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Caveat for Slough Data
Early Data, 1930 - 1943
We have discovered scaled data sheets in our archive and have used it to
replace the data which was in our catalogue for this period. The old data from
our catalogue remains online. The new data is more numerous and it includes
monthly medians. In addition, we have an accompanying caveat and usage
guidelines (below) to give background to the immature nature of ionosonic
sounding at the time.
IMPORTANT
Between 12th October 1936 and 29th October 1938, any foF2 with the value of
113 should be treated as erroneous. This systematic error is produced by a
lowering of the maximum frequency of the sounder.
During the period these soundings were taken, there was less radio interference.
Ionograms started at ~0.7 MHz and the E layer is visible much more - which is
mentioned in early early publications.
Ionospheric History Notes
- Ionospheric sounding started in 1930. The first successful radar sounding was
at 14:30 GMT on the 23 May - the F layer was discovered on frequency 6 at a
height of 230 Km. Soundings were made at half-hourly intervals at a frequency
of 6 MHz.
- Two very good days were June 27th and 30th 1930 at a frequency of 4.3 MHz.
These are a mixture of h'E & h'F layers. They look suspiciously like Low Es
layers and F2.
- In July, August and October of 1930, several frequencies ranging from 3 to 7
Mhz were tried - all were very successful and the height values for E F1 F2
and Es was recorded.
- From January 1931 soundings appeared to concentrate on FoE.
- Twenty-four hourly campaigns began in February 1932 - always starting at 1600
GMT.
- Beginning November 1932, values were rounded up or down to one decimal place.
- On 5th November 1932 the qualifying letter 'F' was used for the first time -
used to indicate spread.
- As of January 1933 (Noon soundings) the sounder was operated six days a week
including Easter Bank Holiday.
- The qualifying letter 'A' was first used on 21st March 1933.
- The qualifying letter 'C' (indicating equipment failure) was first used at
Noon on 6th January 1933. This letter is said to stand for 'cows', who broke
the fence and wandered amongst the aerials - disrupting their performance by
using them as scratching posts.
- On September 18th 1936, the foF2 reached a frequency of 10.7 Mhz. This is the
first time the radar exceeded the 10 MHz milestone.
- During the 1st to 12th September 1939 no data was recorded. This coinsides with
the Battle of Britain.
- On 4th January 1940 at Noon, the first foEs were recorded.
- In September 1943 regular hourly soundings began for most of the values used
today.
- The use of 'sliders' to calculate M3000 was only introduced in ~1951. Before
that the 10 Point method was used.
Richard Henwood
30th March 2004
UK Solar System Data Centre