 1984, the active anti-coincidence has gradually failed. The "C" singles rate is a direct measure of the problem. C rates of 100-200+ counts/sec are typical of good operation, lower rates are a warning of only partial efficiency. The C detector has effectively completely failed by approximately 1990. The C detector failure results (effectively) in increased background and (while it was operating partially) a time-variable background that can be particularly misleading. The AB-C event-type rate and protons/alphas 4-20 MeV/nuc are the most severely effected, although useful measurements are still possible in modest or larger energetic particle events.

 

The points above are direct examples of the complexity in making higher-resolution but processed data available. In all cases, the ultimate determination of data validity and meaning in a given instance is dependent on examination of the detailed pulse-height data in "matrix" format, because such examination is the definitive way that contamination or increased background importance can be assessed. Users therefore need to be somewhat cautious in using this data and be careful not to overinterpret features before consulting with the PI team.

 

2. Graphical Access (Fluxes) (UNDER CONSTRUCTION)

Graphical access will be supported by conversion of the data to the ISTP/IACG standard format (the NSSDC's Common Data Format or CDF) following the ISTP/IACG implementation guidelines and loading of the data to the Space Physics Data Facility's CDAWeb system also now used to access e.g. ISTP Key Parameters. CDAWeb will allow very quick plots of selected data on user-specifiable time scales as well as the ability to list/retrieve data in ASCII.The conversion and loading process is underway at this time.

 

3. Digital Data Access (Fluxes)

Access to digital flux data will be supported in two modes, FTP access to binary files and CDAWeb access to ASCII versions of the data.

H and He Fluxes at 30 Minute Resolution

H, He, Ion fluxes at 6 hour Resolution

Binary Data*

Directory Listing/File Transfer
(for 30 Minute Averages)
Directory Listing/File Transfer
(for 6-Hour Averages)

ASCII Data (via CDAWeb)

Select IMP-8, Energetic Particles and I8_H0_GME dataset
[UNDER CONSTRUCTION]

*Please see below for detailed file and format description.
*Please remember to transfer data in binary, or source, or raw data, mode.

 

Specification of GME Binary Flux File Naming and Format

H and He Fluxes at 30 Minute Resolution

H, He, Ion fluxes at 6 hour Resolution

File Properties

30 minute files typically cover 6 months of data each and are typically 5 MBytes in length.

6 hour files typically cover 2 years of data each and are typically 2 MBytes in length.

File Naming

[YYMMDD is the starting year, month, day of month of a file]

30 Minute Files:
YYMMDD_flux30m_gme_i8_v01.pcr

6 Hour Files:
YYMMDD_flux6hr_gme_i8_v01.pcr

File Structure

Header length

  • total 77 lines
  • or 5782 bytes

Each logical data record in a 30 minute average file is 574 bytes long.

Header length

  • total 102 lines
  • or 7732 bytes

Each logical data record in a 6 hour average file is 774 bytes long.

Notes:

The binary file format for this data is an instance of the PC-Rate self-describing format developed by the Low Energy Cosmic Ray group at the Goddard Laborartory for High Energy Astrophysics (LHEA) and now supporting instrument operations and data analysis for the Wind EPACT experiment.

The files start with a set of ASCII header records each terminated by a carriage-return/line-feed (included in the byte count to the right). The header records include the time coverage and identification of the variables in the file and entirely define the content and format of the following data records.

The header records are followed by a set of binary fixed-length logical data records (no explicit record separators), one for each time. Detailed formats as below. All binary words are in IBM PC byte order and integer / floating point representation.

Logical Data Record Structure

- An integer of fixed value 0 (in integer*2 format)

- The centered time of the record in seconds from January 1, 1970 in real*4 format

- 30 H fluxes and uncertainties, all real*4, in order flux, uncertainty, flux uncertainty etc

- 21 He fluxes and uncertainties, format and order as above

- 2 electron fluxes (nominal and background), format and order as above

- 18 event and singles rates, format and order as above

- An integer of fixed value 0 (zero) (in integer*2 format)

- The centered time of the record in seconds from January 1, 1970 in real*4 format

- 30 H fluxes and uncertainties, all real*4, in order flux, uncertainty, flux uncertainty etc

- 29 He fluxes and uncertainties, format and order as above

- 17 Ion fluxes and uncertainties, format and order as above

- 2 electron fluxes (nominal and background), format and order as above

- 18 event and singles rates, format and order as above

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Questions or Comments


Contact Information

Questions about GME data and/or instrumentation should be directed to the NASA Principal Investigator:

 
Dr. Robert E. McGuire (at Robert.E.McGuire@nasa.gov)
Head, Space Physics Data Facility
Code 672
NASA/Goddard Space Flight Center
Greenbelt MD 20771 USA
 
Phone (with phonemail): 301-286-7794


Authors/Authorizing NASA Official and Curator

Dr. Robert McGuire (see above)
Last Modified: Wednesday 5/6/99 (REM)