A23A-0867
The determination of the aerosol optical thickness over land using different satellite instruments and algorithms
An intercomparison of the aerosol optical thickness (AOT) at 550nm retrieved using different satellite instruments and algorithms based on the analysis of backscattered solar light is performed for a single scene over central Europe on October 13th, 2005. For the first time comparisons have been performed for as many as six instruments on multiple satellite platforms. Ten different algorithms are briefly discussed and intercompared. It was found that on the scale of a single pixel there can be large differences in AOT retrieved over land using different retrieval techniques and instruments. However, these differences are not as pronounced for the average AOT over land. For instance, the average AOT at 550nm for the area 7-12E, 49-53N was equal to 0.14 for MISR, NASA MODIS and POLDER algorithms. It is smaller by 0.01 for the ESA MERIS aerosol product and larger by 0.04 for the MERIS BAER algorithm. AOT as derived using AATSR gives on average larger values as compared to all other instruments, while SCIAMACHY retrievals underestimate the aerosol loading. These discrepancies are explained by uncertainties in a priori assumptions used in the different algorithms and differences in the sensor characteristics. Validation against AERONET shows that MERIS provides the most accurate AOT retrievals for this scene.
A23A-0868
Mineral dust transport characterization from combined MISR/MODIS aerosol retrievals for NAAPS transport model validation
Mineral dust is a major airborne atmospheric constituent. Dust plumes frequently cover geographically large areas; they are among the most prominent and commonly visible features in satellite imagery. An understanding of dust amount and particle property evolution during long-range transport is important for characterizing dust environmental impacts and climate forcing. We present a North Africa dust transport study using MISR and MODIS observations of selected dust events during the summer months of 2000 the timeframe of the Puerto Rico Dust Experiment field campaign. MODIS routinely reports aerosol products over the extended ocean areas, while MISR's instantaneous observations capture dust plumes during several stages of their evolution. As these plumes cross the ocean, MISR's multi- angle retrieval compliments MODIS's nadir-only observations in sun-glint areas, and through sampling of side- scattered light makes it possible to distinguish dust from spherical aerosol components. We analyze MISR and MODIS retrieved aerosol optical thickness and fraction of non-spherical particles, and compare with dust modeling results from the Navy Aerosol Analysis and Prediction System (NAAPS), and as well as available AERONET data. We estimate MISR/MODIS dust removal rates and plume mass observed during multiple stages of transport (close-to-source and progressively down-wind). Our study demonstrates that transport model predictions are needed to fill gaps in MISR/MODIS spatial and temporal coverage, needed for mass flux calculations. We show that NAAPS predictions of dust activity and locations are qualitatively consistent with MISR, MODIS, and AERONET observations. In some cases, NAAPS dust parameterization and deposition rates warrant an improvement, especially at ocean areas close to dust sources.
A23A-0869
Dust Absorption Over Sahara Inferred From MODIS for Four Years
Airborne dust over Sahara can have a significant effect on the Earthfs radiation budget, but most existing observations are available for a limited number of locations, especially near coastal area. Therefore, it is important to find representative dust absorption averaged over whole Sahara area. We estimated dust single scattering albedo averaged over Sahara using MODIS data for 4 years. The method is based on the theory that the critical surface reflectance, for which the TOA reflectance is not affected by the presence of dust, depend on the single scattering albedo (Kaufman,1987 and Kaufman et al.,2001). We derived he critical surface reflectance, by comparing the observed TOA reflectance on less dusty and hazy condition, and estimated the single scattering albedo using the radiative transfer model. The estimated dust single scattering albedo was compared to the past studies which derived the dust absorption from other satellites or ground-based measurements. Use of satellite data over large area and for long terms enables the quantification of the average dust absorption over Sahara including inland.
A23A-0870
Aerosol Optical Thickness over North Africa: Multi Satellite Product Analysis
Daily Aerosol Optical Thickness at 0.55 µm (AOT) over the desert regions is needed for many aerosol related applications such as validation for numerical models. Since a single satellite sensor is not currently able to provide AOT over deserts on a daily basis (except beta version of deep blue product from MODIS Aqua), we have developed a daily AOT product derived from TOMS/OMI Aerosol Index (AI). MISR and TOMS/OMI multi year monthly mean aerosol products are used in development of AOT algorithm. We further examined the AOT data from the ground to validate our methods and results. While previous studies have examined the TOMS AI with limited ground-based sun photometer data, our study extends this to multiple satellite sensors over seven years (2000- 2006). Present study will also compare the above retrieved product with the OMI's operational AOT product over several AERONET locations in the study area.
A23A-0871
A Slow Retrieval Algorithm for Satellite and Surface Based Instruments
We present results of a retrieval algorithm for satellite and ground based instruments using the Arizona radiative transfer code. A state vector describing the atmospheric and surface condition is iteratively modified until the calculated radiances match the observed values. Elements of the state vector include: aerosol concentrations, radius, optical properties, mass-weighted altitudes, chlorophyll concentration and wind speed. While computationally expensive, many assumptions used in other retrieval algorithms are not invoked. We present co- located retrievals for MODIS, SEAWIFS and nearby AERONET sites. MODIS AQUA and SEAWIFS: Ten MODIS (.412 - 2.110 microns) and eight SEAWIFS (.412-.865 microns) radiances (.412-.865 microns) include channels where aerosols absorb and reflect radiation. We focus on retrieving bio-mass burning aerosols that are advected over open ocean. Since chlorophyll absorbs at frequencies where black carbon absorbs, our retrieval algorithm accounts for chlorophyll absorption by simultaneously retrieving both aerosol and chlorophyll amount. Our retrieved chlorophyll concentrations are similar to those from the Ocean Color Group. AERONET: Both Almucantar and Principle plane radiances are used to retrieve the state of the atmosphere and ocean conditions. Our retrieved aerosol size distributions and optical properties are consistent with the aerosol inversions from the AERONET group.
A23A-0872
Aerosol Particle Property Comparisons Between MISR and AERONET Retrieved Values
As the final step in validating the NASA Earth Observing System Terra satellite's Multi-angle Imaging SpectroRadiometer (MISR) aerosol products, an extensive comparison of particle micro-physical properties is being made against the Aerosol Robotic Network (AERONET). Angstrom exponent, single scattering albedo, and size distribution characteristic values and variance envelopes for individual sites and aggregates are compared, stratified by expected aerosol air mass type, optical depth magnitude and season. Specific examples showing strengths and weaknesses of this approach will be shown. Seven years of data from about 52 geographically diverse sites having good long-term measurement records are first stratified by expected air mass types: maritime, biomass burning, desert dust, pollution and continental aerosols. Having observations in at least three of the four seasons is an additional constraint on the selection of sites. The number of actual coincident measurements is limited by requiring AERONET direct sun aerosol optical depth (AOT) data be obtained from a two-hour window centered on the MISR overpass time, and AERONET sky scans, which provide particle micro-physical properties and are taken only once an hour, obtained from a four- hour window also centered on the overpass. Both AERONET sun and sky data are averaged over the measurements obtained within these windows and are then interpolated to MISR wavelengths to facilitate comparison. All AERONET measurements are Level 1.5, Version 2 data. A previous, systematic comparison of MISR and AERONET AOT data [Kahn, Gaitley et al., JGR 110, 2005] was used to improve MISR Standard Aerosol retrieval algorithms. The MISR aerosol products have been almost completely reprocessed with the upgraded algorithms. It is this new, uniformly processed database that is used in the current study, which is aimed at further refining the MISR aerosol products. This work is performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
A23A-0873
Multi-Sensor Data From A-Train Instruments Brought Together for Atmospheric Research
The A-Train is comprised of a series of instruments, developed independently, that measure highly related atmospheric components along the same flight path. In order to intercompare data from this multitude of sensors, researchers must access, subset, visualize, analyze and correlate distributed atmosphere measurements from the various A-Train instruments. The A-Train Data Depot (ATDD) has been operational for over a year, successfully performing the aforementioned functions on behalf of researchers, thus providing co- registered data from the Cloudsat, CALIOP, AIRS, and MODIS instruments for further intercomparisons. Of late, significant data from OMI and POLDER are now included in the depot'. By specifying the desired spatial and temporal range, the researcher can subset, visualize, co-register, and access multi-sensor A-Train data related to: Cloud, aerosol, atmospheric temperature, and water vapor parameters (vertical profile visualizations); Cloud Pressure, cloud top temperature, water vapor, cloud optical thickness, and aerosol products (horizontal strips subsetted +/- 100km from the profile visualizations), and; Cloud pressure parameters (2-D line plots overlayed on the vertical profiles). All data is plotted using the GIOVANNI data exploration tool. A new feature of GIOVANNI is its ability to have collocated and subsetted data sets as well as PNG image files downloaded to the researcher's computing facility. By providing a convenient way to visualize and acquire multi-sensor data, ATDD affords users more time and effort to further their research. http://disc.gsfc.nasa.gov/atdd/
A23A-0874
Remote sensing AOT and microphysical aerosol parameters using SCIAMACHY data and comparison with AERONET Sunphotometer data
In our work, we retrieve aerosol optical thickness and single scattering albedo by inverting O2 A and B-Band spectra measured by the DOAS satellite instrument SCIAMACHY onboard Envisat. We present retrievals over selected AERONET stations to represent different types of aerosols and ground albedos and compare them with coincident sunphotometer measurements. We also present first attemps at retrieving information on the complex refractive index and size distribution of the aerosol using parts of the entire spectrum (0.2-1.5 nm) devoid of strong molecular absorption. Since SCIAMACHY does not support multiple geometries in the Nadir viewing mode, the wide spectral coverage and medium spectral resolution of the instrument are vital to our retrieval. An overview of the inversion procedure and radiative transfer model used for retrieval is also provided.
A23A-0875
Merging MODIS Terra and Aqua Level 3 Aerosol Optical Thickness for Giovanni Online Data Analysis and Visualization
With a vast amount of satellite-obtained environmental data held, the Goddard Earth Sciences Data and Information Services Center (GES DISC) researches ways to combine multi-sensor data to increase their usefulness, and to integrate it in the GES DISC Interactive Online Visualization and Analysis Infrastructure (Giovanni). Here, we studied the performance of various methods for merging-interpolating the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua Level 3 Aerosol Optical Thickness (AOT). To quickly validate the accuracy of the merger, we introduced two confidence functions, which characterize the percentage of the merged AOT pixels as a function of the relative deviation of the merged AOT from original Terra and Aqua AOTs in respect to the original AOT standard deviations or AOT means. Experiment with three different methods for pure merging (no interpolation): simple arithmetic averaging (SIM), maximum likelihood estimate (MLE), and weighting by pixel counts (WPC) demonstrated the relative proximity of the resulting AOTs produced by the three methods with the MLE (SIM) being slightly preferable when validating with respect to AOT standard deviations (AOT means). Another experiment with eight different methods of combined merger-interpolation applied to a variety of scenes with different gap patterns showed that that the absolutely best method is when the merging of Terra and Aqua AOTs is done first followed by Optimal Interpolation to fill in the gaps. The sensitivity of the results to the gap patterns and radius of influence was assessed.
A23A-0876
MISR, MODIS, and POLDER2 Reflectance and Aerosol Product Comparisons
MISR, MODIS and POLDER2 are all space-based instruments dedicated to studying Earth's atmosphere and surface. Due to different calibration methods, the reflectances these instruments generate can differ slightly. These differences affect the interpretation of satellite observations in terms of geophysical products, including aerosol amount and type. In a first part of this study, the reflectances from these three instruments have been compared when the geometrical and temporal conditions have sufficient similarities. All kinds of targets have been considered, from dark water to bright clouds. For almost all the bands, MISR reflectances are at the high end of the reflectance envelope, whereas POLDER2 tends to be at the low end. However, the absolute differences rarely exceed 5% for any of the three instruments. The last part of the presentation will show the comparison of the aerosol amount and properties retrieved by the three sensors for a variety of different aerosol types and atmospheric loadings. Comparisons have been made for retrievals over land and ocean for 60 orbits with good temporal coincidence and which cover a large geographical sampling. This work was funded by the Centre National d"Etudes Spatiales and performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
A23A-0877
Validation of the OMI multi-wavelength aerosol product
One of the science goals of the Ozone Monitoring Instrument (OMI) on board of EOS-Aura is to help answer the question "What is the role of aerosols in climate change?" To this end, properties such as the aerosol UV absorbing index and, for cloud-free scenes, aerosol optical thickness are derived from the near-ultraviolet and visible spectra that are measured by OMI. The application of ultraviolet spectra is especially useful since in that wavelength range, retrievals are less sensitive to surface albedo assumptions and the presence of aerosols may be quantified even above or within clouds. One of the OMI aerosol products makes use of the multi-wavelength algorithm. This algorithm extends the wavelength range employed by the proven TOMS algorithm to visible wavelengths including the 477-nm absorption band of the O2-O2 collision complex that is sensitive to aerosol altitude. This product has been provisionally released and is currently being validated. In this presentation, results of comparisons, both qualitative and quantitative, with AERONET ground-based observations will be shown, as well as results of comparisons with other satellite sensors, especially those on A-Train satellites, such as MODIS and PARASOL. The pixel-wise correlation between OMI and A-Train sensors, varies from good to relatively poor, depending on the region and the prevalent aerosol type. Comparisons with ground-based observations point out problematic areas over land and give clues for further improvement of the algorithm and its cloud-screening procedure. Over oceans, quantitative comparisons with Aqua/MODIS and PARASOL are very good. Monthly regional averages generally show the same seasonal trends as similar observations from MODIS and MISR and prove the worth of the OMI multi-wavelength aerosol algorithm.
A23A-0878
Use of Combined A-Train Observations to Validate GEOS Model Simulated Dust Distributions During NAMMA
During August 2006, the NASA African Multidisciplinary Analyses Mission (NAMMA) field experiment was conducted to characterize the structure of African Easterly Waves and their evolution into tropical storms. Mineral dust aerosols affect tropical storm development, although their exact role remains to be understood. To better understand the role of dust on tropical cyclogenesis, we have implemented a dust source, transport, and optical model in the NASA Goddard Earth Observing System (GEOS) atmospheric general circulation model and data assimilation system. Our dust source scheme is a more physically based scheme than previous incarnations of the model, and we introduce improved dust optical and microphysical processes through inclusion of a detailed microphysical scheme. Here we use A-Train observations from MODIS, OMI, and CALIPSO with NAMMA DC-8 flight data to evaluate the simulated dust distributions and microphysical properties. Our goal is to synthesize the multi-spectral observations from the A-Train sensors to arrive at a consistent set of optical properties for the dust aerosols suitable for direct forcing calculations.
A23A-0879
One year of EARLINET correlative measurements for CALIPSO
EARLINET is the European Aerosol Research Lidar Network providing systematic observations of aerosol profiling on continental scale. At present, the network includes 25 stations distributed over Europe: 10 single backscatter lidar stations, 8 Raman lidar stations with the UV Raman channel for independent measurements of aerosol extinction and backscatter, and 7 multi-wavelength Raman lidar stations for the retrieval of aerosol microphysical properties. EARLINET represents an optimal tool to validate CALIPSO lidar data and to provide the necessary information to fully exploit the data produced from that mission. In particular, aerosol extinction and lidar ratio measurements, provided by the network, will be important for the aerosol retrievals from the backscatter lidar (CALIOP) on board CALIPSO. EARLINET started correlative measurements for CALIPSO since 14 June 2006. A suitable, three-stage strategy for correlative measurements has been implemented within EARLINET on the base of the analysis of the high resolution ground track data provided by NASA. EARLINET correlative measurements are performed at stations located within 80km from the overpasses and additionally at the lidar stations which are closest to the actually overpassed site. Moreover, if a multi-wavelength Raman lidar station is overpassed then also the next closest multi-wavelength Raman lidar station performs a measurement. Each correlative measurement lasts for a minimum of 1 hour centered around the overpass time; longer records of measurements are performed for special case studies (Saharan dust layers, forest fires, long range transport, etc.). Further information from backtrajectory analysis are used to quantitatively study comparisons between CALIPSO and EARLINET observations. EARLINET performed more than 1000 correlative observations during the first operational year of CALIPSO (June 2006 June 2007), first results in terms of comparisons between EARLINET and available CALIPSO products will be presented. ACKNOWLEDGMENTS The financial support by the European Commission under grant RICA-025991 is gratefully acknowledged. The authors also thank the German Weather Service for the air mass backtrajectory analysis and the CALIPSO team of the NASA Langley Research Center for the provision of the CALIPSO high resolution ground track data. CALIPSO data were obtained from the NASA Langley Research Center Atmospheric Science Data Center.
A23A-0880
Data Fusion Approach for Estimating Global Aerosol Radiative Forcing
Among the climate forcing agents, aerosols have been long identified as important modulators of the Earth's energy budget. Several studies based on both observations and modeling have demonstrated their climatic impacts both regionally and globally. But these estimates still remain highly uncertain due to inhomogeneity in their spatial and temporal distributions. Continuous monitoring of the both aerosols and climate variables can help reduce these uncertainties. Observations from multiple satellite sensors that offer global coverage can be used to study the Earth-atmosphere in an integrated fashion. By fusing satellite data, we can utilize the strengths of the individual sensors that may not be otherwise possible. In this study we merge level 2 observations from 3 satellite sensors, the CERES, MODIS and MISR onboard Terra satellite to estimate the top of atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) over global land. Evaluation of fusion of MISR observations within CERES footprint against ground-based AERONET observations will be presented. Regional estimate of SWARF from biomass burning over S. America and dust aerosols over UAE region will also be presented. This study demonstrates the successful application of using merged multi-sensor data in forcing estimation.
A23A-0881
Data Fusion of Imaging Spectroscopy, Lidar, and In-Situ Laboratory Data for Detecting Aerosols from Biomass Burning Events
Aerosols absorb and scatter solar and thermal infrared radiation, thereby altering the radiative balance of the Earth-atmosphere system. This is called the aerosol direct effect. Remote sensing of aerosols from satellites is essential to obtain the contribution of anthropogenic emission to the radiative balance. It is necessary to be able to map their presence and abundance using remote measurements. If we can quantify the occurrence of aerosols from biomass burning using remote sensing, we can improve our understanding of the direct radiative effect. This study uses airborne remote sensing data to understand, identify, and quantify smoke aerosols in the atmosphere. In particular, using Imaging Spectroscopy and lidar data to detect the presence and abundance of aerosols. Airborne remote sensing data was collected over the active Simi Valley wildfire on October 27, 2003 in Southern California. The Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) was flown on a commercially operated Twin Otter aircraft at an altitude of 6 km, and collected 224 channels of radiance data from 380 2400 nm with 10 nm spectral resolution. Shortly after the AVIRIS data collection, the Cloud Physics Lidar (CPL) was flown on the NASA ER-2 at an altitude of 20 km. CPL is a three wavelength instrument that operates at 1064, 532, and 355 nm, with a 30 m vertical and 200 m horizontal resolution. Controlled laboratory measurements of aerosol optics from burning various woods and grasses provide insight and refinement of our understanding of remote sensing data for biomass burning aerosol. In 2006 and 2007 a two-phase project was conducted at the US Forest Service's Fire Science Laboratory to characterize particulate matter generated by biomass burning. The Fire Lab at Missoula Experiment (FLAME) is supported by the Joint Fire Science Program and is a cooperative effort between the National Park Service, the Desert Research Institute, and Colorado State University. FLAME was a series of laboratory measurements of smoke emission of several important fuel types. These fuel types included dominant species of the Southern Californian Chaparral vegetation community. During the 2007 phase of FLAME a portable field spectroradiometer collected radiance data from 380 2400 nm for comparison with AVIRIS. Other in-situ measurements of aerosol optical and chemical properties collected during FLAME will also be compared to the October 27, 2003 remote sensing measurements of wildfire aerosols. This study will quantify the presence of aerosols from biomass burning using remote sensing.
A23A-0882
CALIPSO Aerosol Backscatter and Extinction Characterization Using the MODIS and OMI Products
The CALIPSO lidar observations accumulated since June 2006 have revealed the vertical structure of aerosols in the Earth's atmosphere on an unprecedented global scale. Combining the vertical curtain of CALIPSO data with the wide swath of passive sensor measurements provided by MODIS and/or OMI will allow us not only to depict the three-dimensional distribution of aerosols on a global scale, but also to develop and improve joint retrieval algorithms that take full advantage of the strengths of each instrument. As a first step in this data fusion process, we conduct a statistical analysis comparing the CALIPSO integrated attenuated backscatter (IAB) and aerosol optical depths (AOD) measured at 532 nm to the aerosol data products generated by the MODIS sensor aboard the AQUA satellite and by the OMI instrument flying on the AURA satellite. This analysis includes seasonal and geographical variations of the CALIPSO aerosol IAB, and comparisons with collocated MODIS AOD retrievals. Comparisons are also made to the OMI aerosol index (AI) product, which complements the MODIS AOD over bright surfaces where the MODIS retrieval tends to show diminished accuracies. The combination of CALIPSO IAB and MODIS AOD is then used to infer the aerosol extinction-to-backscatter ratio (lidar ratio), which is a function of chemical composition and particle size distribution, and can be an indicator for aerosol speciation. The CALIPSO analysis framework defines six generic aerosol species or types: clean marine, dust, polluted dust, clean continental, polluted continental, and biomass burning. Separate geographic regions are identified where a single type dominates the local aerosol burden. Within each of these regions, the CALIPSO AOD, which is reported at a spatial resolution of 5-km x ~90-m (90-m is the approximate diameter of the laser footprint), is averaged to 10-km average horizontally. These data are then compared with the coincident MODIS AOD estimates, which are retrieved at a spatial resolution of 10-km x 10-km. Discrepancies between the two measurements may involve difficulties in AOD retrieval over different surface types, or the multi-layer structures of aerosols and clouds. The high spatial resolution of a CALIPSO vertical profile and the nature of an active remote sensing instrument allows unambiguous identification of such cases, and should help improve data quality for the passive sensor retrievals.
A23A-0883
Comparison of Airborne Sunphotometer to MODIS and MISR Retrievals of Aerosol Optical Depth during MILAGRO/INTEX-B
The 14-channel Ames Airborne Tracking Sunphotometer (AATS-14) was operated on a Jetstream 31 (J31) aircraft based in Veracruz, Mexico in March 2006 during MILAGRO/INTEX-B (Megacity Initiative-Local And Global Research Observations /Phase B of the Intercontinental Chemical Transport Experiment). AATS measured aerosol optical depth (AOD) at 13 wavelengths (354-2139 nm) and water vapor column content in 13 flights that sampled clean and polluted airmasses over the Gulf of Mexico and Mexico City. J31 flights were coordinated with overflights of several satellites, including Aqua, Aura, Terra, and Parasol. In this paper we will focus on comparing AATS retrievals of AOD with corresponding AOD values retrieved from spatially and temporally coincident or near-coincident measurements acquired by the satellite sensors MODIS (Aqua and Terra), and MISR (Terra). Our preliminary analyses of 37 coincident observations by AATS and MODIS-Terra and 18 coincident observations between AATS and MODIS-Aqua indicate notable differences between MODIS Collection 004 and Collection 005, the latter representing a reprocessing of the entire MODIS data set completed during 2006. For example, our analyses show that for MODIS Collection 004, 81.9% of spectral MODIS-Terra AOD retrievals fall within the estimated uncertainty range of +- 0.03 +- 0.05 AOD , while 90.5% of MODIS-Aqua AOD retrievals fall within this uncertainty range. By contrast, in collection 005, these values drop to 50.5% and 78.6%, respectively. Reasons for these differences are currently under investigation. In this paper, we will summarize the comparisons between AATS-14 and both MODIS collections regarding AOD, Angstrom exponent and FMF. Collocated measurements by AATS, MODIS-Terra and MISR within three MISR retrieval grid cells over the Gulf of Mexico on March 10 have been analyzed. Mid-visible (at 446 and 558 nm) AOD retrievals produced by the MISR standard operational algorithm Version 19 compare well both with AATS and with MODIS-Terra observations in two of the three MISR grid cells, while the MISR AOD retrievals in the third cell exceed those obtained from AATS or MODIS. MISR near-IR (866nm) AOD retrievals agree with corresponding AATS and MODIS-Terra retrievals within measurement uncertainty.
A23A-0884
A Study of Surface Directional Reflectance Properties To Enhance Aerosol Retrieval Capability Over Land Using MISR Data
The nearly-simultaneous multiangle, multispectral,radiometrically calibrated imagery of the Multi-angle Imaging SpectroRadiometer (MISR) has a nominal spatial resolution of 1.1 km and covers the globe in about 9 days. Once the imagery is co-located and co-registered, an aerosol retrieval is performed, over both land and ocean, using an aerosol model look-up database. The technique for aerosol retrieval over ocean is conventional, namely assuming that measurements in the red and near-IR spectral bands are measurements of radiance scattered only within the atmosphere. Over land, however, the radiance measurements generally are a combination of atmosphereric and surface scattering events, the proportions which vary with wavelength and usually are not known a priori. This makes the retrieval of aersosls over land a much more intractable process. In fact any retrieval of aerosol properties over land from space with a passive instrument requires some constraints to be placed on the surface reflectance properties so that atmospheric radiance can be effectively separated from surface reflected radiance in the measurements. To facilitate the MISR standard aerosol retrieval process over land, it is assumed that the surface directional reflectance at any given location has the same (or very similar) angular form or shape in the different spectral bands. There is some theoretical basis for this assumption, especially when the surface spectral albedos have similar values, but an empirical verification in the context of multiangle remote sensing data is necessary if further progress in aerosol retrieval quality over land is to be made. This poster presents some results of a study to test the surface directional reflectance spectral similarity assumption. It focuses on MISR data taken over a number of AERONET sunphotometer sites with different surface conditions, ranging from urban areas to forested regions, at a spatial scale of 1.1 km. In contrast to MISR data alone, the AERONET data provide an independent and better contrained determination of the aerosol properties at a site during the overpass, which then is used to correct the associated MISR top-of atmosphere imagery for atmospheric effects, resulting in the best estimates of the AERONET site surface spectral directional reflectance at 1.1 km resolution. To understand how the similarity of the angular shape depends on spatial scale, the directional reflectance was retrieveded at a variety of spatial resolutions, starting at 1.1 km pixel centered at the AERONET site and was systematically increased by pixel averaging around the site to 17.6 km resolution, the spatial scale used by the current MISR operational aerosol retrieval. A wide variety of AERONET sites were analyzed to provide information on how the degree of spectral reflectance similarity may relate to surface type. Because MISR data has been available since early 2000 to the present, seasonal and secular trends in surface reflectance variability also were investigated. The similarity condition was quantified at each site by the use of various semi-empirical directional reflectance models which allowed spectral albedo effects to be explicitly taken into account. It is expected that the results of this study will improve the current capability of the MISR aerosol retrieval algorithm over land. This work was performed at the Jet Propulsion Laboratory, California Institute ofTechnology under contract with the National Aeronautics and Space Administration.
A23A-0885
The Intercomparison of Aerosol Properties Measured by SAGE II and SAGE III
Satellite experiments SAGE II and SAGE III measure aerosol extinctions at different wavelengths ranging from 385 nm to 1020 nm for SAGE II and to 1550 nm for SAGE III. However, for many applications the utility of aerosol extinction is limited. The retrieval of more useful aerosol size distribution and integral properties from the measured extinctions presents a real challenge to atmospheric scientists. In this paper, the linear minimizing error (LME) method to retrieve aerosol properties is discussed. This approach assumes that the aerosol size distribution can be approximated by a histogram of number density as a function of particle size. The retrieved number density in each bin and the integral properties, including surface area and volume densities, are expressed as linear combinations of the aerosol extinction coefficients at different wavelengths. The coefficients in the weighted linear combination are obtained by minimizing the average of retrieval errors over a set of testing size distributions. It is found that aerosol volume density can be more accurately retrieved than the surface area density. Since both SAGE II and SAGE III conduced measurements between 2002 and 2005, there are comparison opportunities when their measurement locations on the same day are nearly coincident.In this study, the comparisons of aerosol properties deduced from SAGE II and SAGE III measurements are reported. It is found that the differences are within about 30%.
A23A-0886
Remote Sensing of Dust Activity and Transport in South America
Most of what it is known about dust activity in the Southern Hemisphere and in particular in South America is based on model simulations and very few dedicated observational studies. The satellite record of dust activity shows a mixed and conflicting picture. For example, the TOMS-Aerosol Index reveals active sources of dust in the argentine and bolivian Altiplano region as well as in central and south Argentina. However, aerosol optical depth record from the MODIS detectors does not show any significant activity and export of dust in the area. This study shows with specific examples that dust production and export from South America is significant. However, dust activity is highly irregular and it is difficult to detect. The MODIS aerosol algorithm tends to fail in detecting dust in the region for a variety of reasons: 1) abundant cloudiness during the dust storm 2) frequent glint conditions over the ocean 3) bright surface over the land. Only a dedicated study that includes algorithm modification suited for retrievals in this area (such as relaxing glint angle and/or cloud masking) and the use of a combination of retrievals from different satellite detectors (MODIS, MISR, CALIOP, OMI) can yield a more realistic picture of dust transport in the Southern South America. As a result, satellite detection of dust transport into the South Atlantic and possibly other high latitude regions is currently being underestimated.
A23A-0887
Validation of Aerosol Type Classification from Satellite Remote Sensing
Aerosol type classification from satellite remote sensing has been being one of important problems during recent years since the effect of aerosols to climate is different from one type to another type. Based on improved nadir- viewing satellite sensors, such as Moderate Resolution Imaging Spectrometer (MODIS) and Ozone Monitoring Instrument (OMI), and retrieval algorithms, many studies have been shown the possibility of aerosol type classification from satellite-based remote sensing [cf. Kim et al., 2007; Lee et al., 2007; Jeong and Li, 2005; Kaufman et al., 2005; Higurashi and Nakajima, 2002, etc.]. Despite of the importance of validation, it was difficult to find out the truth due to limitation of aerosol type measurements for validation of retrieved aerosol types. In this study, retrieved aerosol types from MODIS-OMI algorithm and four-channel algorithm were compared with aerosol types from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) data, dust aerosol optical thickness from Multi- functional Transport Satellite-1R (MTSAT-1R), and carbon monoxide column density from Measurements Of Pollution In The Troposphere (MOPITT) for the purpose of validation and inter-comparison. Although the analysis are limited and preliminary, satellite observations showed promising future in understanding the global distribution and characteristics of aerosol type by using well-known, state-of-the-art MODIS and OMI, and possibly other relevant satellites.