Fraunhofer Lines Research Articles

Observation of Circumstellar Gas in the Neighborhood of RZ Psc

The first evidence is found of the existence of circumstellar gas in the nearest surroundings of the UX Ori star RZ Psc. Spectra obtained at the Terskol Observatory, Special Astrophysical Observatory (SAO), and the Nordic Optical Telescope (NOT) reveal a strong variability in the sodium doublet lines that is indicative of a sporadic outflow of matter. Weak variability was also observed in the core of the Hα line. One nontrivial feature of this discovery is that RZ Psc is of spectral class K0 IV. This means that the star has no intrinsic energy resources for creating the observed outflow of matter. There are no emission lines in the star’s spectrum which might indicate that matter is falling into the star so that the observed outflow could be related to an accretion process. We suggest, nevertheless, that the ejection of gas is related to residual (slow) accretion and is driven by a propeller mechanism. The latter is possible if the star has a sufficiently high (on the order of 103 G) magnetic field.

Fraunhofer Lidar Prototype in the Green Spectral Region for Atmospheric Boundary Layer Observations

A lidar detects atmospheric parameters by transmitting laser pulse to the atmosphere and receiving the backscattering signals from molecules and aerosol particles. Because of the small backscattering cross section, a lidar usually uses the high sensitive photomultiplier and avalanche photodiode as detector and uses photon counting technology for collection of weak backscatter signals. Photon Counting enables the capturing of extremely weak lidar return from long distance, throughout dark background, by a long time accumulation. Because of the strong solar background, the signal-to-noise ratio of lidar during daytime could be greatly restricted, especially for the lidar operating at visible wavelengths where solar background is prominent. Narrow band-pass filters must therefore be installed in order to isolate solar background noise at wavelengths close to that of the lidar receiving channel, whereas the background light in superposition with signal spectrum, limits an effective margin for signal-to-noise ratio (SNR) improvement. This work describes a lidar prototype operating at the Fraunhofer lines, the invisible band of solar spectrum, to achieve photon counting under intense solar background. The photon counting lidar prototype in Fraunhofer lines devised was used to observe the atmospheric boundary layer. The SNR was improved 2-3 times by operating the lidar at the wavelength in solar dark lines. The aerosol extinctions illustrate the vertical structures of aerosol in the atmospheric boundary over Qingdao suburban during summer 2011.

An inherent limitation of solar-induced chlorophyll fluorescence retrieval at the O2-A absorption feature in high-altitude areas

The Fraunhofer line discriminator (FLD) principle applied on the atmospheric oxygen absorption feature around 761 nm ( O2-A band) has been widely used to retrieve solar-induced chlorophyll fluorescence (Fs) from remotely sensed data. In this letter, however, we address a violation of the basic assumption caused by O2 absorption feature changes, and we evaluate the impact of diminishing O2 absorption with the increase in ground altitude on Fs retrieval accuracy. The Fs retrieval accuracy substantially decreases in higher ground altitude areas for the standard FLD and three-band FLD methods, in which relative estimation errors increase approximately 70%-80% and 10%-16%, respectively, with an increase in ground altitude from 0.01 to 4.5 km. However, this increasing trend in Fs retrieval error does not occur with the use of the improved FLD (iFLD) method, which exhibits smaller than 5% of changes in relative estimation errors. Analytical analyses reveal the causes of the changes in Fs retrieval accuracy by the three methods. Based on these findings, the iFLD method is recommended to be used in cross-altitude studies or for Fs estimation in higher ground altitude areas under conditions of low radiometric noise, although its high sensitivity to noise should be taken into account. The investigations in this letter further indicate that the impact of ground altitude should be included in the uncertainty budgets of Fs retrievals and should be considered in the interpretation of Fs signals at the O2-A absorption feature.

Global monitoring of terrestrial chlorophyll fluorescence from moderate-spectral-resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2

Abstract. Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5° × 0.5°. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

Darkening of a brightened atom and real energy level via field generated coherence

In contrast to traditional spontaneous generated coherence (SGC), a field generated coherence (FGC)-based atomic scheme is presented for spontaneous emission cancellation. It is easy to achieve an externally controllable experimental and dipole-alignment-independent trapping condition in this four-field-driven five-level atomic system. Consequently, the decay from the central dressed bare energy state (real energy state) of the set of the three upper closely spaced hyperfine decaying energy states of the sodium D2 line is completely cancelled under the trapping condition, exhibiting the novel phenomenon of a darkened bare energy state. Along with this cancellation, effective manipulation and storage of an atomic population in various dressed states of this one-atom quantum system are also explored. Extending to an atomic system of simple probability loss, based on the sodium D1 line, the whole brightened atom can also be darkened under its dipole-alignment-independent trapping condition, representing another experimentally viable, novel and potentially useful phenomenon.

Radiative transfer equation accounting for rotational Raman scattering and its solution by the discrete-ordinates method

Rotational Raman scattering of solar light in Earth's atmosphere leads to the filling-in of Fraunhofer and telluric lines observed in the reflected spectrum. The phenomenological derivation of the inelastic radiative transfer equation including rotational Raman scattering is presented. The different forms of the approximate radiative transfer equation with first-order rotational Raman scattering terms are obtained employing the Cabannes, Rayleigh, and Cabannes–Rayleigh scattering models. The solution of these equations is considered in the framework of the discrete-ordinates method using rigorous and approximate approaches to derive particular integrals. An alternative forward-adjoint technique is suggested as well. A detailed description of the model including the exact spectral matching and a binning scheme that significantly speeds up the calculations is given. The considered solution techniques are implemented in the radiative transfer software package SCIATRAN and a specified benchmark setup is presented to enable readers to compare with own results transparently.

Ground-based detection of calcium and possibly scandium and hydrogen in the atmosphere of HD 209458b

Context: Since the first exoplanetary atmosphere detection using the Hubble Space Telescope, characterization of exoplanet atmospheres from the ground have been playing an increasingly important role in the analysis of such atmospheres thanks to the enhancement of telluric correction techniques. At present, several species have been discovered in the atmosphere of HD 209458b, all of them consistent with theoretical models. Aims: Data acquired using the High Dispersion Spectrograph on the Subaru telescope are re-analysed. We expect to discover new species in the atmosphere of the exoplanet HD 209458b. In addition to shed light on the atmospheric composition, we will derive the radial extension of the absorbents present in the atmosphere of the exoplanet. Methods: We present an alternative method to correct the telluric effects through the analysis of variations in spectral lines with the airmass. To search absorptions due to an exoplanetary atmosphere we implemented an algorithm to automatically search for all the features presenting an atmospheric signature in the transmission spectrum and through the wavelength range in the data. In order to estimate uncertainties we perform a bootstrapping analysis. Results: Absorption excess due to the transitions of Calcium at 6162.17A and 6493.78A, Scandium at 5526.79A, Hydrogen at 6562.8A and Sodium doublet are detected in the transmission spectrum at a level of -0.079+-0.012%, -0.138+-0.013%, -0.059+-0.012%, -0.123+-0.012%, -0.071+-0.016% using pass-bands of 0.5A, 0.4A, 0.5A, 1.1A and 0.6A, respectively. Conclusions: Models predict strong absorption in the Sodium resonance Doublet which was previously detected, also in this analysis. However, this is the first report of Calcium and possibly Scandium in HD 209458b, including the possible ground-based detection of Hydrogen. ... (continues)

THE COSMIC INFRARED BACKGROUND EXPERIMENT ( CIBER ): THE NARROW-BAND SPECTROMETER

We have developed a near-infrared spectrometer designed to measure the absolute intensity of the Solar 854.2 nm CaII Fraunhofer line, scattered by interplanetary dust, in the Zodiacal light spectrum. Based on the known equivalent line width in the Solar spectrum, this measurement can derive the Zodiacal brightness, testing models of the Zodiacal light based on morphology that are used to determine the extragalactic background light in absolute photometry measurements. The spectrometer is based on a simple high-resolution tipped filter placed in front of a compact camera with wide-field refractive optics to provide the large optical throughput and high sensitivity required for rocket-borne observations. We discuss the instrument requirements for an accurate measurement of the absolute Zodiacal light brightness, the measured laboratory characterization, and the instrument performance in flight.

The first spectroscopically identified L dwarf in Praesepe

We have obtained a low-resolution optical spectrum for one of the faintest cluster member candidates in Praesepe with the Optical System for Imaging and low Resolution Integrated Spectroscopy mounted on the 10.4m Gran Telescopio de Canarias. We confirm spectroscopically the first L dwarf member in Praesepe, UGCS J084510.66+214817.1. We derived an optical spectral type of L0.3+/-0.4 and estimated its effective temperature to Teff=2279+/-371 K and a mass of 71.1+/-23.0M_Jup, according to state-of-the-art models, placing it at the hydrogen-burning boundary. We measured the equivalent width of the gravity-sensitive sodium doublet at 8182/8194 A, which adds credit to the membership of this new L dwarf to Praesepe. We also derived a probability of ~20.5% that our candidate would be a field L0 dwarf. We conclude that this object is likely to be a true member of Praesepe, with evidence of being a binary system.

Spatial Resolution Effects on Chlorophyll Fluorescence Retrieval in a Heterogeneous Canopy Using Hyperspectral Imagery and Radiative Transfer Simulation

Increasing attention is being given to chlorophyll fluorescence (F) for global monitoring of vegetation due to its relationship with physiology. New progress has been made in the methodological and technical aspects of signal retrieval with the recently published low-resolution global maps of fluorescence. Nevertheless, little progress has been made in the interpretation of the F signal when quantified in large pixels, an important issue due to the effects of structure, percentage cover, shadows, and background. High-resolution (40 cm) airborne hyperspectral imagery is used in this letter to assess the retrieval of fluorescence by the Fraunhofer line depth method from pure tree crowns and aggregated pixels. Due to canopy heterogeneity, the F signal extracted from aggregated pixels is highly degraded. A poor relationship is obtained between fluorescence extracted from pure tree crowns (Fcrown) and that quantified from pixels aggregating pure tree crowns, shadows, and background (Faggregated) (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.25; p <; 0.01). The relationship between F and stomatal conductance (used as a physiological indicator) decreases as a function of aggregation, yielding R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.69 (p <; 0.01) when calculated from pure tree crowns and R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.38 (p <; 0.05) from pixels containing crown, shadows, and soil. This letter demonstrates the need for methods to accurately retrieve a pure-vegetation fluorescence signal from aggregated pixels. The FluorMODleaf and FluorSAIL models were combined with the geometric forest light interaction model (FLIM) model and led to the “FluorFLIM” model developed for this letter. Simulations conducted with FluorFLIM obtain predictive relationships between Fcrown and Faggregated pixels as a function of percentage cover, enabling the estimation of pure-crown F from aggregated pixels (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.72, p <; 0.01).

Optical design of a near-infrared imaging spectropolarimeter for the Advanced Technology Solar Telescope

In designing the optics of an imaging multi-etalon spectropolarimeter as a post-focus instrument for the Advanced Technology Solar Telescope (ATST), many constraints must be considered. Among these are the large entrance pupil diameter of the telescope (4 m), the demanded large field of view (≥90 arc sec ), high spectral resolving power (≥200,000 ), and limited field-dependent blue-shift of the instrumental profile [≤3 full width at half maximum (FWHM)], which require Fabry-Perot interferometers of large diameter (≥200 mm ), lighted by highly collimated beams. This implies large optical elements and long optical paths. Moreover, to use interference pre-filters with a relatively small diameter (≤70 mm ) and placed between the interferometers to reduce the inter-reflections in axial-mount, a “pupil adapter” must be included with a further increase of the optical path length. Although a multi-etalon spectropolarimeter works in quasi-monochromatic light, the Fraunhofer lines of interest cover a wide range of wavelengths (850 to 1650 nm), which demands a good chromatic aberration control. A low instrumental polarization (≤0.5% ) is also required to allow a high polarimetric precision. Finally, some secondary optical paths are required to perform the initial instrumental setup and to secure the best instrumental performances. A diffraction-limited optical solution for ATST is described that fulfills all the above requirements in a relative small volume.

Observation of neutral sodium above Mercury during the transit of November 8, 2006

We mapped the absorption of sunlight by sodium vapor in the exosphere of Mercury during the transit of Mercury on November 8, 2006, using the IBIS Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope operated by the National Solar Observatory at Sunspot, New Mexico. The measurements were reduced to line-of-sight equivalent widths for absorption at the sodium D2 line around the shadow of Mercury. The sodium absorption fell off exponentially with altitude up to about 600km. However there were regions around north and south polar-regions where relatively uniform sodium absorptions extended above 1000km. We corrected the 0–600km altitude profiles for seeing blur using the measured point spread function. Analysis of the corrected altitude distributions yielded surface densities, zenith column densities, temperatures and scale heights for sodium all around the planet. Sodium absorption on the dawn side equatorial terminator was less than on the dusk side, different from previous observations of the relative absorption levels. We also determined Earthward velocities for sodium atoms, and line widths for the absorptions. Earthward velocities resulting from radiation pressure on sodium averaged 0.8km/s, smaller than a prediction of 1.5km/s. Most line widths were in the range of 20mA after correction for instrumental broadening, corresponding to temperatures in the range of 1000K.

Relationships between net photosynthesis and steady-state chlorophyll fluorescence retrieved from airborne hyperspectral imagery

Previous studies have demonstrated the link between leaf chlorophyll fluorescence and photosynthesis, mainly at the leaf level and under controlled laboratory conditions. The present study makes progress in demonstrating the relationship between steady-state fluorescence and net photosynthesis measured under natural light field conditions both at the leaf and image levels. Ground measurements and airborne campaigns were conducted over two summers to acquire hyperspectral imagery at 40cm resolution and 260 spectral bands in the 400–885nm spectral region. This enabled the identification of pure vegetation pixels to extract their radiance spectra. The datasets were collected in August 2010 and 2011 in the western part of the area included in the Ribera del Duero Designation of Origin (Denominación de Origen), in northern Spain. The experiments were conducted in twelve full production vineyards where two study plots per field were selected to ensure adequate variability in leaf biochemistry and physiological condition. The vineyard fields were selected on the basis of their gradient in leaf nutrition and plant water status and showed variability in leaf pigment values and stomatal conductance. Leaves were collected for destructive sampling and biochemical determination of chlorophyll a+b, carotenoids and anthocyanins in the laboratory. Leaf steady-state and dark-adapted fluorescence parameters, net photosynthesis (Pn) and stomatal conductance (Gs) were measured in the field under natural light conditions. Such data were used as a validation dataset to assess fluorescence–photosynthesis relationships both at the leaf and the image level. The Fraunhofer Line Depth (FLD) principle based on three spectral bands (FLD3) was the method used to quantify fluorescence emission from radiance spectra extracted from pure vegetation pixels identified in the hyperspectral imagery. Fluorescence retrievals conducted using the FLD3 method yielded significant results when compared to ground-measured steady-state Fs (r2=0.48; p<0.01) and Fv′/Fm′ (r2=0.53; p<0.01). The two-year assessment yielded consistent results on the relationship between Pn and Fs both at the leaf level and based on the airborne hyperspectral imagery. At the leaf level, significant relationships were found between leaf Fs and Pn (r2=0.55; p<0.001 for 2010; r2=0.59; p<0.001 for 2011). At the hyperspectral image level, the agreement between leaf Pn and airborne F was consistent for both years separately, yielding significant relationships at p<0.01 for 2010 (r2=0.54) and 2011 (r2=0.41) and a significant relationship at p<0.001 for the aggregated years (r2=0.52). Results show the link between net photosynthesis and steady-state fluorescence obtained under natural sunlight conditions at both leaf and airborne hyperspectral imagery levels.

Propagating waves transverse to the magnetic field in a solar prominence

AbstractWe have observed a quiescent prominence with the Hinode Solar Optical Telescope (SOT) (Ca II and Hα lines), Sacramento Peak Dunn Solar Telescope using the Universal Birefringent Filter (DST/UBF, in Hα, Hβ and Sodium-D lines), THEMIS (Télescope Héliographique pour l Etude du Magnétisme et des Instabilités Solaires/MTR (Multi Raies) spectromagnetograph (He D3), and the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) in EUV over a 4 hour period on 2012 October 10. The small fields of view of the SOT, DST, and MTR are centered on a large prominence footpoint extending towards the surface. This feature appears in the larger field of view of the AIA/304 Å filtergram as a large, quasi-vertical pillar with loops on each side. The THEMIS/MTR data indicate that the magnetic field in the pillar is essentially horizontal and the observations in the optical domain show a large number of horizontally aligned features in the pillar. The data are consistent with a model of cool prominence plasma trapped in the dips of horizontal field lines. The SOT and DST data show what appear to be moving wave pulses. These pulses, which include a Doppler signature, move vertically, perpendicular to the field direction, along quasi-vertical columns of horizontal threads in the pillar. The pulses have a velocity of propagation of about 10 km/s, a wavelength about 2000 km in the plane of the sky, and a period about 280 sec. We interpret these waves in terms of fast magnetosonic waves.

The solar chromospheric Ca and Mg indices from Aura OMI

Direct observations of long‐term variations in solar UV irradiance from satellites, although important for monitoring the energetic forcing of the Earth's atmosphere, is challenging because of the difficulty of accurately tracking instrument response changes. Proxy indexes based on core‐to‐wing ratios of solar Fraunhofer lines, such as the Mg II feature at 280 nm, can minimize the impact of both time‐ and wavelength‐dependent instrument changes to better monitor solar UV activity. Here we present new data sets from the Ozone Monitoring Instrument (OMI) on the Aura satellite, which began operations in late 2004. The high quality of OMI irradiance measurements allows us to construct daily indexes for the Mg II, Ca II K (393.4 nm), Ca II H (396.8 nm), and Mg I (285.2 nm) lines. The OMI Ca II K index is well correlated with the Mg II index measured by multiple instruments, as well as the ground‐based National Solar Observatory (NSO) Ca II K 1.0 Å index data derived from Integrated Sunlight Spectrometer measurements. OMI Ca II K data can be used to evaluate anomalous short‐term features in the NSO data set. The OMI solar data products represent a valuable addition to current data sets.

Optical Faraday rotation with graphene

Plane polarized electromagnetic waves propagating through a dielectric medium parallel to a magnetic field undergo Faraday rotation (FR) of their polarization. “Giant” Faraday rotation by as much as 0.1 rad was recently observed for terahertz waves with graphene over a SiC substrate. We show that for the (more technologically useful) optical frequency range, the same effect may be achieved with interband transitions between Landau levels formed by application of real or pseudo-magnetic fields induced by strain. At some resonant condition, the FR angle shows a sharp transition and sign reversal, which may be used to rotate the polarizations of the sodium doublet D-lines so as to be perpendicular to each other.

Spatio-temporal patterns of chlorophyll fluorescence and physiological and structural indices acquired from hyperspectral imagery as compared with carbon fluxes measured with eddy covariance

This study provides insight into the assessment of the spatio-temporal trends of chlorophyll fluorescence, narrow-band physiological indices, and structural indices acquired with a hyperspectral imager flown over a flux tower in a canopy characterized by small seasonal structural changes and a heterogeneous architecture. A total of seven flights between summer and autumn were conducted with a hyperspectral camera that captured 30cm resolution imagery and 260 spectral bands in the 400-900nm region. This enabled the identification of pure-vegetation tree crown pixels around an eddy covariance flux tower without shadow components or background effects. The hyperspectral imagery was used to study the temporal patterns of canopy fluorescence and reflectance indices related to physiology and canopy structure. The seasonal trends observed in the airborne indices and fluorescence and their relationship with gross primary production (GPP) demonstrated that vegetation indices mostly related to structure such as the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI) yielded non-significant relationships (r2=0.17; p>0.05) due to the small structural changes in the canopy through the season. By contrast, physiological indices related to chlorophyll content (TCARI/OSAVI), light use efficiency (PRI570), and canopy chlorophyll fluorescence calculated through the Fraunhofer Line Depth principle (FLD3) showed a similar seasonal trend to that of GPP measured at the same time of the flights (r2 in the range 0.75–0.84; p<0.01). These results are consistent with the physiological trend observed during summer and autumn, which showed that chlorophyll content increased by 17.9% while the NDVI and the estimated tree crown projected LAI (LAIp) remained almost constant during the experiment (3% variation). The time-series hyperspectral dataset demonstrated that the seasonal trajectories of the NDVI and EVI were weakly related (p>0.05) to the physiological indicators such as TCARI/OSAVI, PRI570 and fluorescence. The spatial variability of the hyperspectral indices investigated through the coefficient of variation (CV) showed that fluorescence around the tower varied up to 17% at the time of the maximum stress (summer), while LAIp showed little variation during that time (CV=1.8%). After the summer stress period, the CV for fluorescence and chlorophyll content decreased in autumn down to 9%. This study demonstrates that small physiological changes occurring in an evergreen canopy were still captured by remote sensing physiological indices and high-resolution airborne fluorescence. These indicators are required for GPP monitoring when the vegetation dynamics are not captured by remote sensing structural indices.

Using field spectroscopy to assess the potential of statistical approaches for the retrieval of sun-induced chlorophyll fluorescence from ground and space

Sun-induced chlorophyll fluorescence (Fs) is an electromagnetic signal emitted in the 650–800nm spectral window by the chlorophyll-a of green leaves. Previous studies demonstrated the retrieval of Fs on a global scale using high spectral resolution measurements by the Fourier Transform Spectrometer (FTS) on board the greenhouse gases observing satellite (GOSAT). The retrieval of Fs from GOSAT-FTS data is based on the modeling of the in-filling of solar Fraunhofer lines by Fs. The first Fs retrieval methods for GOSAT-FTS measurements were based on physical formulations of the radiative transfer between the atmosphere, the surface and the instrument including the Fs emission. As an alternative, a statistical method was also successfully applied to GOSAT data. This method is based on a singular vector decomposition (SVD) technique producing a basis of spectral functions able to model the contribution of the reflected solar radiation to the top-of-atmosphere measurement in a linear way. The Fs signal is included in the forward model as an extra parameter adding to the reflected solar radiation. Here, we use field spectroscopy measurements to provide further experimental evidence on the retrieval of Fs with statistical approaches in both Fraunhofer lines and atmospheric oxygen and water vapor bands. The statistical retrieval method used with GOSAT-FTS data has been adapted to a set of ground-based spectro-radiometer measurements in the 717–780nm range. Retrieval results in the 745–759nm window, which contains only Fraunhofer lines, support the overall approach of estimating Fs from space measurements in that spectral window. Furthermore, the application of the method to broader fitting windows including both Fraunhofer lines and and (oxygen and water vapor) atmospheric bands atmospheric bands has been proven to be very effective to reduce the retrieval noise and has also shown a good comparison with reference O2A-based retrievals. This allows consideration of statistical methods as a powerful option for Fs retrieval from broad-band space-based measurements in the near-infrared.

Using a Homemade Flame Photometer To Measure Sodium Concentration in a Sports Drink

The purpose of this experiment was to create a simple and inexpensive flame photometer to measure the concentration of sodium in beverages, such as Gatorade. We created a nebulizer using small tubing and sprayed the sample into the base of a Bunsen burner. Adjacent to the flame was a photodiode with a filter specific for the emission of the sodium D-line. After making a calibration curve, students could detect the amount of sodium in Gatorade to within 10% of the value on the label. The system costs less than $500 and can be assembled by students and used in an analytical chemistry laboratory course.

The wavelength tunable 589 nm laser output based on singly resonant sum-frequency generation and the measurement of saturate fluorescence spectrum of sodium atom

A wavelength-tunable laser output at 589 nm with high conversion efficiency based on sum-frequency generation by using the technique of single-wavelength extra-cavity resonance is achieved. The two fundamental wavelengths are 1583 nm and 938 nm and the nonlinear crystal is the period-poled lithium niobate. After the frequency of 1583 nm laser was locked to the cavity mode and the frequency of 938 nm laser was scanned, a 589 nm laser output with power of 4.96 mW and wavelength tuning range of 7 GHz was obtained and the stability of the output power is improved effectively with the help of servo feedback loop technique of acousto-optic-modulator. Finally, based on this laser, the saturated fluorescence spectrum of sodium D2 line in the temperature range of 348—413 K (75—140 ℃) were measured. The Doppler-free structures of D2a, D2b and crossover lines on Doppler background were observed, which can provide reference signals for the frequency locking of 589nm laser.