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. These are;

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.
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13/02/97 Chris Davis