B. Cairns - Academia.edu (original) (raw)

Papers by B. Cairns

Research paper thumbnail of Radiation Treatment in the GISS GCM

Research paper thumbnail of On the polarization angle of skylight reflected by natural surfaces: Properties and application for remote sensing of planetary atmospheres

In this study, we focus on the polarization angle of light scattered by terrestrial atmosphere-su... more In this study, we focus on the polarization angle of light scattered by terrestrial atmosphere-surface systems. The polarization angle describes the orientation of the plane in which the linearly polarized portion of light propagates. We show for skylight how this angle varies with the solar zenith angle and that, for skylight reflected by natural surfaces, these variations remain the same for wide ranges of atmospheric conditions and surface properties. This provides a tool for extracting scattering properties of the atmosphere from remote sensing observations of the Earth without any knowledge of the underlying surface. We demonstrate this principle for simulated data, and apply it to observations obtained by an airborne polarimeter over open oceans.

Research paper thumbnail of Research Scanning Polarimeter: calibration and ground-based measurements

SPIE Proceedings, 1999

SpecTIR Corporation has recently completed building the Research Scanning Polarimeter (RSP). This... more SpecTIR Corporation has recently completed building the Research Scanning Polarimeter (RSP). This instrument was designed to provide highly accurate polarimetric measurements both from aircraft and from the ground. The spectral range of the measurements is from 410nm to 2250nm and the field of view of the instrument is scanned over a 120° swath (+/-60° from nadir/zenith). Here we describe the results of the instrumental calibration and the quantitative interpretation of ground-based measurements. Recently we have acquired data using the RSP on an aircraft and a brief discussion of the information content of this data and some preliminary aerosol retrievals over the Pacific ocean are presented.

Research paper thumbnail of Multiple scattering by random particulate media: exact 3D results

Optics Express, 2007

We use the numerically exact superposition T-matrix method to perform extensive computations of e... more We use the numerically exact superposition T-matrix method to perform extensive computations of electromagnetic scattering by a 3D volume filled with randomly distributed wavelength-sized particles. These computations are used to simulate and analyze the effect of randomness of particle positions as well as the onset and evolution of various multiplescattering effects with increasing number of particles in a statistically homogeneous volume of discrete random medium. Our exact results illustrate and substantiate the methodology underlying the microphysical theories of radiative transfer and coherent backscattering. Furthermore, we show that even in densely packed media, the light multiply scattered along strings of widely separated particles still provides a significant contribution to the total scattered signal and thereby makes quite pronounced the classical radiative transfer and coherent backscattering effects.

Research paper thumbnail of Case Studies of Aerosol Retrievals over the Ocean from Multiangle, Multispectral Photopolarimetric Remote Sensing Data

Journal of the Atmospheric Sciences, 2002

To evaluate the global effects of aerosols on the direct radiative balance, tropospheric chemistr... more To evaluate the global effects of aerosols on the direct radiative balance, tropospheric chemistry, and cloud properties of the earth's atmosphere requires high-precision remote sensing that is sensitive to the aerosol optical thickness, size distribution, refractive index, and number density. This study uses the multiangle 0.41-, 0.55-, 0.865-, and 2.25-m channel data from the airborne Research Scanning Polarimeter to retrieve aerosol properties over the Pacific Ocean. It is shown that such photopolarimetric data are highly sensitive to the size distribution and refractive index of aerosol particles, which reduces the nonuniqueness in aerosol retrievals using such data as compared with less comprehensive datasets. Moreover, it is found that polarized reflectances obtained at the shorter wavelengths (0.41 and 0.55 m) are significantly less sensitive to the contribution of the ocean's upwelling light than total reflectance measurements, providing a natural tool for the separation between the estimation of oceanic and atmospheric scattering properties.

Research paper thumbnail of Toward unified satellite climatology of aerosol properties: What do fully compatible MODIS and MISR aerosol pixels tell us?

Journal of Quantitative Spectroscopy and Radiative Transfer, 2009

Because of the global nature of aerosol effects on climate, satellite observations have been and ... more Because of the global nature of aerosol effects on climate, satellite observations have been and will be an indispensable source of information about aerosol characteristics for use in various assessments of climate and climate change. There have been parallel claims of unprecedented accuracy of aerosol retrievals with the moderate-resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR). These claims have been based on limited comparisons with ground-based observations which, however, are not necessarily indicative of the actual global performance of these satellite sensors. Fortunately, both instruments have been flown for many years on the same Terra platform, which provides a unique opportunity to compare fully collocated pixel-level MODIS and MISR aerosol retrievals directly and globally. Our present extensive analysis of $8 years of the MODIS-Terra and MISR aerosol data documents unexpected significant disagreements at the pixel level as well as between long-term and spatially averaged aerosol properties. The only point on which both datasets seem to fully agree is that there may have been a weak increasing tendency in the globally averaged aerosol optical thickness (AOT) over the land and no long-term AOT tendency over the oceans. Overall our new results suggest that the current knowledge of the global distribution of the AOT and, especially, aerosol microphysical characteristics remains unsatisfactory.

Research paper thumbnail of Low-cost long-term monitoring of global climate forcings and feedbacks

Climatic Change, 1995

... Although efforts to measure integrated reflected solar and emitted thermal fluxes are underwa... more ... Although efforts to measure integrated reflected solar and emitted thermal fluxes are underway (Kandel, 1990), measurement of changes in the spectral distribution of the radiation are required to provide diagnostic information about causes of flux changes. Monitoring Rationale ...

Research paper thumbnail of Accurate Monitoring of Terrestrial Aerosols and Total Solar Irradiance: Introducing the Glory Mission

Bulletin of the American Meteorological Society, 2007

The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key... more The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key forcings influencing global climate. One of the mission's principal objectives is to determine the global distribution of detailed aerosol and cloud properties with unprecedented accuracy, thereby facilitating the quantification of the aerosol direct and indirect radiative forcings. The other is to continue the 28-yr record of satellite-based measurements of total solar irradiance from which the effect of solar variability on the Earth's climate is quantified. These objectives will be met by flying two state-of-the-art science instruments on an Earth-orbiting platform. Based on a proven technique demonstrated with an aircraft-based prototype, the Aerosol Polarimetry Sensor (APS) will collect accurate multiangle photopolarimetric measurements of the Earth along the satellite ground track within a wide spectral range extending from the visible to the shortwave infrared. The Total ...

Research paper thumbnail of Using polarimetric remote sensing measurements to estimate ice particle size, optical depth and ice water path during CRYSTAL-FACE

Research paper thumbnail of Inversion of Multi-Angle Radiation Measurements

Research paper thumbnail of Hyperspectral measurements of the solar hot spot using the HyperSpecTIR imaging spectrometer

2004 IEEE Aerospace Conference Proceedings (IEEE Cat. No.04TH8720)

The scan mechanism of the HyperSpecTIR hyperspectral instrument has been modified to allow BRDF m... more The scan mechanism of the HyperSpecTIR hyperspectral instrument has been modified to allow BRDF measurements from an airborne platform. The HyperSpecTIR is a flexible, airborne hyperspectral imager capable of on-the-fly programmability. Such measurements afford the opportunity to study geometric and spectral properties of natural scenes such as fields and canopies, as well as man-made substances such as composite materials and

Research paper thumbnail of The instantaneous cross-spectral density of non-stationary wavefields

Optics Communications, 1987

Research paper thumbnail of Polarization: ground-based upward-looking and aircraft/satellite-based downward-looking measurements

SPIE Proceedings, 1997

It is shown that it is possible to retrieve aerosol properties using polarization measurements fr... more It is shown that it is possible to retrieve aerosol properties using polarization measurements from satellite, or aircraft even when the surface polarization is significant and unknown. This extends the domain for which it is possible to intercompare ground and aircraft/satellite estimates of aerosol properties and allows the retrieval of aerosol properties to be made above bare soil surfaces.

Research paper thumbnail of <title>Accuracy versus speed: evaluation of tradeoffs in atmospheric correction methods</title>

Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery VIII, 2002

In this paper tradeoffs between speed and accuracy for the atmospheric correction of hyperspectra... more In this paper tradeoffs between speed and accuracy for the atmospheric correction of hyperspectral imagery are examined. Among the issues addressed are: the use of scattering calculations on a sparse spectral grid and consequent accuracy and speed tradeoffs; methods for minimizing the required number of quadrature points in multiple scattering calculations; effects of the vertical profiles of aerosols and absorbing gases on atmospheric correction; and efficient approaches for including the effects of sensor variability, or imperfections, on atmospheric correction.

Research paper thumbnail of Combining Active and Passive Measurements for Aerosol Retrievals

The NASA Langley Research Center B200 aircraft which participated in the ARCTAS 2008 campaign car... more The NASA Langley Research Center B200 aircraft which participated in the ARCTAS 2008 campaign carried the passive Research Scanning Polarimeter (RSP) and the active High Spectral Resolution Lidar (HSRL) instrumentation during the summer deployment. These sensors have complementary retrieval capabilities, with the RSP measurements providing a detailed microphysics retrieval capability with limited sensitivity to the details of vertical structure, and the HSRL providing high resolution vertical profile information with a limited (5 pieces of information) microphysical capability. The ideal outcome of a retrieval is to provide the aerosol/cloud model (i.e., vertical distribution of properties) which fits the datasets best in a statistical sense. Within the Maximum A-posteriori Probability (MAP) method an a-priori knowledge of the state is combined with a chi2-statistics measuring the distance between observations and simulation, weighted through a proper estimate of the errors involved...

Research paper thumbnail of CLARREO-type Spectral Polarimetric Simulator Analysis of GCM Aerosol Radiative Properties Sampled at the ARM SGP Site

The ability to detect and attribute climate forcings due to aerosol and surface albedo changes in... more The ability to detect and attribute climate forcings due to aerosol and surface albedo changes in a rapidly changing global climate is an important goal of the CLARREO mission. While spectral polarimetric measurements appear to offer the best prospects for achieving this goal, important questions remain as to the type of information content that can be extracted from polarimetric data. Our approach to study this problem is to make forward calculations with the CLARREO Spectral Polarimetric Simulator using the GISS ModelE aerosol climatology as the aerosol input model. This provides a realistic, although idealized, aerosol mixture consisting of sulfate, nitrate, sea salt, mineral dust, organic, and black carbon components (based on chemistry-transport model simulations) with realistic size, height, and relative humidity dependence. By choosing the ARM SGP Site, we have available at SGP a well-defined spectral surface albedo, as well as a whole suite of ancillary instruments, includin...

Research paper thumbnail of A Investigation of Multiple Scattering and Radiative Transfer

Research paper thumbnail of Airborne Multi-Angle Hyper-Spectral Measurements of White Caps on the Open Ocean

Research paper thumbnail of Preliminary airborne measurement results from the Hyperspectral Polarimeter for Aerosol Retrievals (HySPAR)

ABSTRACT The Hyperspectral Polarimeter for Aerosol Re-trievals (HySPAR) acquires a 120 degree spa... more ABSTRACT The Hyperspectral Polarimeter for Aerosol Re-trievals (HySPAR) acquires a 120 degree spatial, full-Stokes (i.e. including V) line image over 480-960 nm in a single snapshot with no moving parts. Unlike other snapshot polarimeters that typically use multiple boresighted beams or micro-polarizer pixel masks, HySPAR uses an arrangement of birefringent crystals to impart a polarization dependent modulation on the measured spectrum. The modulated spectra can be inverted to yield Stokes spectra. Preliminary airborne measurement results from the Megacity Initiative: Local and Global Research Observa-tions (MILAGRO) campaign will be presented. HySPAR Stokes imagery will be compared to that of the Research Scanning Polarimeter (RSP). These data were acuired during coordinated ight paths of the two aircraft carrying the sensors.

Research paper thumbnail of <title>Aerosol retrieval over urban areas using spatial regression between V/NIR and MIR Hyperion channels</title>

Remote Sensing in Atmospheric Pollution Monitoring and Control, 2004

Determination of aerosol optical depth from satellite remote sensing measurements is extremely co... more Determination of aerosol optical depth from satellite remote sensing measurements is extremely complex due to the large variability of aerosol optical properties. Significant simplification occurs when measurements are taken over water since the ocean reflection signal can be taken ...

Research paper thumbnail of Radiation Treatment in the GISS GCM

Research paper thumbnail of On the polarization angle of skylight reflected by natural surfaces: Properties and application for remote sensing of planetary atmospheres

In this study, we focus on the polarization angle of light scattered by terrestrial atmosphere-su... more In this study, we focus on the polarization angle of light scattered by terrestrial atmosphere-surface systems. The polarization angle describes the orientation of the plane in which the linearly polarized portion of light propagates. We show for skylight how this angle varies with the solar zenith angle and that, for skylight reflected by natural surfaces, these variations remain the same for wide ranges of atmospheric conditions and surface properties. This provides a tool for extracting scattering properties of the atmosphere from remote sensing observations of the Earth without any knowledge of the underlying surface. We demonstrate this principle for simulated data, and apply it to observations obtained by an airborne polarimeter over open oceans.

Research paper thumbnail of Research Scanning Polarimeter: calibration and ground-based measurements

SPIE Proceedings, 1999

SpecTIR Corporation has recently completed building the Research Scanning Polarimeter (RSP). This... more SpecTIR Corporation has recently completed building the Research Scanning Polarimeter (RSP). This instrument was designed to provide highly accurate polarimetric measurements both from aircraft and from the ground. The spectral range of the measurements is from 410nm to 2250nm and the field of view of the instrument is scanned over a 120° swath (+/-60° from nadir/zenith). Here we describe the results of the instrumental calibration and the quantitative interpretation of ground-based measurements. Recently we have acquired data using the RSP on an aircraft and a brief discussion of the information content of this data and some preliminary aerosol retrievals over the Pacific ocean are presented.

Research paper thumbnail of Multiple scattering by random particulate media: exact 3D results

Optics Express, 2007

We use the numerically exact superposition T-matrix method to perform extensive computations of e... more We use the numerically exact superposition T-matrix method to perform extensive computations of electromagnetic scattering by a 3D volume filled with randomly distributed wavelength-sized particles. These computations are used to simulate and analyze the effect of randomness of particle positions as well as the onset and evolution of various multiplescattering effects with increasing number of particles in a statistically homogeneous volume of discrete random medium. Our exact results illustrate and substantiate the methodology underlying the microphysical theories of radiative transfer and coherent backscattering. Furthermore, we show that even in densely packed media, the light multiply scattered along strings of widely separated particles still provides a significant contribution to the total scattered signal and thereby makes quite pronounced the classical radiative transfer and coherent backscattering effects.

Research paper thumbnail of Case Studies of Aerosol Retrievals over the Ocean from Multiangle, Multispectral Photopolarimetric Remote Sensing Data

Journal of the Atmospheric Sciences, 2002

To evaluate the global effects of aerosols on the direct radiative balance, tropospheric chemistr... more To evaluate the global effects of aerosols on the direct radiative balance, tropospheric chemistry, and cloud properties of the earth's atmosphere requires high-precision remote sensing that is sensitive to the aerosol optical thickness, size distribution, refractive index, and number density. This study uses the multiangle 0.41-, 0.55-, 0.865-, and 2.25-m channel data from the airborne Research Scanning Polarimeter to retrieve aerosol properties over the Pacific Ocean. It is shown that such photopolarimetric data are highly sensitive to the size distribution and refractive index of aerosol particles, which reduces the nonuniqueness in aerosol retrievals using such data as compared with less comprehensive datasets. Moreover, it is found that polarized reflectances obtained at the shorter wavelengths (0.41 and 0.55 m) are significantly less sensitive to the contribution of the ocean's upwelling light than total reflectance measurements, providing a natural tool for the separation between the estimation of oceanic and atmospheric scattering properties.

Research paper thumbnail of Toward unified satellite climatology of aerosol properties: What do fully compatible MODIS and MISR aerosol pixels tell us?

Journal of Quantitative Spectroscopy and Radiative Transfer, 2009

Because of the global nature of aerosol effects on climate, satellite observations have been and ... more Because of the global nature of aerosol effects on climate, satellite observations have been and will be an indispensable source of information about aerosol characteristics for use in various assessments of climate and climate change. There have been parallel claims of unprecedented accuracy of aerosol retrievals with the moderate-resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR). These claims have been based on limited comparisons with ground-based observations which, however, are not necessarily indicative of the actual global performance of these satellite sensors. Fortunately, both instruments have been flown for many years on the same Terra platform, which provides a unique opportunity to compare fully collocated pixel-level MODIS and MISR aerosol retrievals directly and globally. Our present extensive analysis of $8 years of the MODIS-Terra and MISR aerosol data documents unexpected significant disagreements at the pixel level as well as between long-term and spatially averaged aerosol properties. The only point on which both datasets seem to fully agree is that there may have been a weak increasing tendency in the globally averaged aerosol optical thickness (AOT) over the land and no long-term AOT tendency over the oceans. Overall our new results suggest that the current knowledge of the global distribution of the AOT and, especially, aerosol microphysical characteristics remains unsatisfactory.

Research paper thumbnail of Low-cost long-term monitoring of global climate forcings and feedbacks

Climatic Change, 1995

... Although efforts to measure integrated reflected solar and emitted thermal fluxes are underwa... more ... Although efforts to measure integrated reflected solar and emitted thermal fluxes are underway (Kandel, 1990), measurement of changes in the spectral distribution of the radiation are required to provide diagnostic information about causes of flux changes. Monitoring Rationale ...

Research paper thumbnail of Accurate Monitoring of Terrestrial Aerosols and Total Solar Irradiance: Introducing the Glory Mission

Bulletin of the American Meteorological Society, 2007

The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key... more The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key forcings influencing global climate. One of the mission's principal objectives is to determine the global distribution of detailed aerosol and cloud properties with unprecedented accuracy, thereby facilitating the quantification of the aerosol direct and indirect radiative forcings. The other is to continue the 28-yr record of satellite-based measurements of total solar irradiance from which the effect of solar variability on the Earth's climate is quantified. These objectives will be met by flying two state-of-the-art science instruments on an Earth-orbiting platform. Based on a proven technique demonstrated with an aircraft-based prototype, the Aerosol Polarimetry Sensor (APS) will collect accurate multiangle photopolarimetric measurements of the Earth along the satellite ground track within a wide spectral range extending from the visible to the shortwave infrared. The Total ...

Research paper thumbnail of Using polarimetric remote sensing measurements to estimate ice particle size, optical depth and ice water path during CRYSTAL-FACE

Research paper thumbnail of Inversion of Multi-Angle Radiation Measurements

Research paper thumbnail of Hyperspectral measurements of the solar hot spot using the HyperSpecTIR imaging spectrometer

2004 IEEE Aerospace Conference Proceedings (IEEE Cat. No.04TH8720)

The scan mechanism of the HyperSpecTIR hyperspectral instrument has been modified to allow BRDF m... more The scan mechanism of the HyperSpecTIR hyperspectral instrument has been modified to allow BRDF measurements from an airborne platform. The HyperSpecTIR is a flexible, airborne hyperspectral imager capable of on-the-fly programmability. Such measurements afford the opportunity to study geometric and spectral properties of natural scenes such as fields and canopies, as well as man-made substances such as composite materials and

Research paper thumbnail of The instantaneous cross-spectral density of non-stationary wavefields

Optics Communications, 1987

Research paper thumbnail of Polarization: ground-based upward-looking and aircraft/satellite-based downward-looking measurements

SPIE Proceedings, 1997

It is shown that it is possible to retrieve aerosol properties using polarization measurements fr... more It is shown that it is possible to retrieve aerosol properties using polarization measurements from satellite, or aircraft even when the surface polarization is significant and unknown. This extends the domain for which it is possible to intercompare ground and aircraft/satellite estimates of aerosol properties and allows the retrieval of aerosol properties to be made above bare soil surfaces.

Research paper thumbnail of <title>Accuracy versus speed: evaluation of tradeoffs in atmospheric correction methods</title>

Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery VIII, 2002

In this paper tradeoffs between speed and accuracy for the atmospheric correction of hyperspectra... more In this paper tradeoffs between speed and accuracy for the atmospheric correction of hyperspectral imagery are examined. Among the issues addressed are: the use of scattering calculations on a sparse spectral grid and consequent accuracy and speed tradeoffs; methods for minimizing the required number of quadrature points in multiple scattering calculations; effects of the vertical profiles of aerosols and absorbing gases on atmospheric correction; and efficient approaches for including the effects of sensor variability, or imperfections, on atmospheric correction.

Research paper thumbnail of Combining Active and Passive Measurements for Aerosol Retrievals

The NASA Langley Research Center B200 aircraft which participated in the ARCTAS 2008 campaign car... more The NASA Langley Research Center B200 aircraft which participated in the ARCTAS 2008 campaign carried the passive Research Scanning Polarimeter (RSP) and the active High Spectral Resolution Lidar (HSRL) instrumentation during the summer deployment. These sensors have complementary retrieval capabilities, with the RSP measurements providing a detailed microphysics retrieval capability with limited sensitivity to the details of vertical structure, and the HSRL providing high resolution vertical profile information with a limited (5 pieces of information) microphysical capability. The ideal outcome of a retrieval is to provide the aerosol/cloud model (i.e., vertical distribution of properties) which fits the datasets best in a statistical sense. Within the Maximum A-posteriori Probability (MAP) method an a-priori knowledge of the state is combined with a chi2-statistics measuring the distance between observations and simulation, weighted through a proper estimate of the errors involved...

Research paper thumbnail of CLARREO-type Spectral Polarimetric Simulator Analysis of GCM Aerosol Radiative Properties Sampled at the ARM SGP Site

The ability to detect and attribute climate forcings due to aerosol and surface albedo changes in... more The ability to detect and attribute climate forcings due to aerosol and surface albedo changes in a rapidly changing global climate is an important goal of the CLARREO mission. While spectral polarimetric measurements appear to offer the best prospects for achieving this goal, important questions remain as to the type of information content that can be extracted from polarimetric data. Our approach to study this problem is to make forward calculations with the CLARREO Spectral Polarimetric Simulator using the GISS ModelE aerosol climatology as the aerosol input model. This provides a realistic, although idealized, aerosol mixture consisting of sulfate, nitrate, sea salt, mineral dust, organic, and black carbon components (based on chemistry-transport model simulations) with realistic size, height, and relative humidity dependence. By choosing the ARM SGP Site, we have available at SGP a well-defined spectral surface albedo, as well as a whole suite of ancillary instruments, includin...

Research paper thumbnail of A Investigation of Multiple Scattering and Radiative Transfer

Research paper thumbnail of Airborne Multi-Angle Hyper-Spectral Measurements of White Caps on the Open Ocean

Research paper thumbnail of Preliminary airborne measurement results from the Hyperspectral Polarimeter for Aerosol Retrievals (HySPAR)

ABSTRACT The Hyperspectral Polarimeter for Aerosol Re-trievals (HySPAR) acquires a 120 degree spa... more ABSTRACT The Hyperspectral Polarimeter for Aerosol Re-trievals (HySPAR) acquires a 120 degree spatial, full-Stokes (i.e. including V) line image over 480-960 nm in a single snapshot with no moving parts. Unlike other snapshot polarimeters that typically use multiple boresighted beams or micro-polarizer pixel masks, HySPAR uses an arrangement of birefringent crystals to impart a polarization dependent modulation on the measured spectrum. The modulated spectra can be inverted to yield Stokes spectra. Preliminary airborne measurement results from the Megacity Initiative: Local and Global Research Observa-tions (MILAGRO) campaign will be presented. HySPAR Stokes imagery will be compared to that of the Research Scanning Polarimeter (RSP). These data were acuired during coordinated ight paths of the two aircraft carrying the sensors.

Research paper thumbnail of <title>Aerosol retrieval over urban areas using spatial regression between V/NIR and MIR Hyperion channels</title>

Remote Sensing in Atmospheric Pollution Monitoring and Control, 2004

Determination of aerosol optical depth from satellite remote sensing measurements is extremely co... more Determination of aerosol optical depth from satellite remote sensing measurements is extremely complex due to the large variability of aerosol optical properties. Significant simplification occurs when measurements are taken over water since the ocean reflection signal can be taken ...