Observing atmospheric HCN on Titan from space and ground-based observatories: an inter-comparison study from Herschel, APEX and IRAM 30m telescopes

<p>In support of the Herschel Space Observatory and in the framework of the program “Water and Related Chemistry in the Solar System” [1], hydrogen cyanide (HCN) on Titan was observed from ground at submillimetre wavelengths. We carried submm heterodyne spectroscopy observations of HCN (4-3) at 345.5 GHz with the Atacama Pathfinder Experiment (APEX) and the APEX-2 heterodyne receiver, and of HCN (3-2) at 265.9 GHz with the Institut de radioastronomie millimétrique (IRAM) 30-m telescope (IRAM 30m) and the Heterodyne Receiver Array (HERA) receiver in Titan atmosphere. Observations were carried out on June 16, 2010, and March 19, 2011, under non-favorable and favorable weather conditions, respectively. We report here the APEX and IRAM 30m observations, and by using a line-by-line radiative transfer code and the least-squares fitting technique, the analysis to infer the HCN abundance. Our HCN mixing-ratio estimations confirm the result of Marten et al. (2002) [2]. We compare our results with the those with Herschel/PACS and SPIRE acquired during 2010 [3,4]. Measured HCN abundances on Titan with data acquired at different epochs and transitions exhibit similar abundance distributions. Beyond the intrinsic scientific interest, these observations proven their usefulness in supporting spacecraft observations of Solar System bodies, in particular, of Titan’s atmosphere.</p> <p>[1] Hartogh, P.; Lellouch, E.; Crovisier, J., et al. 2009, Planetary and Space Science, Volume 57, Issue 13, p. 1596-1606. [2]  Marten, A.; Hidayat, T.; Biraud, Y. et al.  Icarus, 2002, Volume 158, Issue 2, p. 532-544. [3]  Rengel, M.; Sagawa, H.; Hartogh, P., et al. 2014, A&A, 561. [4]  Courtin, R., Swinyard, B. M., Moreno, R., et al. 2011, A&A, 536, L2.</p>

Precision Heterodyne Oxygen-Calibration Spectrometry: Vertical Profiling of Water and Carbon Dioxide in the Troposphere and Lower Stratosphere

<p>We describe the continued development of a new laser heterodyne radiometry (LHR) technique:  Precision Heterodyne Oxygen-Calibration Spectrometry, or PHOCS. The prototype instrument is equipped with two active laser channels for oxygen and water (measured near 1.28 µm) and carbon dioxide (near 1.57 µm) determination. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1.65 µm). Oxygen measurements provide dry gas corrections and – more importantly – determine accurate temperature and pressure profiles that, in turn, improve the precision of the CO<sub>2</sub> and H<sub>2</sub>O column retrievals. Vertical profiling is enabled by interrogating the very low-noise, absorption lines shapes collected by the O(10<sup>-3</sup> cm<sup>-1</sup>) instrument. The presentation will describe (1) the continued development of column concertation retrieval protocols and (2) the results of initial tests performed at the Smithsonian Environmental Research Center in Edgewater, Maryland during the summer/fall of 2019 and spring of 2020.</p>