Fmin, the minimum observable frequency.
Although both instruments are able to measure fmin for over 90% each month
between December 1993 and April 1994, the correlation between the sites is not
good. The scatter of points is so great that no real trend is visible in much
of the data. It has since come to light that a bug existed in the ADEP package,
whereby a strong sporadic E layer confused the system, and the foEs value was
attributed to fmin. This accounts for those points with a low Slough fmin that
have anomalously high Chilton fmin. Despite this erroneous group of points, the
correlation is still not good, and indeed the data from January and February
1994 seems to indicate that fmin measured at Chilton is approximately one half
of that at Slough. That this should be so is not surprising. The minimum
observable frequency is strongly instrument dependent, since it is a function
of Signal to Noise Ratio (SNR) and receiver sensitivity. It has already been
stated that the two instruments differ in both these respects.
Results
- Spring Equinox
- Summer Solstice
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15/05/97 Chris Davis