R. A. Gowen

Space plasma measurements with ion instruments

In this article we examine the factors which affect the determination of the plasma bulk parameters in space, with particular emphasis on the density determination. We make this assessment with reference to a particular instrument, the AMPTE‐UKS ion instrument, in order to be specific, but the issues raised here are likely to be encountered in the use of any space plasma instrument containing electrostatic energy analyzers or microchannel plate detectors. We have established a mathematical formalism for determining these parameters by relating the measured counts to the distribution function in terms of the geometric factor. The geometric factor is determined in the calibration of the instrument which is described in some detail. Among the factors we have considered are our calibration techniques, MCP efficiency, detector energy, and angular resolution, as well as the approximations used in our mathematical formalism. To establish confidence in our determination, we used a computer simulation to look for ...

Square root data compression

Square root data compression is particularly suited to compression of scientific data where there shall be no reconstruction data artifacts, and reconstruction errors are required to be less than specified Poisson statistical noise levels. Its fixed compression ratio also makes it particularly suitable for real-time engineering implementation where telemetry rates and computer memory capacities are constrained. The compression scheme is described together with formulas that determine optimized control parameters to allow any input and compressed dynamic ranges to be accommodated, including joining to uncompressed data regions where zero data errors are desired to protect low count information. Further formulas are presented that allow optimized reconstruction values and maximum reconstruction error limits to be determined. Finally, some examples are presented that demonstrate its particular suitability for scientific applications.