Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

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8. Data Collection - and Analysis
8.1 Instruments -
unetic sensors for geomagnetic induction work on land should meet
as many as possi-ble of the following requirements:
(1) Sufficient sensitivity and time resolution
(2) Directional characteristics which allow observation of the
magnetic variation vector in well-defined, preferably ortho-
gonal components.
(3) Stable compensation of the Earth's permanent field, if re-
quired. The sensors should not show "drift" on a time scale
comparable to the slowest variati-ons to be analysed.
(4) Compensation of temperature effects or linear temperature de-
pendence with well defined temperature coefficients for subse-
quent corrections.
C5) Low power consumpti.on to allow field operations on 57et or dry-
cell batteries (less than 100 n;A at 10 to 20 Volts DC con-
tinuous power drain).
C6 1 Minimurn maintenance, all-owing unattended opera-tions over days,
weeks or months, depending on -the period range to be irlvesti-
gated.
(7) Electric outmpu-t signal, adaptab1.e for digital recording
w
No single sensor system can possib1.y meet all requiremen-ts over thc
full frequency range of natural geornagrletic variations and the
- choice of instruments wil.1 depend on the type of variations under
investigation. They record either the total field M Ho + 6H as
?E
sum of -tl;e s-teady field Ho and the variation field 6H, by coml2ensa.-
tion of Ho, the time--derivative fl : 6f'i or a combina-tion of 61.1 nil
x*
& i1. In geomagnetic latitudes the spectral amplitude distr.Lbution of
6H and 611, averagedoverextended perioss of moderate ma~c5tj.c acti-
vity, is the following:
x the variation field 6H only