An Instrument for Recording ULF-ELF Geomagnetic Fluctuations Measured by Optically Pumped Magnetometers

A small, low-cost, highly sensitive system to record geomagnetic fluctuations on the ocean floor is described. The technique employed is to amplify the effective sensitivity of the Cs-vapor magnetometer with an intermediate stage discriminator amplifier voltagecontrolled oscillator prior to magnetic recording. The resultant overall electronic system noise level obtained is well below the inherent noise level of the sensor, permitting accurate measurement of undersea magnetic fluctuations up to 5 Hz.