Nadir retrieval of ice clouds and dust from NOMAD/UVIS on board Exomars TGO

<p>The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the composition of Mars' atmosphere using a suite of three spectrometers operating in the UV-visible and infrared. NOMAD is a spectrometer operating in ultraviolet (UV), visible and infrared (IR) wavelengths covering large parts of the 0.2-4.3 µm spectral range [1].</p> <p>The UV-visible “UVIS” instrument covers the spectral range from 200 to 650 nm and can perform solar occultation, nadir and limb observations [2]. The main purpose of UVIS is dedicated to the analysis and monitoring of ozone and aerosols such as dust and ice clouds.  In the present work we will present preliminary results of the aerosol retrieval in the UV recorded in nadir geometry: spatial and seasonal distribution of ice clouds and dust.</p> <div> <p> </p> <p>References<br />[1] Vandaele et al. 2018. Space Sci. Rev.<br />[2] Patel et al., 2017. Applied Optics.</p> </div> <p> </p>

Ozone vertical profiles from TGO/NOMAD-UVIS: an inter-comparison of three retrieval schemes

<p>We will present the vertical distribution of <strong>ozone</strong> obtained from <strong>NOMAD-UVIS solar occultations</strong> and we will compare the results of three retrieval schemes.</p><p><strong>NOMAD</strong> (Nadir and Occultation for MArs Discovery) is a spectrometer composed of 3 channels: 1) a solar occultation channel (SO) operating in the infrared (2.3-4.3 μm); 2) a second infrared channel LNO (2.3-3.8 μm) capable of doing nadir, as well as solar occultation and limb; and 3) an ultraviolet/visible channel <strong>UVIS</strong> (200-650 nm) that can work in the three observation modes [1,2].</p><p>The UVIS channel has a spectral resolution <1.5 nm. In the solar occultation mode it is mainly devoted to study the climatology of <strong>ozone</strong> and <strong>aerosols</strong> content [3].</p><p>Since the beginning of operations, on 21 April 2018, NOMAD UVIS acquired more than 4000 solar occultations with an almost complete coverage of the planet.</p><p>NOMAD-UVIS spectra are simulated using three different retrieval scheme:</p><p>1) An onion peeling approach based on [4,5] deriving slant columns at the different altitudes sounded, from which local densities are obtained;</p><p>2) The line-by-line radiative transfer code ASIMUT-ALVL developed at IASB-BIRA [6] using the Optimal Estimation Method to derive the local density profile in one go (on all transmittances of one occultation observation);</p><p>3) A direct onion peeling method deriving sequentially from top to bottom the local densities in the different layers probed.</p><p>We will compare results obtained from the different retrieval methods as well as their uncertainties and we will discuss the advantages and difficulties of each method.</p><p><strong>References</strong></p><p>[1] Vandaele, A.C., et al., Planetary and Space Science, Vol. 119, pp. 233–249, 2015.</p><p>[2] Neefs, E., et al., Applied Optics, Vol. 54 (28), pp. 8494-8520, 2015.</p><p>[3] M.R. Patel et al., In: Appl. Opt. 56.10 (2017), pp. 2771–2782. DOI: 10.1364/AO.56.002771.</p><p>[4] Quémerais, E.,et al. J.Geophys. Res. (Planets)111, 9, 2006.</p><p>[5] Piccialli, A. et al., Planetary and Space Science, 113-114(2015) 321–335</p><p>[6] Vandaele, A.C., et al., JGR, 2008. 113 doi:10.1029/2008JE003140.</p>

Martian visible and ultraviolet dayglow: altitude, latitudinal and seasonal variations observed with NOMAD/TGO

<p>The OI 557.7 nm green line has been measured in the Martian dayglow for the first time with the UVIS visible-ultraviolet spectrograph on board ESA’s Trace Gas Orbiter (Gérard et al., 2020). The first observations started in April 2019 in a special mode where the spacecraft is tilted to observe the limb with the UVIS nadir channel (Vandaele et al., 2015, Patel et al., 2017). The instrument detected the presence of bright green dayglow emission on every of those observations. The main peak altitude is located near 80 km, and its intensity varies as a result of the changing distance from sun, the local time and latitude of the observations. A second, less pronounced, emission peak is observed near 110 km. Photochemical model simulations (Gkouvelis et al., 2018) used the MCD density distribution (Forget et al., 1999) have been made to understand the sources of this airglow emission. It is able to reproduce the altitude and the brightness of the airglow layer. It indicates that the green line dayglow on Mars is essentially produced by photodissociation of CO<sub>2</sub> molecules by solar far ultraviolet radiation (Fox & Dalgarno, 1979). A fraction of the oxygen atoms is formed in the <sup>1</sup>S metastable state that produces the green emission.</p> <p>In this presentation, we describe additional dayside observations obtained since December 2019. For this purpose, the spacecraft has been used in a special mode where it is re-oriented so that the UVIS channel observed the sunlit limb (Lopez-Valverde et al., 2018). We analyse the observed limb profile variations and the changing altitude of the peak emission resulting from the variations of the pressure levels in the mesosphere (Gkouvelis et al., 2020). The measured intensities are compared with model calculations of the O(<sup>1</sup>S) density in the conditions of the observations. The ratio of ultraviolet spectral features relative to the oxygen emission also observed with UVIS will also be analysed. </p> <p>REFERENCES</p> <p>Forget, F. et al., J. Geophys. Res. <strong>104</strong>(E10), 24155-24175 (1999).</p> <p>Fox, J.L. & Dalgarno, J. Geophys. Res. <strong>84</strong>(A12), 7315-7333 (1979).</p> <p>Gérard, J.C. et al., Nature Astronomy, 1-4 (2020), https://doi.org/10.1038/s41550-020-1123-2</p> <p>Gkouvelis, L. et al., J. Geophys.Res., <strong>123</strong>(12), 3119-3132. (2018).</p> <p>Gkouvelis, L. et al.,  Icarus, 341, 113666 (2020).</p> <p>López-Valverde M. et al.,  Space Science Reviews, <strong>214</strong>(1), 29 (2018).</p> <p>Patel, M. R. et al.,  Applied optics, <strong>56</strong>(10), 2771-2782 (2017).</p> <p>Vandaele, A. C. et al.,  Optics Express, <strong>23</strong>(23), 30028-30042 (2015).</p>

A pre-relaxed FBG accelerometer using transverse forces with high sensitivity and improved resonant frequency

Fiber Bragg grating (FBG) accelerometers using transverse forces have higher sensitivity but lower resonant frequency than ones using axial forces. By shortening the distance between the two fixed ends of the FBG, the resonant frequency can be improved without lowing the sensitivity. Here, a compact FBG accelerometer using transverse forces with a slightly pre-relaxed FBG and 25mm distance between the two fixed ends has been demonstrated with the crest-to-trough sensitivity 1.1nm/g at 5Hz and the resonant frequency 42Hz. It reveals that making the FBG slightly pre-relaxed rather than pre-stretched also improves the tradeoff between the sensitivity and resonant frequency. Full Text: PDF References:Kawasaki, B. S. , Hill, K. O , Johnson, D. C. , & Fujii, Y. , "Narrow-band Bragg reflectors in optical fibers", Optics Letters 3, 66 (1978) [CrossRef]K. O. Hill, and G. Meltz, "Fiber Bragg grating technology fundamentals and overview", Journal of Lightwave Technology 15, 1263 (1997) [CrossRef]B. Lee, "Review of the present status of optical fiber sensors", Optical Fiber Technology, 9, 57-79 (2003) [CrossRef]Laudati, A. , Mennella, F. , Giordano, M. , D"Altrui, G. , Tassini, C. C. , & Cusano, A., "A Fiber-Optic Bragg Grating Seismic Sensor", IEEE Photonics Technology Letters, 19, 1991 (2007) [CrossRef]P. F. Costa Antunes, C. A. Marques, H. Varum, and P. S. Andre, "Biaxial Optical Accelerometer and High-Angle Inclinometer With Temperature and Cross-Axis Insensitivity", IEEE Sens. J. 12, 2399 (2012) [CrossRef]Guo, Y. , Zhang, D. , Zhou, Z. , Xiong, L. , & Deng, X., "Welding-packaged accelerometer based on metal-coated FBG", Chinese Optics Letters, 11, 21 (2013). [CrossRef]Zhang, Y. , Zhang, W. , Zhang, Y. , Chen, L. , Yan, T. , & Wang, S. , et al., "2-D Medium–High Frequency Fiber Bragg Gratings Accelerometer", IEEE Sensors Journal, 17, 614(2017) [CrossRef]Xiu-bin Zhu, "A novel FBG velocimeter with wind speed and temperature synchronous measurement", Optoelectronics Letters, 14, 276-279 (2018) [CrossRef]Li, K. , Yau, M. H. , Chan, T. H. T. , Thambiratnam, D., "Fiber Bragg grating strain modulation based on nonlinear string transverse-force amplifier", & Tam, H. Y. , Optics Letters, 38, 311 (2013) [CrossRef]Li, K. , Chan, T. H. T. , Yau, M. H. , Nguyen, T. , Thambiratnam, D. P. , & Tam, H. Y., "Very sensitive fiber Bragg grating accelerometer using transverse forces with an easy over-range protection and low cross axial sensitivity", Applied Optics, 52, 6401 (2013) [CrossRef]Li, K. , Chan, T. H. T. , Yau, M. H. , Thambiratnam, D. P. , & Tam, H. Y., "Biaxial Fiber Bragg Grating Accelerometer Using Axial and Transverse Forces", IEEE Photonics Technology Letters, 26, 1549 (2014). [CrossRef]Li, K. , Chan, T. H. , Yau, M. H. , Thambiratnam, D. P. , & Tam, H. Y., "Experimental verification of the modified spring-mass theory of fiber Bragg grating accelerometers using transverse forces", Applied Optics, 53, 1200-1211(2014) [CrossRef]

FTIR-based spectral line data of the v3 band of NO2 at 6.3 µm and multi-component impurity analysis of NO2 reference gases within the scope of the EMPIR MetNO2 project

<p>Air pollution causes hundreds of thousands of premature deaths every year in Europe [1]. Traffic related Nitrogen dioxide (NO<sub>2</sub>) is a key contributor whose concentration is legislated by the Ambient Air Quality Directive (EU, 2008) [2] and the air quality guidelines (AQGs) set by the World Health Organization (WHO). Atmospheric NO<sub>2</sub> concentration has been widely measured by national, regional and global monitoring networks using different instrumentations. SI-traceability is essential to assure data comparability across networks, underpinning long term trend of ambient NO<sub>2</sub>.</p><p>Traceable and accurate spectral line data [3,4] of NO<sub>2</sub> is essential for optical sensing of NO<sub>2 </sub>using in situ [5] and satellite-based equipment. In particular, it is essential for cost-effective light-weight systems with payload restrictions (e.g. TDLAS system [6], e.g. when installed on drones and balloons for which real time calibration using gas cylinders quickly becomes a burden). Within the scope of the EMPIR (The European Metrology Programme for Innovation and Research) MetNO<sub>2</sub> project [7], spectroscopic measurements of the selected NO<sub>2</sub> CRM (certified reference material) has been carried out using the FTIR infrastructure at PTB to a) derive traceable line data of NO<sub>2</sub>; b) quantify the amount of impurities, such as HNO<sub>3</sub>, N<sub>2</sub>O<sub>4</sub>, NO, N<sub>2</sub>O, CO, H<sub>2</sub>O, etc. Here, we report the line intensity and air-broadening coefficients of the 6.3µm v<sub>3</sub> band of NO<sub>2</sub>. FTIR-based impurity analysis including their temporal evolution will also be presented.</p><p><strong>Acknowledgement</strong></p><p>MK and GL thank for technical support from Kai-Oliver Krauss. This work has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. PTB is member of the European Metrology Network for Climate and Ocean Observation (https://www.euramet.org/european-metrology-networks/climate-and-ocean-observation/).</p><p><strong>References</strong></p><p>[1] Air quality Europe – 2019 report.  EEA Report No 10/2019. https://www.eea.europa.eu/publications/air-quality-in-europe-2019</p><p>[2] Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe. https://www.eea.europa.eu/policy-documents/directive-2008-50-ec-of</p><p>[3] V. Werwein, J. Brunzendorf, G. Li, A. Serdyukov, O. Werhahn, V. Ebert.  Applied Optics 56 (2017)</p><p>[4] V. Werwein, G. Li, J. Brunzendorf, A. Serdyukov, O.Werhahn, V. Ebert. Journal of Molecular Spectroscopy 348, 68-78(2017).</p><p>[5] O. Werhahn O, J.C. Petersen (eds.) 2010 TILSAM technical protocol V1_2010-09-29. Available from:                     http://www.euramet.org/fileadmin/docs/projects/934_METCHEM_Interim_Report.pdf.”</p><p>[6] J. A. Nwaboh, Z. Qu, O. Werhahn and V. Ebert, Applied Optics 56, E84-E93 (2017)</p><p>[7] EMPIR project 16ENV02, “Metrology for Nitrogen Dioxide (MetNO<sub>2</sub>)”, http://em-pir.npl.co.uk/metno2/</p>

Minerva H. Weinstein (1893-1982)

Dr. Minerva H. Weinstein (1893-1982), was the first woman licensed by examination to practice optometry in New York City and the fourth woman licensed in the State of New York. In 1915, Dr. Weinstein graduated from the American Institute of Optometry, becoming the third generation in her family to forge a career in applied optics. She began her practice at one of three family-owned optical shops in the Bronx, where she remained for more than 40 years, diligently serving the needs of her community’s most vulnerable members and tirelessly researching new techniques to improve care for the most difficult vision problems. During her career, she founded the Bronx County Optometric Society and organized the local Woman’s Auxiliary for the Bronx, Manhattan and Brooklyn, as well as the New York state affiliate of the national organization. She was a founding member of the Bronx County Optometric Service, the first free optometry clinic in New York, and went on to expand the service to two additional locations. She also participated in professional women’s organizations, charitable foundations and civic clubs, and represented optometry at community events. Dr. Weinstein’s narrative is unique, but in many ways her family’s story was typical of many immigrants arriving in the U.S. during the late-nineteenth and early twentieth centuries who were successful in improving their lot and passing on a professional legacy to the younger generation−and it is a story that is particularly common among optometry’s founders, and one that resonates in the first two decades of the twenty first century. The story of her career, and the personal details that serve as its backdrop, are also representative of the many challenges faced by the generation of professional women who helped establish the profession of optometry during the inter-war years. This biographical sketch, made possible through research in Minerva Weinstein Papers (MSS 501.4.11) held at the Archives & Museum of Optometry, sheds light on the tremendous debt optometry owes to its founding mothers and highlights the work that remains to complete the narrative of optometry history through new scholarship in hidden collections.