

Standard Archiving Output (SAO) Format

Introduction

Automatic scaling of ionogram data has come a long way and the quality of
the autoscaled data has reached a remarkable level. Consequently the time
has arrived to directly transfer ionosonde data to the World Data Centers
using the Internet. We have begun to equip the Digisondes with Internet
connections. The first Internet links were established between the Okinawa
Digisonde (CRL, Japan) and the WDC-C2 in Tokyo, the Millstone Hill Digisonde
(UML, USA) and the WDC-A in Boulder, Colorado, and Chilton Digisonde (RAL,
GB) and the WDC-C1 in Chilton. All data generated in the Digisonde are made
available for electronic transfer: ionogram data, scaled data, and drift
data.

Starting in 1987, the Ionospheric Informatics Working Group (IIWG) of
Commission G of URSI has developed recommendations for the data formats to
be used for dissemination and archiving of scaled ionogram data and for the
monthly ionospheric characteristics. The IIWG abstained (wisely) from trying
to develop a common data format for the system-dependent ionogram and drift
data.

The attached report gives a detailed description of the Standard Archiving
Output (SAO) format. Each SAO (text) file contains the scaled data for one
ionogram including the echo traces h'(f), echo amplitudes, frequency and
range spread, etc. and the electron density profile.

The upgraded or new Digisondes produce the SAO files in real time for local
recording and/or electronic transfer. The older Digisondes generate only
binary files, but offline editing results are usually stored in the SAO
format. Since these Digisonde ionograms SAO files are now becoming available
to any user either through the WDC sites or via the web pages of the
connected Digisonde stations it seems important to publish a description of
the SAO format.

The SAO format was originally designed for storing Digisonde ionograms
scaled by autoscaling software ARTIST and edited using ADEP utility.
However, in subsequent releases a special effort was made to generalize SAO
design so that it can hold scaled data produced by other sounder systems.
With release of version 4.1, the degree of format universality became high
enough to promote SAO as a standard format for exchange of scaled ionogram
data.

SAO Format version 4.2

The SAO file structure has remained the same since it was developed by the
IIWG in 1989, but the content has been expanded in subsequent releases. The
following is a description of the SAO format version 4.2 [Gamache et al.,
1996].

A SAO file is an ASCII text file with a maximum line length of 120
characters. In order to concisely describe the database some definitions are
necessary. The nomenclature is as follows:
     File     a collection of many Records
     Record   all data for a single observation (ionogram)
     Group    all Lines of a datum type
     Line     a sequence of Elements of a datum type, CR/LF terminated
     Element  a single datum in the specified format

The Record structure is composed of two basic components: a Data Index and
Data. The format and size of the Data Index is fixed. It describes the
contents of the Data in the Record. The Data component of each Record
contains a varying number of Groups as indicated by the Data Index. The
format and length of data varies from one Group to the next; however, all
data Elements within a single Group are of the same type and length. The
number of characters in a given Group can easily exceed the 120 characters
per line limit. In this case, the output overflows to succeeding lines, thus
a data Group may extend over several Lines.

This format design allows storing variable amount of information per
ionogram, depending not only on ionospheric conditions, but also on sounder
system specifics. There is only a subset of Groups that have to be present
in a Record. As explained below, all others may be omitted and their
corresponding index in the Data Index section set to zero. Data systems
engineers have to decide which Groups to use to report data available from
their sounders, if different from Digisonde. There are three situations,
described in detail below, where system-specific data can be readily
ingested using existing SAO-4 format:

   * System Description line (using tokens of an arbitrary format)
   * Operator's Message (using any text format)
   * Sounder Settings (by requesting a version indicator and submitting
     format specification to their local WDC)

Groups 57 to 79 are currently vacant for specification formats of other data
items currently missing from SAO-4. Each addition of a Group has to be
accompanied with a new release of SAO 4 format (versions 4.2, 4.3,... )
which contains format specification for the new Group. If necessary. the
number of vacant Groups may be expanded by addition of new line(s) in the
Data Index.

Data Index

The Data Index contains 80 three digit integers. The position in the list
corresponds to the data for the data Group number. These are shown in Table
1. The first integer is the number of Elements in the data Group 1,
Geophysical Constants, in the current Record. The second integer represents
the number of Elements in the second data Group, System Description, etc. A
value of zero indicates that there is no data for the Group in the Record.
Position 80 of the Data Index array is not used to specify the format of the
data to follow. It is reserved for the SAO 4.2 Version Indicator which is
set to 4.

If the demand for vacant Groups grows beyond the existing limit, the Data
Index will have to expand and include more lines. The 80th element of the
Data Index will still be used as the Version Indicator so that the reading
logic will be aware of extra index lines.

Column Req. of Table 1 indicates which Groups are required to specify in a
minimum content SAO-4 file.

                         Table 1. SAO Record Format

 Group Req.FORTRAN Format              Description              Reference

        x  2(40I3)        DATA FILE INDEX
 1      x  16F7.3         GEOPHYSICAL CONSTANTS                 Table 2
 2         A120           SYSTEM DESCRIPTION AND OPERATOR'S
                          MESSAGE
 3      x  120A1          TIME STAMP AND SOUNDER SETTINGS       Table 3,4,5
 4      x  15F8.3         SCALED IONOSPHERIC CHARACTERISTICS    Table 6,7
 5         60I2           ANALYSIS FLAGS                        Table 8
 6         16F7.3         DOPPLER TRANSLATION TABLE

                          O-TRACE POINTS - F2 LAYER
 7      xx 15F8.3         VIRTUAL HEIGHTS
 8         15F8.3         TRUE HEIGHTS
 9         40I3           AMPLITUDES
 10        120I1          DOPPLER NUMBERS
 11     xx 15F8.3         FREQUENCIES

                          O-TRACE POINTS - F1 LAYER
 12     xx 15F8.3         VIRTUAL HEIGHTS
 13        15F8.3         TRUE HEIGHTS
 14        40I3           AMPLITUDES
 15        120I1          DOPPLER NUMBERS
 16     xx 15F8.3         FREQUENCIES

                          O-TRACE POINTS - E LAYER
 17     xx 15F8.3         VIRTUAL HEIGHTS
 18        15F8.3         TRUE HEIGHTS
 19        40I3           AMPLITUDES
 20        120I1          DOPPLER NUMBERS
 21     xx 15F8.3         FREQUENCIES

                          X-TRACE POINTS - F2 LAYER
 22        15F8.3         VIRTUAL HEIGHTS
 23        40I3           AMPLITUDES
 24        120I1          DOPPLER NUMBERS
 25        15F8.3         FREQUENCIES

                          X-TRACE POINTS - F1 LAYER
 26        15F8.3         VIRTUAL HEIGHTS
 27        40I3           AMPLITUDES
 28        120I1          DOPPLER NUMBERS
 29        15F8.3         FREQUENCIES

                          X-TRACE POINTS - E LAYER
 30        15F8.3         VIRTUAL HEIGHTS
 31        40I3           AMPLITUDES
 32        120I1          DOPPLER NUMBERS
 33        15F8.3         FREQUENCIES

 34        40I3           MEDIAN AMPLITUDES OF F ECHOES
 35        40I3           MEDIAN AMPLITUDES OF E ECHOES
 36        40I3           MEDIAN AMPLITUDES OF ES ECHOES
 37        10E11.6E1      TRUE HEIGHTS COEFFICIENTS F2 LAYER
                          UMLCAR METHOD                         Table 9
 38        10E11.6E1      TRUE HEIGHTS COEFFICIENTS F1 LAYER
                          UMLCAR METHOD                         Table 9
 39        10E11.6E1      TRUE HEIGHTS COEFFICIENTS E LAYER
                          UMLCAR METHOD                         Table 9
 40        6E20.12E2      QUAZI-PARABOLIC SEGMENTS FITTED TO
                          THE PROFILE                           Table 10
 41        120I1          EDIT FLAGS - CHARACTERISTICS          Table 12
 42        10E11.6E1      VALLEY DESCRIPTION - W,D UMLCAR
                          MODEL

                          O-TRACE POINTS - Es LAYER
 43        15F8.3         VIRTUAL HEIGHTS
 44        40I3           AMPLITUDES
 45        120I1          DOPPLER NUMBERS
 46        15F8.3         FREQUENCIES

                          O-TRACE POINTS - E AURORAL LAYER
 47        15F8.3         VIRTUAL HEIGHTS
 48        40I3           AMPLITUDES
 49        120I1          DOPPLER NUMBERS
 50        15F8.3         FREQUENCIES

                          TRUE HEIGHT PROFILE
 51        15F8.3         TRUE HEIGHTS
 52        15F8.3         PLASMA FREQUENCIES
 53        15E8.3E1       ELECTRON DENSITIES [e/cm3]

                          URSI QUALIFYING AND DESCRIPTIVE
                          LETTERS
 54        120A1          QUALIFYING LETTERS
 55        120A1          DESCRIPTIVE LETTERS
 56        120I1          EDIT FLAGS - TRACES AND PROFILE       Table 13

 80        --             (Reserved)

Group 1: Geophysical Constants

The values of the Geophysical Constants shown in Table 2 are specified for
the station producing the data in the file. Frequencies are in MHz, angles
are in degrees.

                       Table 2. Geophysical Constants

       Position  Req                   Description
       1          x  Gyrofrequency (MHz)
       2          x  Dip angle (-90.0 to 90.0 degrees)
       3          x  Geographic Latitude (-90.0 to +90.0 degrees)
       4          x  Geographic Longitude East(0.0 to 359.9 degrees)
       5             Sunspot Number for the current year

Group 2: System Description and Operator's Message

This Group allows the user to give a description of the system which
recorded the data and to store a free format text message. The Group 2 is
given in A120 format, so the Data Index entry for the Group 2 counts total
number of 120-character Lines of text. One text line is used to store system
description; if an operator's message is given, it takes another text line.
Thus, the Data Index can be 0 (no information), 1 (system description) or 2
(system description and operator's message).

The minimum contents of the System Description line should include sounder
model and station IDs. To accomodate all possible station-specific
information in an organized and flexible fashion, the concept of a token is
introduced. System Description line is arranged in comma-separated tokens,
where each token consists of a registered keyword and a data field. The
first token is always the sounder model, local station ID and URSI station
code number. One space character separates sounder model and IDs. Station
IDs are separated by a forward slash. Local station ID is determined by host
institution or sounder manufacturer. URSI station code number is assigned
through World Data Center A for Solar-Terrestrial Physics, contact person
Raymond O. Conkright.

For example, the System Description Line for a UMLCAR Digisonde Portable
Sounder may look like this:

DPS-4 042/MHJ45, ARTIST 1297, NH 1.3, ADEP 2.19

It contains four tokens:

   * DPS-4 042/MHJ45 -- keyword DPS-4 indicates the Digisonde model "DPS-4",
     and data filed 042/MHJ45 contains UMASS Lowell Station ID (042) and
     URSI station code number (MHJ45)
   * ARTIST 1297 -- keyword ARTIST indicates ARTIST software, and 1297 is
     the ARTIST version number,
   * NH 1.3 -- keyword NH indicates true height profile inversion algorithm,
     and 1.3 is the algorithm version number,
   * ADEP 2.19 -- keyword ADEP indicates ADEP software, and 2.19 is the ADEP
     version number.

Thus, each item that the data support engineer needs in include into the
SAO-4 System Description line has to form a token where the item is
preceeded by a keyword. Another example can be given for a DISS sounder:

DISS 038/, NAME Wallops Island, WMOID HIGL BTGS 04231, ARTIST 0790, NH 1.3,
ADEP 2.19

The SAO reading routine works as a simple string parser. It has to get the
first word in the System Description line to identify the sounder system.
Then, depending on the sounder model, it can scan the rest of the line for
keywords and fill appropriate structures with corresponding data field
contents. If the sounder model could not be identified, then the system
Description line is used only as single text line, without analysis of
individual tokens.

Group 3: Timestamp and Sounder Settings

Group 3 contains three fileds: Version Indicator, Timestamp of the
measurement and a Sounder Settings. Only the first two fields are required
in the minimum contents of the Group. In the minimum case, the Version
Indicator should be set to AA as shown in the Table 3.

                     Table 3. Minimum Contents of Group 3

  Number Req.Description                                   Possible Values
  1-2.    x  Version Indicator                             AA
  3-6.    x  4 digit Year.                                 (1976-...)
  7-9.    x  Day of Year                                   (1-366)
  10-11.  x  Month                                         (1-12)
  12-13.  x  Day of Month                                  (1-31)
  14-15.  x  Hour [All times and dates correspond to UT.]  (0-23)
  16-17.  x  Minutes                                       (0-59)
  18-19.  x  Seconds                                       (0-59)

The Sounder Settings field is intended to allow users to assign codes that
identify how the measurement is made with reference to particular sounders.
For each particular sounder system, the format of System Preface Parameters
Group must be personalized and a unique two-letter Version Indicator should
be chosen to distinguish it from other sounder systems. The Version
Indicator is then stored in the first two positions of the Group 3.

DPS data is represented by "FF" Version Indicator, and "FE" is allocated for
Digisonde 256 data. Example formats of this Group for Digisonde Portable
Sounder (DPS) and Digisonde 256 are shown in Table 4 and Table 5,
respectively.


                   Table 4. DPS System Preface Parameters

 Number Description                                        Possible Values
 1-2.   Version Indicator                                  FF
 3-6.   4 digit Year.                                      (1976-...)
 7-9.   Day of Year                                        (1-366)
 10-11. Month                                              (1-12)
 12-13. Day of Month                                       (1-31)
 14-15. Hour [All times and dates correspond to UT.]       (0-23)
 16-17. Minutes                                            (0-59)
 18-19. Seconds                                            (0-59)
 20-22. Receiver Station ID (three digits)                 (000-999)
 23-25. Transmitter Station ID.                            (000-999)
 26.    DPS Schedule                                       (1-6)
 27.    DPS Program                                        (1-7)
 28-32. Start Frequency, 1 kHz resolution                  (01000 - 45000)
 33-36. Coarse Frequency Step, 1 kHz resolution            (1-2000)
 37-41. Stop Frequency, 1 kHz resolution                   (01000 - 45000)
 42-45. DPS Fine Frequency Step, 1 kHz resolution          (0000 - 9999)
 46.    Multiplexing disabled [0 - multiplexing enabled, 1 (0,1)
        - disabled].
 47.    Number of DPS Small Steps in a scan                (1 to F)
 48.    DPS Phase Code                                     (1-4, 9-C)
 49.    Alternative antenna setup [0 - standard, 1 -       (0,1)
        alternative].
 50.    DPS Antenna Options                                (0 to F)
 51.    Total FFT samples [power of 2]                     (3-7)
 52.    DPS Radio Silent Mode [ 1 - no transmission ]      (0,1)
 53-55. Pulse Repetition Rate (pps)                        (0-999)
 56-59. Range Start, 1 km resolution                       (0-9999)
 60.    DPS Range Increment [2 - 2.5 km, 5 - 5 km, A - 10  (2,5,A)
        km]
 61-64. Number of ranges                                   (1-9999)
 65-68. Scan Delay, 15 km units                            (0-1500)
 69.    DPS Base Gain                                      (0-F, encoded)
 70.    DPS Frequency Search Enabled                       (0,1)
 71.    DPS Operating Mode [ 0 - Vertical beam, 5 -        (0-7)
        multi-beam ionogram ]
 72.    ARTIST Enabled                                     (0,1)
 73.    DPS Data Format [ 1 - MMM, 4 - RSF, 5 - SBF ]      (0-6)
 74.    On-line printer selection [ 0 - no printer,1 -     (0,1,2)
        b/w, 2 - color ]
 75-76. Ionogram thresholded for FTP transfer [0-no        (0-20, encoded)
        thresholding]
 77.    High interference condition [ 1 - extra 12 dB      (0,1)
        attenuation ]


              Table 5. Digisonde 256 System Preface Parameters

 Number  CodeDescription                              Possible Values
 1-2.     -  Version Indicator                        FE
 3-6.     -  4 digit Year.                            (1976-...)
 7-9.     -  Day of Year                              (1-366)
 10-11.   -  Month                                    (1-12)
 12-13.   -  Day of Month                             (1-31)
 14-15.      Hour [All times and dates correspond to  (0-23)
          -
             UT.]
 16-17.   -  Minutes                                  (0-59)
 18-19.   -  Seconds                                  (0-59)
 20-30.   -  Digisonde Preface Timestamp              YYDDDHHMMSS
 31.      S  Program Set                              (1-3)
 32.      P  Program Type                             (A,B,C,F,G)
 33-38.   J  Journal                                  encoded
 39-44.   F  Nominal Frequency, 100 Hz resolution     (001000 - 045000)
 45-51.   P# Output Controls                          encoded
 52-53.   SS Start Frequency, 1 MHz resolution        (00-10)
 54.      Q  Frequency Increment                      (0-9,A-C,encoded)
 55-56.   UU Stop frequency, 1 MHz resolution         (01-30)
 57-59.  CAB Test Output                              encoded
 60-62.   V  Station ID                               (000-999)
 63.      X  Phase Code                               (0-F, encoded)
 64.      L  Antenna Azimuth                          (0-F, encoded)
 65.      Z  Antenna Scan                             (0-7, encoded)
 66.      T  Antenna Option and Doppler Spacing       (0-F, encoded)
 67.      N  Number of Samples                        (1-8)
 68.      R  Repetition Rate                          (0,2-8,A,B, encoded)
 69.      W  Pulse width and code                     (0-7, encoded)
 70.      K  Time control                             encoded
 71.      I* Frequency correction                     (0-4, encoded)
 72.      G* Gain correction                          (0-7, encoded)
 73.      H  Range increment                          (0-3,8-C, encoded)
 74.      E  Range start                              (0-7, encoded)
 75.      I  Frequency Search                         (0-7, encoded)
 76.      G  Nominal Gain                             (0-F, encoded)
 77.      -  Spare                                    0

Group 4: Scaled Ionospheric Characteristics

The Scaled Ionospheric Characteristics may be obtained by ARTIST, ADEP, some
other autoscaling or editing/validating software, or typed in manually. All
numbers represent either frequency in Megahertz or altitude in kilometers
except as indicated in Table 6. The format F8.3 (DDDD.DDD) is used to report
the characteristics which is equivalent to 1 kHz precision in frequencies
and 1 m precision in heights. The accuracy of the stored values is usually 1
ionogram pixel (frequency step or height increment) except as indicated in
Table 6.

There are currently 49 Scaled Ionospheric Characteristics defined. It is
possible to report less than 48 characteristics and indicate that in the
Data Index section of the record. Otherwise, all characteristics which are
not scaled for a particular ionogram must be set to a default "No reading"
value. which is 999.900 MHz for frequencies and 9999.000 km for heights.

                 Table 6. Scaled Ionospheric Characteristics

 #   Description                     Units  Accuracy             No reading
 1   foF2 : F2 layer critical        MHz    at least quarter of  9999.000
     frequency, including the               frequency increment
     adjustment by the true height
     profile algorithm
 2   foF1 : F1 layer critical        MHz    1 frequency          9999.000
     frequency                              increment
 3   M(D) = MUF(D)/foF2              -      -                    9999.000
 4   MUF(D) : Maximum usable         MHz    1 frequency          9999.000
     frequency for ground distance          increment
     D
 5   fmin: minimum frequency of      MHz    1 frequency          9999.000
     ionogram echoes                        increment
 6   foEs : Es layer critical        MHz    1 frequency          9999.000
     frequency                              increment
 7   fminF : Minimum frequency of    MHz    1 frequency          9999.000
     F-layer echoes                         increment
 8   fminE : Minimum frequency of    MHz    1 frequency          9999.000
     E-layer echoes                         increment
 9   foE : E layer critical          MHz    1 frequency          9999.000
     frequency                              increment
 10  fxI : Maximum frequency of      MHz    1 frequency          9999.000
     F-trace                                increment
 11  h'F : Minimum virtual height of km     1 height increment   9999.000
     F trace
 12  h'F2 : Minimum virtual height   km     1 height increment   9999.000
     of F2 trace
 13  h'E : Minimum virtual height of km     1 height increment   9999.000
     E trace
 14  h'Es : Minimum virtual height   km     1 height increment   9999.000
     of Es trace
 15  zmE : Peak height of E-layer    km     1 height increment   9999.000
 16  yE : Half thickness of E layer  km     1 height increment   9999.000
 17  QF : Average range spread of F  km     1 height increment   9999.000
     layer
 18  QE : Average range spread of E  km     1 height increment   9999.000
     layer
 19  DownF : Lowering of F trace to  km     1 height increment   9999.000
     the leading edge
 20  DownE : Lowering of E trace to  km     1 height increment   9999.000
     the leading edge
 21  DownEs : Lowering of Es trace   km     1 height increment   9999.000
     to the leading edge
 22  FF : Frequency spread between   MHz    1 frequency          9999.000
     fxF2 and fxI                           increment
 23  FE : Frequency spread beyond    MHz    1 frequency          9999.000
     foE                                    increment
 24  D : Distance for MUF            km     1 km                 9999.000
     calculation
 25  fMUF : MUF/OblFactor            MHz    1 frequency          9999.000
                                            increment
 26  h'(fMUF) : Virtual height at    MHz    1 height increment   9999.000
     MUF/OblFactor frequency
 27  delta_foF2 : Adjustment to the  MHz    1 kHz                9999.000
     scaled foF2 during profile
     inversion
 28  foEp : predicted value of foE   MHz    ±0.3 MHz             9999.000
 29  f(h'F) : frequency at which h'F MHz    1 frequency          9999.000
     occurs                                 increment
 30  f(h'F2) : frequency at which    MHz    1 frequency          9999.000
     h'F2 occurs                            increment
 31  foF1p : predicted value of      MHz    ± 0.5 MHz            9999.000
     foF1
 32  peak height of F2 layer         km                          9999.000
 33  peak height of F1 layer         km                          9999.000
 34  zhalfNm : the true height at    km     1 km                 9999.000
     half the maximum density in the
     F2 layer
 35  foF2p : predicted value of      MHz    ± 2.0 MHz            9999.000
     foF2
 36  fminEs : minimum frequency of   MHz    1 frequency          9999.000
     Es layer                               increment
 37  yF2 : half thickness of the F2  km     100 m                9999.000
     layer, parabolic model
 38  yF1 : half thickness of the F1  km     100 m                9999.000
     layer, parabolic model
 39  TEC : total electron content    1016   -                    9999.000
                                     m-2

 40  Scale height at the F2 peak     km     1km                  9999.000
 41  B0, IRI thickness parameter     km     -                    9999.000
 42  B1, IRI profile shape           -      -                    9999.000
     parameter

 43  D1, IRI profile shape           -      -                    9999.000
     parameter, F1 layer
 44  foEa, critical frequency of     MHz    1 frequency          9999.000
     auroral E layer                        increment
 45  h'Ea, minimum virtual height of km     1 height increment   9999.000
     auroral E layer trace
 46  foP, highest ordinary wave      MHz    1 frequency          9999.000
     critical frequency of F region         increment
     patch trace
 47  h'P, minimum virtual height of  km     1 height increment   9999.000
     the trace used to determine
     foP

 48  fbEs, blanketing frequency of   MHz    1 frequency          9999.000
     Es layer                               increment
 49  Type Es                         -      See Table 7          9999.000
Type Es is a letter characteristic which has to be reported in the Table 6
as a number using Lookup Table 7.

              Table 7. Lookup Table for Type Es Characteristic

    Type Es Value reported in Group 4            Description
    A       1.0                      Auroral
    C       2.0                      Cusp
    D       3.0                      below 95 km
    F       4.0                      Flat
    H       5.0                      Height discontinuity with normal E
    K       6.0                      in the presence of night E
    L       7.0                      Flat Es below E
    N       8.0                      Non-standard
    Q       9.0                      Diffuse and non-blanketing
    R       10.0                     Retardation

Group 5: ARTIST Analysis Flags

The ARTIST Analysis Flags are a sequence of two digit integers (60I2 format)
which indicate and qualify some of the ARTIST scaled results. Table 8 is a
description of the flags and the meaning of their possible values.




                            Table 8. ARTIST Flags

 Position Content                        Description

 1        1      foE scaled using E-region trace data
          2      No E-region trace obtained, only predicted foE available
          3      No E-region trace obtained, but foE scaled using F trace

 2        0      No F trace scaled
          1      E layer profile only
          2      Separate soliutions for E and F layers
          4      Frequency range error in E trace
          5      Frequency range error in F2 trace
          6      Frequency range error in F1 trace
          7      Physically unreasonable E trace
          8      Physically unreasonable F2 trace
          9      Physically unreasonable F1 trace
          10     F1 layer solution too thick
          11     Oscillating solution in F1 layer
          12     F2 trace too short
          13     F1 trace too short
          18     Oscillating solution in F1 layer
          25     Root in F1 layer too severe to correct
          26     Root in F2 layer too severe to correct

 3               Not used

 4        0      foF1 not scaled
          1      foF1 scaled

 5        0      No AWS Qualifier applies
          1      Blanketing Sporadic E
          2      Non-Deviative Absorption
          3      Equipment Outage
          4      foF2 greater than equipment limits
          5      fmin lower than equipment limits
          6      Spread F
          7      foF2 less than foF1
          8      Interference
          9      Deviative absorption

 6-9             Not used

 10       0-5    Confidence level, 0-highest confidence, 5-lowest
                 confidence

 11-19           Not used

 20              Internal ARTIST use

Group 6: Doppler Translation Table

The Doppler Translation Table is a sequence of floating point numbers in the
16F7.3 format which convert the trace Doppler Number into a Doppler
frequency in Hertz. These numbers should be read into a floating point
array. Using the Doppler Number as an index to that array will result in the
Doppler shift for the scaled trace point in question. The first element of
the Doppler translation table corresponds to the Doppler number 0.

Trace Points

The following Groups include ionogram trace information obtained in some
automated or interactive manner. The data format and content is identical
for any of the F2, F1, E, or Es traces with either ordinary (O) or
extraordinary (X) polarization although not all traces may be present in any
one ionogram. For example, the ARTIST program currently does not scale the
complete X-traces, however space has been provided for implementation of
this feature at a later date.

The data for each trace are contained in five Groups. For the F2 O-trace
they are in Groups 7, 8, 9, 10, and 11; for the F1 O-trace they are in
Groups 12, 13, 14, 15, and 16; etc. (see Table 1). The groups for sporadic
E, auroral night E leayrs and all extraordinary data groups do not contain
the true height group. Also, Groups 51, 52, and 53 are reserved for an
accurate representation of the electron density profile, including the
valley. There is a one-to-one positional correspondence between elements in
these five Groups, in that the first Virtual Height, True Height, Amplitude,
Doppler Number and Frequency all correspond to the first Trace point on the
ionogram. The same is true of the second point, and so on throughout the
entire trace.

Autoscaling or editing software may interpolate or extrapolate missing trace
points to maintain consistent frequency stepping within the trace or provide
better accuracy of the scaled characteristics. Because of explicit
specification of all trace point frequencies in the SAO format, the
interpolated or extrapolated points may be omitted. However, in this case
the value of true hieght obtained for that frequency will be missing as
well. If included, the interpolated/extrapolated points shall be reported
with amplitude set to 0 and Doppler number set to 9.

Groups 7, 12, 17, 22, 26, 30, 43, 47: Trace Virtual Heights

This group consists of a number of Virtual Heights in 15F8.3 format for the
layer indicated. The number of these heights depends upon the length of the
trace on the corresponding ionogram. Virtual Heights are reported in
kilometers of altitude.

Groups 8, 13, 18: True Heights

This group consists of a number of True Heights in 15F8.3 format for the
layer indicated. The number of these heights depends upon the length of the
trace on the corresponding ionogram (compare to complete profiles
specification in Groups 51-53). True Heights are reported in kilometers of
altitude.

Groups 9, 14, 19, 23, 27, 31, 44, 48: Trace Amplitudes

The amplitude in dB of each trace point is recorded in 40I3 format.

Groups 10, 15, 20, 24, 28, 32, 45, 49: Trace Doppler Numbers

The Doppler Number, as measured by the Digisonde, for each trace point is
recorded here in 120I1 format. To convert this number to an actual Doppler
shift in Hertz, use this integer as the index to the Doppler Translation
Table provided in Group 6. Index for 8 element Doppler Translation Table
runs from 0 to 7. Value 9 is reported for interpolated or extrapolated
points where information about Doppler frequency shift is unavailable.

Groups 11, 16, 21, 25, 29, 33, 46, 50: Trace Frequencies

The frequency (in MHz) of the trace point is given in this Group in the
15F8.3 format. Originally, this Group was provided for the possibility of
uneven frequency stepping and would normally be left empty for Digisonde
ionograms with a constant frequency step. This is no longer acceptable. The
sounder settings which are required to restore linear step frequencies can
be obtained only from a valid Sounder Settings Group 3 and Scaled
Characteristics Group 4 and may appear to be missing for some sounder
systems.

Group 34: Median Amplitude of F Echo

These values are an amplitude in dB for the F trace. It is calculated every
integer MHz between fminF and foF2. See Code 4 for fmin and foF2. The Median
Amplitude is calculated by taking the median of the trace amplitudes over a
0.5 MHz in frequency by five height range rectangle and then scaling this
median value to appear as if it were at 100 km altitude.

Group 35: Median Amplitude of E Echo

Same as per Code 34, but for the E echo between fminE and foE.

Group 36: Median Amplitude of Es Echo

Same as per Code 34, but for the Es echo between fminE and foEs.

Group 37: True Height Coefficients for the F2 Layer

The True Height Data for F2 layer from the UMLCAR method are stored in the
E11.6E1 format. There are up to 10 elements. The meaning of each element is
given in Table 9.

                      Table 9. True Height Coefficients

        Position Parameter                Description
        1        fstart   Start frequency (MHz) of the F2 layer
        2        fend     The end frequency of the F2 layer
        3        zpeak    The height of the peak of the F2 layer
        4        dev      The fitting error in km/point.
        5-9      A0-A4    Shifted Chebyshev polynomial coefficients
        10       zhalfNm  Height at half peak electron density

Group 38: True Height Coefficients for the F1 Layer

The True Height Data for the F1 layer from the UMLCAR method have the same
format as those for the F2 layer (Group 37) above with the exception of
zhalfNm (see Table 9).

Group 39: True Height Coefficients for the E Layer

The True Height Data for the E layer from the UMLCAR method have a format
very similar to that for the F2 and F1 layers (Codes 37 and 38) above. The
difference lies in that there are only seven elements stored in this Group.
The first four parameters are fstart, fend, zpeak and dev as defined for the
F2 layer. There are, however, only three coefficients for the shifted
Chebyshev polynomials (A0 - A2) for the E layer true height.

Group 40: Quazi-Parabolic Segments Fitted to the Profile

An arbitrary number of parabolic segments may be fitted to the profile to
approximate its shape. Each segment can be expressed as:

     fN2 = A/R2 + B/R + C

where

     fN is the plasma frequency in MHz,
     A, B, and C are the parabolic coefficients
     R is the distance from the center of the Earth in km, which varies from
     R1 to R2 for the segment.

If n segments are fitted to the profile, the Group 40 will contain n+1
entries.  The first n entries store 6 values per segment (R1, R2, A, B, C,
and fitting error E) in the E20.12E2 format, and the last lines contains the
Earth radius, as is shown in Table 10.
                 Table 10. QP Segments reported in Group 40

              #  Value 1 Value 2 Value 3Value 4 Value 5 Value 6
             1   R11     R12     A1     B1      C1      E1
             2   R21     R22     A2     B2      C2      E2
             ...
             n   Rn1     Rn2     An     Bn      Cn      En
             n+1 Re         -       -      -       -       -

The Earth radius, Re,  is the actual value used in the fitting process and
is given in SAO file to ensure proper restoring of the profile shape.


Group 41: Edit Flags: Characteristics

The edit flags are written in 120I1 format and are used to indicate whether
the reported ionospheric characteristics are result of autoscaling, manual
input, or long-term prediction. One edit flag is a sum of three indicators,
EDITED(1), PREDICTED(2) and VALIDATED(4). Table 11 shows possible
combinations of the indicators.

       Table 11. Edit Flag (characteristics) and its possible meanings

 EDITED PREDICTED          EDIT FLAG               Description
                 VALIDATED
                           VALUE
   0        0        0      0+0+0 = 0  autoscaled value
   0        0                          autoscaled value, validated by an
                     4      0+0+4 = 4
                                       operator
   1        0                          manually specified value; the
                     4      1+0+4 = 5  autoscaled value was incorrect or
                                       unavailable
   0        2        0      0+2+0 = 2  long-term prediction

The position in the edit flag list corresponds to the order of the
characteristics listed in Table 6. A complete list is given in Table 12. The
edit flags may be used to set the slash (/) indicators in the URSI-IIWG
characteristics database, if the indicators are not given in the Groups
54-55.

                    Table 12. Edit Flags: Characteristics

 #   Scaled Characteristic                   Description
 1   foF2                 F2 layer critical frequency
 2   foF1                 F1 layer critical frequency
 3   M(D)                 M-factor, MUF(D)/foF2, for distance D
 4   MUF(D)               Maximum usable frequency for distance D
 5   fmin                 Minimum frequency for E or F echoes
 6   foEs                 Es layer critical frequency
 7   fminF                Minimum frequency of F-trace
 8   fminE                Minimum frequency of E-trace
 9   foE                  E layer critical frequency
 10  fxI                  Maximum frequency of F-trace
 11  h'F                  Minimum virtual height of F trace
 12  h'F2                 Minimum virtual height of F2 trace
 13  h'E                  Minimum virtual height of E trace
 14  h'Es                 Minimum virtual height of Es layer
 15  HOM                  Peak of E layer using parabolic model
 16  Ym                   Corresponding half thickness of E layer
 17  QF                   Average range spread of F-trace
 18  QE                   Average range spread of E-trace
 19  Down F2              Lowering of F-trace maximum to leading edge
 20  Down E               Lowering of E-trace maximum to leading edge
 21  Down Es              Lowering of Es-trace maximum to leading edge
 22  FF                   Frequency spread between fxF2 and fxI
 23  FE                   As FF but considered beyond foE
 24  D                    Distance used for MUF calculation
 25  fMUF(D)              MUF(D)/obliquity factor(
 26  h'MUF(D)             Virtual height at fMUF
 27  foF2c                correction to add to foF2 to get actual foF2
 28  foEp                 Predicted foE
 29  f(h'F)               Frequency at which hminF occurs
 30  f(h'F2)              Frequency at which hminF2 occurs
 31  foF1p                Predicted foF1
 32  Zpeak                Peak height F2 layer
 33  ZpeakF1              Peak height F2 layer
 34  zhalfnm              Height at half peak electron density
 35  foF2p                Predicted foF2
 36  fminEs               Minimum frequency of Es layer
 37  YF2                  Half-thickness of F2 layer in parabolic model
 38  YF1                  Half-thickness of F1 layer in parabolic model
 39  TEC                  Total electron content
 40  HscaleF2             Scale height at F2 peak
 41  B0                   IRI thickness parameter
 42  B1                   IRI profile shape parameter
 43  D1                   IRI F1 profile shape parameter
 44  foEa                 Critical frequency of auroral E layer
 45  h'Ea                 Minimum virtual height of auroral E layer trace
 46  foP                  Highest ordinary wave critical frequency of F
                          region patch trace
 47  h'P                  Minimum virtual height of the trace used to
                          determine foP
 48  fbEs                 Blanketing frequency of Es layer
 49  Type Es              Type of Es layer

Group 42: Valley Characteristics UMLCAR model

The current content for this Group is two parameters describing the width
and depth of the valley region in the UMLCAR model.

Group 51-53: True Height Profile

The complete true height profile of electron density up to 800 km is given
here, including all layers and the valley. The profile is reported with the
true height as the argument of the N(h) function, i.e. all heights within
the valid range are scanned with a fixed increment, say, 1 km, and put in
Group 51. Corresponding frequencies and electron densities are given in
Group 52 and Group 53. Also, a few additional height points are reported in
the groups: all peak heights of the layers and the starting height of the
profile. The additional points might not be multiples of the height
increment. One-to-one positional correspondence of individual elements in
Groups 51-53 is preserved, so that, for example, the first element of Groups
51-53 refers to the starting height of the profile.

The height increment and coverage for the profile specification is
determined by the program which created the SAO file.

Group 54-55: Qualifying and Descriptive Letters

These two groups store URSI Qualifying (Group 54) and Descriptive (Group 55)
letters [URSI Handbook of Ionogram Interpretation and Reduction, 1972] using
120A1 format. The letters are used by manual scaling operators to reflect
reliability of measurement and indicate the presence of certain ionospheric
phenomena. The layout of the Groups 54-55 corresponds to Table 6 (Scaled
Ionospheric Characteristics). The number of items stored in the Groups 54
and 55 must be the same as in Group 6.

When no qualifying or descriptive letter is applied to a characteristic but
its value has been verified or edited, the correspoding entry in the Group
54 should read "/" (forward slash) and Group 55 should read " " (space) [see
IIWG regulations, Table 3, here]. For autoscaled data, the IIWG regulations
suggest storing "/" in both groups, but SAO-4 file created by the
autoscaling software may simply omit Groups 54 and 55 and report only Group
41 (Edit Flags).

Group 56: Edit Flags: Traces and Profile

The edit flags are written in 120I1 format and correspond to whether
ionogram traces and profile were modified as a result of manual scaling of
the data. Autoscaling software must not report this group to distinguish it
from the manual editing/validating. If no trace points were adjusted and
profile was not recalculated in the process of manual editing/validation,
the Group 56 must still be reported with all zero settings to distinguish it
from autoscaled data.

                  Table 13. Edit Flags: Traces and Profile

        #  Name                       Description
        1  F2 trace F2 trace points were edited
        2  F1 trace F1 trace points were edited
        3  E trace  E trace points were edited
        4  z(h)     true height was recalculated with edited traces
        5  Es trace Es trace points were edited

References

Gamache R. R., I.A. Galkin,  and B. W. Reinisch, "A Database Record
Structure for Ionogram Data", University of Lowell Center for Atmospheric
Research, UMLCAR 96-01, 1996.

URSI Handbook of Ionogram Interpretation and Reduction. Ed. W.R.Pigott and
K.Rawer. WDC-A for STP, 1972.

  ------------------------------------------------------------------------

Last Modified: September 2, 1999
