URSI IIWG Format For Archiving Monthly Ionospheric Characteristics "CHARS"

Introduction

The Ionospheric Informatics Working Group (IIWG) of URSI Commission G had recommended the CHARS format as a standard for ionogram data dessimination and archival in 1989. This format was then accepted as the URSI standard at the URSI general Assmebly in Prague, 1990. This report present the general description of the CHARS format with the latest updates as of November 1997.

CHARS Format for Ionospheric Characteristics

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

Data Header

Then, a repeating format of (12A10) is used to list the Names of the particular characteristics being archived. There are K of them, hence more that one line might be required to fit all names. For example if one were archiving only the critical frequencies 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 enhanced 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 profile of ionosphere 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 are 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.
 

Table 1. IIWG CHARS File Structure for Flexible Data Rates

File Section	FORTRAN Format	Description
Station Header	A30	Station Name
	A5	Station code
	I4	Meridian time used by station on records
	F5.1	Latitude N
	F5.1	Longitude E
	A10	Scaling type: Manual/Automatic
	A10	Data editing: Edited/Non-edited/Mixed
	A30	Ionosonde system name
Data Header	30I4... *	Year
		Month
		Number of days in the month, M
		Number of Characteristics, K
		Numbers of measurements total
		Numbers of measurements for each of the M days (Ni, i=1..M)
	12A10...*	Names
	12A10...*	Units
	12A10...*	List of corresponding URSI codes
	20(3I2)...*	Measurement times HH:MM:SS for each of M days, (Ni values)
Data Group	24(I3,2A1)...*	N1 values of characteristic 1 (Day 1)
		N2 values of characteristic 1 (Day 2)
		...
		NM values of characteristic 1 (Day M)
	24(I3,2A1)	24 hourly medians for characteristic 1
	24(I2,I3)	24 x 2 hourly counts and ranges
	24(I3,2A1)	24 hourly upper quartiles
	24(I3,2A1)	24 hourly lower quartiles
	24(I3,2A1)	24 hourly upper deciles
	24(I3,2A1)	24 hourly lower deciles
		Repeated for characteristic 2
		...
		Repeated for characteristic K

* The format is repeated for as many lines as needed to store the data
 
 

Data Group

The IIWG Workshop 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 which 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. 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.

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, "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.

Reinisch B.W., and X. Huang, Automatic calculation of electron density profiles from digital ionograms, 3, Processing of bottomside ionograms, Radio Sci., 18, 472-492, 1983.

Tang, J., R.R. Gamache, and B.W. Reinisch, Progress on ARTIST improvements, Sci. Rep. No. 14, GL-TR-89-0185, Air Force Geophys. Lab., Hanscom AFB, Mass., 1989.