Wavelet Compression Performance of MMS/FPI Plasma Count Data with Plasma Environment

The Fast Plasma Investigation (Pollock et al., 2016, https://doi.org/10.1007/s11214-016-0245-4; FPI) onboard the Magnetospheric Multiscale mission (Burch, Moore, et al., 2016, https://doi.org/10.1007/s11214-015-0164-9; MMS) uses a discrete wavelet transform and bit plane encoder (DWT/BPE; Winterrowd et al., 2010, https://doi.org/10.1109/AERO.2010.5446664) for data compression. This is the first plasma spectrometer suite to use this method of compression and thus serves as a benchmark for future plasma spectrometers. Flight data from MMS confirm viability of this compression algorithm in large areas of the magnetosphere. Because much of the FPI data were compressed losslessly on orbit, this flight data can be used as seed data to investigate performance of the DWT/BPE-based compression at increased rates of compression. In this study, data from several representative regions of the magnetosphere have been compressed to increasingly small sizes and the resulting error was analyzed. Wavelet-based compression is shown to be effective in all regions of the magnetosphere and solar wind for plasma count data, with performance varying with local environment. Specifically, plasma distributions that are characterized by low temperature and/or low density are compressed better leading to excellent performance in plasma regions such as solar wind and the magnetosheath. In general, ion data are compressed better than electron data, primarily due to a higher drift velocity of ions relative to their thermal speed and lower count rates. DWT/BPE compression can therefore be recommended for future instruments measuring count data in Earth's magnetosphere and in solar wind.