The Morphology of Naturally Enhanced Ion-acoustic Lines Observed in ESR 42m Data

Abstract

The Real Time Graph program is capable of generating, as an output, a spectral panel and a power panel, that change in terms of shape and size in response to back-scattered incoherent radar signals. A spectral shape criterion and a power profile criterion are used to evaluate and differentiate between different morphologies for each observed spectra. Analytically, using comparative analysis, four major categories are identified: a normal morphology, a Naturally Enhanced Ion-Acoustic Lines (NEIALs) morphology, a hard object morphology (satellite, space debris, etc.), and a turned-off transmitter morphology. Thirty data dumps are identified as NEIALs, which are investigated in terms of their spectral morphologies and the variations between each type of NEIALs. A “Flambeau”-like spectral shape, along with a “hill”-like power profile, is a distinctive feature of NEIALs. Particular spectra may contain mixed spectral morphologies, such as NEIALs along with hard object(s). NEIALs events may be contained and processed in one single data dump as well in two, three, four, or five consecutive data dumps. The analysis of NEIALs spectral shapes and the corresponding power profiles indicate that the highest intensity of scattered power comes from altitudes between 400 km and 600 km, but most likely about 500 km. We find that the down-shifted ion line shoulder is more often enhanced compared with the up-shifted ion line shoulder. The majority of data dumps show spectral line enhancements that are down-shifted in frequency, while no significant evidence is found for spectral line enhancements that are up-shifted in frequency.