R. Kahn - Academia.edu (original) (raw)
Papers by R. Kahn
You can't always get what you want… MISR flight direction plume height Forward-viewing camera app... more You can't always get what you want… MISR flight direction plume height Forward-viewing camera apparent position Changes in geometric perspective with angle Diner 2003 MISR flight direction plume height Backward-viewing camera parallax Changes in geometric perspective with angle Diner 2003 MISR Plume Heights-The California Camp Fire
You can't always get what you want… MISR flight direction plume height Forward-viewing camera app... more You can't always get what you want… MISR flight direction plume height Forward-viewing camera apparent position Changes in geometric perspective with angle Diner 2003 MISR flight direction plume height Backward-viewing camera parallax Changes in geometric perspective with angle Diner 2003 MISR Plume Heights-The California Camp Fire
Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in di... more Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in diameter, from less than 0.1 µm to more than 100 µm. This wide size range makes dust a unique aerosol species with the ability to interact with many aspects of the Earth system, including radiation, clouds, hydrology, atmospheric chemistry, and biogeochemistry. This review focuses on coarse and super-coarse dust aerosols, which we respectively define as dust particles with a diameter between 2.5 - 10 µm and 10 - 62.5 µm. We review several lines of observational evidence indicating that coarse and super-coarse dust particles are transported farther than previously expected and that the abundance of these particles is substantially underestimated in current global models. We synthesize previous studies that used observations, theories, and model simulations to highlight the impacts of coarse and super-coarse dust aerosols on the Earth system, including their effects on dust-radiation interac...
Site location of each Love My Air sensor, as well as summary statistics of minute-level measureme... more Site location of each Love My Air sensor, as well as summary statistics of minute-level measurements from the co-located sensors included in the analysis PM2.5 (μg/m 3) Temperature (0 C) RH (%) Dewpoint (0 C) Sensor ID Co-location Information Latitude Longitude Minutes operatio nal Mean Median Min-Max Mean Mean Mean CS2 Co-located at I25 Globeville
Geophysical Research Letters
Atmospheric gravity waves can be excited by explosive volcanic eruptions and may reach Earth'... more Atmospheric gravity waves can be excited by explosive volcanic eruptions and may reach Earth's upper atmosphere. In this study, we report on mesoscale concentric gravity waves observed in the mesopause airglow layer following the La Soufriere volcano eruption in April 2021. A large ash plume observed by the spaceborne Multi‐angle Imaging SpectroRadiometer instrument on April 10 reached ∼20 km. Temporal evolution of the volcanic ash plume was provided by the GOES‐16 Advanced Baseline Imager. Nightglow gravity waves were observed by the Visible Infrared Imaging Radiometer Suite Day Night Band. These waves had horizontal wavelengths of ∼25–40 km, and took about a half‐to‐1 hr to travel from the tropopause to the mesopause. Some concentric ionospheric disturbance signatures are also seen in Global Navigation Satellite System‐total electron content maps. We found the launch of gravity waves to be highly correlated with the elevated ash plume from explosive eruptions.
Proceedings of the National Academy of Sciences, 2016
The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative... more The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with th...
Atmospheric Measurement Techniques, 2018
The dispersion of particles from wildfires, volcanic eruptions, dust storms, and other aerosol so... more The dispersion of particles from wildfires, volcanic eruptions, dust storms, and other aerosol sources can affect many environmental factors downwind, including air quality. Aerosol injection height is one source attribute that mediates downwind dispersion, as wind speed and direction can vary dramatically with elevation. Using plume heights derived from space-based, multi-angle imaging, we examine the impact of initializing plumes in the NOAA Air Resources Laboratory's Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model with satellite-measured vs. nominal (model-calculated or VAACreported) injection height on the simulated dispersion of six large aerosol plumes. When there are significant differences in nominal vs. satellite-derived particle injection heights, especially if both heights are in the free troposphere or if one injection height is within the planetary boundary layer (PBL) and the other is above the PBL, differences in simulation results can arise. In the cases studied with significant nominal vs. satellite-derived injection height differences, the HYS-PLIT model can represent plume evolution better, relative to independent satellite observations, if the injection height in the model is constrained by hyper-stereo satellite retrievals.
Journal of Geophysical Research, 2008
We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, ... more We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus-7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground-based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol-rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol-rainfall relationships.
Journal of Geophysical Research: Planets, 1999
The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively i... more The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively investigated using data from three seasons of our Hubble Space Telescope synoptic monitoring program (1993-1997). A subset of the 1996-1997 images covers the landing site of the Mars Pathfinder including a set of images taken after touchdown. Using multicolor imaging from the Wide Field Planetary Camera and the Wide Field Planetary Camera 2, we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch. The analysis technique models calibrated data using a multiple scattering radiative transfer code. Our results support the initial results of Clancy et aI. [1996a] regarding changes between the aphelion and perihelion climate of Mars and provide a more detailed look at the development and decay of the cloud belt. Comparing our dust optical depths to those of the Viking landers for the same seasons, we note a and in sprin•. Our observations of the Pathfinder site in July !997 reveal a dust opacity in •ood a•reement •ith that reported by Pathfinder [S•h ½• ½•.• 1997b]. In addition• the serendipitous occurrence of a dust storm in Valles Marineris in late June 1997 allo•s us to derive a set of dust single scatterin• albedos for use in more accurately modelin• the dust•s radiative properties and e•ects.
ABSTRACT The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) o... more ABSTRACT The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) on the NASA B200 aircraft has acquired extensive datasets of aerosol extinction (532 nm), optical thickness (532 nm), backscatter (532 and 1064 nm), and aerosol depolarization (532 and 1064 nm) profiles coincident with measurements from the Terra and A Train satellites. The HSRL measurements of aerosol intensive optical properties [i.e. aerosol depolarization (532, 1064), extinction/backscatter ratio (``lidar ratio'') (532 nm), and backscatter color ratio (532/1064)], which provide qualitative information about the aerosol physical properties, have been used in a classification procedure to identify major aerosol types and apportion aerosol optical thickness among these aerosol types. This presentation describes how the aerosol types derived from the HSRL data have been used to help assess and interpret aerosol measurements acquired by the CALIPSO and MISR sensors. CALIPSO extinction and backscatter retrievals rely on an algorithm that attempts to identify and classify the aerosol type using surface type, layer altitude, integrated attenuated backscatter, and depolarization ratio. Comparisons of the aerosol types derived from the CALIOP measurements and simulated by the GOCART aerosol transport model have generally shown good agreement among major aerosol types. However, in some cases the CALIOP algorithm misclassifies the aerosol type which results in errors in the CALIOP aerosol extinction and optical thickness measurements. Therefore, the aerosol intensive parameters and aerosol types derived from the coincident airborne HSRL measurements have been used to assess the aerosol types derived from the CALIPSO measurements and simulated by GOCART. The HSRL measurements show that aerosol type often varies with altitude. Consequently, column average measurements of aerosol type derived from passive satellite (e.g. MODIS, MISR) and surface (e.g. AERONET) sensors often represent some mixture of aerosol types. Using the HSRL aerosol type analyses and the aerosol measurements derived from MISR, which provides some qualitative indication of aerosol size, absorption, and shape for the entire atmospheric column, we examine the impact of the vertical variability on the column retrievals of aerosol optical properties.
Journal of Atmospheric and Oceanic Technology, 2016
As atmospheric reflectance dominates top-of-the-atmosphere radiance over ocean, atmospheric corre... more As atmospheric reflectance dominates top-of-the-atmosphere radiance over ocean, atmospheric correction is a critical component of ocean color retrievals. This paper explores the operational Sea-viewing Wide Field-of-view Sensor (SeaWiFS) algorithm atmospheric correction with ~13 000 coincident surface-based aerosol measurements. Aerosol optical depth at 440 nm (AOD440) is overestimated for AOD below ~0.1–0.15 and is increasingly underestimated at higher AOD; also, single-scattering albedo (SSA) appears overestimated when the actual value <~0.96. AOD440 and its spectral slope tend to be overestimated preferentially for coarse-mode particles. Sensitivity analysis shows that changes in these factors lead to systematic differences in derived ocean water-leaving reflectance (Rrs) at 440 nm. The standard SeaWiFS algorithm compensates for AOD anomalies in the presence of nonabsorbing, medium-size-dominated aerosols. However, at low AOD and with absorbing aerosols, in situ observations a...
Aerosols are solid or liquid particles suspended in the air, and those observed by satellite remo... more Aerosols are solid or liquid particles suspended in the air, and those observed by satellite remote sensing are typically between about 0.05 and 10 microns in size. (Note that in traditional aerosol science, the term "aerosol" refers to both the particles and the medium in which they reside, whereas for remote sensing, the term commonly refers to the particles only. In this article, we adopt the remote-sensing definition.) They originate from a great diversity of sources, such as wildfires, volcanoes, soils and desert sands, breaking waves, natural biological activity, agricultural burning, cement production, and fossil fuel combustion. They typically remain in the atmosphere from several days to a week or more, and some travel great distances before returning to Earth's surface via gravitational settling or washout by precipitation. Many aerosol sources exhibit strong seasonal variability, and most experience inter-annual fluctuations. As such, the frequent, global co...
IEEE Transactions on Geoscience and Remote Sensing, 2009
Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging... more Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, are greatly improving our understanding of global aerosol optical depth (AOD). Yet, there are sampling issues. MODIS' specific orbital geometry, convolved with the need to avoid bright surfaces (glint, desert, clouds, etc.), means that AOD can be under-or over-sampled in places. When deriving downstream products, such as daily or monthly gridded AOD, one must consider the spatial and temporal density of the measurements relative to the gradients of the true AOD. Additionally, retrieval confidence criteria should be considered. Averaged products are highly dependent on choices made for data aggregation and weighting, and sampling errors can be further propagated when deriving regional or global "mean" AOD. Different choices for aggregation and weighting result in estimates of regional and global means varying by 30% or more. The impacts of a particular averaging algorithm vary by region and surface type and can be shown to represent different tolerance for clouds and retrieval confidence.
Multi-Sensor Theory Changes in volcanic emissions correspond to variations in the magma plumbing ... more Multi-Sensor Theory Changes in volcanic emissions correspond to variations in the magma plumbing system. By tracking emissions (Fig. 1) we aim to help understand the processes occurring at depth. Satellite-based remote sensing data was collected from multiple NASA polar orbiting instruments with significant data records (13-18 years). Stereo anaglyphs of volcanic plumes in Kamchatka. To view in 3D, please use glasses provided. A) Shiveluch, November 23, 2014; B) Kliuchevskoi, June 29, 2007; C) Karymsky, February 27 2015; and D) Zhupanovsky, November 9, 2014. Note: North is to the left in each anaglyph.
2.1 Regulation of GSK-3 activity through phosphorylation by upstream kinases. 2.1.1 Inhibitory N-... more 2.1 Regulation of GSK-3 activity through phosphorylation by upstream kinases. 2.1.1 Inhibitory N-terminal phosphorylation When serine 9 of GSK-3 (or serine 21 of GSK-3) is phosphorylated, it mimicks a primed, intramolecular pseudosubstrate that acts in cis as a competitive inhibitor of GSK-3 activity (Cross et al., 1995). The crystal structure of GSK-3 revealed that the negatively charged phosphate on primed substrates fits into a pocket of positively charged residues in the www.intechopen.com Molecular Mechanisms Underlying Pluripotency and Lineage Commitment-The Role of GSK-3 371 substrate binding cleft of the kinase, thereby placing the substrate into the proper orientation for GSK-3-mediated phosphorylation (Bax et al., 2001; Dajani et al., 2001; ter Haar et al., 2001). This pocket also binds the phosphorylated N-terminal peptide of GSK-3 when it is phosphorylated at S9/S21-competing out exogenous substrates and hence, interfering with activity. There are several kinases capable of inhibiting GSK-3 through S9/S21 phosphorylation, including PKB/Akt, p70 ribosomal S6 kinase, p90 ribosomal S6 kinase, protein kinase A and certain protein kinase Cs (
You can't always get what you want… MISR flight direction plume height Forward-viewing camera app... more You can't always get what you want… MISR flight direction plume height Forward-viewing camera apparent position Changes in geometric perspective with angle Diner 2003 MISR flight direction plume height Backward-viewing camera parallax Changes in geometric perspective with angle Diner 2003 MISR Plume Heights-The California Camp Fire
You can't always get what you want… MISR flight direction plume height Forward-viewing camera app... more You can't always get what you want… MISR flight direction plume height Forward-viewing camera apparent position Changes in geometric perspective with angle Diner 2003 MISR flight direction plume height Backward-viewing camera parallax Changes in geometric perspective with angle Diner 2003 MISR Plume Heights-The California Camp Fire
Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in di... more Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in diameter, from less than 0.1 µm to more than 100 µm. This wide size range makes dust a unique aerosol species with the ability to interact with many aspects of the Earth system, including radiation, clouds, hydrology, atmospheric chemistry, and biogeochemistry. This review focuses on coarse and super-coarse dust aerosols, which we respectively define as dust particles with a diameter between 2.5 - 10 µm and 10 - 62.5 µm. We review several lines of observational evidence indicating that coarse and super-coarse dust particles are transported farther than previously expected and that the abundance of these particles is substantially underestimated in current global models. We synthesize previous studies that used observations, theories, and model simulations to highlight the impacts of coarse and super-coarse dust aerosols on the Earth system, including their effects on dust-radiation interac...
Site location of each Love My Air sensor, as well as summary statistics of minute-level measureme... more Site location of each Love My Air sensor, as well as summary statistics of minute-level measurements from the co-located sensors included in the analysis PM2.5 (μg/m 3) Temperature (0 C) RH (%) Dewpoint (0 C) Sensor ID Co-location Information Latitude Longitude Minutes operatio nal Mean Median Min-Max Mean Mean Mean CS2 Co-located at I25 Globeville
Geophysical Research Letters
Atmospheric gravity waves can be excited by explosive volcanic eruptions and may reach Earth'... more Atmospheric gravity waves can be excited by explosive volcanic eruptions and may reach Earth's upper atmosphere. In this study, we report on mesoscale concentric gravity waves observed in the mesopause airglow layer following the La Soufriere volcano eruption in April 2021. A large ash plume observed by the spaceborne Multi‐angle Imaging SpectroRadiometer instrument on April 10 reached ∼20 km. Temporal evolution of the volcanic ash plume was provided by the GOES‐16 Advanced Baseline Imager. Nightglow gravity waves were observed by the Visible Infrared Imaging Radiometer Suite Day Night Band. These waves had horizontal wavelengths of ∼25–40 km, and took about a half‐to‐1 hr to travel from the tropopause to the mesopause. Some concentric ionospheric disturbance signatures are also seen in Global Navigation Satellite System‐total electron content maps. We found the launch of gravity waves to be highly correlated with the elevated ash plume from explosive eruptions.
Proceedings of the National Academy of Sciences, 2016
The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative... more The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with th...
Atmospheric Measurement Techniques, 2018
The dispersion of particles from wildfires, volcanic eruptions, dust storms, and other aerosol so... more The dispersion of particles from wildfires, volcanic eruptions, dust storms, and other aerosol sources can affect many environmental factors downwind, including air quality. Aerosol injection height is one source attribute that mediates downwind dispersion, as wind speed and direction can vary dramatically with elevation. Using plume heights derived from space-based, multi-angle imaging, we examine the impact of initializing plumes in the NOAA Air Resources Laboratory's Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model with satellite-measured vs. nominal (model-calculated or VAACreported) injection height on the simulated dispersion of six large aerosol plumes. When there are significant differences in nominal vs. satellite-derived particle injection heights, especially if both heights are in the free troposphere or if one injection height is within the planetary boundary layer (PBL) and the other is above the PBL, differences in simulation results can arise. In the cases studied with significant nominal vs. satellite-derived injection height differences, the HYS-PLIT model can represent plume evolution better, relative to independent satellite observations, if the injection height in the model is constrained by hyper-stereo satellite retrievals.
Journal of Geophysical Research, 2008
We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, ... more We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus-7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground-based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol-rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol-rainfall relationships.
Journal of Geophysical Research: Planets, 1999
The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively i... more The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively investigated using data from three seasons of our Hubble Space Telescope synoptic monitoring program (1993-1997). A subset of the 1996-1997 images covers the landing site of the Mars Pathfinder including a set of images taken after touchdown. Using multicolor imaging from the Wide Field Planetary Camera and the Wide Field Planetary Camera 2, we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch. The analysis technique models calibrated data using a multiple scattering radiative transfer code. Our results support the initial results of Clancy et aI. [1996a] regarding changes between the aphelion and perihelion climate of Mars and provide a more detailed look at the development and decay of the cloud belt. Comparing our dust optical depths to those of the Viking landers for the same seasons, we note a and in sprin•. Our observations of the Pathfinder site in July !997 reveal a dust opacity in •ood a•reement •ith that reported by Pathfinder [S•h ½• ½•.• 1997b]. In addition• the serendipitous occurrence of a dust storm in Valles Marineris in late June 1997 allo•s us to derive a set of dust single scatterin• albedos for use in more accurately modelin• the dust•s radiative properties and e•ects.
ABSTRACT The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) o... more ABSTRACT The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) on the NASA B200 aircraft has acquired extensive datasets of aerosol extinction (532 nm), optical thickness (532 nm), backscatter (532 and 1064 nm), and aerosol depolarization (532 and 1064 nm) profiles coincident with measurements from the Terra and A Train satellites. The HSRL measurements of aerosol intensive optical properties [i.e. aerosol depolarization (532, 1064), extinction/backscatter ratio (``lidar ratio'') (532 nm), and backscatter color ratio (532/1064)], which provide qualitative information about the aerosol physical properties, have been used in a classification procedure to identify major aerosol types and apportion aerosol optical thickness among these aerosol types. This presentation describes how the aerosol types derived from the HSRL data have been used to help assess and interpret aerosol measurements acquired by the CALIPSO and MISR sensors. CALIPSO extinction and backscatter retrievals rely on an algorithm that attempts to identify and classify the aerosol type using surface type, layer altitude, integrated attenuated backscatter, and depolarization ratio. Comparisons of the aerosol types derived from the CALIOP measurements and simulated by the GOCART aerosol transport model have generally shown good agreement among major aerosol types. However, in some cases the CALIOP algorithm misclassifies the aerosol type which results in errors in the CALIOP aerosol extinction and optical thickness measurements. Therefore, the aerosol intensive parameters and aerosol types derived from the coincident airborne HSRL measurements have been used to assess the aerosol types derived from the CALIPSO measurements and simulated by GOCART. The HSRL measurements show that aerosol type often varies with altitude. Consequently, column average measurements of aerosol type derived from passive satellite (e.g. MODIS, MISR) and surface (e.g. AERONET) sensors often represent some mixture of aerosol types. Using the HSRL aerosol type analyses and the aerosol measurements derived from MISR, which provides some qualitative indication of aerosol size, absorption, and shape for the entire atmospheric column, we examine the impact of the vertical variability on the column retrievals of aerosol optical properties.
Journal of Atmospheric and Oceanic Technology, 2016
As atmospheric reflectance dominates top-of-the-atmosphere radiance over ocean, atmospheric corre... more As atmospheric reflectance dominates top-of-the-atmosphere radiance over ocean, atmospheric correction is a critical component of ocean color retrievals. This paper explores the operational Sea-viewing Wide Field-of-view Sensor (SeaWiFS) algorithm atmospheric correction with ~13 000 coincident surface-based aerosol measurements. Aerosol optical depth at 440 nm (AOD440) is overestimated for AOD below ~0.1–0.15 and is increasingly underestimated at higher AOD; also, single-scattering albedo (SSA) appears overestimated when the actual value <~0.96. AOD440 and its spectral slope tend to be overestimated preferentially for coarse-mode particles. Sensitivity analysis shows that changes in these factors lead to systematic differences in derived ocean water-leaving reflectance (Rrs) at 440 nm. The standard SeaWiFS algorithm compensates for AOD anomalies in the presence of nonabsorbing, medium-size-dominated aerosols. However, at low AOD and with absorbing aerosols, in situ observations a...
Aerosols are solid or liquid particles suspended in the air, and those observed by satellite remo... more Aerosols are solid or liquid particles suspended in the air, and those observed by satellite remote sensing are typically between about 0.05 and 10 microns in size. (Note that in traditional aerosol science, the term "aerosol" refers to both the particles and the medium in which they reside, whereas for remote sensing, the term commonly refers to the particles only. In this article, we adopt the remote-sensing definition.) They originate from a great diversity of sources, such as wildfires, volcanoes, soils and desert sands, breaking waves, natural biological activity, agricultural burning, cement production, and fossil fuel combustion. They typically remain in the atmosphere from several days to a week or more, and some travel great distances before returning to Earth's surface via gravitational settling or washout by precipitation. Many aerosol sources exhibit strong seasonal variability, and most experience inter-annual fluctuations. As such, the frequent, global co...
IEEE Transactions on Geoscience and Remote Sensing, 2009
Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging... more Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, are greatly improving our understanding of global aerosol optical depth (AOD). Yet, there are sampling issues. MODIS' specific orbital geometry, convolved with the need to avoid bright surfaces (glint, desert, clouds, etc.), means that AOD can be under-or over-sampled in places. When deriving downstream products, such as daily or monthly gridded AOD, one must consider the spatial and temporal density of the measurements relative to the gradients of the true AOD. Additionally, retrieval confidence criteria should be considered. Averaged products are highly dependent on choices made for data aggregation and weighting, and sampling errors can be further propagated when deriving regional or global "mean" AOD. Different choices for aggregation and weighting result in estimates of regional and global means varying by 30% or more. The impacts of a particular averaging algorithm vary by region and surface type and can be shown to represent different tolerance for clouds and retrieval confidence.
Multi-Sensor Theory Changes in volcanic emissions correspond to variations in the magma plumbing ... more Multi-Sensor Theory Changes in volcanic emissions correspond to variations in the magma plumbing system. By tracking emissions (Fig. 1) we aim to help understand the processes occurring at depth. Satellite-based remote sensing data was collected from multiple NASA polar orbiting instruments with significant data records (13-18 years). Stereo anaglyphs of volcanic plumes in Kamchatka. To view in 3D, please use glasses provided. A) Shiveluch, November 23, 2014; B) Kliuchevskoi, June 29, 2007; C) Karymsky, February 27 2015; and D) Zhupanovsky, November 9, 2014. Note: North is to the left in each anaglyph.
2.1 Regulation of GSK-3 activity through phosphorylation by upstream kinases. 2.1.1 Inhibitory N-... more 2.1 Regulation of GSK-3 activity through phosphorylation by upstream kinases. 2.1.1 Inhibitory N-terminal phosphorylation When serine 9 of GSK-3 (or serine 21 of GSK-3) is phosphorylated, it mimicks a primed, intramolecular pseudosubstrate that acts in cis as a competitive inhibitor of GSK-3 activity (Cross et al., 1995). The crystal structure of GSK-3 revealed that the negatively charged phosphate on primed substrates fits into a pocket of positively charged residues in the www.intechopen.com Molecular Mechanisms Underlying Pluripotency and Lineage Commitment-The Role of GSK-3 371 substrate binding cleft of the kinase, thereby placing the substrate into the proper orientation for GSK-3-mediated phosphorylation (Bax et al., 2001; Dajani et al., 2001; ter Haar et al., 2001). This pocket also binds the phosphorylated N-terminal peptide of GSK-3 when it is phosphorylated at S9/S21-competing out exogenous substrates and hence, interfering with activity. There are several kinases capable of inhibiting GSK-3 through S9/S21 phosphorylation, including PKB/Akt, p70 ribosomal S6 kinase, p90 ribosomal S6 kinase, protein kinase A and certain protein kinase Cs (