Differences in scaling techniques between the KEL and the DPS
Although ionograms from the KEL machine are recorded digitally, the only way
to scale the data is to print out the ionograms onto paper and submit the
plots to an individual skilled in scaling the required parameters. This has
the advantage that the full set of URSI standard descriptive letters
(UAG report 23) can be used to account for any parameter that requires
additional explanation. Once these parameters have been recorded, they have
to be typed into a database. This is both time consuming and costly.
In contrast, data from the DPS can be processed digitally, using the software
package ADEP (Artist Data Editing and Printing). With this software, the
parameters can be scaled much more quickly, but there is no provision, as yet,
for the addition of qualifying letters. As a result, the parameter 'type of Es'
cannot be scaled, as it is comprised entirely of qualifying letters. In
addition, 'fbEs' and 'm(3000)F1' are not catered for with this package.
This leaves eleven common parameters with which to make a comparison.
- fmin, the minimum frequency recorded in the F layer trace.
- foEs, the critical frequency of the sporadic E layer.
- foF2, the critical frequency of the F2 layer.
- fxI, the maximum frequency recorded in the F layer trace (both o
- h'Es, the virtual height of the sporadic E layer.
- h'F, the virtual height of the F layer
- m(3000)F2, the maximum usable frequency of transmission over 3000km,
divided by the F2 layer density.
- foE, the critical frequency of the E layer.
- foF1, the critical frequency of the F1 layer.
- h'E, the virtual height of the E layer.
- h'F2, the virtual height of the F2 layer.
Automatic versus manual scaling
The differences in scaling techniques between the instruments adds yet another
variable to the comparison. It is both an advantage and a drawback with ADEP
that an ionogram is scaled automatically. The advantage is that general
ionospheric parameters can be obtained instantly from the data. This is of
great importance to facilities that require immediate availability of
scaled data, such as in radio communications. For the purposes of long term
monitoring however, such an immediate turn around is unnecessary. It is
inevitable that some noisy or highly complicated ionograms will be
misinterpreted by an automatic scaling technique, and it is
important that each ionogram is checked before the scaled values are accepted.
For example, at Chilton, it has been found that values of the sporadic E layer
critical frequency, foEs, given by ADEP, are frequently confused with
independent echoes at higher frequencies. It is important that
such anomalies are corrected. In order to account for this, the Chilton data
set was also analyzed by an experienced ionogram scaler. The experience of such
a person greatly adds to the quality of the data. In addition to checking for
values that are wrong, an experienced scaler using the ADEP software is able
to carry out fine adjustments to the automatic profile. In general, this does
not greatly affect the parameters, but some, for example M3000(F2), are very
sensitive to the chosen screen coordinates. A small change in the points
selected on the screen can significantly affect the value of the output.
In addition, some features of the automated process may only become apparent
when comparing Chilton and Slough data. The accuracy of the ADEP software must
be considered as a possible cause of any differences that come out of such a
study. With such an intensive task as analysing months of ionogram data, it is
inevitable that some of the incorrect automatic values slip through.
13/02/97 Chris Davis