A new telluric KCl probe using Filloux's AgAgCl electrode

The measurement of the telluric field's long-time variations requires stable instruments in the period range above 1 day. Obviously, most problems arise from drifting voltages between the telluric probes. Good results have been achieved using a three chamber Hempfling KCl probe together with Filloux's AgAgCl electrode. However, a one chamber probe of 0.6 m length and 0.06 m diameter filled with saturated KCl solution may be sufficient for some applications and additionally allows permanent control of the electrolyte's salt concentration. In a field test the telluric field at a single site was simultaneously observed using one and three chamber probes separated by 25 and 55 m resp. For periods shorter than 1 hour the noise level of the electrodes was found to be less than 1 (mV)²/Hz whereas in the period range between 1 hour and 1 day it increases to 100 (mV)²/Hz. Consequently, surveys investigating long periods of the telluric field can be carried out using small electrode separations of a few tens of meters. Furthermore, the stability of this probe negates the need to interrupt the time series for servicing of the probe. However, the one chamber probe is somewhat inferior to the three chamber probe with regard to temperature dependence at long periods.