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Journal of Quantitative Spectroscopy and Radiative Transfer 01/2013; 116:1 - 16. · 3.19 Impact Factor
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ABSTRACT: The Markov chain formalism for polarized radiative transfer through a vertically inhomogeneous atmosphere is linearized comprehensively with respect to the aerosol and polarizing surface properties. For verification, numerical results are compared to those obtained by the finite difference method. We demonstrate the use of the linearized code as part of a retrieval of aerosol and surface properties for an atmosphere overlying a black and Fresnel-reflecting ocean surface.
Applied Optics 06/2012; 51(16):3491--3507. · 1.41 Impact Factor
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ABSTRACT: The Markov chain formalism for polarized radiative transfer through a vertically inhomogeneous atmosphere is linearized comprehensively with respect to the aerosol and polarizing surface properties. For verification, numerical results are compared to those obtained by the finite difference method. We demonstrate the use of the linearized code as part of a retrieval of aerosol and surface properties for an atmosphere overlying a black and Fresnel-reflecting ocean surface.
Applied Optics 06/2012; 51(16):3491-507. · 1.41 Impact Factor
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ABSTRACT: Currently, many satellite-based aerosol retrievals make use of lookup tables (LUTs) containing precomputed solutions to the radiative transfer (RT) equation. The benefit of this strategy is the avoidance of expensive runtime calculations, but its main drawback is that the LUTs discretize what is inherently a continuous, multivariate solution space. The operational retrieval algorithm for the Multi-angle Imaging SpectroRadiometer (MISR), for example, compares the observations to a set of 74 aerosol mixtures, each composed of particle models having prescribed optical properties and size distributions. In a recent “blind” study comparing the performance of several satellite retrieval algorithms on simulated data over a black surface, the MISR algorithm performed reasonably well in recovering the “true” spectral aerosol optical depths (AODs), but because the correct aerosol model was not contained within the MISR LUT, the retrieved AODs were biased low by ~ 14%. This motivated an investigation of whether an optimization approach, in which the aerosols are modeled by a set of continuously variable parameters recovered using nonlinear least-squares, could improve the results. In this paper, we demonstrate that such an approach using Levenberg–Marquardt optimization yields superior accuracy. Advances in computer speed, development of more efficient RT codes, and algorithm innovations will be necessary for this approach to satisfy the demands of a global, production-level satellite aerosol retrieval process, especially when used in conjunction with future instruments having enhanced sensitivity to diverse aerosol properties.Research highlights► Satellite-based aerosol retrievals often use precomputed lookup tables (LUTs). ► This avoids computational load but limits solutions to discrete, prescribed models. ► If the correct aerosol is not present in the LUT, results may be biased. ► Using simulated satellite data, we investigated an alternative retrieval approach. ► Levenberg-Marquardt optimization yielded superior results compared to the LUT method.
Atmospheric Research 01/2012; · 1.91 Impact Factor
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ABSTRACT: We report on a way of building bidirectional surface reflectivity into the Markov chain formalism for polarized radiative transfer through a vertically inhomogeneous atmosphere. Numerical results are compared to those obtained by the Monte Carlo method, showing the accuracy of the Markov chain method when 90 streams are used to compute the radiation from a Rayleigh-plus-aerosol atmosphere that overlies a surface with a bidirectional reflection function consisting of both depolarizing and polarizing parts.
Optics Letters 06/2011; 36(11):2083-5. · 3.40 Impact Factor
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ABSTRACT: Multiangle Spectropolarimetric Imager (MSPI) sensitivity to static and time-varying polarization errors is examined. For a system without noise, static polarization errors are accurately represented by the calibration coefficients, and therefore do not impede correct mapping of measured to input Stokes vectors. But noise is invariably introduced during the detection process, and static polarization errors reduce the system's signal-to-noise ratio (SNR) by increasing noise sensitivity. Noise sensitivity is minimized by minimizing the condition number of the system data reduction matrix [Appl. Opt.41, 619 (2002)]. The sensitivity of condition numbers to static polarization errors is presented. The condition number of the nominal MSPI data reduction matrix is approximately 1.1 or less for all fields. The increase in the condition number above 1 results primarily from a quarter wave plate and mirror coating retardance magnitude errors. Sensitivity of the degree of linear polarization (DoLP) error with respect to time-varying diattenuation and retardance error was used to set a time-varying diattenuation magnitude tolerance of 0.005 and a time-varying retardance magnitude tolerance of ±0.2°. A Monte Carlo simulation of the calibration and measurements using anticipated static and time-varying errors indicates that MSPI has a probability of 0.9 of meeting its 0.005 DoLP uncertainty requirement.
Applied Optics 05/2011; 50(14):2080-7. · 1.41 Impact Factor
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David J Diner,
Ab Davis,
Bruce Hancock,
Sven Geier,
Brian Rheingans,
Veljko Jovanovic,
Michael Bull,
David M Rider,
Russell A Chipman,
Anna-Britt Mahler,
Stephen C McClain
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ABSTRACT: We report on the construction and calibration of a dual photoelastic-modulator (PEM)-based polarimetric camera operating at 660?nm. This camera is our first prototype for a multispectral system being developed for airborne and spaceborne remote sensing of atmospheric aerosols. The camera includes a dual-PEM assembly integrated into a three-element, low-polarization reflective telescope and provides both intensity and polarization imaging. A miniaturized focal-plane assembly consisting of spectral filters and patterned wire-grid polarizers provides wavelength and polarimetric selection. A custom push-broom detector array with specialized signal acquisition, readout, and processing electronics captures the radiometric and polarimetric information. Focal-plane polarizers at orientations of 0 degrees and -45 degrees yield the normalized Stokes parameters q=Q/I and u=U/I respectively, which are then coregistered to obtain degree of linear polarization (DOLP) and angle of linear polarization. Laboratory test data, calibration results, and outdoor imagery acquired with the camera are presented. The results show that, over a wide range of DOLP, our challenging objective of uncertainty within +/-0.005 has been achieved.
Applied Optics 05/2010; 49(15):2929-46. · 1.41 Impact Factor
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David J. Diner,
Thomas P. Ackerman,
Amy Braverman,
Carol J. Bruegge,
Mark J. Chopping,
Eugene E. Clothiaux,
Roger Davies,
Larry Di Girolamo,
Ralph A. Kahn,
Yuri Knyazikhin, [......],
Jan-Peter Muller,
Anne W. Nolin,
Bernard Pinty,
Michel M. Verstraete,
Dong L. Wu,
Michael J. Garay,
Olga V. Kalashnikova,
Anthony B. Davis,
Edgar S. Davis,
Russell A. Chipman
IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2010, July 25-30, 2010, Honolulu, Hawaii, USA, Proceedings; 01/2010
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ABSTRACT: Global and regional mapping of aerosol properties, including column amount, particle type and effective size, is of great
interest for environmental and climate studies. Increased aerosol production results in decreased insolation (a direct aerosol
effect), mitigating the rise in global surface air temperature caused by enhanced concentrations of greenhouse gases, though
on different spatial and temporal scales [Charlson et al., 1992; Kiehl and Briegleb, 1993; Andreae, 1995]. Indirect aerosol effects include an alteration of cloud particle properties (size, single scattering albedo) that can modify
cloud scattering properties, lifetimes, and precipitation amount. Although oceans cover the majority of the Earth’s surface,
land areas are the source of most aerosols and essentially all anthropogenic production. As a consequence, there is a tendency
to find the largest aerosol optical depth values over land and coastal ocean. Monitoring of these vast areas on a frequent,
global basis can be effectively accomplished only by means of space-based instruments. However, land and coastal waters generally
have complex, heterogeneous, and a priori unknown surface reflectance characteristics, making the retrieval of aerosol properties in these locations particularly troublesome.
The problem stems from the fact that the radiance measured at the top of the atmosphere (TOA) is a mixture of two components
— radiance scattered solely by the atmosphere and radiance produced by multiple surface-atmosphere scattering interactions
which is eventually transmitted up through the atmosphere to space. The successful retrieval process must be able to separate
and explicitly describe these two radiance components, resulting in a determination of both the aerosol properties and the
surface reflectance characteristics.
08/2009: pages 267-293; , ISBN: 978-3-540-69396
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IEEE T. Geoscience and Remote Sensing. 01/2009; 47:4095-4114.
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ABSTRACT: The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard Terra acquires imagery at 275-m resolution at nine angles ranging from 0º to 70º off-nadir. This multi-angle capability facilitates the stereoscopic retrieval of smoke heights associated with near-source plumes. A new visualization and analysis program called MISR INteractive eXplorer (MINX) takes advantage of wind-direction information inherent in smoke plumes from active fires to determine plume heights and wind speeds at higher resolution and with greater accuracy than provided by the standard, operational MISR product. Among the software tool's many features are several designed for in-depth study of plumes, including animations of the nine MISR camera images that provide a visual 3-D perspective, and interactive digitization of plumes in order to automatically retrieve heights and winds. Aerosol properties from MISR, and fire power based on infrared brightness temperatures from MODIS (also on Terra) are archived along with the retrieved height and wind data. MINX retrievals have sufficient spatial detail to provide valuable input to studies of plume dynamics as well as large-scale climatological studies. Current efforts are focusing on fires in North America, but application to other areas of the world is also envisioned. Case study examples will be presented to illustrate MINX capabilities.
Proc SPIE 03/2008; 7089:708909.
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ABSTRACT: A dual-photoelastic-modulator- (PEM-) based spectropolarimetric camera concept is presented as an approach for global aerosol monitoring from space. The most challenging performance objective is to measure degree of linear polarization (DOLP) with an uncertainty of less than 0.5% in multiple spectral bands, at moderately high spatial resolution, over a wide field of view, and for the duration of a multiyear mission. To achieve this, the tandem PEMs are operated as an electro-optic circular retardance modulator within a high-performance reflective imaging system. Operating the PEMs at slightly different resonant frequencies generates a beat signal that modulates the polarized component of the incident light at a much lower heterodyne frequency. The Stokes parameter ratio q = Q/I is obtained from measurements acquired from each pixel during a single frame, providing insensitivity to pixel responsivity drift and minimizing polarization artifacts that conventionally arise when this quantity is derived from differences in the signals from separate detectors. Similarly, u = U/I is obtained from a different pixel; q and u are then combined to form the DOLP. A detailed accuracy and tolerance analysis for this polarimeter is presented.
Applied Optics 01/2008; 46(35):8428-45. · 1.41 Impact Factor
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IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2008, July 8-11, 2008, Boston, Massachusetts, USA, Proceedings; 01/2008
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ABSTRACT: One important objective of the Multi-angle Imaging SpectroRadiometer (MISR) is retrieving global aerosol loading and microphysical properties. Accuracy depends on many factors, including the availability of a complete catalog of particle types with their associated size distributions, shapes, single-scattering albedos, vertical profiles, and spectral radiative characteristics. Co-equal to this need is the availability of a well-designed, well-characterized instrument, with a calibration that is maintained post-launch. This allows accurate radiance and retrieval products to be made, adjusting for instrument changes. MISR performance has been intensively studied throughout the design, pre-flight, and post-launch mission phases. To establish the absolute radiometric scale, annual vicarious calibration (VC) exercises have been conducted. In addition, an on-board-calibrator (OBC) allows more frequent testing of camera degradations. Together, the VC and OBC processes have allowed MISR to achieve an absolute calibration uncertainty of 4% or better (1σ confidence level) for bright land targets. Additional fine-tunings have been made following analysis of lunar-view campaign data, and from a statistical analysis of Earth observations. These studies led to slight camera-to-camera adjustments, which are important in improving the aerosol retrieval process. Validation of the response at the lower end of the dynamic range has also been accomplished using a dark-water study. With these studies complete, MISR calibration is now in an operational mode, and data users can be assured the resulting data products are stable with time. Such records meet the needs of a program designed to support climate change and provide long-term monitoring of the Earth's atmosphere and radiative fluxes.
Remote Sensing of Environment 01/2007; 107:2-11. · 4.57 Impact Factor
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ABSTRACT: Through acquisition of well-calibrated near-nadir and oblique-angle imagery (0° - 70° zenith angles) at moderately high spatial resolution (275 m - 1.1 km), the Multi-angle Imaging SpectroRadiometer (MISR) experiment aboard NASA's Terra satellite has taken atmospheric remote sensing in new directions. Retrieval algorithms that were largely conceptual prior to Terra launch in 1999 have led to publicly available aerosol and cloud products with direct application to global climate and particulate air quality research. Automated algorithms making use of stereoscopic parallax, time lapse among the nine angular views, and the variation in radiance with view angle, scattering angle, and wavelength (446-866 nm) make possible unique data sets including geometric cloud and aerosol plume heights derived independently of emissivity or temperature assumptions; height-resolved cloud-tracked winds; and aerosol optical depth and particle type over a wide variety of surfaces including bright desert source regions. To illustrate these capabilities, examples of regional and global MISR data products, quantitative evaluations of product accuracies based on comparisons with independent data sources, and time series showing seasonal and interannual variations are presented here. Future sensor improvements aimed at building upon MISR heritage, including expanding the spectral coverage to ultraviolet and shortwave infrared wavelengths, adding polarization channels, and widening the sensor swath, are also discussed.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
11/2006;
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David J. Diner,
Bobby H. Braswell,
Roger Davies,
Nadine Gobron,
Jiannan Hu,
Yufang Jin,
Ralph A. Kahn,
Yuri Knyazikhin,
Norman Loeb,
Jan-Peter Muller,
Anne W. Nolin,
Bernard Pinty,
Crystal B. Schaaf,
Gabriela Seiz,
Julienne Stroeve
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ABSTRACT: Passive optical multiangle observations make possible the retrieval of scene structural characteristics that cannot be obtained with, or require fewer underlying assumptions than, single-angle sensors. Retrievable quantities include aerosol amount over a wide variety of surfaces (including bright targets); aerosol microphysical properties such as particle shape; geometrically-derived cloud-top heights and 3-D cloud morphologies; distinctions between polar clouds and ice; and textural measures of sea ice, ice sheets, and vegetation. At the same time, multiangle data are necessary for accurate retrievals of radiative quantities such as surface and top-of-atmosphere albedos, whose magnitudes are governed by structural characteristics of the reflecting media and which involve angular integration over intrinsically anisotropic intensity fields. Measurements of directional radiation streams also provide independent checks on model assumptions conventionally used in satellite retrievals, such as the application of 1-D radiative transfer theory, and provide data required to constrain more sophisticated, 3-D approaches. In this paper, the value of multiangle remote sensing in establishing physical correspondence and self-consistency between scene structural and radiative characteristics is demonstrated using simultaneous observations from instruments aboard NASA's Terra satellite (MISR, CERES, ASTER, and MODIS). Illustrations pertaining to the remote sensing of clouds, aerosols, ice, and vegetation properties are presented.
Remote Sensing of Environment 01/2005; 97:495-518. · 4.57 Impact Factor
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ABSTRACT: The Multi-angle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite has demonstrated the capability to retrieve aerosol optical depths, surface bidirectional reflectance factors, and hemispherical reflectances over a wide variety of land surface types. In particular, its multiangular imaging design has enabled the application of algorithms that minimize sensitivity of the aerosol retrievals to the brightness of the underlying surface. The novel aerosol algorithm that was developed prior to launch has had notable quantitative success. Over certain scene types, however, the approach contained obvious spatial artifacts, so a postlaunch refinement to the algorithm was implemented. It constrains the retrieved aerosol models and optical depths such that the implied angular shape of the surface hemispherical–directional reflectance factor (HDRF) is similar among all of the MISR wavelengths. This upgrade has resulted in three tangible benefits: (1) the occurrence of outliers has been dramatically reduced, (2) correlations with AERosol RObotic NETwork (AERONET) aerosol sunphotometer data are quantitatively improved, and (3) the quality of surface products is markedly enhanced. MISR Level 2 aerosol and surface products are archived at the NASA Langley Atmospheric Sciences Data Center. Those having version numbers v0012 and higher incorporate this upgrade in the data processing software.
Remote Sensing of Environment 01/2005; 94:155-171. · 4.57 Impact Factor
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01/2004: pages 103-115; , ISBN: 90-5809-693-9
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Bernard Pinty,
Nadine Gobron,
Michel M. Verstraete,
Frédéric Mélin,
Jean-Luc Widlowski,
Yves Govaerts, David J. Diner,
Eric J. Fielding,
David L. Nelson,
Raul Madariaga,
Martitia P. Tuttle
Eos Transactions American Geophysical Union 01/2003; 84:37-48.
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ABSTRACT: New sensors exhibiting advanced technical specifications motivate the development of improved algorithms to take advantage of the enhanced performances of these sensors. In the particular case of the Multiangle Imaging Spectroradiometer (MISR) instrument, the angular sampling of the scattered radiance field, coupled with high spatial resolution and accurate radiometric calibration, justifies the implementation of physically based algorithms to optimally interpret the data and extract high-level information. This paper proposes a new approach to the reliable and accurate characterization of vegetated areas on the basis of data gathered in space and to the delivery of improved products to meet increasingly demanding user requests. An exploratory study based on advanced very high-resolution radiometer (AVHRR) data shows the potential of approaches based on advanced models but also points out the limitations associated with the use of data from monodirectional instruments. By contrast, a preliminary investigation conducted with synthetic MISR-like multiangular data illustrates the potential of analyzing data of high radiometric quality with advanced models to move toward a more complete characterization of terrestrial surfaces.
01/2000; 105549(16):539-17.
