Fraunhofer Lines Research Articles

Early Water Stress Detection Using Leaf-Level Measurements of Chlorophyll Fluorescence and Temperature Data

The purpose of this paper was to investigate the early water stress in maize using leaf-level measurements of chlorophyll fluorescence and temperature. In this study, a series of diurnal measurements, such as leaf chlorophyll fluorescence (Fs), leaf spectrum, temperature and photosynthetically active radiation (PAR), were conducted for maize during gradient watering and filled watering experiments. Fraunhofer Line Discriminator methods (FLD and 3FLD) were used to obtain fluorescence from leaves spectrum. This simulated work using the SCOPE model demonstrated the variations in fluorescence and temperature in stress levels expressed by different stress factors. In the field measurement, the gradient experiment revealed that chlorophyll fluorescence decreased for plants with water stress relative to well-water plants and Tleaf-Tair increased; the filled watering experiment stated that chlorophyll fluorescence of maize under water stress were similar to those of maize under well-watering condition. In addition, the relationships between the Fs, retrieved fluorescence, Tleaf-Tair and water content were analyzed. The Fs determination resulted to the best coefficients of determination for the normalized retrieved fluorescence FLD/PAR (R2 = 0.54), Tleaf-Tair (R2 = 0.48) and water content (R2 = 0.71). The normalized retrieved fluorescence yielded a good coefficient of determination for Tleaf-Tair (R2 = 0.48). This study demonstrated that chlorophyll fluorescence could reflect variations in the physiological states of plants during early water stress, and leaf temperature confirmed the chlorophyll fluorescence analysis results and improved the accuracy of the water stress detection.

The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra

The atmospheres of exoplanets are commonly studied by observing the transit of the planet passing in front of its parent star. The obscuration of part of the stellar disk during a transit will reveal aspects of its surface structure resulting from general centre-to-limb variations (CLVs). These become apparent when forming the ratio between the stellar light in and out of transit. These phenomena can be seen particularly clearly during the progress of a penumbral lunar eclipse, where the Earth transits the solar disk and masks different regions of the solar disk as the eclipse progresses. When inferring the properties of the planetary atmosphere, it is essential that this effect originating at the star is properly accounted for. Using the data observed from the 2014-April-15 lunar eclipse with the ESPaDOnS spectrograph mounted on the Canada France Hawaii Telescope (CFHT), we have obtained for the first time a time sequence of the penumbral spectra. These penumbral spectra enable us to study the centre-to-limb variations of solar Fraunhofer lines when the Earth is transiting Sun. The Na i and Ca ii absorption features reported from previous lunar eclipse observations are demonstrated to be CLV features, which dominate the corresponding line profiles and mask possible planetary signal. Detecting atmospheric species in exoplanets via transit spectroscopy must account for the CLV effect.

Monitoring of somatic cells in milk via laser analytical techniques for the early detection of mastitis

Mastitis is an inflammatory infection of the mammary glands in dairy cattle, which causes a pronounced increase in milk somatic cell count accompanied by changes in milk elemental and molecular composition. The aim of the present study was to use different laser analytical techniques for fast, accurate, and easy diagnosis of mastitis. Both laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques were used for this purpose. The study was performed on milk samples taken from 150 Holstein cows. The results obtained by LIBS showed that in healthy milk (milk from uninfected cows), the intensities of calcium spectral lines were clearly higher than in mastitic milk samples. On the contrary, the intensities of the two sodium D-lines were higher in mastitic milk than in the healthy milk. A linear relationship exists between the sodium spectral line intensities and the average of corresponding somatic cell count (SCC). Adopting LIF, the fluorescence intensity was also found to correlate linearly with the SCC of milk samples. Comparing the two proposed laser analytical techniques with other conventional techniques showed that the proposed techniques are faster, much easier, cost-effective, and can be used in situ to monitor somatic cells for diagnosis of mastitis.

Investigation of the Hα spectral line and the Na D sodium doublet in the spectrum of the post-AGB star HD 161796

Variability of the profile of the Hα line and the Na D sodium doublet in the spectrum of HD 161796 was studied based on the spectrograms obtained with the 2-meter telescope of Shamakhy Astrophysical Observatory (National Academy of Sciences of Azerbaijan). It was found that the radial velocity and the equivalent width of the Hα line profile and the equivalent width of the sodium doublet vary in synchrony with changes in the V light curve amplitude that occur with a known period P of 62 days. The radial velocity of the D2 line of the sodium doublet (Na I λ 588.9953 nm) varies in antiphase with the variations of the V light curve, the radial velocity of the Hα line, and the equivalent widths of Hα and D2.

Measurement of Three-Dimensional Temperature Field of Flickering Premixed Flame with and without Coflow

The three-dimensional (3D) temperature field of the flickering flame with and without coflow can be measured using the flame reaction technique combined with tomographic reconstruction. This combined experimental technique facilitates the non-intrusive measurement of the unsteady 3D temperature field of a premixed methane/air flame. The target flame visualization, which was achieved by the flame reaction of sodium in the supplied mists of sodium chloride solution and line-of-sight intensity images of the flame, was transformed into the temperature field using calibration with the sodium D-line reversal method combined with imaging from six CCD cameras located around the flame. The uncertainty in tomographic temperature measurement was confirmed for the steady axisymmetric flame under the influence of strong coflow. Tomographic temperature measurements were applied to the flickering flame with and without coflow, and the results were analyzed using proper orthogonal decomposition (POD) to understand the unsteady behavior of the temperature field of the flickering flame. The flickering energy was found to be dominant in the first two POD modes. Flame flickering with and without coflow was found to be dominant in the axisymmetric and non-axisymmetric modes, respectively. The characteristics of the flickering flame with and without coflow are discussed in this paper, based on spectrum analysis. The results suggest that the structure of the flickering flame is highly modified by the presence of even a small magnitude of coflow.

High-resolution transmission spectrum of the Earth's atmosphere-seeing Earth as an exoplanet using a lunar eclipse

AbstractWith the rapid developments in the exoplanet field, more and more terrestrial exoplanets are being detected. Characterizing their atmospheres using transit observations will become a key datum in the quest for detecting an Earth-like exoplanet. The atmospheric transmission spectrum of our Earth will be an ideal template for comparison with future exo-Earth candidates. By observing a lunar eclipse, which offers a similar configuration to that of an exoplanet transit, we have obtained a high-resolution and high signal-to-noise ratio (SNR) transmission spectrum of the Earth's atmosphere. This observation was performed with the High Resolution Spectrograph at Xinglong Station, China during the total lunar eclipse in December 2011. We compare the observed transmission spectrum with our atmospheric model, and determine the characteristics of the various atmospheric species in detail. In the transmission spectrum, O2, O3, O2 · O2, NO2 and H2O are detected, and their column densities are measured and compared with the satellites data. The visible Chappuis band of ozone produces the most prominent absorption feature, which suggests that ozone is a promising molecule for the future exo-Earth characterization. Due to the high resolution and high SNR of our spectrum, several novel details of the Earth atmosphere's transmission spectrum are presented. The individual O2 lines are resolved and O2 isotopes are clearly detected. Our new observations do not confirm the absorption features of Ca II or Na I which have been reported in previous lunar eclipse observations. However, features in these and some other strong Fraunhofer line positions do occur in the observed spectrum. We propose that these are due to a Raman-scattered component in the forward-scattered sunlight appearing in the lunar umbral spectrum. Water vapour absorption is found to be rather weak in our spectrum because the atmosphere we probed is relatively dry, which prompts us to discuss the detectability of water vapour in Earth-like exoplanet atmospheres.

First results from a rotational Raman scattering cloud algorithm applied to the Suomi National Polar-orbiting Partnership (NPP) Ozone Mapping and Profiler Suite (OMPS) Nadir Mapper

Abstract. This paper reports initial results from an Ozone Mapping and Profiler Suite (OMPS) Nadir Mapper cloud pressure and cloud fraction algorithm. The OMPS cloud products are intended for use in OMPS ozone or other trace-gas algorithms. We developed the OMPS cloud products using a heritage algorithm developed for the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. The cloud pressure algorithm utilizes the filling-in of ultraviolet solar Fraunhofer lines by rotational Raman scattering. The OMPS cloud products are evaluated by comparison with OMI cloud products that have been compared in turn with other collocated satellite data including cloud optical thickness profiles derived from a combination of measurements from the CloudSat radar and MODerate-resolution Imaging Spectroradiometer (MODIS). We find that the probability density functions (PDFs) of effective cloud fraction retrieved from OMPS and OMI measurements are very similar. The PDFs of the OMPS and OMI cloud pressures are comparable. However, OMPS retrieves somewhat higher pressures on average. The current NASA total ozone retrieval algorithm makes use of a monthly gridded cloud pressure climatology developed from OMI. This climatology captures much of the variability associated with the relevant cloud pressures. However, the use of actual cloud pressures retrieved with OMPS in place of the OMI climatology changes OMPS total column ozone estimates locally (presumably in the correct direction) only in areas with large differences between climatological and actual cloud pressures. The ozone differences can be up to 5% in such areas.

Wind circulation regimes at Venus’ cloud tops: Ground-based Doppler velocimetry using CFHT/ESPaDOnS and comparison with simultaneous cloud tracking measurements using VEx/VIRTIS in February 2011

We present new results based on ground-based Doppler spectroscopic measurements, obtained with the ESPaDOnS spectrograph at Canada–France–Hawaii telescope (CFHT) and simultaneous observations of velocity fields, obtained from space by the VIRTIS-M instrument on board the Venus Express spacecraft. These measurements are based on high-resolution spectra of Fraunhofer lines in the visible to NIR range (0.37–1.05μm) acquired on February 19–21, 2011 at a resolution of about 80,000, measuring Venus’ winds at 70km, using incoming solar radiation scattered by cloud top particles in the observer’s direction (Widemann, T., et al., [2007]. Planet. Space Sci. 55, 1741–1756; Widemann, T., et al., [2008]. Planet. Space Sci. 56, 1320–1334). The zonal wind field has been characterized by latitudinal bands, at a phase angle Φ=(68.7±0.3)°, between +10°N and 60°S, by steps of 10°, and from [ϕ-ϕE]=-50° to sub-Earth longitude ϕE=0°, by steps of 12°. From space, VIRTIS-M UV (0.38μm) imaging exposures on the dayside were acquired simultaneously in orbit 1786, providing the first simultaneous cloud-tracking measurements with Doppler velocimetry. From the ground, we measured a zonal mean background velocity of v‾z=(117.3±18.0)ms-1 on February 19, andv‾z=(117.5±14.5)ms-1 on February 21. We detect an unambiguous poleward meridional flow on the morning dayside hemisphere of (18.8±12.3)ms−1 on February 19/21. Latitudinal variations of the zonal and meridional winds are further compared with the simultaneous VIRTIS data. We discuss temporal variability as well as its statistical significance.

CORRECTING FOR TELLURIC ABSORPTION: METHODS, CASE STUDIES, AND RELEASE OF THE TelFit CODE

Ground-based astronomical spectra are contaminated by the Earth's atmosphere to varying degrees in all spectral regions. We present a Python code that can accurately fit a model to the telluric absorption spectrum present in astronomical data, with residuals of $\sim 3-5\%$ of the continuum for moderately strong lines. We demonstrate the quality of the correction by fitting the telluric spectrum in a nearly featureless A0V star, HIP 20264, as well as to a series of dwarf M star spectra near the 819 nm sodium doublet. We directly compare the results to an empirical telluric correction of HIP 20264 and find that our model-fitting procedure is at least as good and sometimes more accurate. The telluric correction code, which we make freely available to the astronomical community, can be used as a replacement for telluric standard star observations for many purposes.

Narrower atomic filter at 422.7 nm based on thermal Ca beam

So far, the only Ca magneto-optic atomic filters reported are based on a heated Ca cell, and the transmission spectrum obtained is double-peaked with 3 GHz effective passband limited by Doppler broadening. A magneto-optic atomic filter with single-peaked transmission spectrum of sub-Doppler bandwidth based on the thermal Ca atomic beam is firstly experimentally demonstrated. The fast Ca dipole transition (1S0–1P1) at 422.7 nm, which matches a strong solar Fraunhofer line, was utilized. A folded nine-beam traveling wave configuration is employed, and the maximum transmission efficiency is measured to be 7.3 %. A sub-Doppler transmission bandwidth of 590 MHz, much narrower than the 2.2 GHz Doppler width in the heated atomic cell, is obtained for the first time.

FLD-based retrieval of sun-induced chlorophyll fluorescence from medium spectral resolution airborne spectroscopy data

Sun-induced chlorophyll fluorescence (Fs) is the radiation flux emitted from chlorophyll molecules and can be used as a remote sensing (RS) observable to be linked to plant photosynthesis. Recently, significant progress has been made to quantify Fs from RS data, but both retrieval and interpretation of Fs remain challenging. In the case of airborne sensors with a medium spectral resolution (<2–4nm), Fs is typically estimated using the Fraunhofer Line Depth (FLD) approach focusing on atmospheric O2 absorption bands. Most critical for accurate Fs retrievals based on such methods is the characterization of atmospheric scattering and absorption processes during data acquisition. So far, detailed experimental evidence on the retrieval accuracy of airborne measured Fs is lacking. We performed an experiment using a low-flying aircraft equipped with a non-imaging spectrometer acquiring medium spectral resolution data during the course of one day, using a repeat-track approach with changing flight altitudes. Fs in the near infrared was retrieved using a semi-empirical approach constraining the FLD based Fs retrieval from the O2-A absorption band at 760nm by using non-fluorescent surfaces. We used a local sensitivity analysis to assess Fs retrieval biases related to observational and atmospheric parameters. Our results demonstrate a reliable Fs retrieval from airborne data using reference surfaces and indicate the need for accurate knowledge of atmospheric scattering and absorption processes. This study contributes to an estimation of the total error budget of Fs retrievals and will serve as a practical guideline for Fs retrieval schemes to be applied to medium resolution airborne spectroscopy data.

Plasmonic Fraunhofer-wavelength narrow-band filter based on calcium film

We theoretically investigate plasmonic properties of a calcium film in a Kretschmann excitation scheme. Based on surface plasmon polaritons, the absorbance of the calcium film can be as high as 100% for the p-polarization, much higher than the absorbance for the s-polarization at the wavelength of 422.7nm, correspondingly to the g Fraunhofer line. The 45nm thick film of calcium has a high reflectance of about 76% at 422.7nm for s-polarization. But for p-polarization, there is a minimum in the reflectivity curves at the angle of 19°. The narrow-band filter based on calcium film is particularly suited for working with conventional calcium atomic filter and on-chip integration due to its solid-state bulky feature. Furthermore, the plasmonic filter based on the calcium film is described that may offers new applications in angle- and polarization-sensitive sensor and the detection of weak laser light.

Fluorescence, PRI and canopy temperature for water stress detection in cereal crops

Narrow-band multispectral remote sensing techniques and thermal imagery were investigated for water stress detection in cereal crops. Visible and near infrared AISA Eagle (Specim, Finland) and thermal AHS-160 (Sensytech Inc., USA) imageries were acquired with an airborne survey on a farm-level experimental site where maize (Zea mays L.) and sorghum (Sorghum bicolor L.) were grown with three different irrigation treatments. Vegetation biophysical and eco-physiological measurements were collected concurrently with the airborne campaign. Leaf fluorescence yield (ΔF/Fm′) resulted to be a good indirect measure of water stress. Therefore, ΔF/Fm′ measurements were compared against remotely sensed indicators: (i) the Photochemical Reflectance Index (PRI), (ii) the sun-induced chlorophyll fluorescence at 760nm (F760), retrieved by the Fraunhofer line depth method and (iii) the canopy temperature (TC) calculated decoupling soil and vegetation contributions. TC was related to ΔF/Fm′ with the highest determination coefficient (R2=0.65), followed by PRI586 (reference band at 586nm) (R2=0.51). The relationship with F760 was significant but weaker (R2=0.36). The coefficient of determination increased up to 0.54 when pigment concentration was considered by multiplying ΔF/Fm′ and chlorophyll content, confirming the close relationship between passive fluorescence signal, pigment content and light photosystem efficiency. PRI586, F760 and TC maps were produced in maize and sorghum plots. The differences in the average values of PRI586, F760 and TC extracted from the plots with different water treatments showed that water treatments were well discriminated in maize plots by the three remotely sensed indicators. This was confirmed by the visual observation of the PRI586, F760 and TC maps, while in sorghum plots, F760 and TC appeared more sensitive to water stress compared to PRI586.

Solar control of sodium escape from Io

AbstractWe report ground‐based spectroscopic observations of the Io sodium cloud before and after eclipse by Jupiter, in a search for possible effects of sunlight on the total atomic sodium content in Io's exosphere. These observations test the importance of the Sun in maintaining the supply of atoms from the thicker atmosphere, which lies close to the surface, to the thinner, more extended, sodium cloud. We performed ground‐based spectroscopy of the sodium doublet at 589 nm with a high‐resolution échelle spectrograph on the Italian National Telescope Galileo on La Palma Island. We find that the total atomic sodium content immediately after eclipse falls by a factor of ~4 during eclipse and recovers to preeclipse values on a timescale of ~5 h. We evaluate potential causes of the precipitous drop including condensation of the atmosphere, collapse of the ionosphere, and changes in atmospheric chemistry. We conclude that most plausible cause of the drop in atomic sodium production is the interruption of photodissociation of sodium‐bearing molecules during eclipse. We discuss further implications of this change in atmospheric chemistry.

Development of a canopy Solar-induced chlorophyll fluorescence measurement instrument

A portable solar-induced chlorophyll fluorescence detecting instrument based on Fraunhofer line principle was designed and tested. The instrument has a valid survey area of 1.3 × 1.3 meter when the height was fixed to 1.3 meter. The instrument uses sunlight as its light source. The instrument is quipped with two sets of special photoelectrical detectors with the centre wavelength at 760 nm and 771 nm respectively and bandwidth less than 1nm. Both sets of detectors are composed of an upper detector which are used for detecting incidence sunlight and a bottom detector which are used for detecting reflex light from the canopy of crop. This instrument includes photoelectric detector module, signal process module, A/D convert module, the data storage and upload module and human-machine interface module. The microprocessor calculates solar-induced fluorescence value based on the A/D values get from detectors. And the value can be displayed on the instrument's LCD, stored in the flash memory of instrument and can also be uploaded to PC through the PC's serial interface. The prototype was tested in the crop field and the results demonstrate that the instrument can measure the solar-induced chlorophyll value exactly with the correlation coefficients was 0.9 compared to the values got from Analytical Spectral Devices FieldSpec Pro spectrometer. This instrument can diagnose the plant growth status by the acquired spectral response.

Characterization of Process Conditions in Industrial Stainless Steelmaking Electric Arc Furnace Using Optical Emission Spectrum Measurements

Emission spectroscopy is a potential method for gaining information on electric arc furnace (EAF) process conditions. Previous studies published in literature on industrial EAF emission spectra have focused on a smaller scales and DC arc furnaces. In this study emission spectrum measurements were conducted for 140t AC stainless steelmaking EAF at Outokumpu Stainless Oy, Tornio Works, Finland. Four basic types of emission spectra were obtained during the EAF process cycle. The first one is obscured by scrap steel, the second is dominated by thermal radiation of the slag, the third is dominated by alkali peaks and sodium D-lines and the fourth is characterized by multiple atomic emission peaks. The atomic emission peaks were identified by comparing them to the NIST database for atomic emission lines and previous laboratory measurements on EAF slag emission spectra. The comparison shows that the optic emission of an arc is dominated by slag components. Plasma conditions were analyzed by deriving plasma temperature from optical emissions of Ca I lines. The analysis suggests that accurate information on plasma conditions can be gained from outer plasma having a plasma temperature below 7000 K (6727 °C).

Suppression of fine-structure splitting and oscillator strength of sodium D-line in a Debye plasma

We investigate theoretically the influence of static plasma screening on relativistic spin-orbit interaction-induced fine-structure splitting of the D-line doublet arising from the transitions 3p1/2–3s1/2 and 3p3/2–3s1/2 of the valence electron of a sodium atom embedded in a model plasma environment. The many-electron atomic problem is formulated first as an effective one-electron problem in which the interaction between the optically active valence electron and the atomic ion core is represented by an accurate parametric model potential including core-polarization correction, and then the plasma effect on the atomic system is simulated by the Debye-screening model for the valence-core interaction. It is observed that the magnitude of spin-orbit energy shift reduces for both the upper component 3p3/2 and the lower component 3p1/2 with increasing plasma screening strength, thereby reducing the spin-orbit energy separation between these two components as the screening becomes stronger. As a consequence, the magnitude of fine-structure splitting between the D1 and D2 line energies of sodium drops significantly with stronger plasma screening. The optical (absorption) oscillator strength for 3s → 3p transition is seen to reduce with stronger screening and this leads to a screening-induced gradual suppression of the 3p → 3s spontaneous decay rate.

NEAR-INFRARED METALLICITIES, RADIAL VELOCITIES, AND SPECTRAL TYPES FOR 447 NEARBY M DWARFS

We present metallicities, radial velocities and near-infrared spectral types for 447 M dwarfs determined from moderate resolution (R~2000) near-infrared (NIR) spectra obtained with IRTF/SpeX. These M dwarfs are targets of the MEarth Survey, a transiting planet survey searching for super Earths around mid-to-late M dwarfs within 33pc. We present NIR spectral types and new IRTF spectral templates in the Z, J, H and K-bands, created using M dwarfs with near-solar metallicities. We developed two spectroscopic distance calibrations that use NIR spectral type or an index based on the curvature of the K-band continuum. Our distance calibration has a scatter of 14%. We searched 27 NIR spectral lines and 10 spectral indices for metallicity sensitive features, taking into account correlated noise in our estimates of the errors on these parameters. We calibrated our relation using 36 M dwarfs in common proper pairs with an F, G or K-type star of known metallicity. We validated the physical association of these pairs using proper motions, radial velocities and spectroscopic distance estimates. Our resulting metallicity calibration uses the sodium doublet at 2.2um as the sole indicator for metallicity. It has an accuracy of 0.12dex inferred from the scatter between the metallicities of the primaries and the estimated metallicities of the secondaries. Our relation is valid for NIR spectral types from M1V to M5V and for -1.0<[Fe/H]<+0.35dex. We present a new metallicity relation using J-H and J-K colors that directly relates two observables: the distance from the M dwarf main sequence and equivalent width of the sodium line at 2.2um. We measured radial velocities by modeling telluric features to determine the absolute wavelength calibration of our spectra, and used M dwarf binaries, observations at different epochs, and comparison to precisely measured radial velocities to demonstrate 4.4km/s accuracy.

Carbon Monitoring Satellite (CarbonSat): assessment of atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; retrieval errors by error parameterization

Abstract. Carbon Monitoring Satellite (CarbonSat) is one of two candidate missions for ESA's Earth Explorer 8 (EE8) satellite to be launched around the end of this decade. The overarching objective of the CarbonSat mission is to improve our understanding of natural and anthropogenic sources and sinks of the two most important anthropogenic greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4). The unique feature of CarbonSat is its "GHG imaging capability", which is achieved via a combination of high spatial resolution (2 km × 2 km) and good spatial coverage (wide swath and gap-free across- and along-track ground sampling). This capability enables global imaging of localized strong emission source, such as cities, power plants, methane seeps, landfills and volcanos, and likely enables better disentangling of natural and anthropogenic GHG sources and sinks. Source–sink information can be derived from the retrieved atmospheric column-averaged mole fractions of CO2 and CH4, i.e. XCO2 and XCH4, by inverse modelling. Using the most recent instrument and mission specification, an error analysis has been performed using the Bremen optimal EStimation DOAS (BESD/C) retrieval algorithm. We assess the retrieval performance for atmospheres containing aerosols and thin cirrus clouds, assuming that the retrieval forward model is able to describe adequately all relevant scattering properties of the atmosphere. To compute the errors for each single CarbonSat observation in a one-year period, we have developed an error parameterization scheme comprising six relevant input parameters: solar zenith angle, surface albedo in two bands, aerosol and cirrus optical depth, and cirrus altitude variations. Other errors, e.g. errors resulting from aerosol type variations, are partially quantified but not yet accounted for in the error parameterization. Using this approach, we have generated and analysed one year of simulated CarbonSat observations. Using this data set we estimate that systematic errors are for the overwhelming majority of cases (≈ 85%) below 0.3 ppm for XCO2 (below 0.5 ppm for 99.5%) and below 2 ppb for XCH4 (below 4 ppb for 99.3%). We also show that the single-measurement precision is typically around 1.2 ppm for XCO2 and 7 ppb for XCH4 (1σ). The number of quality-filtered observations over cloud- and ice-free land surfaces is in the range of 33 to 47 million per month depending on season. Recently it has been shown that terrestrial vegetation chlorophyll fluorescence (VCF) emission needs to be considered for accurate XCO2 retrieval. We therefore retrieve VCF from clear Fraunhofer lines located around 755 nm and show that CarbonSat will provide valuable information on VCF. We estimate that the VCF single-measurement precision is approximately 0.3 mW m−2 nm−1 sr−1 (1σ).

Flickering characteristics and temperature field of premixed methane/air flame under the influence of co-flow

The flickering characteristics and the temperature field of an axisymmetric premixed methane/air flame under the influence of co-flow are studied experimentally using the image analysis and the flame reaction technique. The premixed flame is visualized by the alkali metal solution of sodium (Na) for characterizing the flickering characteristics. The temperature measurement of the flame is carried out using the flame reaction technique combined with the relationship between the local intensity of the flame and the temperature from the sodium D-line reversal method, and the influence of the number density distribution of Na on the measured temperature field is corrected by the measurement integrated analysis of the flame with the iterative procedure. This technique is validated by the local temperature measurement in the steady flame under the influence of co-flow using the thermocouple calibrated by the sodium D-line reversal method. The flame visualization and temperature measurement in the flickering flame of the premixed methane/air flame indicates that the flame contour and the temperature field oscillate periodically with the flickering frequency due to the Kelvin–Helmholtz instability of the flame. The oscillation amplitude decreases and the frequency increases gradually with the co-flow velocity increases similar to the observation in the diffusion flame in literature, while the oscillation amplitude grows with the equivalence ratio increases. These changes in the flickering characteristics of the flame are caused by the variations of the temperature field in the premixed flame.