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NASA NTRS2020

Optimized Profile Retrievals of Aerosol Microphysical Properties from Simulated Spaceborne Multiwavelength Lidar

This work is an expanded study of one previously published onretrievals of aerosol microphysical properties from space-borne multiwavelengthlidarmeasurements. The earlier studiesand this one weredone in the framework of the NASA Aerosol-Clouds-Ecosystems (now the Aerosol Clouds Convection and Precipitation) NASA mission. The focus here is on the capabilities of a simulated spacebornemultiwavelengthlidar system for retrieving aerosol complex refractive index (m = mr+ imi) and spectral single scattering albedo (SSA(λ)), although other bulk parameters such as effective (reff) radius and particle volume (V) and surface (S) concentrations are also studied. The novelty presented here is the use of recently published, case dependent optimized-constraints on the microphysical retrievals using three backscattering coefficients (β) at 355, 532 and 1064 nm and two extinction coefficients (α) at 355 and 532 nm, typically known as the stand-alone 3β+2α lidar inversion. Case-dependent optimized-constraints (CDOC) limit the ranges of refractive index, both real (mr) and imaginary (mi) parts, and of radii that are permitted in the retrievals. Such constraints are selected directly from the 3β+2α41measurements through an analysis of the relationship between spectral dependence of aerosol extinction-to-backscatter ratios (LR) and the Ångström exponent of extinction. The analyses presented here for different sets ofsize distributions and refractive indices reveal that the direct determination of CDOCareonly feasible for cases where the uncertaintiesin the input optical data areless than 15 %.Forthe same simulated spacebornesystem and yield than in Whiteman et al., (2018), we demonstrated that the use of CDOC as essential for the retrievals of refractive index and also largely improved retrieval of bulk parameters. A discussion of the global representativeness of CDOC is presented using simulated lidar data from a 24-hour satellite track using GEOS model output to initialize the lidar simulator.We found that CDOCare representative of many aerosol mixtures in spite of some outliers (e.g. highly hydrated particles) associatedwith the assumptions of bimodal size distributions and of the same refractive index for fine and coarse modes. Moreover, sensitivity tests performed using synthetic data reveal that retrievals of imaginary refractive index (mi) and SSA are extremely sensitive to β(355).

NASA Aerosol-Clouds-Ecosystems↗
NASA NTRS2021

OMPS LP Version 2.0 Multi-wavelength Aerosol Extinction Coefficient Retrieval Algorithm

The OMPS Limb Profiler (LP) instrument is de-signed to provide high-vertical-resolution ozone and aerosol profiles from measurements of the scattered solar radiation in the 290–1000 nm spectral range. It collected its first Earth limb measurement on 10 January 2012 and continues to provide daily global measurements of ozone and aerosol profiles from the cloud top up to 60 and 40 km, respectively. The relatively high vertical and spatial sampling allow detection and tracking of sporadic events when aerosol particles are injected into the stratosphere, such as volcanic eruptions or pyro cumulonimbus (PyroCb) events. In this paper we discuss the newly released Version 2.0 OMPS multi-wavelength aerosol extinction coefficient retrieval algorithm. The algorithm now produces aerosol extinction profiles at 510, 600, 674, 745, 869 and 997 nm wavelengths. The OMPS LP Version 2.0 data products are compared to the SAGE III/ISS, OSIRIS and CALIPSO missions and shown to be of good quality and suitable for scientific studies. The comparison shows significant improvements in the OMPS LP retrieval performance in the Southern Hemisphere (SH) and at lower altitudes. These improvements arise from use of the longer wavelengths, in contrast with the V1.0 and V1.5 OMPS aerosol retrieval algorithms, which used radiances only at 675 nm and therefore had limited sensitivity in those regions. In particular, the extinction coefficients at 745, 869 and 997 nm are shown to be the most accurate, with relative accuracies and precisions close to 10% and 15%, respectively, while the 675 nm relative accuracy and precision are on the order of 20%. The 510 nm extinction coefficient is shown to have limited accuracy in the SH and is only recommended for use between 20–24 km and only in the Northern Hemisphere. The V2.0 retrieval algorithm has been applied to the complete set of OMPS LP measurements, and the new dataset is publicly available.

OMPS↗
NASA NTRS2021

Adaptive Data Screening for Multi-Angle Polarimetric Aerosol and Ocean Color Remote Sensing Accelerated by Automatic Differentiation

Remote sensing measurements from multi-angle polarimeters (MAPs) contain rich aerosol microphysical property information, and these sensors have been used to perform retrievals in optically complex atmosphere and ocean systems. Previous studies have concluded that, generally, five moderately separated viewing angles in each spectral band provide sufficient accuracy for aerosol property retrievals, with performance gradually saturating as angles are added above that threshold. The Hyper-Angular Rainbow Polarimeter (HARP) instruments provide high angular sampling with a total of 90-120 unique angles across four bands, a capability developed mainly for liquid cloud retrievals. In practice, not all view angles are optimal for aerosol retrievals due to impacts of clouds, sun glint, and other impediments. The many viewing angles of HARP can provide resilience to these effects, if the impacted views are screened from the dataset, as the remaining views may be sufficient for successful analysis. In this study, we discuss how the number of available viewing angles impacts aerosol and ocean color retrieval uncertainties, as applied to two versions of the HARP instrument. AirHARP is an airborne prototype that was deployed in the ACEPOL field campaign, while HARP2 is an instrument in development for the upcoming NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission. Based on synthetic data, we find that a total of 20-30 angles across all bands (i.e. five to eight viewing angles per band) are sufficient to achieve good retrieval performance. Following from this result, we develop an adaptive multi-angle polarimetric data screening (MAPDS) approach to evaluate data quality by comparing measurements with their best-fitted forward model. The FastMAPOL retrieval algorithm is used to retrieve scene geophysical values, by matching an efficient, deep learning-based, radiative transfer emulator to observations. The data screening method effectively identifies and removes viewing angles affected by thin cirrus clouds and other anomalies, improving retrieval performance. This was tested with AirHARP data, and we found agreement with the High Spectral Resolution Lidar-2 (HSRL-2) aerosol data. The data screening approach can be applied to modern satellite remote sensing missions, such as PACE, where a large amount of multi-angle, hyperspectral, polarimetric measurements will be collected.

multi-angle polarimeter↗
NASA NTRS2022

Characterizing Aerosol From Space With the MODerate Resolution Imaging Spectroradiometer (Modis) on the Terra and Aqua Satellites

Aerosols, the small, suspended liquid and solid particles in the atmosphere, have myriad effects on climate, weather, and air quality. When the NASA Earth-Observing System’s (EOS) Terra and Aqua satellites launched in 1999 and 2002, they each included many advanced sensors that have been used for aerosol research. In particular, the MODerate-resolution Imaging Spectroradiometer (MODIS) deployed on both satellites, has provided key data relating to aerosol loading and relative aerosol type on the global scale. Three different algorithms, known as “Dark Target”, “Deep Blue” and “MAIAC”, use different subsets of MODIS measurements and different assumptions to create various products such as Aerosol Optical Depth (AOD), fine mode fraction (FMF) and single scattering albedo (SSA). Although all three derive AOD in cloud-free conditions, each algorithm has different strengths and weaknesses in different areas of the globe and under different conditions. Here, we provide a short summary of each algorithm, description of products, and basic information about downloading and using the products. We also provide some examples of how MODIS aerosol products are used. Finally, we add a quick discussion about how these algorithms and products will continue after MODIS leaves orbit.

MODIS↗
NASA NTRSDate not supplied

Models, in Situ, and Remote Sensing of Aerosols (MIRA) International Working Group

There is a natural partitioning of scientific interest amongst three focus areas of aerosol research: modeling, in situ measurements, and remote sensing observations. The community benefits when these groups interact, with overall benefits towards advancing our understanding of climate, weather, and air quality. To this end, MIRA seeks to foster international collaborations across disciplines and regional boundaries and offers a complementary association with established international working groups. Within the present framework, MIRA has identified four initial focus areas, with opportunities to add more by the working group. One effort advances knowledge of the aerosol lidar ratio for different aerosol compositions and locations to improve backscatter lidar retrievals from satellites and ground-based instruments. Another effort seeks to improve aerosol optical parameters used by climate and radiative transfer models. A third effort focuses on harmonizing aerosol assimilation models with satellite measurement retrievals, and a fourth interest seeks to develop retrievals of aerosol Particulate Matter from remote sensing measurements. The presentation will provide an overview of MIRA and ways for the community to engage.

aerosols↗
NASA NTRSDate not supplied

Simulating Sulfate Aerosol Size in the Hunga Tonga Plume: Comparisons with Observations

Using the NASA GEOS Chemistry Climate Model (CCM) coupled to a detailed sectional aerosol microphysical model, we have simulated the January 2022 Hunga Tonga-Hunga Ha’apai (HTHH) plume. We have developed a version of the Global Modeling Initiative (GMI) chemistry mechanism to include the requisite sulfur chemistry and coupled it to the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics within the GEOS CCM. Our simulations focus on the lifecycle of stratospheric sulfur injected by the eruption–from the oxidation of the injected sulfur dioxide to the nucleation, growth, coagulation, hydration, and eventual settling of the volcanic sulfate aerosol particles. In order to constrain the simulated microphysics, we focus on comparing our model to observations with aerosol size information, namely in-situ particle counter observations and multi-wavelength satellite observations from OMPS-LP and SAGE-III. This eruption provides an interesting test case for our model; both the modeled gas-phase chemistry as well as the modeled aerosol microphysics are perturbed by the massive injection of water that accompanied the primary sulfur emissions from the eruption.

aerosols↗
NASA NTRS2023

The Mars Atmosphere Water Ice Aerosol Climatology by MRO/CRISM: 5 Mars Years of Observations

We use near-infrared spectra returned from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) to provide retrievals of the column-integrated optical depth of water ice aerosols for more than 5 Martian years between Mars Year (MY) 28 at Ls = 112° (27 September 2006) and MY 33 at Ls = 213° (30 August 2016). We have developed a radiative transfer model for this purpose that retrieves aerosol opacity from the water ice aerosol feature near 3.3 μm using CRISM hyperspectral observations for the first time. The resulting retrievals well depict the main features in the water ice aerosol climatology with repeatable patterns every Martian year. The aphelion cloud belt (ACB) is observed between 10°S and 30°N, with peak optical depth around Ls = 90°. Apart from the global dust storm during MY 28, modest interannual variability in the water ice aerosol optical depth is observed in the ACB. The north polar hood is observed at latitudes poleward of 45°N throughout northern spring and summer seasons and reappears in northern winter. The south polar hood is observed in early to mid-southern autumn, reaching latitudes around 60°S, and re-emerging during southern winter between 45°S and 60°S. A lack of water ice aerosols is repeatedly seen in the southern hemisphere throughout southern spring and summer. High optical depth in the ACB is observed over the volcanoes of Olympus Mons, Elysium, and the Tharsis bulge, as well as over Hellas Basin.

Mars↗
NASA NTRSDate not supplied

Airborne High Spectral Resolution Lidar Measurements of Aerosols over Major Metropolitan Areas

NASA Langley Research Center airborne High Spectral Resolution Lidars have participated in several NASA field missions designed to study air quality over major metropolitan regions. Data from these instruments reveal the temporal and spatial variabilities of aerosol distributions over these urban areas, quantify aerosol backscatter, extinction, and depolarization near the surface, and provide additional relevant information regarding aerosol optical thickness, mixed layer height, and aerosol type. We show that measurements of surface PM2.5 concentrations typically are more directly related to coincident near-surface measurements of aerosol extinction than coincident measurements of aerosol optical thickness.

lidar↗
NASA NTRSDate not supplied

AERACEPT (Aerosol Rapid Analysis Combined Entry Probe/sonde Technology): Enabling Technology for Planetary Atmospheric Science Probes

Aerosols –clouds, hazes, and dusts –are a key part of planetary mass and energy balance, but difficult to study remotely. Current technology limits in situ measurements to once-in-a-lifetime flagship missions, which is not enough to characterize such highly dynamic systems. AERACEPT (AErosol Rapid Analysis Combined Entry Probe/sonde Technology) is an early-stage technology allowing asingle aeroshell body toact as both anentry vehicle and aerosol-samplingpassivedescent sonde, using the aeroshell’sown velocityto drive aerosol capture and separationthrough a series of embedded inlets.It takes advantage ofrecently developed thermal protection materials (3D-CC and 3MDCP)in combination withheritage aerosol sampling technologies fromboth planetary and airborne science (high-speed inlets and particle separation). By eliminating the need for heat shield separation, deployable parachutes, ordescent control, AERACEPT reducesthe mass, volume, and complexity ofplanetary aerosol sampling. Verifying AERACEPT’s performance involves modeling interdependencies between the size and geometry of the sampling inlets, the material response of the hypersonic phase of entry, the thermal conditions throughout the probe’s descent, the subsonic flow and particle sampling efficiency, the needed amount of sample, andthe cadence at which the sample can be analyzed. AERACEPT’s current predictions, using the Nephele Venus cloud mission concept (sampling between 63km to 39km, all subsonic) indicates AERACEPT can obtain >20 μL of particle material (roughly 10x the limit of detection) from droplets larger than 0.2 μm, with sample heating limited to <15 K above ambient. Validation testing for the thermal material response model has recently been performed at the UIUC Plasmatron facility, and for the flow and particle capture models is planned for this fall at the Ames Fluid Mechanics Laboratory.

AERACEPT↗
NASA NTRS2026

Satellite Optical Remote Sensing of Clouds and Aerosols: From Particle Single-Scattering and Gaseous Absorption Through Radiative Transfer to Retrieval Products

Clouds and aerosols are fundamental regulators of Earth’s radiation budget and climate system, influencing both solar and terrestrial radiation through scattering, absorption, and emission processes. Accurate characterization of their physical and radiative properties from space requires a rigorous understanding of particle single-scattering, gaseous absorption, and radiative transfer in the atmosphere, as well as reliable inversion methods. This review synthesizes the physical foundations and algorithmic implementations of satellite-based passive optical remote sensing of clouds and aerosols, spanning the ultraviolet to thermal infrared spectral range. Beginning with electromagnetic scattering theory and state-of-the-art methods for computing single-scattering by nonspherical particles and computationally efficient methods for accounting for atmospheric absorption, we discuss the radiative transfer framework underpinning cloud and aerosol retrievals. The connection between single-scattering and multiple-scattering is rigorously formulated. We then summarize operational and research-grade retrieval techniques, including cloud masking and thermodynamic phase determination, CO₂ slicing for cloud-top pressure, the Nakajima-King shortwave bi-spectral, and infrared split-window approaches for cloud optical thickness and effective particle size, inversion algorithms for determining aerosol properties from multi-spectral and/or multi-angle radiometric and polarimetric measurements, and active-passive sensing synergy. Examples of the global cloud and aerosol climatologies are illustrated using observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR). Furthermore, the unique strengths of active remote sensing techniques based on spaceborne lidar observations are briefly elaborated in the context of studying ice clouds composed of randomly and horizontally oriented ice crystals, which is a significant challenge for conventional passive remote sensing techniques. By connecting physical theory to practical retrievals, this review highlights both the maturity of current methodologies and the remaining challenges in reducing uncertainties in particle morphology, vertical structure, absorption, and aerosol-cloud interactions. Furthermore, the impact of artificial intelligence (AI) on atmospheric remote sensing is briefly addressed.

Aerosols↗
NASA NTRS1974

A method to measure the atmospheric aerosol content using ERTS-1 data

The apparent gradual increase of particles in the atmosphere has received considerable attention in recent years due to the possible effect of atmospheric aerosols on the earth's climate. The ERTS-1 satellite offered the opportunity of determining the feasibility of monitoring the atmospheric aerosol content on a global basis, as suggested by theoretical studies, which showed a linear relationship between the upwelling earth atmosphere radiance and the aerosol content. This relationship was investigated at two test sites, San Diego and the Salton Sea, using the MSS radiance data, with ground truth observations of the aerosol content being made with a Volz photometer at the time of the satellite overpasses. Significant results, relating the radiance over water surfaces to the atmospheric aerosol content, have been obtained. The results indicate that the MSS channels, 4, 5 and 6 centered at 0.55, 0.65 and 0.75 micron have comparable sensitivity, and that the aerosol content can be determined within + or - 10% with the assumed measurement errors of the MSS.

Griggs, M.↗
NASA NTRS1976

Atmospheric aerosols: Their Optical Properties and Effects (supplement)

A digest of technical papers is presented. Topics include aerosol size distribution from spectral attenuation with scattering measurements; comparison of extinction and backscattering coefficients for measured and analytic stratospheric aerosol size distributions; using hybrid methods to solve problems in radiative transfer and in multiple scattering; blue moon phenomena; absorption refractive index of aerosols in the Denver pollution cloud; a two dimensional stratospheric model of the dispersion of aerosols from the Fuego volcanic eruption; the variation of the aerosol volume to light scattering coefficient; spectrophone in situ measurements of the absorption of visible light by aerosols; a reassessment of the Krakatoa volcanic turbidity, and multiple scattering in the sky radiance.

Source record↗
NASA NTRS1977

Microphysical processes affecting stratospheric aerosol particles

Physical processes which affect stratospheric aerosol particles include nucleation, condensation, evaporation, coagulation and sedimentation. Quantitative studies of these mechanisms to determine if they can account for some of the observed properties of the aerosol are carried out. It is shown that the altitude range in which nucleation of sulfuric acid-water solution droplets can take place corresponds to that region of the stratosphere where the aerosol is generally found. Since heterogeneous nucleation is the dominant nucleation mechanism, the stratospheric solution droplets are mainly formed on particles which have been mixed up from the troposphere or injected into the stratosphere by volcanoes or meteorites. Particle growth by heteromolecular condensation can account for the observed increase in mixing ratio of large particles in the stratosphere. Coagulation is important in reducing the number of particles smaller than 0.05 micron radius. Growth by condensation, applied to the mixed nature of the particles, shows that available information is consistent with ammonium sulfate being formed by liquid phase chemical reactions in the aerosol particles. The upper altitude limit of the aerosol layer is probably due to the evaporation of sulfuric acid aerosol particles, while the lower limit is due to mixing across the tropopause.

Hamill, P.↗
NASA NTRS1978

Elemental characteristics of aerosols emitted from a coal-fired heating plant

Size differentiated aerosols were collected downstream from a heating plant fueled with eastern coal and analyzed using particle induced X-ray emission technique. Based on aerosol masses collected in various size ranges, the aerosol size distribution is determined to be trimodal, with the three peaks centered at 0.54 microns, 4.0 microns, and 11.0 microns, respectively. Of the various trace elements present in the aerosols, sulphur is the only element that shows very strong concentration in the smallest size group. Iron is strongly concentrated in the 4.0 micron group. Potassium, calcium, and titanium also exhibit stronger concentration in the 4.0 micron group than any other group. Other trace elements - vanadium, chromium, manganese, nickel, copper, and barium - are equally divided between the 0.54 microns and the 4.0 microns groups. Apparently, all of the trace elements - except S - enter aerosols during the initial formation and subsequent condensation phases in the combustion process. Excess concentration of sulphur in the 0.54 microns group can only be accounted for by recondensation of sulphur vapors on the combustion aerosols and gas-to-particle phase conversion of sulfate vapors at the stack top.

Singh, J. J.↗
NASA NTRS1978

Aerosol and nucleation research in support of NASA cloud physics experiments in space

Tasks performed in the development of an ice nucleus generator which, within the facility concept of the ACPL, would provide a test aerosol suitable for a large number and variety of potential experiments are described. The impact of Atmospheric Cloud Physics Laboratory scientific functional requirements on ice nuclei generation and characterization subsystems was established. Potential aerosol generating systems were evaluated with special emphasis on reliability, repeatability and general suitability for application in Spacelab. Possible contamination problems associated with aerosol generation techniques were examined. The ice nucleating abilities of candidate test aerosols were examined and the possible impact of impurities on the nucleating abilities of those aerosols were assessed as well as the relative merits of various methods of aerosol size and number density measurements.

Vali, G.↗
NASA NTRS1978

Properties of the stratospheric aerosol layer studied with a one-dimensional computer model

Aerosol particle effects are often neglected in theoretical studies of stratospheric phenomena. In reality, the particulate matter normally found above the tropopause may influence the terrestrial radiation balance, catalyze heterogeneous chemical interactions, and serve as a tracer of atmospheric motions. The paper proposes a one-dimensional model of the stratospheric aerosol layer, and it is used to compare aerosol theory with observational data. The model considers gaseous sulfur photochemistry and the physical aerosol processes of nucleation, coagulation, sedimentation, and diffusion. Calculations of the effects on the aerosol layer of stratospheric injections of aluminum oxide particles by Space Shuttle engines and of sulfur dioxide molecules by volcanic activity are performed. The relation between measured aerosol variability and changes in stratospheric air temperatures and vertical transport rates are discussed.

Turco, R. P.↗
NASA NTRS1979

A one-dimensional model describing aerosol formation and evolution in the stratosphere. I - Physical processes and mathematical analogs. II - Sensitivity studies and comparison with observations

A new time-dependent one-dimensional model of the stratospheric sulfate aerosol layer is developed. The model treats atmospheric photochemistry and aerosol physics in detail and includes the interaction between gases and particles explicitly. It is shown that the numerical algorithms used in the model are quite precise. Sensitivity studies and comparison with observations are made. The simulated aerosol physics generates a particle layer with most of the observed properties. The sensitivity of the calculated properties to changes in a large number of aeronomic aerosol parameters is discussed in some detail. The sensitivity analysis reveals areas where the aerosol model is most uncertain. New observations are suggested that might help resolve important questions about the origin of the stratospheric aerosol layer.

Turco, R. P.↗
NASA NTRS1980

Atmospheric aerosols and climate

The impact of terrestrial aerosols on the earth's climate and solar and infrared radiation budget are considered. Attention is given to the optical properties of aerosols, that is, optical depth, the single scattering albedo, and the asymmetry parameter, and to the relation between the optical depth and surface temperature for tropospheric and stratospheric aerosols. Also considered are experimental projects to determine the single scattering albedo, as well as the optical properties of natural aerosols such as sea salt, soil, and sulfates, and their variability. In addition, the impact of volcanic activity and the question of whether aerosols cause climatic warming or cooling are discussed, and the available observational evidence linking aerosols and climate is reviewed.

Toon, O. B.↗