"CHARS" : URSI IIWG Format For Archiving Monthly Ionospheric Characteristics

Bodo W. Reinisch, Center for Atmospheric Research, University of Massachusetts,
600 Suffolk Street, Lowell, MA 01854, USA

Bodo_Reinisch@uml.edu, http://ulcar.uml.edu

Introduction

The format "CHARS" is now used by the World Data Centers (WDC) for archiving monthly ionospheric characteristics; it was first introduced in 1989 by Gamache and Reinisch [1989a]. The CHARS "database" is actually a collection of the flat ASCII files each storing a month of data. This design was essentially an inexpensive way to provide potential users of the data with a platform-independent access to the CHARS database contents. The FORTRAN source code for reading the CHARS files has been released in a Scientific Report [Gamache and Reinisch, 1994]. The software for automatic assembly of CHARS files from the individual ionogram SAO files (see SAO Document in this INAG Newsletter) is currently under development.

The Ionospheric Informatics Working Group (IIWG) of URSI Commission G had recommended the CHARS format as a standard for scaled ionogram data dissemination and archival in 1989. This format was then accepted as the URSI standard at the URSI General Assembly in Prague, 1990. This report, prepared with the help of Ivan Galkin, Xueqin Huang and Jim Scali, presents the general description of the CHARS format with the latest updates as of November 1997. A description of the CHARS document is also contained on our web site. Comments on improvements, errors, or inconsistencies should be sent to the University of Massachusetts Lowell.

CHARS Format for Ionospheric Characteristics

The CHARS file is a flat ASCII text file containing all available data for a month, including the time series of major characteristics and their hourly statistical features (medians, deciles, etc.) It is reasonable to expect that the sounding schedule would not be strictly regular within the observation month. To solve a problem of uneven time sampling, a special header record is introduced into CHAR files [Gamache and Reinisch, 1989b] to serve as a key to encoding/decoding the remainder of the file.

Historically, the maximum length of individual text lines in a CHARS file was set to 120 characters so that it still could be printed without wrapping. The number of lines in a file is determined by the number of days in the month, the number of measurements made each day, and the number of characteristics being archived.

The structure of the CHARS file is shown in Table 1. It consists of two headers, Station Header and Data Header, followed by the main Data Group.

Station Header

The Station Header is one line comprising informative and encoding data. It contains the Station Name and location (A30) format; the Station Code in (A5) format; the meridian time used by the station to indicate if time is recorded in UT or LT on the records is given next in (I4) format followed by the station coordinates, Latitude N and Longitude E both in (F5.1) format; next there are two (A10) format variables describing the Scaling type, this takes the value Manual or Automatic, and the Data editing variable which can be Edited, Non-Edited, or Mixed.; last in this line is space for the Ionosonde system name in (A30) format. Total length of the Station Header is 99 characters plus CR and LF.

Data Header

Data Header contains information necessary to properly arrange and represent the Data Group. It starts with the Year, Month, Number of days in the month, M; the Number of characteristics archived in the CHARS file, K; the Total number of measurements reported for the CHARS file, and the Number of daily measurements made for each of the M days. Two lines of integers in (30I4) format are required to store this part.

Then, a repeating format of (12A10) is used to list the Names of the particular characteristics being archived. There is K of them, hence more than one line might be required to fit all names. For example if only the critical frequencies were archived, foF2, foF1, and foE, K would be three, and the characteristics list would be ' foF2' ' foF1' ' foE'. A list of the names of the characteristics, the units, and URSI codes taken from UAG23 [Piggott and Rawer, 1978] are given in Table 2. The URSI list has been expanded with characteristics that are scaled by the Digisonde ARTIST [Reinisch and Huang, 1983; Tang et al. 1989]. The Chebyshev coefficients [Huang and Reinisch, 1996] used to represent the electron density profiles are also given, also the best B0 and B1 parameters [Reinisch and Huang, 1997] for the IRI F2-profile, and the calculated ionospheric electron content.

Next, the Units corresponding to the characteristics list (see Table 2) are given in the file, these are in (12A10) repeating format. The last lines of the Data Header are for the URSI codes specified for each of the characteristics (see Table 2) and written in (60A2) repeating format.

From the information in this Data Header one knows immediately how many data for the time or for each characteristic are to be read. From the number of measurements for each day the time data can be separated into the times for the individual days of the month and the measured characteristics can uniquely be associated with a given time on a given day.

Finally, the Data Header contains the measurement times for the month. With uneven time spacing the measurement times must be recorded to associate with the reported characteristics. This requires that hours, minutes, and seconds of each measurement be entered into the database. To conserve space, the times are written once per month and the reported characteristics are written to correspond to these times. The measurement times are written in a (30(3I2)) repeating format corresponding to the hours, minutes, and seconds, HHMMSS, of the measurements. The number of lines needed for this is determined by the data sampling rate for the month.

Data Group

The Data Group contains the actual values of the characteristics and the corresponding hourly medians and statistics. The group is comprised of a number of lines per each archived characteristic which are repeated for each characteristic. The order of the characteristics follows that given in the "List of characteristics". On a per characteristic basis, for each characteristic one has the N1 values of the characteristic for day 1 corresponding to the reported measurement times for day 1. These are followed by the values for day 2, day 3, ... for each of the M days of the month. The characteristics are written in a repeating (24(I3,2A1)) format corresponding to the integer value (I3) of the characteristic and the qualifying and descriptive letters [see UAG 23]. The actual values of the characteristics can be obtained by multiplying the integer value by the value found in the corresponding Units list (group 2) of the database record (see Table 2). Thus a value of 86 reported for foF2 is multiplied by the Units factor 0.1 MHz to give a foF2 value of 8.6 MHz.

The IIWG Workshop 1989 suggested the use of two slashes, //, in place of the qualifying and descriptive letters for monthly characteristics data that were autoscaled but not validated or "edited", i.e. where no quality control procedure has been applied. This code has been extended to consider data that have been edited but no descriptive or qualifying letters introduced. With two positions to fill and the use of a single or double slash there are four codes that can be defined. The first is no slashes implying the use of the descriptive or qualifying letters. The next is the use of two slashes which signifies no editing and no intended use of des/qual letters. The third choice is to put a slash in the first position followed by a blank. This is used to signify autoscaled data that have been edited but no descriptive or qualifying letters are used. The last possibility is a blank in the first position followed by the slash. This is not currently used thus it leaves the possibility for future extension of the code. The codes are summarized in Table 3.

Immediately following the characteristics data are the hourly medians given in a (24(I3,2A1)) format; the counts for the hourly medians and the range in (24(I2,I3)) format; the upper quartiles in a (24(I3,2A1)) format; the lower quartiles in a (24(I3,2A1)) format; then the upper deciles in a (24(I3,2A1)) format; and finally the lower quartiles again in a (24(I3,2A1)) format.

The above sections are repeated for each characteristic given in the "characteristics list." This completes the CHARS file, i.e. a month of characteristics data.

References

Gamache R. R. and B. W. Reinisch, Proceedings from the International Workshop on "Digital Ionogram Data Formats for World Data Center Archiving," University of Lowell Center for Atmospheric Research, November 1989a.

Gamache R. R. and B. W. Reinisch, Ionogram Characteristics at Uneven Data Rates, Presented at URSI Working Group G.4 Ionospheric Informatics International Workshop, July, 1989, University of Lowell Center for Atmospheric Research, 1989b

Gamache R. R. and B. W. Reinisch, Ionospheric Characteristics Data Format for Archiving at the World Data Centers, University of Lowell Center for Atmospheric Research, Sci.Report 467, 1994.

Huang X. and B.W.Reinisch, Vertical .Electron density profiles from the Digisonde network, Adv. Space Res. 6, 121-129, 1996

B.W. Reinisch and X. Huang, Automatic Calculation of Electron Density Profiles from Digital Ionograms. 3. Processing of bottomside ionogramsRadio Science, 18, 477-492 1983

Reinisch, B. W. and X. Huang, Fitting the IRI F2-profile function to measured bottomside profiles, Adv. Space Res., in print, 1997

Piggott W. R. and K. Rawer, Editors, U.R.S.I. Handbook of Ionogram Interpretation and Reduction, World Data Center A for Solar-Terrestrial Physics Report UAG-23, and 23A, Boulder CO (1978).

Tang J., R. R. Gamache, and B. W. Reinisch, Progress on ARTIST Improvements, Sci. Report No. 14, GL-TR-89-0185, 1989.

Table 1. IIWG CHARS File Structure for Flexible Data Rates

Table 2. List of Characteristics, URSI codes, and Units

Table 2. List of Characteristics, URSI codes, and Units (continued)

Table 2. List of Characteristics, URSI codes, and Units (continued)

Table 2. List of Characteristics, URSI codes, and Units (continued)

Table 2. List of Characteristics, URSI codes, and Units (continued)

21.7 Table 3. IIWG Codes for the Descriptive and Qualifying Fields of the Characteristics.