Polar Plasma Wave Instrument (PWI), Low Frequency Waveform Receiver, ~0.01 sec resolution fields

The Low-Frequency Waveform Receiver (LFWR) is designed to provide an extension of the High Frequency Waveform Receiver into the frequency range below 25 Hz. The LFWR consists of six parallel low-pass filters connected to the three orthogonal electric field sensors and to the triaxial search coils. The input signals are band limited to a frequency range from 0.1 to 25 Hz and are sam- pled by a 12-bit analog-to-digital converter. The six LFWR channels are sampled simultaneously at a rate of 100 samples s-1. The dynamic range of the LFWRis approximately 72 dB with fixed gain. An FFT on 256 or 464 values, depending on the snapshot size, was used in calibrating the data; i.e., perform FFT, calibrate andin frequency domain, perform inverse FFT to get calibrated time series. Coordinate System Used: local magnetic field-aligned, a spacecraft centered coordinate system where Z is parallel to the local B-field determined from Polar MFE, X points outward and lies in the plane defined by the Z-axis and the radial vector from the earth to the spacecraft, and Y completes a right-handed system and points eastward. The X- and Z-axes are contained in the north-south plane. The three orthogonal magnetic field components are given in units of nT/Sec rather than nT because the response of the searchcoils across the passband is not flat. In order to obtain units of nT, the data would need to be digitally filtered to the frequency of interest and then integrated over time. Integrating over the entire passband could possibly destroy the resolution of the higher frequency components since the low frequency noise, if present, will dominate. Data are bandpass filtered. The valid range of data in the frequency domain is from 0.5 to 22.5 Hz. Reference:..Gurnett, D.A. et al, The Polar plasma wave instrument, Space Science Reviews, Vol. 71, pp. 597-622, 1995.