The GEOTAIL Magnetic Field Experiment.

The Geotail spacecraft carries a high-resolution Magnetic Field Experiment to provide magnetic field data in the frequency range below 50 Hz. This experiment includes dual fluxgate magnetometers and a search coil magnetometer. Fluxgate sensors are mounted at distances of 4 m and 6 m from the spacecraft on a deployable mast to reduce spacecraft-generated noises. Both outboard and inboard fluxgate magnetometers have 7 automatically switchable ranges from ±16 nT to ±65536 nT (full scale) and resolutions equivalent to a 15-bit A/D conversion in each range. The basic sampling rate for the A/D conversion is 128 Hz for both magnetometers. Sampled signals are averaged to 16 vectors/s for the outboard magnetometer and 4 vectors/s for the inboard magnetometer for telemetry. Time-derivatives of magnetic field in the frequency range of 1-50 Hz (128 vector-samples/s) are acquired by the three-component search coil magnetometer (located on another mast), separated by 4 m from the spacecraft. Fluxgate data are continuously obtained at the same rate for both real-time and recorded modes of operation, while search coil data are only acquired in the real-time telemetry operation. The instruments were operated after the time of mast deployment on September 4, 1992, and are presently working in all modes as designed. The details of this experiment and initial observations are presented.