Survey of caveats in low-energy particle measurements: Ulysses/HI-SCALE and ACE/EPAM Instruments

“Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies” (HI-SCALE) onboard the ULYSSES spacecraft, and “Electron, Proton, and Alpha Monitor” (EPAM) onboard the ACE spacecraft, are very similar instruments and were designed to make measurements of ions and electrons over a broad range of energy and intensity. The ions (Ei≥50 keV) and electrons (Ee≥30 keV) are detected by five separate solid-state detector telescopes, oriented to provide essentially complete pitch-angle coverage from the spinning spacecraft. In this work, through detailed data-analysis (i) we perform a comprehensive quality assessment on, and (ii) depict a detailed survey of day-of-year (DOYs) with existing contamination in the high-resolution low-energy particle measurements recorded by the HI-SCALE and EPAM instruments, throughout the years 1991-2009 (i.e. during the total Ulysses mission lifetime) and 1997-2011, respectively. Two major types of contamination were revealed in our analysis: (i) "solar X-ray contamination" due to saturation (by solar photons) in two (of the four) detector sectors, during the telescope's direct exposure to the solar disk, and (ii) "cross-talk contamination" due to electrons being recorded as ions and vice versa. The results presented in this work will prove to be valuable to future users of these unique data sets and to designers of similar future instruments, supported by SEP validation and propagation models.