Galileo Photopolarimeter/Radiometer Experiment

Ground based lidars are widely used all over for the study of physical and optical properties of aerosols and clouds in the atmosphere. The observed parameters on aerosols and clouds and their dependence on various meteorological parameters are being studied using the ground based lidars at different laboratories. But the results obtained are mostly applicable to local / regional particular to the lidar observation site. Space borne lidar is a unique system for observing the global distribution of aerosols and clouds. It provides vertical profiles of the physical properties of the clouds and aerosols with global coverage. Such data is useful for the validation of climate models and for process studies related to the climate change and also for studies on transport of aerosols and pollutants. Retrieval of optical properties of clouds and aerosols from the data obtained by the space borne lidar is very complex. Currently we are developing algorithms to produce calibrated data products for space borne and ground based lidars. A software to produce simulated lidar backscatter profiles applicable to space borne and ground based lidars has been developed, which generates data that matches the expected performance of the lidars under varying conditions. Output simulated data includes 1064 nm total backscatter profiles and 532 nm profiles for both the parallel and perpendicular polarization states. This paper describes the methodology used for inverting the ground based lidar data and the strategy for validating the data which will be obtained from the proposed space borne lidar to be launched by ISRO.

A study on the variations of optical and physical properties of aerosols over a tropical semi-arid station during grassland fire

We are based at the French-Italian research station Concordia on the east high Antarctic plateau (75°S, 123°E, 3233m). It is one of the remotest, coldest, driest places on Earth, we are 1200 km from the coast and our nearest neighbour is 600 km away: the Russian station Vostok. The landscape is an immense white, flat surface of compacted snow extending 1000 km in all directions. The snow and ice on which we walk is more than 3 km thick. Living here is like living on another planet, ‘Planet Concordia’ or ‘White Mars’. During the nine months of winter from February to November, the station is completely isolated from the rest of the world. No plane or vehicle can reach us, even in an emergency as the harsh weather conditions make all travel impossible. We have experienced temperatures down to –80°C and three months of complete darkness. The multicultural crew is consists of 13 people: seven for logistics and six scientists. We are five Italians, one Swiss, one English and six French. This year we are three women and ten men from 24 to 56 years old. We must rely on our own skills and teamwork while being prepared to face any kind of emergency through training, fire, rescue and medical exercises. Antarctica is the largest, most extreme, multi-disciplinary, open-air scientific laboratory that helps us understand the mechanisms that regulate our planet, its climate, its history and offers a platform to observe and understand the structure of the universe, as well as charting the adaptation of humans to harsh environments. Thanks to the Antarctic Treaty, nations worldwide collaborate peacefully with respect for this environment in the name of science. We are one of very few stations at the heart of the Antarctic continent, so Concordia stands as an important node in the Earth Observatory Grid, for fields such as meteorology, seismology, geomagnetism and atmospheric chemistry. Lorenzo Moggio: 30 years old, Italian physicist, research fellow at the Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. This is my second winter spent at Concordia, I was here in 2010 as well. Giampietro Casasanta: 35 years old, Italian physicist with a PhD in Remote Sensing and research fellow at the Rome Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. I am in charge of the Italian glaciology and remote sensing experiments. Our tasks are to maintain and assure the scientific instruments work, retrieve the data run a first analysis and send it to Europe on a daily basis. We measure radiative balances at Earth’s surface, Meterological variables, optical and physical properties of aerosols, properties of clouds. We have at our disposal broadband and spectral radiometers in the shortwave, longwave and ultraviolet part of the electromagnetic spectrum, particle counters and sizers, lidar, sodar, sonic anemometers, automatic weather stations and sounding stations equipped with: barometers, anemometers, thermo-hygrometers, GPS and radio transmitters/receivers. Beth Healey: British medical doctor. I am running studies for the European Space Agency on the crew and myself to see how we adapt to living in this extreme environment. Our nine-month isolation living completely cut off from the world with low air pressure is similar in many ways to the stress astronauts will endure during a long spaceflight. I am running experiments on morale, eyesight, blood pressure and even searching for new life! http://www.esa.int/concordia Ask Us Anything about life here and the science we do! Moderator note: Due to a scheduling mix up they will not be able to answer questions at the normal time (turns out it's 1:30 am their time right now!) We will work on getting them online as soon as is reasonable, sorry for the confusion! Edit: We have started, sorry for the delay. Proof: http://imgur.com/joZLQvf

A spectrometer that can capture two orthogonal polarization components of s light beam is demanded for polarization sensitive imaging system. Here, we describe the design and implementation of a high speed spectrometer for simultaneous capturing of two orthogonal polarization components, i.e. vertical and horizontal components, of light beam. The design consists of a polarization beam splitter, two polarization-maintain optical fibers, two collimators, a single line-scan camera, a focusing lens, and a reflection blaze grating. The alignment of two beam paths was designed to be symmetrically incident on the blaze side and reverse blaze side of reflection grating, respectively. The two diffracted beams were passed through the same focusing lens and focused on the single line-scan sensors of a CMOS camera. The two spectra of orthogonal polarization were imaged on 1000 pixels per spectrum. With the proposed setup, the amplitude and shape of the two detected spectra can be controlled by rotating the collimators. The technique for optical alignment of spectrometer will be presented and discussed. The two orthogonal polarization spectra can be simultaneously captured at a speed of 70,000 spectra per second. The high speed dual spectrometer can simultaneously detected two orthogonal polarizations, which is an important component for the development of polarization-sensitive optical coherence tomography. The performance of the spectrometer have been measured and analyzed.

Abstract. Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite, 12 years (2003–2014) of aerosol and cloud properties were used to statistically quantify aerosol–cloud interaction (ACI) over the Baltic Sea region, including the relatively clean Fennoscandia and the more polluted central–eastern Europe. These areas allowed us to study the effects of different aerosol types and concentrations on macro- and microphysical properties of clouds: cloud effective radius (CER), cloud fraction (CF), cloud optical thickness (COT), cloud liquid water path (LWP) and cloud-top height (CTH). Aerosol properties used are aerosol optical depth (AOD), Ångström exponent (AE) and aerosol index (AI). The study was limited to low-level water clouds in the summer. The vertical distributions of the relationships between cloud properties and aerosols show an effect of aerosols on low-level water clouds. CF, COT, LWP and CTH tend to increase with aerosol loading, indicating changes in the cloud structure, while the effective radius of cloud droplets decreases. The ACI is larger at relatively low cloud-top levels, between 900 and 700 hPa. Most of the studied cloud variables were unaffected by the lower-tropospheric stability (LTS), except for the cloud fraction. The spatial distribution of aerosol and cloud parameters and ACI, here defined as the change in CER as a function of aerosol concentration for a fixed LWP, shows positive and statistically significant ACI over the Baltic Sea and Fennoscandia, with the former having the largest values. Small negative ACI values are observed in central–eastern Europe, suggesting that large aerosol concentrations saturate the ACI.

A closure study of aerosol optical properties at a regional background mountainous site in Eastern China

Enhancement of the hygroscopicity parameter kappa of rural aerosols in northern Taiwan by anthropogenic emissions

A field program for the measurement of the physical and chemical properties of aerosols and clouds was conducted at Whiteface Mountain, N.Y., during an 8-week period in June, July, and August 1983. Analysis of two-stage Nuclepore filter samples by proton-induced X-ray emission (PIXE) spectroscopy showed that most (85 to 90%) of the aerosol sulfate was in the accumulation mode (modal radius r - 0.1 μm) and that ≅90% of total sulfate originated southwest of the Whiteface Mountain site. During a typical pollution episode originating in the Midwest, the total aerosol sulfate concentration was 19 pg m −3, or 63 of total dry aerosol, which was - 30 gg m− s. Scavenging of sulfate aerosol by clouds was found to be greater than 95% efficient in clouds of 0.5gm−3 liquid water content. Measured pH values when the air mass trajectories were from the southwest were systematically lower than when the trajectories were from the northwest or northeast, i.e., 3.4 vs 4.4 and 4.8. In the southwest sector water samples, S04−2 and N03− were highly correlated to each other and to free H+, Ca2−, Cl−, Pb, and Ba.

<p>In the recent decade, frequently occurring severe haze events in the North China Plain (NCP) have triggered numerous studies on the underlying formation mechanisms, and the contribution of multiphase chemistry on haze formation becomes one of the focal points. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM<sub>2.5 </sub>pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM<sub>1</sub> and PM<sub>2.5 </sub>show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter k and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 ± 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions.</p><p>

The interactions between clouds, aerosols, and solar and terrestrial radiation play  key roles in the Earth’s Climate. Despite a long history of satellite observations, further high-quality novel observations are needed for atmospheric model evaluation and process studies. It has been recognized that true height-resolved global observations of cloud and aerosol properties are essential for making progress. EarthCARE is an upcoming ESA/JAXA mission scheduled to fly in 2024, focusing on providing these observations.Operating in a sun-synchronous orbit at 393 km altitude with a descending node at 14:00, EarthCARE's payload comprises two innovative active (Atmospheric UV High spectral resolution Lidar - ATLID and Cloud Profiling Doppler Radar - CPR provided by Japan) and two passive (Multi-Spectral Imager - MSI and Broad-Band Radiometer - BBR) instruments. Using these instruments, EarthCARE will provide global profiles of clouds, aerosols, and precipitation properties, along with co-located radiative TOA flux measurements. These atmospheric microphysical properties and associated radiative fluxes will be used to evaluate the representation of aerosols, clouds, and precipitation in weather forecast and climate models, contributing to the improvement of parameterization schemes. The ESA scientific retrieval processors fully exploit the synergy of these observations. EarthCARE will provide twenty-five science (Level 2) products. These products include nadir profiles of cloud, aerosol and precipitation properties along with constructed three-dimensional cloud-aerosol-precipitation domains and associated derived radiative properties, such as heating rates. The final L2 processor compares the forward modeled top-of-atmosphere broad-band radiances and fluxes based on the constructed 3D atmospheric scenes with those measured by the BBR in order to assess and improve the quantitative understanding of the role of clouds and aerosols in the Earth's radiation budget.This presentation will provide an overview of the EarthCARE mission, its data processors and scientific products.

Surface-based observations of polar radiative fluxes are limited to a small number of coastal stations in both polar regions, a few Arctic Ocean drifting ice stations, and a few interior Antarctic stations. Long-term monitoring of the surface and top of the atmosphere radiation balances and the factors that affect them, as well as an analysis of their spatial patterns, will therefore require the use of satellite data. The authors consider whether one can estimate the radiation balance accurately enough for climate change studies, say to within 5 W m/sup -2/. To answer this question they first address how well one can retrieve those geophysical parameters that are used in the estimation of the radiative fluxes: surface temperature and albedo, cloud and aerosol properties, and atmospheric temperature and humidity profiles. The highly reflective snow/ice surface, frequent temperature inversions, persistent ice crystal precipitation, and absence of solar radiation for many months are a few of the factors unique to polar regions that result in ambiguous solutions in the retrieval of cloud, aerosol, and surface properties. The authors present a method of estimating surface and top of the atmosphere radiative fluxes from visible, near-infrared, and thermal satellite data. A procedure is described and applied to AVHRR imagery of the Beaufort Sea during the March-April 1992 Leads Experiment (LEADEX). This combined satellite-in situ data set allows to assess the accuracies with which the radiation balance components can be measured, and provides guidance for future research.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time-delay signature (TDS) and effective bandwidth (EBW) are two key performance indexes to evaluate a chaos signal generated by a laser system including delay-time feedback. In this paper, we propose and simulate a technical scheme to optimize the TDS and EBW of chaotic signal generated by a slave vertical-cavity surface-emitting laser (S-VCSEL) under chaotic optical injection from a master vertical-cavity surface-emitting laser (M-VCSEL), which is subjected to double external-cavity feedback. First, based on the spin-flip model of a VCSEL subjected to two double external-cavity feedback, the time series of two orthogonal polarization components (referred to as X-component (X-PC) and Y-component (Y-PC), respectively) in the M-VCSEL can be obtained. Furthermore, with the help of self-correlation function (SF) analysis method, the TDSs of X-PC and Y-PC can be evaluated. The results show that through selecting suitable system operation parameters, X-PC and Y-PC in the M-VCSEL can simultaneously output chaotic signals with equivalently average intensity and weak TDS. Under optimized operation parameters, the peak values of the SF (σ) of the chaotic signal are 0.20 for X-PC and 0.16 for Y-PC, respectively, and the EBWs of the chaotic signal are 10.72 GHz for X-PC and 10.10 GHz for Y-PC, respectively. The chaotic signals output from the M-VCSEL under optimized operation parameters are injected into the S-VCSEL for further weakening TDS and enhancing EBW. Through examining the evolution rules of TDS and EBW of polarization-resolved chaotic signals in the parameter space composed of injection strength and frequency detuning, the ranges of optimizing injection parameters are determined for achieving two-channel chaotic signals with well suppressed TDS (σ 15 GHz).

A [formula omitted] beat frequency He–Ne laser equipped with bireflectance cavity mirror

We report on switching the intensity correlation or anticorrelation by changing the polarization basis for measuring light that has already propagated through the electromagnetically induced transparency (EIT) medium of the 5S1/2 (F = 2) − 5P1/2 (F ′ = 1) transition of 87Rb atoms. When a linearly polarized laser beam interacts with the EIT medium in the Hanle configuration, selection of the polarization basis after the optical field has already interacted with the atoms was found to significantly affect the intensity-intensity correlation of the two orthogonal polarization components. We compared the second-order correlation functions of two postselected polarization bases (linear and circular), and the polarization basis effect on the second-order correlation functions as a function of the applied magnetic field was numerically calculated using an eight-level atomic model.

This Letter presents a spectral-domain, polarization-sensitive optical coherence tomography (PS-OCT) system, where the light collection from the two arms of the interferometer is performed exclusively using single-mode fibers and couplers, and the two orthogonal polarization components are sequentially detected by a single line camera. Retardance measurements can be affected by polarimetric effects because of fiber birefringence and diattenuation in fiber couplers. This configuration bypasses such issues by performing polarization selection before the collection fiber through the combination of a polarization rotator and a linear polarizer. Retardance calibration is achieved with a Berek compensator. Similar net retardance maps of a birefringent phantom are obtained for two different settings of induced fiber birefringence, effectively demonstrating the tolerance of the configuration to fiber-based disturbances.