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Entropy 2014, 16(2), 1134-1168; doi:10.3390/e16021134
Article

Signal Processing for the Measurement of the Deuterium/Hydrogen Ratio in the Local Interstellar Medium

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1 Physics Institute, University of Bern, Sidlerstrasse 5, Bern 3012, Switzerland 2 Space Research Centre, Polish Academy of Sciences, Bartycka 18A, Warsaw 00-716, Poland 3 Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA 4 Southwest Research Institute, San Antonio, TX 78228-0510, USA and University of Texas at San Antonio, San Antonio, TX 78249, USA 5 Space Science Center and Department of Physics, University of New Hampshire, 39 College Road, Durham, NH 03824, USA
* Author to whom correspondence should be addressed.
Received: 9 August 2013 / Revised: 18 December 2013 / Accepted: 11 February 2014 / Published: 24 February 2014
(This article belongs to the Special Issue Advanced Signal Processing in Heliospheric Physics)
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Abstract

We report on a comprehensive signal processing procedure for very low signal levels for the measurement of neutral deuterium in the local interstellar medium from a spacecraft in Earth orbit. The deuterium measurements were performed with the IBEX-Lo camera on NASA’s Interstellar Boundary Explorer (IBEX) satellite. Our analysis technique for these data consists of creating a mass relation in three-dimensional time of flight space to accurately determine the position of the predicted D events, to precisely model the tail of the H events in the region where the H tail events are near the expected D events, and then to separate the H tail from the observations to extract the very faint D signal. This interstellar D signal, which is expected to be a few counts per year, is extracted from a strong terrestrial background signal, consisting of sputter products from the sensor’s conversion surface. As reference we accurately measure the terrestrial D/H ratio in these sputtered products and then discriminate this terrestrial background source. During the three years of the mission time when the deuterium signal was visible to IBEX, the observation geometry and orbit allowed for a total observation time of 115.3 days. Because of the spinning of the spacecraft and the stepping through eight energy channels the actual observing time of the interstellar wind was only 1.44 days. With the optimised data analysis we found three counts that could be attributed to interstellar deuterium. These results update our earlier work.
Keywords: energetic neutral atoms; deuterium; D/H ratio; ISM; 3D-TOF analysis; IBEX-Lo energetic neutral atoms; deuterium; D/H ratio; ISM; 3D-TOF analysis; IBEX-Lo
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Rodríguez Moreno, D.F.; Wurz, P.; Saul, L.; Bzowski, M.; Kubiak, M.A.; Sokół, J.M.; Frisch, P.; Fuselier, S.A.; McComas, D.J.; Möbius, E.; Schwadron, N. Signal Processing for the Measurement of the Deuterium/Hydrogen Ratio in the Local Interstellar Medium. Entropy 2014, 16, 1134-1168.

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