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Sea salt aerosol (SSA) significantly affects the atmospheric albedo, the radiation balance of the Earth, and has consequences for global and regional climate. There is currently no reliable radiative large-scale aerosol model of the marine and coastal atmosphere. All these lead to uncertainties in radiation boxes, short-term weather forecasts, and climate models and to uncertainties in interpretation of the lidar return data obtained and at the development of new lidar systems. The MaexPro model is shown to calculate adequately the aerosol extinction coefficients $\varepsilon (\lambda)$ and the concentration of SSA particles for different wind regimes, fetches, and humidity. The calculated $\varepsilon (\lambda)$ profiles well agree with the experimental data and with calculations using Advanced Navy Aerosol Model (ANAM) and MODTRAN codes. A new approach in studying the influence of the meteorological parameters on spectral $\varepsilon (\lambda)$ gives a new explanation for previously obtained conflicting experimental data, namely, to the effect of decreasing transparency, manifested in the coastal zone, and makes it possible indirectly to account for the type of air mass (marine or coastal). It is shown that the particle size distribution functions and spectral $\varepsilon (\lambda)$ , calculated using the model with the input parameters corresponding most closely to the conditions of experiment, agree well with observations, using OLAF transmissometer, and calculations using MODTRAN code and the experimental results receiving the same conditions of observations (numerical or field). The results obtained are of interest both in the calculations of radiative characteristics of the atmosphere and in interpretation of the lidar return data and calibration signal when developing new lidar systems.

A simple method that reproducibly creates validation/reference materials for comparison of methods that measure the carbonaceous content of atmospheric particulate matter deposited on filter media at concentrations relevant to atmospheric levels has been developed and evaluated. Commonly used methods to determine the major carbonaceous components of particles collected on filters include optical attenuation for “Black” (BC) and “Brown” (BrC) carbon, thermal-optical analysis (TOA) for “Elemental” (EC) and “Organic” (OC) carbon, and total combustion for “Total” carbon (TC). The new method uses a commercial inkjet printer to deposit ink containing both organic and inorganic components onto filter substrates at programmable print densities (print levels, as specified by the printer–software combination). A variety of filter media were evaluated. The optical attenuation (ATN) of the deposited sample was determined at 880 nm and 370 nm. Reproducibility or precision (as standard deviation or in percent as coefficient of variation) in ATN for Teflon-coated glass-fiber, Teflon, and cellulose substrates was better than 5%. Reproducibility for other substrates was better than 15%. EC and OC measured on quartz-fiber filters (QFF) compared to ATN measured at 880 nm and 370 nm on either QFF or Teflon-coated glass-fiber yielded R2 > 0.92 and >0.97, respectively. Four independent laboratories participated in a round robin study together with the reference laboratory. The propagated standard deviation among the five groups across all print levels was

In this study, LED based mini-lidar to install into Mars rover has been developed. Its aim is to capture the dynamics of dust twister called “Dust Devil”. For Mars rover installation, there are large restrictions of 10cm3 optics size, 1kg weight, 1W power consumption, etc. We have developed its concept model, and conducted the demonstration experiment. The LED mini-lidar is equipped with a high speed photon counter, of which data sampling interval is 1ns, corresponding to a range bin of 0.15m, and a high repetition pulsed LED beam, of which repetition frequency is greater than 500kHz. Transmitting optical pulse power was

Human activities are changing the composition of Earth's atmosphere, and thus influence the air quality. In that respect, one of the most important elements of the atmosphere are aerosols. They play a fundamental role in physical and chemical processes affecting both air quality and regional and global climate. Aerosols affect the Earth’s radiative balance both in the cloud-free and the cloudy atmosphere. These so-called direct and indirect aerosol effects which depend on the chemical and physical aerosol properties still represent an uncertain factor in estimates about climate change. The direct effect of aerosols is related with scattering and absorption of solar radiation, and as a consequence, reduction of the amount of radiation reaching the surface (e.g. IPCC 2001). In case of indirect effects, we distinguish the first and the second one. Aerosols act as cloud condensation nuclei (CCN), modifying the optical and radiative properties of clouds, e.g. albedo. This is known as the first indirect effect (Twomey, 1977). The second indirect effect is related to the shift in the cloud droplet spectrum resulting from the nucleation. It is seen by a decrease in precipitation and an increase in cloud lifetime (e.g. Charlson et al., 1992). The best parameters that quantify the direct aerosol effect are the aerosol extinction, linked also to atmospheric visibility, and the aerosol optical thickness. The aerosol extinction reveals how aerosols attenuate the solar radiation in relation to a given distance (e.g. per km); the aerosol optical thickness is the extinction integrated over a whole column of atmosphere (usually in the vertical from the surface to the top of the atmosphere). Aerosol extinction can be derived from in-situ measurements (aerosol counters, impactors) or from path-integrated measurements (transmissometer); aerosol optical thickness is usually obtained from sun photometer measurements. Nowadays, in the era of AERONET, information about the aerosol optical thickness (AOT) is available online for nearly 400 sites in the world; only in Europe the number of AERONET station is more than 80. Hence, more and more researchers try to find a relationship between the aerosol optical thickness (AOT) and PM10 (particulate matter with an aerodynamic diameter of less than 10 um) in order to use it as an indicator of air quality. It should be emphasized that the aerosol optical thickness values represent vertical column-integrated properties whereas the PM10 data are the “surface” data. This kind of comparison is justified in the well-mixed boundary layer. Therefore not always both parameters are well correlated. Nevertheless, such a relationship between (AOT) and PM10 would be useful in air quality monitoring. The variation of the extinction coefficient with wavelength can be presented as a power law function with a constant (related to the power factor) known as the Angstrom coefficient.

Random scattering and absorption of light by tiny particles in aerosols, like fog, reduce situational awareness and cause unacceptable down-time for critical systems or operations. Computationally efficient light transport models are desired for computational imaging to improve remote sensing capabilities in degraded optical environments. To this end, we have developed a model based on a weak angular dependence approximation to the Boltzmann or radiative transfer equation that appears to be applicable in both the moderate and highly scattering regimes, thereby covering the applicability domain of both the small angle and diffusion approximations. An analytic solution was derived and validated using experimental data acquired at the Sandia National Laboratory Fog Chamber facility. The evolution of the fog particle density and size distribution were measured and used to determine macroscopic absorption and scattering properties using Mie theory. A three-band (0.532, 1.55, and 9.68 µm) transmissometer with lock-in amplifiers enabled changes in fog density of over an order of magnitude to be measured due to the increased transmission at higher wavelengths, covering both the moderate and highly scattering regimes. The meteorological optical range parameter is shown to be about 0.6 times the transport mean free path length, suggesting an improved physical interpretation of this parameter.

We describe how reference filter characteristics (unexposed weights) can influence instrument-reported attenuation (thereby black carbon concentrations) using the OT21 (SootScan Optical Transmissometer), in the case of Emfab filters. Reference filters (unexposed filters) with higher unexposed weights (pre-weights) compared to that of sample filters are found to reduce the instrument-reported aerosol sample attenuation measurement; reference filters weighing less than the sample filter results in the reverse outcome. This sensitivity can lead to significant under- and over-estimation by the instrument (estimated mean absolute error: ∼ 10 and 16 ATN units for infrared (IR) and ultraviolet (UV) channels, respectively, in our tests, which represent 44% and 15% errors, respectively). We find that the error is linear with respect to difference in the unexposed filter weights of the sample and reference filters. We report two equations (one for IR, one for UV) for correcting the Transmissometer output based on experimental data, which allow use of any unexposed Emfab filter as the reference filter; application of correction parameters to data here reduces the error to 2 and 3 ATN units, respectively, for IR and UV (10% and 3% errors, respectively). The research leading to these results received funding from the European Research Council under ERC Grant Agreement number 336167 for the CHAI Project. We are thankful to field staff of CHAI project and Sri Ramachandra University, Chennai for their collaboration throughout the monitoring and measurements. Filter weight data is available from the corresponding author on request.

Aerosol chemistry measurements were performed during the routine monitoring periods in the urban atmosphere of Gwangju, Korea. Routine aerosol monitoring was carried out every sixth day in order to investigate the dependence of domestic sources and air mass transport characteristics on physicochemical and optical properties of atmospheric aerosol. Aerosol optical properties; atmospheric extinction and scattering coefficients were also measured continuously with a transmissometer and a nephelometer, respectively in order to investigate the causes of visibility impairment. Prevailing atmospheric condition was classified into four categories; one affected by stagnant condition (D), one affected by continental and domestic aerosols (CD), one affected by marine and domestic aerosols (MD), and one affected by continental, marine and domestic aerosols (CMD). Atmospheric condition type was further classified into thirteen sub-categories with the occurrences of episodic events such as Asian dust storm, biomass burning, and airborne pollen. The air mass types of D, CD, MD, and CMD were observed to be 11, 18, 43, and 78 events out of total 150 events, respectively. The fine mass concentration increased under continental air mass types. The average fine mass concentration of 23.0 ± 8.6 μg m−3 for CD type was slightly larger than that of 20.7 ± 5.2 μg m−3 for CMD type. Both of them were higher than that for D (18.9 ± 4.5 μg m−3) type. Increments of the fine mass concentrations for Asian dust storm (A) and Biomass-burning (B) events ranged from 141 to 151% and from 152 to 160% compared to those for D and CD types, respectively. The increments in the mass concentrations of nitrate, OC, EC, and BC for CD and CMD types in comparison with D air mass type were calculated to be approximately 17, 6, 8, and 22%, respectively. The mean mass extinction efficiency of PM10 was relatively higher in D (3.6 ± 1.6 m2 g−1) type and B events (4.1 ± 1.5 m2 g−1), but it was the lowest in MD air mass type. The aerosols observed in Gwangju were found to be influenced by the continental aerosol during the A events. Aerosol of CMD air mass type caused mainly poor visibility. The visibility reduction of Gwangju was influenced by the increase of carbonaceous particles under both domestically stagnant condition and air mass pathway from the continent. And ammonium sulfates and ammonium nitrates contributed the largest in CMD air mass type.

In this paper investigation of a Z-bench transmissometer to accommodate a 3D printed back-to-back horn is presented. Altering the performance of a standard Z-bench by introducing a 3-D printed 300 GHz back-to-back horn system requires a change in the Z-bench configuration. Such changes have been performed and investigated, whilst results of the altered system are demonstrated. The measurement campaign has demonstrated that a Z-bench, with back-to-back horn in operation can lead to an enhancement in the system performance. Additionally, it is demonstrated that 3-D printing can be used to prototype complex devices, such as horns, for sub-THz techniques.

A maritime environment presents a complex problem for propagating a laser through its turbulent nature. The environment includes standard aerosols, sea surface spray, and atmospheric turbulence when propagating along horizontal, vertical, or slant angled paths. Atmospheric measurements of the turbulence structure (Cn 2) and Fried’s coherence length (r0) were taken in a maritime environment using an IR Laser beacon at 1.06 microns mounted on an unmanned aerial system (UAS) at varying distances and slant angles using a Differential Image Motion Monitor (DIMM) and Wide-Angle Teleradiometric Transmissometer (WATT). The DIMM measured the coherence length, r0 and atmospheric turbulence strength, Cn 2 from the IR Laser beacon source as it propagated through the atmosphere. The WATT measured the transmissivity of the IR Laser beacon through the atmosphere.

This paper presents a chemical characterization of fine particulate matter (PM25) in air masses passing through Thohoyandou and further determines their sources. PM25 samples were collected and quantified using the gravimetric method. X-ray fluorescence, smoke stain reflectometer, optical transmissometer and scanning electron microscopy - energy dispersive X-Ray spectroscopy were used to determine the chemical and morphological composition of the particulate matter. The source apportionment was done using principal component analysis while the HYSPLIT model was used to depict the long-range transport clusters. The mean of concentrations of PM25, soot, black carbon and UVPM were 10.9 ug/m³, 0.69x10-5 m-1, 1.22 μg/m³ and 1.40 μg/m³, respectively. A total of 24 elements were detected in the PM25 with Pd, Sn, Sb, Mg, Al, and Si being the dominant elements. SEM-EDS have shown the presence of irregular, flat and spherical particles which is associated with crustal material and industrial emissions. Source apportionment analysis revealed six major sources of PM25 in Thohoyandou namely, crustal materials, industrial emissions, vehicular emissions, urban emissions, fossil fuel combustion and fugitive-Pd. Air parcels that pass through Thohoyandou were clustered into four groupings. The major pathways were from the SW Indian Ocean, Atlantic Ocean, and inland trajectories. Clusters from the ocean are associated with low concentration, while inland clusters are associated with high concentration of PM25. The PM25 levels occasionally exceeded the daily WHO guideline (25 μg/m³) in Thohoyandou and the sources of PM25 extend beyond the borders. This study recommends that further studies need to be carried out to assess the health impacts of PM25 in Thohoyandou.

This best practice document was developed under the Rolling Deck to Repository project by a small working group comprised of the document authors. These recommendations are specifically for transmissometers installed within a research vessel’s (RVs) scientific flow-through sea water (underway) system. They are not focused on transmissometers used for CTD/Rosette casts, though some information may be applicable. All underway transmissometers in the academic research fleet presently are WET Labs (henceforth Sea-Bird) C-Stars. Review of available sensors shows this will continue to be the most available and adaptive device. The Goal of this document is to provide best practices for operators that will improve access to transmissometer data and metadata to support routine data quality evaluation and science application. Published Refereed Current 14.A TRL 9 Actual system "mission proven" through successful mission operations (ground or space) Best Practice Manual (incl. handbook, guide, cookbook etc)

Suspended particulate matters (SPM) in coastal waters were investigated with an approach combining suspended particulate matter concentrations (SPMCs) measured by an optical backscatter sensor (OBS), particle size distributions measured by a laser in situ scattering transmissometer (LISST), and the fractal theory. The aim was to investigate whether changes in the fractal dimension indicate variations in the SPM composition. The method relies on the fractal theory that relates the floc excess density ∆ρ to the ratio between floc size Df and primary particle size Dp as follows: Δρ = (ρp – ρw)[Df/Dp]nf − 3. The best-fit fractal dimension nf was determined by matching the OBS-derived SPMC and the SPMC calculated from the LISST assuming fixed primary particle size and density. This method was applied to measurements from four tidal cycles characterized by different organic matter (OM) contents. Spurious data caused by schlieren were identified and discarded. The fractal dimension was relatively homogeneous over each tidal cycle except one where a strong apparent decrease in the fractal dimension was related to an important episode of sediment resuspension. This apparent decrease could result from the limit of the LISST to measure valid data when SPMC is high enough to induce multiple scattering and/or a change in the SPM population in suspension. Results showed also strong differences between the tidal cycles such as an increase of the fractal dimension with increasing OM content. Sensitivity analyses of fractal dimension and settling velocity were performed on major parameters: primary particle size and density, slope of the OBS calibration relationship, and optical model of inversion of the LISST. Results showed that the assumed primary particle size and the OBS calibration relationship significantly affect fractal dimension and settling velocity calculations.

A laser transmissometer is regarded as a promising visibility meter used in airports around the world. Based on the particle size distributions of rain and fog, we have numerically simulated the transmissions of photons through rain and fog using the Monte-Carlo method. The visibility errors induced by the single and multiple-scattering effects are discussed for different configurations of the optical system, considering the particle size distributions of the rain and fog. The simulation results show that the single scattering is the main factor introducing the visibility errors, and the multiple-scattering effect may be not negligible, especially for the low-visibility atmosphere, e.g., fog. Our simulation results further reveal that reducing the receiver aperture and increasing the baseline length of the optical system may effectively suppress the visibility errors caused by the scattering effects, which gives us important considerations on the design of the optical systems of the laser transmissometer.

All modes of surface transportation can be disrupted by visibility degradation caused by airborne volcanic ash. Despite much qualitative evidence of low visibility on roads following historical eruptions worldwide, there have been few detailed studies that have attempted to quantify relationships between visibility conditions and observed impacts on network functionality and safety. In the absence of detailed field observations, such gaps in knowledge can be filled by developing empirical datasets through laboratory investigations. Here, we use historical eruption data to estimate a plausible range of ash-settling rates and ash particle characteristics for Auckland city, New Zealand. We propose and implement a new experimental set-up in controlled laboratory conditions, which incorporates a dual-pass transmissometer and solid aerosol generator, to reproduce these ash-settling rates and calculate visual ranges through the associated airborne volcanic ash. Our findings demonstrate that visibility is most impaired for high ash-settling rates (i.e. > 500 g m−2 h−1) and particle size is deemed the most influential ash characteristic for visual range. For the samples tested (all

This paper proposes a novel alignment system based on the measurement of optical path using a light beam scanning mode in a transmissometer. The system controls both the probe beam and the receivin...

Principles of constructing an optical sensor for measuring a meteorological visibility range are considered. A new relationship for the visibility range determination is obtained. An optical scheme of the meteorological visibility range sensor is described and characteristics of the new sensor are presented.

Optical carbon analysis measurements were performed on Teflon filters from the Federal Reference Method (FRM) network in New York over the period 2015–2019. The optical measurements were performed using an inline Magee Scientific OT21 transmissometer coupled to the robotic weighing system (RWS) that measures PM2.5 mass gravimetrically. Light attenuation from the Teflon filters was compared to elemental carbon (EC) measured on quartz-fiber filters across 8 locations from the Chemical Speciation Network (CSN). The coefficients of determination (R2) were highest at urban locations (where EC concentrations were highest) and lowest at the remote rural sites. The regression slopes provided mass absorption cross-sections (MAC) from 9.12 to 11.0 m2/g at 880 nm which are in agreement with literature values. Transmissometer measurements of black carbon (BC) were also compared to Aethalometer® BC as well as EC from a semi-continuous Sunset Laboratory Inc. OCEC carbon analyzer at two locations. BC estimated from the optical measurements decreased by approximately 30 % over the 2015–2019 period consistent with the replacement of older heavy duty diesel (HDD) vehicles. BC was highest across urban locations and lowest in the rural sites. At the urban locations BC was generally highest in winter and summer, whereas at the rural sites BC was highest in summer. Both locations showed the lowest BC was in spring. Weekday vs weekend analysis revealed BC was on average lower at the weekend by approximately 20 % in NYC and 9–16 % in upstate locations.

To explore the controlling factors for mass absorption efficiency (MAE) of elemental carbon (EC) in fine particles (PM2.5), major chemical compositions in size-segregated aerosol samples and bulk PM2.5 samples and light absorption coefficient (bap) of PM2.5 samples under dry condition were measured during four seasons in an urban environment in Guangzhou of south China. On seasonal average, absorption Angstrom exponent (AAE) in the wavelength range of 370–880 nm measured by a transmissometer or in the range of 370–950 nm measured by an aethalometer ranged from 0.95 to 1.02 and from 1.01 to 1.14, respectively. The estimated EC MAE at 550 nm in PM2.5 were 10.1 ± 1.0, 8.9 ± 0.7, 9.1 ± 1.0 and 9.1 ± 0.7 m2 g−1 in spring, summer, autumn and winter, respectively, which were evidently higher than the value of 7.5 m2 g−1 for “pure EC”. More than 61% of EC mass in PM2.1 was distributed in the droplet mode (0.43–2.1 μm), which should be related to hygroscopic growth of aged EC particle as well as external mixing with coating materials. No significant correlations were found between EC MAE and mass fraction of EC or mass ratio of (SO42-+NO3−+OC)/EC in the droplet mode. The deliquescence of aerosol was primarily determined by NH4NO3, and the high EC MAE was mainly related to high nitrate mass concentration and positive ΔRH (ambient relative humidity minus deliquescence relative humidity of NH4NO3).

Optical instruments that measure the particulate beam attenuation and backscattering coefficients have been used widely to estimate suspended particulate mass (SPM) in various environments. In pycnoclines, density differences can cause significant forward light scattering (schlieren). This fluid-induced scattering increases the measured by instruments with small acceptance angles that are open to the environment (not pumped). When the 1-m bin-averaged buoyancy frequency (N) exceeds 0.05 s−1 in the Columbia River estuary, inaccurate estimates of are observed by such instruments. The schlieren phenomena do not affect the and measured with a pumped transmissometer or a backscattering meter. It follows that to obtain a reliable proxy of SPM in a highly stratified environment, the use of either a backscattering sensor or a pumped transmissometer is required.

Our mechanistic understanding of the processes controlling the ocean's biological pump is limited, in part, by our lack of observational data at appropriate timescales. The “optical sediment trap” (OST) technique utilizes a transmissometer on a quasi-Lagrangian platform to collect sedimenting particles. This method could help fill the observational gap by providing autonomous measurements of particulate carbon (PC) flux in the upper mesopelagic ocean at high spatiotemporal resolution. Here, we used a combination of field measurements and laboratory experiments to test hydrodynamic and zooplankton-swimmer effects on the OST method, and we quantitatively calibrated this method against PC flux measured directly in same-platform, neutrally buoyant sediment traps (NBSTs) during 5 monthly cruises at the Bermuda Atlantic Time-series Study (BATS) site. We found a well-correlated, positive relationship (R2=0.66, n=15) between the OST proxy, and the PC flux measured directly using NBSTs. Laboratory tests showed that scattering of light from multiple particles between the source and detector was unlikely to affect OST proxy results. We found that the carbon-specific attenuance of sinking particles was larger than literature values for smaller, suspended particles in the ocean, and consistent with variable carbon: size relationships reported in the literature for sinking particles. We also found evidence for variability in PC flux at high spatiotemporal resolution. Our results are consistent with the literature on particle carbon content and optical properties in the ocean, and support more widespread use of the OST proxy, with proper site-specific and platform-specific calibration, to better understand variability in the ocean biological pump.

Quantification of visible ambient plume opacity measurements using compact and smartphone digital still cameras (DSCs), and Digital Optical Method (DOM) are evaluated here. A new camera calibration method that employs exposure value compensation in place of exposure time or radiance of a surface is described and evaluated. This new and simpler method allows an automatic exposure controlled DSC to be calibrated using its own DSC settings. We also test the use of color in place of grayscale pixel values (PVs) to measure opacity. Finally, we determine the uncertainty of the opacity measurements. Two compact DSCs and two smartphone DSCs are tested to measure plume opacity values of smoke generated with an outdoor smoke generator, in comparison to the plume opacity values measured with an in-stack transmissometer. Results show that: 1) smartphone DSCs, like compact DSCs, can pass opacity measurement requirements set by USEPA; 2) the new simpler calibration method generates values within 5% in opacity on average compared to opacity values from the reference transmissometer; 3) non-uniform background color dominates the uncertainty of opacity measurements, and such uncertainty is wavelength dependent; and 4) the diffusive scattering parameter, used in DOM’s transmission model, is lower for black plumes than white plumes, and is wavelength dependent. These results improve our understanding of using DSCs and the parameters that introduce uncertainty to DOM to improve measurements of plume opacity that can improve protection of human health.

With the rising standards and increasing quality of life, it has become a need to measure visibility and optical parameters for general purposes such as to predict the safe speed limit for vehicles and define the safe working conditions in factories etc. Traditional visiometers are too costly to be deployed in large numbers. However the advancement in computation technology leads to low-cost visibility measurement techniques such as calculation of different parameters that affect visibility and to create mathematical models of the channel. Modeling for visibility measurement requires proper understanding of all the optical parameters of a given entity. Also, measurement of a single parameter using low-cost data acquisition system and electronic components is insufficient to define visibility. Different paradigms need to be examined in order to unmask all the aspects of the entity under consideration. Many efforts have been made to study factors influencing visibility but they encountered various problems during measurements in real time. So to parameterize different characteristics of the medium, a technique is proposed which can be implemented in real time. The objective of this work is to list the various parameters whose value can be added according to the need for low-cost visibility measurement. The indexed parameters are unaccustomed to the literature of optical density and visibility measurement. Furthermore, the paper contains description of the system, principle of its operation and some results of the field test conducted for the purpose.

Optical countermeasures are widely used nowadays and quite often a laser is used as the optical source. Unfortunately such a laser beam can become severely distorted by optical turbulence when propagating through the atmosphere, resulting in effects such as beam spreading, beam wander, irradiance fluctuations, and loss of spatial coherence. These effects can be (partially) overcome using knowledge of the atmospheric conditions, as well as techniques to correct for amplitude and phase distortions. Our research focuses on the characterization of the atmospheric conditions, using adaptive optics, an in-house developed multi-aperture transmissometer, as well as a plenoptic sensor using phase distortion algorithms to compensate for effects caused by (strong) turbulence conditions.

This paper presents submillimeter wave (SMMW) propagation and meteorological measurements obtained using the TAIPAS system operated continuously over a period from August 15 to August 30, 2018. The TAIPAS system is a 320-340 GHz, coherent, line-of-sight transmissometer which can be used to measure propagated power and spectral properties of directional electromagnetic (EM) waves at SMMW frequencies at and around the 325.153 GHz water vapor absorption line.The overall goal of the TAIPAS project is to develop a comprehensive predictive model relevant for atmospheric propagation in the range of ~1 MHz - 3000 GHz.

This research and development effort designs and tests new multi-laser transmissometer algorithms and hardware for ocean optical classification and autonomous biofouling detection. The system expands the collection of inherent optical properties and enables in-situ wavelength optimization for future optical communication links. Undersea testing succeeded and was contingent on several accomplishments, including developing robust algorithms, integrating opto-electronics within a custom chassis, and engineering a handheld-sized pressure vessel suitable for diverse field experimentation. The project verifies the feasibility of key enablers—autonomy, environmental classification, biofouling detection, and laser propagation—for remote undersea platforms with low size, weight, and power.

In this study, we developed a method for calibrating forward scatter meters (FSMs) against transmissometers for measuring visibility under laboratory conditions, and we designed and constructed a novel fog chamber for calibrating FSMs indoors. The fog chamber was used to simulate a controlled visibility environment, and a transmissometer was installed on both ends of the fog chamber as the standard. The developed method involved a comparison of the FSMs and transmissometer in a group of fog events. FSMs were installed on both sides of the optical path between the transmitter and receiver of the transmissometer. The chamber door was closed, and, after creating fog to simulate low-visibility conditions, measurements were collected from the FSMs and transmissometer every minute while the fog dissipated very slowly. The measurement errors of the FSM could then be calculated. To evaluate this method, tests were conducted in the fog chamber, and the results show that the fog chamber could simulate visibility from 10 m to 10 000 m, while the FSMs could only be calibrated below a visibility of 1 500 m due to the baseline of the transmissometer. The fog homogeneity was controlled within 1.2% or less, and the stability was limited to 5% per 30 min. These parameters are reasonably homogeneous and stable for FSM - transmissometer comparison. Three PWD22 FSMs were calibrated using this method, and the calibration uncertainties were estimated to be in the range of 7.8% to 9.2%.

Southeast Asia is one of the major regions of biomass burning in the world. To investigate the light absorption properties of carbonaceous aerosols produced from biomass burning, mass concentrations of PM2.5 and its major chemical compositions were obtained by filter sampling, and aerosol absorption coefficient (bap) at 370 nm (bap-370nm) and at 880 nm (bap-880nm) were synchronously determined for the sampled filters using a transmissometer in urban Chiang Mai of Northern Thailand during the dry season in 2019. On campaign average, the reconstructed PM2.5 mass from the measured chemical components accounted for 99% of the measured PM2.5 mass, in which organic matters (OM) accounted for 64 ± 10%. Hardwood burning was identified as the dominant source of carbonaceous aerosols. The measured aerosol absorption Angstrom exponent (AAE) at 370–880 nm (AAE370–880nm) was 1.71 ± 0.24. Mass absorption efficiency (MAE) of elemental carbon (EC) and organic carbon (OC) was estimated using a multiple linear regression model between bap and mass concentrations of EC and OC, resulting in campaign-average values of 8.11 m2 g−1 and 0.24 m2 g−1 at 880 nm and 21.06 m2 g−1 and 2.57 m2 g−1 at 370 nm, respectively, which were evidently larger than those in other cities worldwide. The contributions of EC to bap in 370–880 nm spectrum region ranged from 49 ± 5% to 79 ± 3%, and those of OC ranged from 51 ± 5% to 21 ± 3%. Results from this study suggested a potentially significant impact of carbonaceous aerosols on direct radiative forcings in the dry season over Southeast Asia and downwind regions.

According to Koschmieder's law, a mathematical model of contrast between a single black object and the sky background is established. Based on this principle, we built a black target visiometer system using a photograph of a black object taken with an industrial camera, that has a relatively simple structure and automated operation. In this study, three commercial visibility instruments–a forward scatter meter (CJB-3A) and two atmospheric transmission meters (LT31, VM100)–were compared to the black target visiometer system. Our results show that, within visibility ranges of up to 10 km, 1) all of the instruments agree well at low visibility and agree poorly at a visibility exceeding 5 km; 2) the forward scattering instrument has high bias at low visibility because particle absorption is not included; and 3) the best agreement with the black target method was obtained with the simple transmissometer rather than the forward scatter instrument or the hybrid transmissometer for a visibility range of up to 10 km.

The calculated results of extinction characteristics of visible and infrared radiation for large semi-transparent crystals are obtained by hybrid technique, which is a combination of the geometric optics method and the physical optics method. Energy and polarization characteristics of the radiation extinction in terms of the elements of the extinction matrix for individual large crystals and ensemble of crystals are discussed. Influences of particle shapes, aspect ratios, parameters of size distribution, complex refractive index, orientation of crystals, wavelength, and the polarization state of an incident radiation on the extinction are illustrated. It is shown that the most expressive and stable features of energy and polarization characteristics of the extinction are observed in the midinfrared region, despite the fact that the ice particles significantly absorb the radiant energy of this spectrum. It is demonstrated that the polarized extinction characteristics can reach several tens of percent at IR wavelengths. For the large crystals, the conditions of occurrence of the spectral behavior of the extinction coefficient in the visible, near-IR, and mid-IR wavelength ranges are determined.

Cho, J.H.; Son, Y.B.; Shin D.-H.; Moh, T.J.; Jang S.; Lee S.Y.; Lim D.G., and Kum B.C., 2020. Changes in underwater visibility due to turbidity associated with Typhoon Soulik. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 417-421. Coconut Creek (Florida), ISSN 0749-0208.Changes of visibility in the water column off the southern coast of Korea due to the effects of Typhoon Soulik (Aug. 22–23, 2018; 955 hPa; maximum wind speed, 40 m/s) were investigated. The beam attenuation coefficient (BAC) was measured using a transmissometer (C-Star; Wet Labs, Inc.), and visibility range was calculated using the conversion method employed by the US Navy. For comparison and verification of the data, a conductivity–depth–temperature (CTD) probe (SBE19 Plus; Sea-Bird Scientific) equipped with optical backscatter and fluorescence sensors was deployed simultaneously with the transmissometer. The Secchi depth was also estimated during each cast to improve accuracy. The Secchi depth deviated by up to 20% from the calculated visibility range. Additionally, during continuous observation of BAC from the seafloor upward, a light source (color temperature: 6,500 K) was installed on a 5-m bar with length markings, and a video camera recorded changes in visibility. Daily Geostationary Ocean Color Imager (GOCI) satellite data were used to identify changes in surface visibility in the study area. Before the typhoon, the visibility in the water column was in the range 25–30 m. Near the seafloor, visibility approached 0 m due to a 3–6-m turbidity current. The visibility distance was significantly shorter in the bottom layers based on video images. Four days after Typhoon Soulik had passed over the Korean Peninsula, the visibility was in the range 2.6–9.0 m in the upper layers of the water column, increasing gradually to 11 m in the middle layers. The size of the turbid bottom current did not differ significantly between observations before and after the typhoon. Surface visibility calculated from satellite data also decreased by 20–30% compared to that before the typhoon.