Comparison of the original and reanalyzed Chilton data from December
These comparisons have exposed several differences between the data at each of
the ionosonde sites. In order that the foibles of ADEP scaling could be in
some way deconvolved from the other effects, the data from December 1993 were
reanalysed. By doing this it was hoped to reveal those differences that can be
attributed to the idiosyncrasies of ADEP which can only be countered by
A comparison of the two sets of December 1993 data illustrates the types of
error that ADEP can introduce. The data that was reanalysed after several
months experience with the ADEP package differs from the initial analysed data
in several significant ways. For most parameters, there is approximately four
percent of scaled values that are no longer considered valid. Experience with
ADEP has enabled the scaler to over rule certain values that would previously
have been accepted. This gives some indication of the percentage of a
parameter's values that are incorrectly attributed by ADEP.
When the common data are plotted against each other, the newly scaled
parameters such as foF2, fxI, h'f and h'f2 are on the whole very
similar to the original scaled values, with only the occasional rogue
point. For some of the other parameters however, there are significant
differences between the scaled parameters.
- M3000(F2) values show a significant spread with more values being revised
upwards rather than downwards. This can be attributed to the sensitive nature
of the M3000(F2) value to the shape of the virtual height profile, as detailed
above. It is probable that a large proportion of the difference between Slough
and Chilton values of M3000(F2) is a direct result of this sensitivity.
- With fmin, the biggest change between the original and revised scaled
values, is that a number of erroneously low fmin values have been
increased. This leads to a distribution of points that are more biased towards
higher Chilton values.
- The fact that ADEP sets a minimum value of foE at all
times where it cannot be measured means that there is still 100 percent common
data for this parameter. The revised points are evenly distributed about the
expected line. An interesting feature to notice is that the lower values (up
to 1.4 Mhz) are in perfect agreement. This is probably a result of ADEP's
predictive capabilities too.
- Most of the foEs values are in very good agreement, but there is a
larger proportion of points (6%) that have subsequently been discarded. Of the
common points there are five revised points that differ from the original
values by more than one Mhz. These are most probably rogue foEs values that
slipped through the checking process on the previous analysis. Out of a total
of around 650 ionograms, this represents a tiny fraction of the data (0.8
- The very small percentage of common foF1 data was reduced even further
after reanalysis. 3.64 percent of the data from the initial analysis was
discarded, while only 0.55 percent of the reanalysed data had newly attributed
foF1 values. The three common points agree well.
- The most significant change to any one parameter's values was with
h'E. Although the common data was over 95 percent, most of the new
values were significantly greater than before. This is a consequence of ADEP
scaling. In order to estimate all the other parameters, a value of foE must be
chosen. If blanketing occurs, this value is set to any remaining E-region
echoes. As these are around the critical frequency, the value of h'E that they
give is anomalously large. Similarly, if blanketing is occurring, any E trace
that is scaled has an h'E that is affected by the underlying ionisation. A
significant proportion of h'E points that had previously been given values,
were set to 90 km in the new analysis (the default value of ADEP), indicating
that these values had been discarded. Values of h'f had a similar distribution
ot foEs, in that there was a very good agreement between the initial and
reanalysed points, with a few outliers.
18/02/97 Chris Davis