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Peroxy radical detection for airborne atmospheric measurements using absorption spectroscopy of NO<sub>2</sub>
摘要： Development of an airborne instrument for the determination of peroxy radicals (PeRCEAS – peroxy radical chemical enhancement and absorption spectroscopy) is reported. Ambient peroxy radicals (HO2 and RO2, R being an organic chain) are converted to NO2 in a reactor using a chain reaction involving NO and CO. Provided that the amplification factor, called effective chain length (eCL), is known, the concentration of NO2 can be used as a proxy for the peroxy radical concentration in the sampled air. The eCL depends on radical surface losses and must thus be determined experimentally for each individual setup. NO2 is detected by continuous-wave cavity ring-down spectroscopy (cw-CRDS) using an extended cavity diode laser (ECDL) at 408.9 nm. Optical feedback from a V-shaped resonator maximizes transmission and allows for a simple detector setup. CRDS directly yields absorption coefficients, thus providing NO2 concentrations without additional calibration. The optimum 1σ detection limit is 0.3 ppbv at an averaging time of 40 s and an inlet pressure of 300 hPa. Effective chain lengths were determined for HO2 and CH3O2 at different inlet pressures. The 1σ detection limit at an inlet pressure of 300 hPa for HO2 is 3 pptv for an averaging time of 120 s.
关键词： peroxy radicals,NO2,cavity ring-down spectroscopy,airborne measurements,absorption spectroscopy,chemical amplification
更新于2025-09-23 15:22:29
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Aerosol Retrieval in the Autumn and Winter From the Red and 2.12 μm Bands of MODIS
摘要： In the autumn and winter, aerosol is the important atmospheric pollutant over the Beijing–Tianjin–Hebei region. For monitoring aerosol in the autumn and winter, the lack of vegetation and the aging of MODIS sensor are two problems that needed to be solved. In this paper, after analyzing the characteristics of aerosol radiance in the red and shortwave infrared (2.12 μm) bands of MODIS, we develop a new algorithm for terrestrial aerosol with the assumption that the re?ectance ratio between the red and 2.12 μm bands is invariant. With MODIS data over the Beijing–Tianjin–Hebei region from September 2016 to February 2017, the algorithm is applied to aerosol retrieval. The retrieved aerosol optical depth images show that our algorithm can retrieve aerosol over sparse vegetation, and the validation with the AERONET/PHOTONS Beijing site shows that the correlation is greater than 0.9% and 77% of the retrievals fall within the expected error. An error analysis shows that a 2% error in the proportion of the soot component can lead to 15% retrieval error, and over more than 60% of the surface area, the error from the changes in the ratio between the red and 2.12 μm bands can lead to retrieved errors less than 0.1.
关键词： infrared measurements,remote sensing,Aerosol,atmospheric measurements
更新于2025-09-23 15:21:21
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Carrier concentration and transport in Be-doped InAsSb for infrared sensing applications
摘要： Accurate p-type doping of the active region in III-V infrared detectors is essential for optimizing the detector design and overall performance. While most III-V detector absorbers are n-type (e.g., nBn), the minority carrier devices with p-type absorbers would be expected to have relatively higher quantum efficiencies due to the higher mobility of minority carrier electrons. However, there are added challenges to determining the hole carrier concentration in narrow bandgap InAsSb due to the potential for electron accumulation at the surface of the material and at its interface with the layer grown directly below it. Electron accumulation layers form high conductance electron channels that can dominate both resistivity and Hall-effect transport measurements. Therefore, to correctly determine the bulk hole concentration and mobility, temperature- and magnetic-field-dependent transport measurements in conjunction with Multi-Carrier Fit analysis were utilized on a series of p-doped InAs0.91Sb0.09 samples on GaSb substrates. The resulting hole concentrations and mobilities at 77 K (300 K) are 1.6×1018 cm-3 (2.3×1018 cm-3) and 125 cm2 V-1 s-1 (60 cm2 V-1 s-1), respectively, compared with the intended Be-doping of ~2×1018 cm-3. A surface treatment experiment is conducted to associate one of the electron conducting populations to the surface. Variable temperature (15 – 390 K) measurements confirmed the different carrier species present in the sample and enabled the extraction of the bulk heavy hole, interface carriers and surface electron transport properties. For the bulk carrier, a thermal activation of intrinsic carriers is identified at high temperatures with a bandgap of EG ~ 258 meV and the low temperature data suggests an activation energy of EA ~ 22 meV for the Be dopant atoms. Finally, temperature analysis confirms a surface carrier electron with resulting mobilities and sheet concentrations at 30 K (300 K) of 4500 cm2 V-1 s-1 (4300 ± 100 cm2 V-1 s-1) and 5.6×1010 cm-2 (6×1010 ± 2×1010 cm-2), respectively.
关键词： Hall-effect measurements,magneto-transport,beryllium doping,III-V infrared detectors,InAsSb
更新于2025-09-23 15:21:21
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Disentangling stellar activity from exoplanetary signals with interferometry
摘要： Stellar activity can express as many forms at stellar surfaces: dark spots, convective cells, bright plages. Particularly, dark spots and bright plages add noise on photometric data or radial velocity measurements used to detect exoplanets, and thus lead to false detection or disrupt their derived parameters. Since interferometry provides a very high angular resolution, it may constitute an interesting solution to distinguish the signal of a transiting exoplanet and that of stellar activity. It has also been shown that granulation adds bias in visibility and closure phase measurements, affecting in turn the derived stellar parameters. We analyze the noises generated by dark spots on interferometric observables and compare them to exoplanet signals. We investigate the current interferometric instruments able to measure and disentangle these signals, and show that there is a lack in spatial resolution. We thus give a prospective of the improvements to be brought on future interferometers, which would also significantly extend the number of available targets.
关键词： closure phase measurements,interferometry,bright plages,dark spots,granulation,exoplanetary signals,visibility,stellar activity
更新于2025-09-23 15:21:21
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Differential Column Measurements Using Compact Solar-Tracking Spectrometers
摘要： We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH4 and CO2 within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.1% for XCO2 and XCH4 using an optimum integration time of 10 min, which corresponds to standard deviations of 0.04 ppm, and 0.2 ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind minus upwind column gradient ?XCH4 across dairy farms in the Chino California area and using the data to verify emissions reported in the literature. Spatial column gradient ratios ?XCH4/?XCO2 were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5-10 minutes) of XCO2 and XCH4, and to show that they represent atmospheric phenomena. Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations, and less subject to errors associated with small-scale transport phenomena.
关键词： compact solar-tracking spectrometers,urban emissions,differential column measurements,CH4,CO2
更新于2025-09-23 15:21:21
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Adaption of an array spectroradiometer for total ozone column retrieval using direct solar irradiance measurements in the UV spectral range
摘要： A compact array spectroradiometer that enables precise and robust measurements of solar UV spectral direct irradiance is presented. We show that this instrument can retrieve total ozone column (TOC) accurately. The internal stray light, which is often the limiting factor for measurements in the UV spectral range and increases the uncertainty for TOC analysis, is physically reduced so that no other stray-light reduction methods, such as mathematical corrections, are necessary. The instrument has been extensively characterised at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. During an international total ozone measurement intercomparison at the Iza?a Atmospheric Observatory in Tenerife, the high-quality applicability of the instrument was verified with measurements of the direct solar irradiance and subsequent TOC evaluations based on the spectral data measured between 12 and 30 September 2016. The results showed deviations of the TOC of less than 1.5 % from most other instruments in most situations and not exceeding 3 % from established TOC measurement systems such as Dobson or Brewer.
关键词： stray-light reduction,direct solar irradiance measurements,array spectroradiometer,total ozone column,UV spectral range
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Multi-Frequency Microwave Resonance Cavity for Nondestructive Core Plug Measurements
摘要： This work describes the theory, design and testing of a multi-frequency microwave cavity. The cavity measures the complex permittivity of core plugs of rocks, consolidated soil or sea ice. The core plugs can have commercially available diameter dimensions (0.02 meters - 0.038 meters) and for maximum height of 0.055 meters. The cavity measures the complex permittivity at five resonant frequencies between 1 GHz and 3.5 GHz of the TM0np mode. An infrared temperature sensor measures the temperature of the core plug under testing. This cavity allows for a more accurate characterization of the core composition. Initial complex permittivity measurements of six different shale core plugs were conducted. Results show that permittivity spectra can be correlated to the clay content and total organic content (TOC) of the shales. The latter is a function of the maturity of the rock. Moreover, initial results indicate the importance of water and salinity on shale samples.
关键词： sea ice,dielectric measurement,geology,Permittivity measurement,soil,well logging,geophysical measurement,microwave measurements
更新于2025-09-23 15:21:21
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A novel approach for the extraction of cloud motion vectors using airglow imager measurements
摘要： The paper explores the possibility of implementing an advanced photogrammetric technique, generally employed for satellite measurements, on airglow imager, a ground-based remote sensing instrument primarily used for upper atmospheric studies, measurements of clouds for the extraction of cloud motion vectors (CMVs). The major steps involved in the algorithm remain the same, including image processing for better visualization of target elements and noise removal, identification of target cloud, setting a proper search window for target cloud tracking, estimation of cloud height, and employing 2-D cross-correlation to estimate the CMVs. Nevertheless, the implementation strategy at each step differs from that of satellite, mainly to suit airglow imager measurements. For instance, climatology of horizontal winds at the measured site has been used to fix the search window for target cloud tracking. The cloud height is estimated very accurately, as required by the algorithm, using simultaneous collocated lidar measurements. High-resolution, both in space and time (4 min), cloud imageries are employed to minimize the errors in retrieved CMVs. The derived winds are evaluated against MST radar-derived winds by considering it as a reference. A very good correspondence is seen between these two wind measurements, both showing similar wind variation. The agreement is also found to be good in both the zonal and meridional wind velocities with RMSEs < 2.4 m s?1. Finally, the strengths and limitations of the algorithm are discussed, with possible solutions, wherever required.
关键词： lidar measurements,photogrammetric technique,MST radar,cloud motion vectors,ground-based remote sensing,airglow imager
更新于2025-09-23 15:21:21
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[IEEE 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Trebic, Czech Republic (2018.9.18-2018.9.20)] 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Advanced Luminance Modeling of Light Sources for Simulation and Computational Purposes of Lighting Parameters
摘要： The last decade is the time of a very dynamic development of lighting technology. This development covers many areas that complement each other. The development of light sources, luminaires, measurement techniques and design methods make it necessary to develop new, effective tools to support the design and analysis of lighting equipment. In lighting technology, the most common analysis is made of such parameters as the illuminance, luminance distribution and discomfort glare, inseparable from the specificity of modern light sources. A characteristic feature of almost all of them is high luminance, on the level of 107 – 108 cd/m2. High luminance facilitates the design of very precise optical systems, but also it is strongly associated with the possibility of discomfort associated with glare. Current methods of glare analysis in simulation software are related to conversion to the average luminance value of the luminaire, saved as simplified light parameters in electronic files (IES, LDT or similar). Currently the calculations take place as a result of calculation ratio the value of luminous intensity in a given direction and the surface area of the dimension of the luminaires in the same direction. This can lead to a significant understatement of the luminance of the luminaire in any situation where luminous intensity comes from the heterogeneous luminance distribution on the surface of the luminaire. This situation most often occurs in luminaires with high-luminance light sources with a reflector system and in the case of multi-source luminaires with lenses - eg multi-LED luminaires. The paper presents advanced methods of luminance modelling of light sources developed as a result of digital measurements of luminance distributions. A comparative analysis of the accuracy of the simulation calculations of the analytical lighting fixture model will be presented. The results will be compared to the classic ray tracing methods used in currently used models.
关键词： luminance measurements,ILMD,light source models,simulations
更新于2025-09-23 15:21:21
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[IEEE 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Trebic, Czech Republic (2018.9.18-2018.9.20)] 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Measurements of the Luminance Distribution in the Classroom Using the SkyWatcher Type System
摘要： The aim of this work is to determine the possibility of using an automated Skywatcher system to analyze luminance distributions on selected surfaces, such as ceilings, walls, etc. The paper presents luminance distribution of the wall and ceiling surfaces of a classroom, using a typical luminance meter cooperating with the Skywatcher system. The use of a matrix luminance meter was also analyzed and compared with Skywatcher system. The results obtained were compared with numerical calculations in DIALux and Relux software.
关键词： luminance measurements,Skywatcher,matrix luminance meter,DIALux,interior lighting,Relux
更新于2025-09-23 15:21:21