scholarly journals Detection of Air Turbulence Using a Spectral Fitting Method for an Airborne Doppler LIDAR

2011 ◽  
Vol 59 (692) ◽  
pp. 236-243 ◽  
Author(s):  
Takashi ASAHARA ◽  
Toshiharu INAGAKI ◽  
Hamaki INOKUCHI
Keyword(s):  
Doppler Lidar ◽  
Spectral Fitting ◽  
Air Turbulence ◽  
Fitting Method

scholarly journals Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

2018 ◽  
Author(s):  
Joshua M. Chadney ◽  
Daniel K. Whiter
Keyword(s):  
Water Vapour ◽  
Atmospheric Parameter ◽  
Atmospheric Parameters ◽  
Atmospheric Water ◽  
Echelle Spectrograph ◽  
Atmospheric Water Vapour ◽  
Spectral Fitting ◽  
Fitting Method ◽  
Airglow Emissions ◽  
High Throughput Imaging

Abstract. We have developed a spectral fitting method to retrieve upper atmospheric parameters at multiple altitudes simultaneously during times of aurora, allowing us to measure neutral temperatures and column densities of water vapour. We use the method to separate airglow OH emissions from auroral O+ and N2 in observations between 725–740 nm using the High Throughput Imaging Echelle Spectrograph (HiTIES), located on Svalbard. In this paper, we describe our new method and show the results of Monte-Carlo simulations using synthetic spectra which demonstrate the validity of the spectral fitting method as well as provide an indication of uncertainties on the retrieval of each atmospheric parameter.

scholarly journals Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

2018 ◽  
Vol 7 (4) ◽  
pp. 317-329 ◽  
Author(s):  
Joshua M. Chadney ◽  
Daniel K. Whiter
Keyword(s):  
Water Vapour ◽  
Atmospheric Parameter ◽  
Atmospheric Parameters ◽  
Atmospheric Water ◽  
Echelle Spectrograph ◽  
Atmospheric Water Vapour ◽  
Spectral Fitting ◽  
Fitting Method ◽  
Airglow Emissions ◽  
High Throughput Imaging

Abstract. We have developed a spectral fitting method to retrieve upper atmospheric parameters at multiple altitudes simultaneously during times of aurora, allowing us to measure neutral temperatures and column densities of water vapour. We use the method to separate airglow OH emissions from auroral O+ and N2 in observations between 725 and 740 nm using the High Throughput Imaging Echelle Spectrograph (HiTIES) located on Svalbard. In this paper, we describe our new method and show the results of Monte Carlo simulations using synthetic spectra which demonstrate the validity of the spectral fitting method and provide an indication of uncertainties on the retrieval of each atmospheric parameter. We show that the method allows for the retrieval of OH temperatures with an uncertainty of 6 % when contamination by N2 emission is small. N2 temperatures can be retrieved with uncertainties down to 3 %–5 % when N2 emission intensity is high. We can determine the intensity ratio between the O+ doublets at 732 and 733 nm (which is a function of temperature) with an uncertainty of 5 %.

Sounding of the clear-air turbulence by Doppler lidar: numerical simulation

2002 ◽  
Author(s):  
Viktor A. Banakh ◽  
Igor N. Smalikho ◽  
Christian Werner
Keyword(s):  
Numerical Simulation ◽  
Doppler Lidar ◽  
Air Turbulence

scholarly journals Spectral fitting method for obtaining the refractive index and thickness of chalcogenide films

2021 ◽  
Author(s):  
Ning Mao ◽  
Baoan Song ◽  
lei Pan ◽  
xinli liu ◽  
Changgui Lin ◽  
...  
Keyword(s):  
Refractive Index ◽  
Chalcogenide Films ◽  
Spectral Fitting ◽  
Fitting Method

scholarly journals A cloud algorithm based on the O<sub>2</sub>-O<sub>2</sub> 477 nm absorption band featuring an advanced spectral fitting method and the use of surface geometry-dependent Lambertian-equivalent reflectivity

2018 ◽  
Vol 11 (7) ◽  
pp. 4093-4107 ◽  
Author(s):  
Alexander Vasilkov ◽  
Eun-Su Yang ◽  
Sergey Marchenko ◽  
Wenhan Qin ◽  
Lok Lamsal ◽  
...  
Keyword(s):  
Absorption Band ◽  
Cross Sections ◽  
Gas Absorption ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Surface Geometry ◽  
Vertical Column ◽  
Spectral Fitting ◽  
Fitting Procedure ◽  
Fitting Method

Abstract. We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud optical centroid pressure (OCP), from oxygen dimer (O2-O2) absorption at 477 nm after determining an effective cloud fraction (ECF) at 466 nm, a wavelength not significantly affected by trace-gas absorption and rotational Raman scattering. The retrieved cloud products are intended for use as inputs to the operational nitrogen dioxide (NO2) retrieval algorithm for the Ozone Monitoring Instrument (OMI) flying on the Aura satellite. The cloud algorithm uses temperature-dependent O2-O2 cross sections and incorporates flexible spectral fitting techniques that account for specifics of the surface reflectivity. The fitting procedure derives O2-O2 slant column densities (SCDs) from radiances after O3, NO2, and H2O absorption features have been removed based on estimates of the amounts of these species from independent OMI algorithms. The cloud algorithm is based on the frequently used mixed Lambertian-equivalent reflectivity (MLER) concept. A geometry-dependent Lambertian-equivalent reflectivity (GLER), which is a proxy of surface bidirectional reflectance, is used for the ground reflectivity in our implementation of the MLER approach. The OCP is derived from a match of the measured O2-O2 SCD to that calculated with the MLER method. Temperature profiles needed for computation of vertical column densities are taken from the Global Modeling Initiative (GMI) model. We investigate the effect of using GLER instead of climatological LER on the retrieved ECF and OCP. For evaluation purposes, the retrieved ECFs and OCPs are compared with those from the operational OMI cloud product, which is also based on the same O2-O2 absorption band. Impacts of the application of the newly developed cloud algorithm to the OMI NO2 retrieval are discussed.

Numerical simulation of Doppler lidar detection of clear-air turbulence

2002 ◽  
Author(s):  
Viktor A. Banakh ◽  
Igor N. Smalikho ◽  
Christian Werner
Keyword(s):  
Numerical Simulation ◽  
Doppler Lidar ◽  
Air Turbulence

scholarly journals S stars and s-process in the Gaia era

2018 ◽  
Vol 620 ◽  
pp. A148 ◽  
Author(s):  
S. Shetye ◽  
S. Van Eck ◽  
A. Jorissen ◽  
H. Van Winckel ◽  
L. Siess ◽  
...  
Keyword(s):  
Asymptotic Giant Branch ◽  
Joint Analysis ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Spectral Fitting ◽  
Fitting Method ◽  
Red Giant ◽  
Process Elements ◽  
Process Element ◽  
Hr Diagram

Context. S stars are transition objects between M-type giants and carbon stars on the asymptotic giant branch (AGB). They are characterized by overabundances of s-process elements. Roughly half of them are enhanced in technetium (Tc), an s-process element with no stable isotope, while the other half lack technetium. This dichotomy arises from the fact that Tc-rich S stars are intrinsically producing s-process elements and have undergone third dredge-up (TDU) events, while Tc-poor S stars owe their s-process overabundances to a past pollution by a former AGB companion which is now an undetected white dwarf, and since the epoch of the mass transfer, technetium has totally decayed. Aims. Our aim is to analyse the abundances of S stars and gain insights into their evolutionary status and on the nucleosynthesis of heavy s-process elements taking place in their interior. In particular, the location of extrinsic and intrinsic S stars in the HR diagram will be compared with the theoretical onset of the TDU on the thermally pulsing AGB. Methods. A sample of 19 S-type stars was analysed by combining HERMES high-resolution spectra, accurate Gaia Data Release 2 (GDR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Various stellar parameters impact the atmospheric structure of S stars, not only effective temperature, gravity, metallicity and microturbulence but also C/O and [s/Fe]. We show that photometric data alone are not sufficient to disentangle these parameters. We present a new automatic spectral-fitting method that allows one to constrain the range of possible atmospheric parameters. Results. Combining the derived parameters with GDR2 parallaxes allows a joint analysis of the location of the stars in the Hertzsprung–Russell diagram and of their surface abundances. For all 19 stars, Zr and Nb abundances are derived, complemented by abundances of other s-process elements for the three Tc-rich S stars. These abundances agree within the uncertainties with nucleosynthesis predictions for stars of corresponding mass, metallicity and evolutionary stage. The Tc dichotomy between extrinsic and intrinsic S stars is seen as well in the Nb abundances: intrinsic, Tc-rich S stars are Nb-poor, whereas extrinsic, Tc-poor S stars are Nb-rich. Most extrinsic S stars lie close to the tip of the red giant branch (RGB), and a few are located along the early AGB. All appear to be the cooler analogues of barium stars. Barium stars with masses smaller than 2.5 M⊙ turn into extrinsic S stars on the RGB, because only for those masses does the RGB tip extend to temperatures lower than ~4200 K, which allows the ZrO bands distinctive of S-type stars to develop. On the contrary, barium stars with masses in excess of ~2.5 M⊙ can only turn into extrinsic S stars on the E-AGB, but those are short-lived, and thus rare. The location of intrinsic S stars in the HR diagram is compatible with them being thermally-pulsing AGB stars. Although nucleosynthetic model predictions give a satisfactory distribution of s-process elements, fitting at the same time the carbon and heavy s-element enrichments still remains difficult. Finally, the Tc-rich star V915 Aql is challenging as it points at the occurrence of TDU episodes in stars with masses as low as M ~ 1 M⊙.

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