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Near-infrared remote sensing of Los Angeles trace gas distributions from a mountaintop site
摘要： The Los Angeles basin is a significant anthropogenic source of major greenhouse gases (CO2 and CH4) and the pollutant CO, contributing significantly to regional and global climate change. We present a novel approach for monitoring the spatial and temporal distributions of greenhouse gases in the Los Angeles basin using a high-resolution spectroscopic remote sensing technique. A new Fourier transform spectrometer called CLARS-FTS has been deployed since May, 2010, at Jet Propulsion Laboratory (JPL)'s California Laboratory for Atmospheric Remote Sensing (CLARS) on Mt. Wilson, California, for automated long-term measurements of greenhouse gases. The instrument design and performance of CLARS-FTS are presented. From its mountaintop location at an altitude of 1673 m, the instrument points at a programmed sequence of ground target locations in the Los Angeles basin, recording spectra of reflected near-IR solar radiation. Column-averaged dry-air mole fractions of greenhouse gases (XGHG) including XCO2, XCH4, and XCO are retrieved several times per day for each target. Spectra from a local Spectralon? scattering plate are also recorded to determine background (free tropospheric) column abundances above the site. Comparisons between measurements from LA basin targets and the Spectralon? plate provide estimates of the boundary layer partial column abundances of the measured species. Algorithms are described for transforming the measured interferograms into spectra, and for deriving column abundances from the spectra along with estimates of the measurement precision and accuracy. The CLARS GHG measurements provide a means to infer relative, and possibly absolute, GHG emissions.
关键词： column abundances,remote sensing,greenhouse gases,Fourier transform spectrometer,Los Angeles basin
更新于2025-09-23 15:22:29
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Indirect predissociation of highly excited singlet states of N <sub/><b>2</b> </sub>
摘要： Indirect predissociation of the b(cid:2) 1(cid:1)+u (v = 20) level of N2 is studied experimentally by vacuum-ultraviolet photoabsorption employing synchrotron radiation and a Fourier-transform spectrometer, and interpreted with the aid of a quantitative model of interacting 1(cid:2)u and 1(cid:1)+u, bound and unbound states which solves the coupled Schr?dinger equation. An observed rotationally-localised peak in the b(cid:2)(20) predissociation linewidths is identi?ed by the model as arising from an interaction with a strongly predissociated and unobserved bound level of the mixed c3 1(cid:2)u and o3 1(cid:2)u Rydberg states. This leads to the dissociation of b(cid:2)(20) into the continuum of the b 1(cid:2)u valence state. The residual observed predissociation of b(cid:2) 1(cid:1)+u (v = 20) apart from the rotationally-localised peak cannot be explained by a mechanism of 1(cid:2)u and 1(cid:1)+u interaction, and must involve states of higher multiplicity.
关键词： Fourier-transform spectrometer,coupled Schr?dinger equation,vacuum-ultraviolet photoabsorption,N2,Indirect predissociation,synchrotron radiation
更新于2025-09-23 15:21:01
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The mechanical and thermal setup of the GLORIA spectrometer
摘要： The novel airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) measures infrared emission of atmospheric trace constituents. GLORIA comprises a cooled imaging Fourier transform spectrometer, which is operated in unpressurized aircraft compartments at ambient temperature. The whole spectrometer is pointed by the gimbal towards the atmospheric target. In order to reach the required sensitivity for atmospheric emission measurements, the spectrometer optics needs to operate at a temperature below 220 K. A lightweight and compact design is mandatory due to limited space and high agility requirements. The cooled optical system needs to withstand high pressure and temperature gradients, humidity, and vibrations. A new cooling system based on carbon dioxide and liquid nitrogen combined with high-performance insulation has been developed to meet the mechanical, thermal, and logistical demands. The challenging mechanical and spatial requirements lead to the development of a novel rigid linear slide design in order to achieve the large optical path difference for high spectral resolution. This paper describes the mechanical and thermal setup of GLORIA and presents the performance results on two different research aircrafts.
关键词： cooling system,atmospheric trace constituents,Fourier transform spectrometer,thermal design,mechanical design,GLORIA,infrared emission,airborne
更新于2025-09-10 09:29:36
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Optical Characterization of the SPT-3G Camera
摘要： The third-generation South Pole Telescope camera is designed to measure the cosmic microwave background across three frequency bands (centered at 95, 150 and 220 GHz) with ～ 16,000 transition-edge sensor (TES) bolometers. Each multi-chroic array element on a detector wafer has a broadband sinuous antenna that couples power to six TESs, one for each of the three observing bands and both polarizations, via lumped element ?lters. Ten detector wafers populate the detector array, which is coupled to the sky via a large-aperture optical system. Here we present the frequency band characterization with Fourier transform spectroscopy, measurements of optical time constants, beam properties, and optical and polarization ef?ciencies of the detec- tor array. The detectors have frequency bands consistent with our simulations and have high average optical ef?ciency which is 86, 77 and 66% for the 95, 150 and 220 GHz detectors. The time constants of the detectors are mostly between 0.5 and 5 ms. The beam is round with the correct size, and the polarization ef?ciency is more than 90% for most of the bolometers.
关键词： Frequency bands,Beam,Fourier transform spectrometer,Cosmic microwave background,Transition-edge sensor,Polarization,Optical ef?ciency,Time constant
更新于2025-09-09 09:28:46
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Case Studies of the Impact of Orbital Sampling on Stratospheric Trend Detection and Derivation of Tropical Vertical Velocities: Solar Occultation versus Limb Emission Sounding
摘要： This study investigates the representativeness of two types of orbital sampling applied to stratospheric temperature and trace gas fields. Model fields are sampled using real sampling patterns from the Aura Microwave Limb Sounder (MLS), the HALogen Occultation Experiment (HALOE) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The MLS sampling acts as a proxy for a dense uniform sampling pattern typical of limb emission sounders, while HALOE and ACE-FTS represent coarse non-uniform sampling patterns characteristic of solar occultation instruments. First, this study revisits the impact of sampling patterns in terms of the sampling bias, as previous studies have done. Then, it quantifies the impact of different sampling patterns on the estimation of trends and their associated detectability. In general, we find that coarse non-uniform sampling patterns may introduce non-negligible errors in the inferred magnitude of temperature and trace gas trends and necessitate considerably longer records for their definitive detection. Lastly, we explore the impact of these sampling patterns on tropical vertical velocities derived from stratospheric water vapor measurements. We find that coarse non-uniform sampling may lead to a biased depiction of the tropical vertical velocities and, hence, to a biased estimation of the impact of the mechanisms that modulate these velocities. These case studies suggest that dense uniform sampling such as that available from limb emission sounders provides much greater fidelity in detecting signals of stratospheric change (for example, fingerprints of greenhouse gas warming and stratospheric ozone recovery) than coarse non-uniform sampling such as that of solar occultation instruments.
关键词： Atmospheric Chemistry Experiment Fourier Transform Spectrometer,trace gas fields,HALogen Occultation Experiment,Aura Microwave Limb Sounder,orbital sampling,stratospheric temperature,tropical vertical velocities,trend detection
更新于2025-09-09 09:28:46
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Fourier transform spectrometer measurements of column CO<sub>2</sub> at Sodankyl?, Finland
摘要： Fourier transform spectrometer (FTS) observations at Sodankyl?, Finland (67.4? N, 26.6? E) have been performed since early 2009. The FTS instrument is participating in the Total Carbon Column Observing Network (TCCON) and has been optimized to measure abundances of the key greenhouse gases in the atmosphere. Sodankyl? is the only TCCON station in the Fennoscandia region. Here we report the measured CO2 time series over a 7-year period (2009–2015) and provide a description of the FTS system and data processing at Sodankyl?. We ?nd the lowest monthly column CO2 values in August and the highest monthly values during the February–May season. Inter-annual variability is the highest in the June–September period, which correlates with the growing season. During the time period of FTS measurements from 2009 to 2015, we have observed a 2.2 ± 0.2 ppm increase per year in column CO2. The monthly mean column CO2 values have exceeded 400 ppm level for the ?rst time in February 2014.
关键词： CO2,Sodankyl?,TCCON,Fourier transform spectrometer,greenhouse gases
更新于2025-09-09 09:28:46
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Recording Raman Spectra Using a Dynamic Fourier Transform Spectrometer
摘要： We have developed a dynamic Fourier transform spectrometer for recording Raman spectra in the near-IR range (800–1100 nm). Stability and reliability of operation of the spectrometer is achieved by using corner re? ectors in the design as mirrors in the main channel. In order to record a weak Raman signal, we set up a white light channel in the spectrometer which enables locking into the zero optical path difference when summing the interferograms over several scans. A reference channel with sampling frequency λ/4 lets us improve the sampling accuracy and the signal-to-noise ratio of the emission spectra. Using our spectrometer, we recorded the Raman spectra of test substances with known positions of the emission lines: 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP, C24H16N2O2), stilbene (C14H12), acetylsalicylic acid (C9H8O4). Comparison of the POPOP Raman spectra obtained on the dynamic Fourier transform spectrometer and a diffraction spectrometer for the same experimental conditions showed that they qualitatively matched, and the time required to record the spectrum on the dynamic Fourier transform spectrometer was 4 times shorter.
关键词： Raman spectroscopy,dynamic Fourier transform spectrometer,white-light channel,Fourier transform spectrometer in the visible and near-IR ranges,corner re? ector
更新于2025-09-04 15:30:14
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Accurate mobile remote sensing of XCO<sub>2</sub> and XCH<sub>4</sub> latitudinal transects from aboard a research vessel
摘要： A portable Fourier transform spectrometer (FTS), model EM27/SUN, was deployed onboard the research vessel Polarstern to measure the column-average dry air mole fractions of carbon dioxide (XCO2) and methane (XCH4) by means of direct sunlight absorption spectrometry. We report on technical developments as well as data calibration and reduction measures required to achieve the targeted accuracy of fractions of a percent in retrieved XCO2 and XCH4 while operating the instrument under field conditions onboard the moving platform during a 6-week cruise on the Atlantic from Cape Town (South Africa, 34? S, 18? E; 5 March 2014) to Bremerhaven (Germany, 54? N, 19? E; 14 April 2014). We demonstrate that our solar tracker typically achieved a tracking precision of better than 0.05? toward the center of the sun throughout the ship cruise which facilitates accurate XCO2 and XCH4 retrievals even under harsh ambient wind conditions. We define several quality filters that screen spectra, e.g., when the field of view was partially obstructed by ship structures or when the lines-of-sight crossed the ship exhaust plume. The measurements in clean oceanic air, can be used to characterize a spurious air-mass dependency. After the campaign, deployment of the spectrometer alongside the TCCON (Total Carbon Column Observing Network) instrument at Karlsruhe, Germany, allowed for determining a calibration factor that makes the entire campaign record traceable to World Meteorological Organization (WMO) standards. Comparisons to observations of the GOSAT satellite and concentration fields modeled by the European Centre for Medium-Range Weather Forecasts (ECMWF) Copernicus Atmosphere Monitoring Service (CAMS) demonstrate that the observational setup is well suited to provide validation opportunities above the ocean and along interhemispheric transects.
关键词： solar tracker,EM27/SUN,atmospheric greenhouse gases,XCO2,XCH4,Fourier transform spectrometer,shipborne measurements
更新于2025-09-04 15:30:14