The crystallization behaviour of some glasses in the CaO–ZnO–Al2O3–SiO2 system was investigated u... more The crystallization behaviour of some glasses in the CaO–ZnO–Al2O3–SiO2 system was investigated using different heattreatment parameters. Cr2O3 and CaF2 were used as nucleating agents. Differential thermal analysis, X-ray diffraction, dilatometry and scanning electron microscopy were used in this study. Melilite, αand β-willemite, anorthite, wollastonite, pseudowollastonite and petedunnite phases developed in the investigated glasses. The formation of compatible and incompatible phase assemblages and the effect of Cr2O3 and CaF2 are illustrated. Glass-ceramics with fine-grained microstructures and CTE values ranging from 36 to 73 × 10 K in the 20-700°C range were obtained.
Geoscience and Remote Sensing IEEE International Symposium, 2004
We present the distributions of the lidar observable optical properties for dust, continental pol... more We present the distributions of the lidar observable optical properties for dust, continental pollution and marine aerosols using the Cloud Physics Lidar (CPL, ef.) measurements. This study uses CPL measurements during CRYSTAL-FACE off the coast of Florida to extract probability distribution functions (PDFs) of the lidar depolarization ratios (delta), and the ratio of the backscatter at 1064 nm to 532
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007
Case studies from the first three months of the Cloud and Aerosol Lidar and Infrared Pathfinder S... more Case studies from the first three months of the Cloud and Aerosol Lidar and Infrared Pathfinder Spaceborne Observations (CALIPSO) measurements of lofted aerosol layers are analyzed using transmittance [Young, 1995] and two-wavelength algorithms [Vaughan et al., 2004] to determine the aerosol extinction-to-backscatter ratios at 532 and 1064 nm. The transmittance method requires clear air below the layer so that the transmittance through the layer can be determined. Suitable scenes are selected from the browse images and clear air below features is identified by low 532 nm backscatter signal and confirmed by low depolarization and color ratios. The transmittance and two-wavelength techniques are applied to a number of lofted layers and the extinction-to-backscatter ratios are compared with values obtained from the CALIPSO aerosol models [Omar et al., 2004]. The results obtained from these studies are used to adjust the aerosol models and develop observations based extinction-to-backscatter ratio look-up tables and phase functions. Values obtained by these techniques are compared to S a determinations using other independent methods with a goal of developing probability distribution functions of aerosol type-specific extinction to backscatter ratios. Method Given a solution of the particulate backscatter at 532 nm β 532,p , the two-wavelength method uses a least squares method to minimize the difference between the attenuated total backscatter measurement at 1064 nm, B 1064 and the right hand side of eq. (1).
2011 IEEE MTT-S International Microwave Symposium, 2011
To homogenize the 1 B + field and decrease specific absorption rate (SAR) profile for MRI at 7T, ... more To homogenize the 1 B + field and decrease specific absorption rate (SAR) profile for MRI at 7T, more degrees of freedom are needed and different excitation approaches are required. Multi-channel transceiver arrays based on microstrip resonator (MSR) is a promising approach for signal excitation and reception at ultrahigh-field (UHF) MRI. Travelling wave approach is another method for excitation based
2010 3rd International Symposium on Applied Sciences in Biomedical and Communication Technologies (ISABEL 2010), 2010
... Reson Med. (2006). [2] Vaughan J, DelaBarre L, Snyder C, Adriany G, Collins C, Van de Moortel... more ... Reson Med. (2006). [2] Vaughan J, DelaBarre L, Snyder C, Adriany G, Collins C, Van de Moortele PF, Ritter J, Strupp J, Andersen P, Tian J, Smith M Ugurbil K. RF image optimization at 7T and 9.4T. 2005; Miami p. 953. [3] Ibrahim T, Lee R, Robitaille P. “Effect of RF coil ...
Atmospheric Chemistry and Physics Discussions, 2010
The Bihar pollution pool is a large wintertime increase in pollutants over the eastern parts of t... more The Bihar pollution pool is a large wintertime increase in pollutants over the eastern parts of the Indo Gangetic basin. We use improved carbon monoxide (CO) retrievals from the recent Measurements of Pollution in the Troposphere (MOPITT) version 4 data along with the aerosol data from the latest version 3 of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar instrument and the tropospheric ozone residual products from the Total Ozone Mapping Spectrometer (TOMS)/Solar Backscattered Ultraviolet (SBUV) and Ozone Monitoring Instrument (OMI)/Microwave Limb Sounder (MLS) database to characterize this pollution pool. The feature is seen primarily in the lower troposphere from about November to February with strong concomitant increase in CO, aerosol optical depth and tropospheric ozone columns. The height resolved aerosol data from CALIPSO confirm the trapping of the pollution pool at the lowest altitudes. The observations indicate that MOPITT can capture this low altitude phenomenon even in winter conditions as indicated by the averaging kernels.
We are demonstrating on a few cases the capability of CALIPSO to retrieve the 532 nm lidar ratio ... more We are demonstrating on a few cases the capability of CALIPSO to retrieve the 532 nm lidar ratio over the ocean when CloudSat surface scattering cross section is used as a constraint. We are presenting the algorithm used and comparisons with the column lidar ratio retrieved by the NASA airborne high spectral resolution lidar. For the three cases presented here, the agreement is fairly good. The average CALIPSO 532 nm column lidar ratio bias is 13.7% relative to HSRL, and the relative standard deviation is 13.6%. Considering the natural variability of aerosol microphysical properties, this level of accuracy is significant since the lidar ratio is a good indicator of aerosol types. We are discussing dependencies of the accuracy of retrieved aerosol lidar ratio on atmospheric aerosol homogeneity, lidar signal to noise ratio, and errors in the optical depth retrievals. We are obtaining the best result (bias 7% and standard deviation around 6%) for a nighttime case with a relatively constant lidar ratio (in the vertical) indicative of homogeneous aerosol type.
We use measurements and models to develop aerosol models for use in the inversion algorithms for ... more We use measurements and models to develop aerosol models for use in the inversion algorithms for the Cloud Aerosol Lidar and Imager Pathfinder Spaceborne Observations (CALIPSO). Radiance measurements and inversions of the AErosol RObotic NETwork (AERONET 1, 2) are used to group global atmospheric aerosols using optical and microphysical parameters. This study uses more than 10 5 records of radiance measurements, aerosol size distributions, and complex refractive indices to generate the optical properties of the aerosol at more 200 sites worldwide. These properties together with the radiance measurements are then classified using classical clustering methods to group the sites according to the type of aerosol with the greatest frequency of occurrence at each site. Six significant clusters are identified: desert dust, biomass burning, urban industrial pollution, rural background, marine, and dirty pollution. Three of these are used in the CALIPSO aerosol models to characterize desert dust, biomass burning, and polluted continental aerosols. The CALIPSO aerosol model also uses the coarse mode of desert dust and the fine mode of biomass burning to build a polluted dust model. For marine aerosol, the CALIPSO aerosol model uses measurements from the SEAS experiment 3. In addition to categorizing the aerosol types, the cluster analysis provides all the column optical and microphysical properties for each cluster.
Thomas H. Chyba, Doyle A. Temple, Scott Bailey, Arthur Bowman, Wei Gong, Ali Omar, Russell Battle... more Thomas H. Chyba, Doyle A. Temple, Scott Bailey, Arthur Bowman, Wei Gong, Ali Omar, Russell Battle, Belicia Bradley, John Davis, Mika Edmondson, Anne Futrell, Chadwick Giles, Clarence Glenn, David Harper, Lincoln Haughton, Demetra Johnson, Ayana Jordan, Nasira Latif, ...
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT form only given, as follows. The magnetic field generated by a conventional MSR is inhom... more ABSTRACT form only given, as follows. The magnetic field generated by a conventional MSR is inhomogeneous along the resonator axis. It is strong at the center and weak at the terminating ends. To homogenize the B1+ field, it is required to modify the traditional MSR. Recently, an approach based on alternating impedance MSR has been presented. Another configuration of alternating impedance MSR is proposed. Results indicate that, the alternating impedance MSR with circular elements is the best coil in terms of B1+ field homogeneity.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2013
ABSTRACT Five years of CALIPSO lidar layer products are used to study transpacific transport of A... more ABSTRACT Five years of CALIPSO lidar layer products are used to study transpacific transport of Asian dust. We focus on possible changes to dust intrinsic optical properties during the course of transport, with specific emphasis on changes to particulate depolarization ratio (PDR). PDR distributions for Asian dust transported across the Pacific are compared to previously reported PDR distributions for African dust transported across the Atlantic. African dust shows a slight decreasing trend in PDR during westward transport across the Atlantic during its most active long-range transport season in summer. Asian dust, on the other hand, shows some spatial variability in PDR over the Pacific during its most active long-range transport season in spring. The dust PDR is generally smaller over the ocean than over the Tarim basin and nearby downwind regions. PDR also shows a decreasing trend with latitude moving northward toward the Arctic, together with an increasing trend in the dust aerosol optical depth (AOD) when passing over polluted Asian regions. Possible explanations include (i) the mixing of dust externally or internally with other types of aerosol over the heavily developed industrial regions in East Asia, and (ii) the downstream mixing of dust plumes from different source regions (i.e., Tarim and Gobi). Dust from different source regions exhibits relatively large differences in PDR, with mean values of 0.34±0.07, 0.28±0.06, and 0.30±0.08, respectively, over the Tarim basin, Gobi Desert and Northwest African source regions. Different transport mechanisms are seen for African dust and Asian dust. Asian dust transport is originated by cold fronts and driven by westerly jets. In contrast, summer African transatlantic dust transport is driven by trade winds and is generally well confined in altitude in the free troposphere throughout the tropics and subtropics.
An extensive dust storm originating on 17 August 2006 in North Africa was observed and tracked by... more An extensive dust storm originating on 17 August 2006 in North Africa was observed and tracked by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. Over the next several days, the dust layer moved westward across the Atlantic Ocean and into the Gulf of Mexico. The initial stages of the event were examined using a sequence of CALIPSO measurements. The first of these was acquired very near the source on 18 August. Successive measurements were made over the Atlantic Ocean on 19 and 20 August, at respective locations approximately $1300 km and $2400 km from the source region. The later stages of the event were assessed using measurements acquired by the NASA Langley Research Center airborne HSRL over the Gulf of Mexico on 28 August. Within the free troposphere, the intrinsic optical properties of the dust remain relatively unchanged for the first 3 d of transport over the Atlantic Ocean. This is consistent with previous in situ measurements that have shown that there is little change in the size distribution of dust as it crosses the Atlantic. After the 10 d journey to the Gulf of Mexico, some changes are seen in the lidar ratios, the backscatter color ratio, and the optical depth ratio. The linear depolarization ratio appears to remain essentially constant ($0.32) at all four locations mentioned above, demonstrating a notable consistency in the dust particle nonsphericity. The measured 532 nm lidar ratios are 41 ± 3, 41 ± 4, 41 ± 6 and 45.8 ± 0.8 sr, respectively, at locations near the source, over the Atlantic Ocean, and in the Gulf of Mexico. The corresponding 1064 nm lidar ratios are 52 ± 5, 55 ± 5, 54 ± 13 and 44 ± 8.3 sr. The 532 nm lidar ratios are consistent with previous measurements and with CALIPSO's prelaunch models. The lidar ratios retrieved at 1064 nm are somewhat larger than would be expected on the basis of existing modeling studies. The backscatter color ratios are 0.74 ± 0.07, 0.75 ± 0.08, 0.72 ± 0.04 and 0.62 ± 0.01, and the optical depth ratios are 0.97 ± 0.02, 1.01 ± 0.05, 0.93 ± 0.17 and 0.62 ± 0.13, respectively.
We determine the extinction-to-backscatter (S a) ratios of dust using (1) airborne in situ measur... more We determine the extinction-to-backscatter (S a) ratios of dust using (1) airborne in situ measurements of microphysical properties, (2) modeling studies, and (3) the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations recorded during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment conducted from Sal, Cape Verde during August to September 2006. Using CALIPSO measurements of the attenuated backscatter of lofted Saharan dust layers, we apply the transmittance technique to estimate dust S a ratios at 532 nm and a two-color method to determine the corresponding 1064 nm S a. This method yielded dust S a ratios of 39.8 ± 1.4 and 51.8 ± 3.6 sr at 532 and 1064 nm, respectively. Second, S a at both wavelengths is independently calculated using size distributions measured aboard the NASA DC-8 and estimates of Saharan dust complex refractive indices applied in a T-Matrix scheme. We found S a ratios of 39.1 ± 3.5 and 50.0 ± 4 sr at 532 and 1064 nm, respectively, using the T-Matrix calculations applied to measured size spectra. Finally, in situ measurements of the total scattering (550 nm) and absorption coefficients (532 nm) are used to generate an extinction profile that is used to constrain the CALIPSO 532 nm extinction profile and thus generate a stratified 532 nm S a. This method yielded an S a ratio at 532 nm of 35.7 sr in the dust layer and 25 sr in the marine boundary layer consistent with a predominantly sea-salt aerosol near the ocean surface. Combinatorial simulations using noisy size spectra and refractive indices were used to estimate the mean and uncertainty (one standard deviation) of these S a ratios. These simulations produced a mean (± uncertainty) of 39.4 (±5.9) and 56.5 (±16.5) sr at 532 and 1064 nm, respectively, corresponding to percentage uncertainties of 15% and 29%. These results will provide a measurements-based estimate of the dust S a for use in backscatter lidar inversion algorithms such as CALIOP (Cloud-Aerosol Lidar With Orthogonal Polarization).
This study examines seasonal variations of the vertical distribution of aerosols through a statis... more This study examines seasonal variations of the vertical distribution of aerosols through a statistical analysis of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar observations from June 2006 to November 2007. A data-screening scheme is developed to attain good quality data in cloud-free conditions, and the polarization measurement is used to separate dust from non-dust aerosol. The CALIPSO aerosol observations are compared with aerosol simulations from the Goddard Chemistry Aerosol Radiation Transport (GOCART) model and aerosol optical depth (AOD) measurements from the MODerate resolution Imaging Spectroradiometer (MODIS). The CALIPSO observations of geographical patterns and seasonal variations of AOD are generally consistent with GOCART simulations and MODIS retrievals especially near source regions, while the magnitude of AOD shows large discrepancies in most regions. Both the CALIPSO observation and GOCART model show that the aerosol extinction scale heights in major dust and smoke source regions are generally higher than that in industrial pollution source regions. The CALIPSO aerosol lidar ratio also generally agrees with GOCART model within 30% on regional scales. Major differences between satellite observations and GOCART model are identified, including (1) an underestimate of aerosol extinction by GOCART over the Indian sub-continent, (2) much larger aerosol extinction calculated by GOCART than observed by CALIPSO in dust source regions, (3) much weaker in magnitude and more concentrated aerosol in the lower atmosphere in CALIPSO observation than GOCART model over transported areas in midlatitudes, and (4) consistently lower aerosol scale height by CALIPSO observation than GOCART model. Possible factors contributing to these differences are discussed.
Journal of Atmospheric and Oceanic Technology, 2009
The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization li... more The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization lidar that performs global profiling of aerosols and clouds in the troposphere and lower stratosphere. CALIOP is the primary instrument on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, which has flown in formation with the NASA A-train constellation of satellites since May 2006. The global, multiyear dataset obtained from CALIOP provides a new view of the earth’s atmosphere and will lead to an improved understanding of the role of aerosols and clouds in the climate system. A suite of algorithms has been developed to identify aerosol and cloud layers and to retrieve a variety of optical and microphysical properties. CALIOP represents a significant advance over previous space lidars, and the algorithms that have been developed have many innovative aspects to take advantage of its capabilities. This paper provides a brief overview of the CALIPSO m...
Global cloud-top height statistics of marine-boundary-layer clouds are derived from the Cloud-Aer... more Global cloud-top height statistics of marine-boundary-layer clouds are derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Level 2 aerosol and cloud layer products. The boundary-layer lapse rate in the northeast region of the Pacific Ocean is investigated using sea surface temperature (SST) data from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), cloudtop temperature data from the Moderate Resolution Imaging Spectroradiometer (MODIS), and cloud-top height data from CALIPSO. Based on the lapse rate derived from the combined CALIPSO/MODIS/AMSR-E measurements, cloud-top heights in regions within CALIPSO tracks are derived from AMSR SST and MODIS cloud temperature to test the validity of this approach. For homogeneous low-level clouds, the results agree with the cloud-top height from the collocated CALIPSO cloud-top height measurements. These results suggest that the database of derived lapse rates from the combined measurements can be applied to study cloud-top height climate statistics using the MODIS and AMSR data when CALIPSO observations are not available.
The light extinction and direct forcing properties of the atmospheric aerosol were investigated f... more The light extinction and direct forcing properties of the atmospheric aerosol were investigated for a midwestern rural site (Bondville, IL) using field measurements, a semi-empirical light extinction model, and a radiative transfer code. Model inputs were based on the site measurements ...
The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET)... more The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET) data, and based on aerosol categorization results, the global ADRF is estimated. The CRM-2.1.2, a stand-alone version of the radiative transfer model implemented in NCAR's community climate model, CCM-3.6, is used for the evaluation. A method of determining the aerosol optical parameters is proposed for the ADRF calculation using AERONET data. Linear regression in the log-log plane makes it possible to represent the wavelength-dependent optical properties in the model using AERONET measurements. The local ADRF is estimated at Gosan, Jeju in Korea in Spring from 2001 to 2003, and the ground-based radiation measurements during the ACE-Asia IOP are used to validate the calculation. Using 3 years of AERONET data, the mean forcing efficiency at 500 nm at Gosan in Spring season is evaluated as À80.5713.2 Wm À2 at the surface and À29.974.9 Wm À2 at the top of atmosphere (TOA). The seasonal variations of the ADRF at eight AERONET sites are calculated from AERONET climatology data. The ADRF calculation at the TOA is compared with the CERES/Terra measurement, and the comparison verifies that the methodology used in this study is suitable for the global ADRF evaluation. Finally, the ADRF values in 14 regions are evaluated. Large ADRF values in Asia and Sahara regions suggest the relative importance of the aerosols on the energy budget in these regions.
Global satellite observations of lidar backscatter measurements acquired by the Cloud-Aerosol Lid... more Global satellite observations of lidar backscatter measurements acquired by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission and collocated sea surface wind speed data from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), are used to investigate the relation between wind driven wave slope variance and sea surface wind speed. The new slope variance-wind speed relation established from this study is similar to the linear relation from Cox-Munk (1954) and the log-linear relation from Wu (1990) for wind speed larger than 7 m/s and 13.3 m/s, respectively. For wind speed less than 7 m/s, the slope variance is proportional to the square root of the wind speed, assuming a two dimensional isotropic Gaussian wave slope distribution. This slope variance-wind speed relation becomes linear if a one dimensional Gaussian wave slope distribution and linear slope variance-wind speed relation are assumed. Contributions from whitecaps and subsurface backscattering are effectively removed by using 532 nm lidar depolarization measurements. This new slope variance-wind speed relation is used to derive sea surface wind speed from CALIPSO single shot lidar measurements (70 m spot size), after correcting for atmospheric attenuation. The CALIPSO wind speed result agrees with the collocated AMSR-E wind speed, with 1.2 m/s rms error. Ocean surface with lowest atmospheric loading and moderate wind speed (7-9 m/s) is used as target for lidar calibration correction.
The crystallization behaviour of some glasses in the CaO–ZnO–Al2O3–SiO2 system was investigated u... more The crystallization behaviour of some glasses in the CaO–ZnO–Al2O3–SiO2 system was investigated using different heattreatment parameters. Cr2O3 and CaF2 were used as nucleating agents. Differential thermal analysis, X-ray diffraction, dilatometry and scanning electron microscopy were used in this study. Melilite, αand β-willemite, anorthite, wollastonite, pseudowollastonite and petedunnite phases developed in the investigated glasses. The formation of compatible and incompatible phase assemblages and the effect of Cr2O3 and CaF2 are illustrated. Glass-ceramics with fine-grained microstructures and CTE values ranging from 36 to 73 × 10 K in the 20-700°C range were obtained.
Geoscience and Remote Sensing IEEE International Symposium, 2004
We present the distributions of the lidar observable optical properties for dust, continental pol... more We present the distributions of the lidar observable optical properties for dust, continental pollution and marine aerosols using the Cloud Physics Lidar (CPL, ef.) measurements. This study uses CPL measurements during CRYSTAL-FACE off the coast of Florida to extract probability distribution functions (PDFs) of the lidar depolarization ratios (delta), and the ratio of the backscatter at 1064 nm to 532
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007
Case studies from the first three months of the Cloud and Aerosol Lidar and Infrared Pathfinder S... more Case studies from the first three months of the Cloud and Aerosol Lidar and Infrared Pathfinder Spaceborne Observations (CALIPSO) measurements of lofted aerosol layers are analyzed using transmittance [Young, 1995] and two-wavelength algorithms [Vaughan et al., 2004] to determine the aerosol extinction-to-backscatter ratios at 532 and 1064 nm. The transmittance method requires clear air below the layer so that the transmittance through the layer can be determined. Suitable scenes are selected from the browse images and clear air below features is identified by low 532 nm backscatter signal and confirmed by low depolarization and color ratios. The transmittance and two-wavelength techniques are applied to a number of lofted layers and the extinction-to-backscatter ratios are compared with values obtained from the CALIPSO aerosol models [Omar et al., 2004]. The results obtained from these studies are used to adjust the aerosol models and develop observations based extinction-to-backscatter ratio look-up tables and phase functions. Values obtained by these techniques are compared to S a determinations using other independent methods with a goal of developing probability distribution functions of aerosol type-specific extinction to backscatter ratios. Method Given a solution of the particulate backscatter at 532 nm β 532,p , the two-wavelength method uses a least squares method to minimize the difference between the attenuated total backscatter measurement at 1064 nm, B 1064 and the right hand side of eq. (1).
2011 IEEE MTT-S International Microwave Symposium, 2011
To homogenize the 1 B + field and decrease specific absorption rate (SAR) profile for MRI at 7T, ... more To homogenize the 1 B + field and decrease specific absorption rate (SAR) profile for MRI at 7T, more degrees of freedom are needed and different excitation approaches are required. Multi-channel transceiver arrays based on microstrip resonator (MSR) is a promising approach for signal excitation and reception at ultrahigh-field (UHF) MRI. Travelling wave approach is another method for excitation based
2010 3rd International Symposium on Applied Sciences in Biomedical and Communication Technologies (ISABEL 2010), 2010
... Reson Med. (2006). [2] Vaughan J, DelaBarre L, Snyder C, Adriany G, Collins C, Van de Moortel... more ... Reson Med. (2006). [2] Vaughan J, DelaBarre L, Snyder C, Adriany G, Collins C, Van de Moortele PF, Ritter J, Strupp J, Andersen P, Tian J, Smith M Ugurbil K. RF image optimization at 7T and 9.4T. 2005; Miami p. 953. [3] Ibrahim T, Lee R, Robitaille P. “Effect of RF coil ...
Atmospheric Chemistry and Physics Discussions, 2010
The Bihar pollution pool is a large wintertime increase in pollutants over the eastern parts of t... more The Bihar pollution pool is a large wintertime increase in pollutants over the eastern parts of the Indo Gangetic basin. We use improved carbon monoxide (CO) retrievals from the recent Measurements of Pollution in the Troposphere (MOPITT) version 4 data along with the aerosol data from the latest version 3 of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar instrument and the tropospheric ozone residual products from the Total Ozone Mapping Spectrometer (TOMS)/Solar Backscattered Ultraviolet (SBUV) and Ozone Monitoring Instrument (OMI)/Microwave Limb Sounder (MLS) database to characterize this pollution pool. The feature is seen primarily in the lower troposphere from about November to February with strong concomitant increase in CO, aerosol optical depth and tropospheric ozone columns. The height resolved aerosol data from CALIPSO confirm the trapping of the pollution pool at the lowest altitudes. The observations indicate that MOPITT can capture this low altitude phenomenon even in winter conditions as indicated by the averaging kernels.
We are demonstrating on a few cases the capability of CALIPSO to retrieve the 532 nm lidar ratio ... more We are demonstrating on a few cases the capability of CALIPSO to retrieve the 532 nm lidar ratio over the ocean when CloudSat surface scattering cross section is used as a constraint. We are presenting the algorithm used and comparisons with the column lidar ratio retrieved by the NASA airborne high spectral resolution lidar. For the three cases presented here, the agreement is fairly good. The average CALIPSO 532 nm column lidar ratio bias is 13.7% relative to HSRL, and the relative standard deviation is 13.6%. Considering the natural variability of aerosol microphysical properties, this level of accuracy is significant since the lidar ratio is a good indicator of aerosol types. We are discussing dependencies of the accuracy of retrieved aerosol lidar ratio on atmospheric aerosol homogeneity, lidar signal to noise ratio, and errors in the optical depth retrievals. We are obtaining the best result (bias 7% and standard deviation around 6%) for a nighttime case with a relatively constant lidar ratio (in the vertical) indicative of homogeneous aerosol type.
We use measurements and models to develop aerosol models for use in the inversion algorithms for ... more We use measurements and models to develop aerosol models for use in the inversion algorithms for the Cloud Aerosol Lidar and Imager Pathfinder Spaceborne Observations (CALIPSO). Radiance measurements and inversions of the AErosol RObotic NETwork (AERONET 1, 2) are used to group global atmospheric aerosols using optical and microphysical parameters. This study uses more than 10 5 records of radiance measurements, aerosol size distributions, and complex refractive indices to generate the optical properties of the aerosol at more 200 sites worldwide. These properties together with the radiance measurements are then classified using classical clustering methods to group the sites according to the type of aerosol with the greatest frequency of occurrence at each site. Six significant clusters are identified: desert dust, biomass burning, urban industrial pollution, rural background, marine, and dirty pollution. Three of these are used in the CALIPSO aerosol models to characterize desert dust, biomass burning, and polluted continental aerosols. The CALIPSO aerosol model also uses the coarse mode of desert dust and the fine mode of biomass burning to build a polluted dust model. For marine aerosol, the CALIPSO aerosol model uses measurements from the SEAS experiment 3. In addition to categorizing the aerosol types, the cluster analysis provides all the column optical and microphysical properties for each cluster.
Thomas H. Chyba, Doyle A. Temple, Scott Bailey, Arthur Bowman, Wei Gong, Ali Omar, Russell Battle... more Thomas H. Chyba, Doyle A. Temple, Scott Bailey, Arthur Bowman, Wei Gong, Ali Omar, Russell Battle, Belicia Bradley, John Davis, Mika Edmondson, Anne Futrell, Chadwick Giles, Clarence Glenn, David Harper, Lincoln Haughton, Demetra Johnson, Ayana Jordan, Nasira Latif, ...
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT form only given, as follows. The magnetic field generated by a conventional MSR is inhom... more ABSTRACT form only given, as follows. The magnetic field generated by a conventional MSR is inhomogeneous along the resonator axis. It is strong at the center and weak at the terminating ends. To homogenize the B1+ field, it is required to modify the traditional MSR. Recently, an approach based on alternating impedance MSR has been presented. Another configuration of alternating impedance MSR is proposed. Results indicate that, the alternating impedance MSR with circular elements is the best coil in terms of B1+ field homogeneity.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2013
ABSTRACT Five years of CALIPSO lidar layer products are used to study transpacific transport of A... more ABSTRACT Five years of CALIPSO lidar layer products are used to study transpacific transport of Asian dust. We focus on possible changes to dust intrinsic optical properties during the course of transport, with specific emphasis on changes to particulate depolarization ratio (PDR). PDR distributions for Asian dust transported across the Pacific are compared to previously reported PDR distributions for African dust transported across the Atlantic. African dust shows a slight decreasing trend in PDR during westward transport across the Atlantic during its most active long-range transport season in summer. Asian dust, on the other hand, shows some spatial variability in PDR over the Pacific during its most active long-range transport season in spring. The dust PDR is generally smaller over the ocean than over the Tarim basin and nearby downwind regions. PDR also shows a decreasing trend with latitude moving northward toward the Arctic, together with an increasing trend in the dust aerosol optical depth (AOD) when passing over polluted Asian regions. Possible explanations include (i) the mixing of dust externally or internally with other types of aerosol over the heavily developed industrial regions in East Asia, and (ii) the downstream mixing of dust plumes from different source regions (i.e., Tarim and Gobi). Dust from different source regions exhibits relatively large differences in PDR, with mean values of 0.34±0.07, 0.28±0.06, and 0.30±0.08, respectively, over the Tarim basin, Gobi Desert and Northwest African source regions. Different transport mechanisms are seen for African dust and Asian dust. Asian dust transport is originated by cold fronts and driven by westerly jets. In contrast, summer African transatlantic dust transport is driven by trade winds and is generally well confined in altitude in the free troposphere throughout the tropics and subtropics.
An extensive dust storm originating on 17 August 2006 in North Africa was observed and tracked by... more An extensive dust storm originating on 17 August 2006 in North Africa was observed and tracked by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. Over the next several days, the dust layer moved westward across the Atlantic Ocean and into the Gulf of Mexico. The initial stages of the event were examined using a sequence of CALIPSO measurements. The first of these was acquired very near the source on 18 August. Successive measurements were made over the Atlantic Ocean on 19 and 20 August, at respective locations approximately $1300 km and $2400 km from the source region. The later stages of the event were assessed using measurements acquired by the NASA Langley Research Center airborne HSRL over the Gulf of Mexico on 28 August. Within the free troposphere, the intrinsic optical properties of the dust remain relatively unchanged for the first 3 d of transport over the Atlantic Ocean. This is consistent with previous in situ measurements that have shown that there is little change in the size distribution of dust as it crosses the Atlantic. After the 10 d journey to the Gulf of Mexico, some changes are seen in the lidar ratios, the backscatter color ratio, and the optical depth ratio. The linear depolarization ratio appears to remain essentially constant ($0.32) at all four locations mentioned above, demonstrating a notable consistency in the dust particle nonsphericity. The measured 532 nm lidar ratios are 41 ± 3, 41 ± 4, 41 ± 6 and 45.8 ± 0.8 sr, respectively, at locations near the source, over the Atlantic Ocean, and in the Gulf of Mexico. The corresponding 1064 nm lidar ratios are 52 ± 5, 55 ± 5, 54 ± 13 and 44 ± 8.3 sr. The 532 nm lidar ratios are consistent with previous measurements and with CALIPSO's prelaunch models. The lidar ratios retrieved at 1064 nm are somewhat larger than would be expected on the basis of existing modeling studies. The backscatter color ratios are 0.74 ± 0.07, 0.75 ± 0.08, 0.72 ± 0.04 and 0.62 ± 0.01, and the optical depth ratios are 0.97 ± 0.02, 1.01 ± 0.05, 0.93 ± 0.17 and 0.62 ± 0.13, respectively.
We determine the extinction-to-backscatter (S a) ratios of dust using (1) airborne in situ measur... more We determine the extinction-to-backscatter (S a) ratios of dust using (1) airborne in situ measurements of microphysical properties, (2) modeling studies, and (3) the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations recorded during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment conducted from Sal, Cape Verde during August to September 2006. Using CALIPSO measurements of the attenuated backscatter of lofted Saharan dust layers, we apply the transmittance technique to estimate dust S a ratios at 532 nm and a two-color method to determine the corresponding 1064 nm S a. This method yielded dust S a ratios of 39.8 ± 1.4 and 51.8 ± 3.6 sr at 532 and 1064 nm, respectively. Second, S a at both wavelengths is independently calculated using size distributions measured aboard the NASA DC-8 and estimates of Saharan dust complex refractive indices applied in a T-Matrix scheme. We found S a ratios of 39.1 ± 3.5 and 50.0 ± 4 sr at 532 and 1064 nm, respectively, using the T-Matrix calculations applied to measured size spectra. Finally, in situ measurements of the total scattering (550 nm) and absorption coefficients (532 nm) are used to generate an extinction profile that is used to constrain the CALIPSO 532 nm extinction profile and thus generate a stratified 532 nm S a. This method yielded an S a ratio at 532 nm of 35.7 sr in the dust layer and 25 sr in the marine boundary layer consistent with a predominantly sea-salt aerosol near the ocean surface. Combinatorial simulations using noisy size spectra and refractive indices were used to estimate the mean and uncertainty (one standard deviation) of these S a ratios. These simulations produced a mean (± uncertainty) of 39.4 (±5.9) and 56.5 (±16.5) sr at 532 and 1064 nm, respectively, corresponding to percentage uncertainties of 15% and 29%. These results will provide a measurements-based estimate of the dust S a for use in backscatter lidar inversion algorithms such as CALIOP (Cloud-Aerosol Lidar With Orthogonal Polarization).
This study examines seasonal variations of the vertical distribution of aerosols through a statis... more This study examines seasonal variations of the vertical distribution of aerosols through a statistical analysis of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar observations from June 2006 to November 2007. A data-screening scheme is developed to attain good quality data in cloud-free conditions, and the polarization measurement is used to separate dust from non-dust aerosol. The CALIPSO aerosol observations are compared with aerosol simulations from the Goddard Chemistry Aerosol Radiation Transport (GOCART) model and aerosol optical depth (AOD) measurements from the MODerate resolution Imaging Spectroradiometer (MODIS). The CALIPSO observations of geographical patterns and seasonal variations of AOD are generally consistent with GOCART simulations and MODIS retrievals especially near source regions, while the magnitude of AOD shows large discrepancies in most regions. Both the CALIPSO observation and GOCART model show that the aerosol extinction scale heights in major dust and smoke source regions are generally higher than that in industrial pollution source regions. The CALIPSO aerosol lidar ratio also generally agrees with GOCART model within 30% on regional scales. Major differences between satellite observations and GOCART model are identified, including (1) an underestimate of aerosol extinction by GOCART over the Indian sub-continent, (2) much larger aerosol extinction calculated by GOCART than observed by CALIPSO in dust source regions, (3) much weaker in magnitude and more concentrated aerosol in the lower atmosphere in CALIPSO observation than GOCART model over transported areas in midlatitudes, and (4) consistently lower aerosol scale height by CALIPSO observation than GOCART model. Possible factors contributing to these differences are discussed.
Journal of Atmospheric and Oceanic Technology, 2009
The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization li... more The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization lidar that performs global profiling of aerosols and clouds in the troposphere and lower stratosphere. CALIOP is the primary instrument on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, which has flown in formation with the NASA A-train constellation of satellites since May 2006. The global, multiyear dataset obtained from CALIOP provides a new view of the earth’s atmosphere and will lead to an improved understanding of the role of aerosols and clouds in the climate system. A suite of algorithms has been developed to identify aerosol and cloud layers and to retrieve a variety of optical and microphysical properties. CALIOP represents a significant advance over previous space lidars, and the algorithms that have been developed have many innovative aspects to take advantage of its capabilities. This paper provides a brief overview of the CALIPSO m...
Global cloud-top height statistics of marine-boundary-layer clouds are derived from the Cloud-Aer... more Global cloud-top height statistics of marine-boundary-layer clouds are derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Level 2 aerosol and cloud layer products. The boundary-layer lapse rate in the northeast region of the Pacific Ocean is investigated using sea surface temperature (SST) data from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), cloudtop temperature data from the Moderate Resolution Imaging Spectroradiometer (MODIS), and cloud-top height data from CALIPSO. Based on the lapse rate derived from the combined CALIPSO/MODIS/AMSR-E measurements, cloud-top heights in regions within CALIPSO tracks are derived from AMSR SST and MODIS cloud temperature to test the validity of this approach. For homogeneous low-level clouds, the results agree with the cloud-top height from the collocated CALIPSO cloud-top height measurements. These results suggest that the database of derived lapse rates from the combined measurements can be applied to study cloud-top height climate statistics using the MODIS and AMSR data when CALIPSO observations are not available.
The light extinction and direct forcing properties of the atmospheric aerosol were investigated f... more The light extinction and direct forcing properties of the atmospheric aerosol were investigated for a midwestern rural site (Bondville, IL) using field measurements, a semi-empirical light extinction model, and a radiative transfer code. Model inputs were based on the site measurements ...
The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET)... more The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET) data, and based on aerosol categorization results, the global ADRF is estimated. The CRM-2.1.2, a stand-alone version of the radiative transfer model implemented in NCAR's community climate model, CCM-3.6, is used for the evaluation. A method of determining the aerosol optical parameters is proposed for the ADRF calculation using AERONET data. Linear regression in the log-log plane makes it possible to represent the wavelength-dependent optical properties in the model using AERONET measurements. The local ADRF is estimated at Gosan, Jeju in Korea in Spring from 2001 to 2003, and the ground-based radiation measurements during the ACE-Asia IOP are used to validate the calculation. Using 3 years of AERONET data, the mean forcing efficiency at 500 nm at Gosan in Spring season is evaluated as À80.5713.2 Wm À2 at the surface and À29.974.9 Wm À2 at the top of atmosphere (TOA). The seasonal variations of the ADRF at eight AERONET sites are calculated from AERONET climatology data. The ADRF calculation at the TOA is compared with the CERES/Terra measurement, and the comparison verifies that the methodology used in this study is suitable for the global ADRF evaluation. Finally, the ADRF values in 14 regions are evaluated. Large ADRF values in Asia and Sahara regions suggest the relative importance of the aerosols on the energy budget in these regions.
Global satellite observations of lidar backscatter measurements acquired by the Cloud-Aerosol Lid... more Global satellite observations of lidar backscatter measurements acquired by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission and collocated sea surface wind speed data from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), are used to investigate the relation between wind driven wave slope variance and sea surface wind speed. The new slope variance-wind speed relation established from this study is similar to the linear relation from Cox-Munk (1954) and the log-linear relation from Wu (1990) for wind speed larger than 7 m/s and 13.3 m/s, respectively. For wind speed less than 7 m/s, the slope variance is proportional to the square root of the wind speed, assuming a two dimensional isotropic Gaussian wave slope distribution. This slope variance-wind speed relation becomes linear if a one dimensional Gaussian wave slope distribution and linear slope variance-wind speed relation are assumed. Contributions from whitecaps and subsurface backscattering are effectively removed by using 532 nm lidar depolarization measurements. This new slope variance-wind speed relation is used to derive sea surface wind speed from CALIPSO single shot lidar measurements (70 m spot size), after correcting for atmospheric attenuation. The CALIPSO wind speed result agrees with the collocated AMSR-E wind speed, with 1.2 m/s rms error. Ocean surface with lowest atmospheric loading and moderate wind speed (7-9 m/s) is used as target for lidar calibration correction.
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