Aerogeophysics in Finland 1972-2004 - arkisto.gsf.fi - Geologian ...

electronics of the EM systems, GTK has been able
to reduce the systemic noise to a minimum. For example,
the angle between the wing and the EM coil
holder (see Fig. 6a) is very important, as well as the
type of the rigid fixing.
A similar dual frequency EM system installed in
the Twin Otter has been designed for the Cessna Caravan.
The system in the Cessna Caravan was first
test flown in April 1999 and made ready for production
surveys in June of the same year. The coil con-
Fig. 6a. The EM wingtip installation in the Twin Otter. Photo: Kai Nyman
Fig. 6b. The EM pod fitting to the Twin Otter wing. Photo: Kai Nyman
Geological Survey of Finland, Special Paper 39
The “Three-in-One” aerogeophysical concept of GTK in 2004
figuration of the EM system is the same in both aircraft,
but due to shorter wingspan the distance between
the transmitter and receiver coils in the Cessna
Caravan is only 16.96 m. The coil dimensions and
weight of the wingtip installations were also modified
for the Cessna. Figure 7 shows the new technique
for fitting the EM pod to the wingtip. Instead
of mounting the wingtip system to the supporting
structure inside the wing, as in the case of Twin Otter,
the EM pod was affixed to the aluminium plate
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