Wrapping of carbon nanotubes (CNTs) by single-stranded DNA (ssDNA) was found to be sequence-dependent. A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that ...self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the smaller diameter and metallic tubes, whereas late fractions are enriched in the larger diameter and semiconducting tubes.
The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) is an eight-band (355, 380, 445, 470, 555, 660, 865, 935 nm) pushbroom camera, measuring polarization in the 470, 660, and 865 nm bands, ...mounted on a gimbal to acquire multiangular observations over a ±67° along-track range. The instrument has been flying aboard the NASA ER-2 high altitude aircraft since October 2010. AirMSPI employs a photoelastic modulator-based polarimetric imaging technique to enable accurate measurements of the degree and angle of linear polarization in addition to spectral intensity. A description of the AirMSPI instrument and ground data processing approach is presented. Example images of clear, hazy, and cloudy scenes over the Pacific Ocean and California land targets obtained during flights between 2010 and 2012 are shown, and quantitative interpretations of the data using vector radiative transfer theory and scene models are provided to highlight the instrument's capabilities for determining aerosol and cloud microphysical properties and cloud 3-D spatial distributions. Sensitivity to parameters such as aerosol particle size distribution, ocean surface wind speed and direction, cloud-top and cloud-base height, and cloud droplet size is discussed. AirMSPI represents a major step toward realization of the type of imaging polarimeter envisioned to fly on NASA's Aerosol-Cloud-Ecosystem (ACE) mission in the next decade.
Anthopogenic savanna fires in sub‐Saharan Africa emit smoke that affects cloudiness in the region. We measured the cloud response to fire aerosols using aerosol data from the Multi‐angle Imaging ...SpectroRadiometer (MISR) and cloud fraction data from the morning and afternoon overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. Considering the same cloud scene from the morning and afternoon satellite observations allowed us to observe the temporal relationship between clouds and aerosols. Level 2 data from 35 individual scenes during the fire season (December) between 2006 and 2010 were analyzed to quantify changes in MODIS cloud fraction from morning (10:30 A.M. local time) to afternoon (1:30 P.M. local time) in the presence of different morning aerosol burdens (from MISR). We controlled for the local meteorology by analyzing scenes from November, when fire activity and aerosol optical depth were low but cloud fraction and meteorological variables (boundary layer height, pressure, total column water vapor, temperature, and convective available potential energy) were similar to those of the fire season. High‐fire‐driven aerosol optical depth (AOD) was associated with reduced cloud fraction in both the raw and meteorologically normalized data. Fire aerosols reduced the relative cloud fraction in all sky conditions, but the effects were progressively larger in high‐AOD conditions. These results may provide observational evidence of the semidirect cloud decimation effect in tropical regions and suggest a positive feedback loop between anthropogenic burning and cloudiness—where more aerosols lead to decreased clouds, increased surface exposure and drying, more fire, and thus more aerosols—which is consistent with previous studies linking smoke aerosols to reduced cloudiness and vice versa.
Key Points
Fire‐emitted aerosols reduce cloud fraction from morning to afternoon
Higher aerosol burdens were associated with larger reductions in cloud fraction
Observations may provide evidence of a semidirect aerosol effect
Comparisons of the Multi‐angle Imaging SpectroRadiometer (MISR) aerosol optical depths (AOD) with those of the AErosol RObotic NETwork (AERONET) were made at four desert sites, covering a two‐year ...time period from December 2000 to November 2002. The two data sets show good correlation with no obvious systematic biases or trends, demonstrating MISR's ability to retrieve reliable visible and near infrared AOD over surfaces with relatively high reflectance. For MISR AOD obtained at 17.6 km spatial resolution, the estimated uncertainty is about 0.08. When the spatial resolution was degraded to 52.8 km, the estimated AOD uncertainty decreased to about 0.05. Year‐long time‐series comparisons of MISR and AERONET AOD at the four desert sites showed that MISR can quantitatively capture the temporal nature of strong dust activity in desert regions.
A synergistic algorithm for producing global leaf area index and fraction of absorbed photosynthetically active radiation fields from canopy reflectance data measured by MODIS (moderate resolution ...imaging spectroradiometer) and MISR (multiangle imaging spectroradiometer) instruments aboard the EOS‐AM 1 platform is described here. The proposed algorithm is based on a three‐dimensional formulation of the radiative transfer process in vegetation canopies. It allows the use of information provided by MODIS (single angle and up to 7 shortwave spectral bands) and MISR (nine angles and four shortwave spectral bands) instruments within one algorithm. By accounting features specific to the problem of radiative transfer in plant canopies, powerful techniques developed in reactor theory and atmospheric physics are adapted to split a complicated three‐dimensional radiative transfer problem into two independent, simpler subproblems, the solutions of which are stored in the form of a look‐up table. The theoretical background required for the design of the synergistic algorithm is discussed.
The aim of this study is to theoretically investigate the sensitivity of the Multi-angle Imaging SpectroRadiometer (MISR) operational (version 22) Dark Water retrieval algorithm to aerosol ...non-sphericity over the global oceans under actual observing conditions, accounting for current algorithm assumptions. Non-spherical (dust) aerosol models, which were introduced in version 16 of the MISR aerosol product, improved the quality and coverage of retrievals in dusty regions. Due to the sensitivity of the retrieval to the presence of non-spherical aerosols, the MISR aerosol product has been successfully used to track the location and evolution of mineral dust plumes from the Sahara across the Atlantic, for example. However, the MISR global non-spherical aerosol optical depth (AOD) fraction product has been found to have several climatological artifacts superimposed on valid detections of mineral dust, including high non-spherical fraction in the Southern Ocean and seasonally variable bands of high non-sphericity. In this paper we introduce a formal approach to examine the ability of the operational MISR Dark Water algorithm to distinguish among various spherical and non-spherical particles as a function of the variable MISR viewing geometry. We demonstrate the following under the criteria currently implemented: (1) Dark Water retrieval sensitivity to particle non-sphericity decreases for AOD below about 0.1 primarily due to an unnecessarily large lower bound imposed on the uncertainty in MISR observations at low light levels, and improves when this lower bound is removed; (2) Dark Water retrievals are able to distinguish between the spherical and non-spherical particles currently used for all MISR viewing geometries when the AOD exceeds 0.1; (3) the sensitivity of the MISR retrievals to aerosol non-sphericity varies in a complex way that depends on the sampling of the scattering phase function and the contribution from multiple scattering; and (4) non-sphericity artifacts occur at those view-illumination geometries where dust aerosols are indistinguishable from certain types of cirrus particles. Based on these results, we suggest that interested parties use caution with the version 22 MISR Dark Water aerosol non-sphericity product in situations where cirrus may be present.
It is well established that smoke particles modify clouds, which in turn affects climate. However, no study has quantified the temporal dynamics of aerosol‐cloud interactions with direct ...observations. Here for the first time, we use temporally offset satellite observations from northern Africa between 2006 and 2010 to quantitatively measure the effect of fire aerosols on convective cloud dynamics. We attribute a reduction in cloud fraction during periods of high aerosol optical depths to a smoke‐driven inhibition of convection. We find that higher smoke burdens limit upward vertical motion, increase surface pressure, and increase low‐level divergence—meteorological indicators of convective suppression. These results are corroborated by climate simulations that show a smoke‐driven increase in regionally averaged shortwave tropospheric heating and decrease in convective precipitation during the fire season. Our results suggest that in tropical regions, anthropogenic fire initiates a positive feedback loop where increased aerosol emissions limit convection, dry the surface, and enable increased fire activity via human ignition.
Key Points
Satellite observations of temporal dynamics of aerosol‐cloud interactions
Fire aerosols in Africa suppress convection and decrease cloud fraction
Smoke inhibits convection via semidirect effects
MISR observations of Etna volcanic plumes Scollo, S.; Kahn, R. A.; Nelson, D. L. ...
Journal of Geophysical Research: Atmospheres,
27 March 2012, Letnik:
117, Številka:
D6
Journal Article
Recenzirano
Odprti dostop
In the last twelve years, Mt. Etna, located in eastern Sicily, has produced a great number of explosive eruptions. Volcanic plumes have risen to several km above sea level and created problems for ...aviation and the communities living near the volcano. A reduction of hazards may be accomplished using remote sensing techniques to evaluate important features of volcanic plumes. Since 2000, the Multiangle Imaging SpectroRadiometer (MISR) on board NASA's Terra spacecraft has been extensively used to study aerosol dispersal and to extract the three‐dimensional structure of plumes coming from anthropogenic or natural sources, including volcanoes. In the present work, MISR data from several explosive events occurring at Etna are analyzed using a program named MINX (MISR INteractive eXplorer). MINX uses stereo matching techniques to evaluate the height of the volcanic aerosol with a precision of a few hundred meters, and extracts aerosol properties from the MISR Standard products. We analyzed twenty volcanic plumes produced during the 2000, 2001, 2002–03, 2006 and 2008 Etna eruptions, finding that volcanic aerosol dispersal and column height obtained by this analysis is in good agreement with ground‐based observations. MISR aerosol type retrievals: (1) clearly distinguish volcanic plumes that are sulphate and/or water vapor dominated from ash‐dominated ones; (2) detect even low concentrations of volcanic ash in the atmosphere; (3) demonstrate that sulphate and/or water vapor dominated plumes consist of smaller‐sized particles compared to ash plumes. This work highlights the potential of MISR to detect important volcanic plume characteristics that can be used to constrain the eruption source parameters in volcanic ash dispersion models. Further, the possibility of discriminating sulphate and/or water vapor dominated plumes from ash‐dominated ones is important to better understand the atmospheric impact of these plumes.
Key Points
MISR retrieves important plume features
MISR retrieves even low concentrations of volcanic ash
MISR distinguishes sulphate and/or water vapor and ash dominated volcanic plumes
The Multi-angle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite has demonstrated the capability to retrieve aerosol optical depths, surface bidirectional reflectance factors, and ...hemispherical reflectances over a wide variety of land surface types. In particular, its multiangular imaging design has enabled the application of algorithms that minimize sensitivity of the aerosol retrievals to the brightness of the underlying surface. The novel aerosol algorithm that was developed prior to launch has had notable quantitative success. Over certain scene types, however, the approach contained obvious spatial artifacts, so a postlaunch refinement to the algorithm was implemented. It constrains the retrieved aerosol models and optical depths such that the implied angular shape of the surface hemispherical–directional reflectance factor (HDRF) is similar among all of the MISR wavelengths. This upgrade has resulted in three tangible benefits: (1) the occurrence of outliers has been dramatically reduced, (2) correlations with AERosol RObotic NETwork (AERONET) aerosol sunphotometer data are quantitatively improved, and (3) the quality of surface products is markedly enhanced. MISR Level 2 aerosol and surface products are archived at the NASA Langley Atmospheric Sciences Data Center. Those having version numbers v0012 and higher incorporate this upgrade in the data processing software.
PDF
