Retrieval of aerosol properties over land surfaces: capabilities of multiple-viewing-angle intensity and polarization measurements

Hasekamp, Otto; Landgraf, Jochen

doi:10.1364/ao.46.003332

Cited by 205 publications

(170 citation statements)

References 31 publications

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“…Reasons for this include a brighter and more heterogeneous surface reflectance, diversity in aerosol microphysical properties, difficulties in cloud identification and, particularly near strong aerosol sources, heterogeneity of the aerosol itself. The limited information content of current and previous instruments of this type (Hasekamp and Landgraf, 2007) has led to the development of many different AOD retrieval algorithms, utilising the strengths and mitigating the weaknesses of each sensor (e.g., Kokhanovsky and de Leeuw, 2009).…”

Section: Introductionmentioning

confidence: 99%

Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS

et al. 2012

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Abstract. This study evaluates a new spectral aerosol optical depth (AOD) dataset derived from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) measurements over land. First, the data are validated against Aerosol Robotic Network (AERONET) direct-sun AOD measurements and found to compare well on a global basis. If only data with the highest quality flag are used, the correlation is 0.86 and 72 % of matchups fall within an expected absolute uncertainty of 0.05 + 20 % (for the wavelength of 550 nm). The quality is similar at other wavelengths and stable over the 13-yr (1997-2010) mission length. Performance tends to be better over vegetated, low-lying terrain with typical AOD of 0.3 or less, such as found over much of North America and Eurasia. Performance tends to be poorer for low-AOD conditions near backscattering geometries, where SeaWiFS overestimates AOD, or optically-thick cases of absorbing aerosol, where SeaWiFS tends to underestimate AOD. Second, the SeaWiFS data are compared with midvisible AOD derived from the Moderate Resolution Imaging Spectrometer (MODIS) and Multiangle Imaging Spectroradiometer (MISR). All instruments show similar spatial and seasonal distributions of AOD, although there are regional and seasonal offsets between them. At locations where AERONET data are available, these offsets are largely consistent with the known validation characteristics of each dataset. With the results of this study in mind, the SeaWiFS over-land AOD record is suitable for quantitative scientific use.

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Section: Introductionmentioning

confidence: 99%

Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS

et al. 2012

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“…Measurements of aerosol abundances and microphysical properties are necessary for monitoring their distribution and for providing insight into the physical processes governing their environmental impacts. Theoretical sensitivity studies, e.g., [3,4] and observations from aircraft and spacecraft suggest that passive remote sensing of aerosol microphysics (using reflected sunlight as the illumination source) benefits from multispectral and multiangular observations, and is enhanced through incorporation of polarization, e.g., [5][6][7][8][9][10]. Radiative transfer calculations [3] imply that in order to meet the stringent requirements of aerosol climate impact assessments [11], inclusion of polarimetry with uncertainty in degree of linear polarization (DOLP) less than ±0.005 improves significantly upon the information content of multiangular spectral intensity measurements.…”

Section: Introductionmentioning

confidence: 99%

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Diner

Martonchik

et al. 2012

Atmosphere

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Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the OPEN ACCESSAtmosphere 2012, 3 592 surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.

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“…This technique is described for atmospheric remote sensing by Rodgers (2000), and more specifically for multi-angle polarimetric remote sensing of aerosols by, for example, Hasekamp and Landgraf (2007), Knobelspiesse et al (2012) and Xu and Wang (2015). This analysis uses the same software for Radiative Transfer (RT) and other computations as Knobelspiesse et al (2012).…”

Section: Information Content Analysismentioning

confidence: 99%

“…can also be used to predict the uncertainty of parameters that are not explicitly retrieved, but derived from retrieved parameters (Hasekamp and Landgraf (2007)). If the definition of a parameter, a, is generalized such that a = G(x), then the uncertainty for a is…”

Section: ŝmentioning

confidence: 99%

Remote sensing of aerosols with small satellites in formation flight

Knobelspiesse¹,

Nag²

2018

Preprint

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Abstract. Determination of aerosol optical properties with orbital passive remote sensing is a difficult task, as observations often have limited information. Multi-angle instruments, such as the Multi-angle Imaging SpectroRadiometer (MISR) and the POlarization and Directionality of the Earth's Reflectances (POLDER), seek to address this by making information rich multi-angle observations, which can be used to better retrieve aerosol optical properties. The paradigm for such instruments is that each angle view is made from one platform, with, for example, a gimbaled sensor or multiple fixed view angle sensors. 5This restricts the observing geometry to a plane within the scene Bidirectional Reflectance Distribution Function (BRDF ) observed at the top of the atmosphere (TOA). New technological developments, however, support sensors on small satellites flying in formation, which could be a beneficial alternative. Such sensors may have only one viewing direction each, but the agility of small satellites allows one to control this direction and change it over time. When such agile satellites are flown in formation and their sensors pointed to the same location at approximately the same time, they could sample a distributed set 10 of geometries within the scene BRDF . In other words, observations from multiple satellites can take a variety view zenith and azimuth angles, and are not restricted to one azimuth plane as is the case with a single multi-angle instrument. It is not known, however, if this is as potentially capable as a multi-angle platform for the purposes of aerosol remote sensing. Using a systems engineering tool coupled with an information content analysis technique, we investigate the feasibility of such an approach for the remote sensing of aerosols. These tools test the mean results of all geometries encountered in an orbit. We 15 find that small satellites in formation are equally capable as multi-angle platforms for aerosol remote sensing, as long as their calibration accuracies and measurement uncertainties are equivalent. As long as the viewing geometries are dispersed throughout the BRDF , it appears the quantity of view angles determines the information content of the observations, not the specific observation geometry. Given the smoothly varying nature of BRDF 's observed at the TOA, this is reasonable, and supports the viability of aerosol remote sensing with small satellites flying in formation. The incremental improvement in 20 information content that we found with number of view angles also supports the concept of a resilient mission comprised of multiple satellites that are continuously replaced as they age or fail.

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Retrieval of aerosol properties over land surfaces: capabilities of multiple-viewing-angle intensity and polarization measurements

Cited by 205 publications

References 31 publications

Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS

Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Remote sensing of aerosols with small satellites in formation flight

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