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ABSTRACT: Shallow waters are very important for human and biological activity. Remote sensing of these areas is challenging, as it requires separation of ocean (or lake) bottom, water and atmospheric effects. In this paper we describe a concept and theory for spaceborne recovery of the underwater depth map, optical characteristics of the water and atmosphere, and the descattered ocean bottom. The sensing is based on multi-angular geometry and polarization. An orbiting platform captures a subspace of the Earth's light field, which is sensitive to the atmospheric and water characteristics. Consequently, it is possible to invert the image formation process using the acquired data. Recovery is simplified using recent findings about natural characteristics of deep water backscatter and surface transmissivity. It also exploits accumulated historical sounding data.
Computational Photography (ICCP), 2011 IEEE International Conference on; 05/2011
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ABSTRACT: In this paper, Multi-angle Imaging SpectroRadiometer (MISR) aerosol product attributes are described, including geometry and algorithm performance flags. Actual retrieval coverage is mapped and explained in detail using representative global monthly data. Statistical comparisons are made with coincident aerosol optical depth (AOD) and Angstrom exponent (ANG) retrieval results from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The relationship between these results and the ones previously obtained for MISR and MODIS individually, based on comparisons with coincident ground-truth observations, is established. For the data examined, MISR and MODIS each obtain successful aerosol retrievals about 15% of the time, and coincident MISR-MODIS aerosol retrievals are obtained for about 6%-7% of the total overlap region. Cloud avoidance, glint and oblique-Sun exclusions, and other algorithm physical limitations account for these results. For both MISR and MODIS, successful retrievals are obtained for over 75% of locations where attempts are made. Where coincident AOD retrievals are obtained over ocean, the MISR-MODIS correlation coefficient is about 0.9; over land, the correlation coefficient is about 0.7. Differences are traced to specific known algorithm issues or conditions. Over-ocean ANG comparisons yield a correlation of 0.67, showing consistency in distinguishing aerosol air masses dominated by coarse-mode versus fine-mode particles. Sampling considerations imply that care must be taken when assessing monthly global aerosol direct radiative forcing and AOD trends with these products, but they can be used directly for many other applications, such as regional AOD gradient and aerosol air mass type mapping and aerosol transport model validation. Users are urged to take seriously the published product data-quality statements.
IEEE Transactions on Geoscience and Remote Sensing 01/2009; 47(12):4095 - 4114. · 2.89 Impact Factor
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Ralph A Kahn,
Michael J Garay,
David L Nelson,
Kevin K Yau,
Michael A Bull,
Barbara J Gaitley,
John V Martonchik,
Robert C Levy,
Citation : Kahn,
M J Garay,
D L Nelson,
K K Yau,
M A Bull,
B J Gaitley, J V Martonchik,
R C Levy
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ABSTRACT: 1] Although the current Multiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite passive remote sensing midvisible aerosol optical thickness (AOT) products are accurate overall to about 0.05 or 20%, they differ systematically on a global, monthly average basis, by about 0.03 to 0.05. Some key climate change and other applications require accuracies of 0.03 or better. The instruments are sufficiently stable and well characterized, and have adequate signal-to-noise, to realize such precision. However, assumptions made in the current standard aerosol retrieval algorithms produce AOT biases that must be addressed first. We identify the causes of AOT discrepancies over dark water under typical, relatively low AOT conditions and quantify their magnitudes on the basis of detailed analysis. Examples were selected to highlight key issues for which there are coincident MISR, MODIS, and Aerosol Robotic Network (AERONET) observations. Instrument calibration and sampling differences, assumptions made in the MISR and MODIS standard algorithms about ocean surface boundary conditions, missing particle property or mixture options, and the way reflectances used in the retrievals are selected each contribute significantly to the observed differences under some circumstances. Cloud screening is also identified as a factor, though not fully examined here, as are the relatively rare high-AOT cases over ocean. Specific algorithm upgrades and further studies indicated by these findings are discussed, along with recommendations for effectively using the currently available products for regional and global applications. (2007), Satellite-derived aerosol optical depth over dark water from MISR and MODIS: Comparisons with AERONET and implications for climatological studies, J. Geophys. Res., 112, D18205, doi:10.1029/2006JD008175.
Journal of Geophysical Research 11/2007; 112(D18205). · 3.02 Impact Factor
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D. Huang,
Y. Knyazikhin,
R. E. Dickinson,
M. Rautiainen,
P. Stenberg,
M. Disney,
P Lewis,
A. Cescatti,
Y Tian,
W. Verhoef, J.V. Martonchik,
R. B. Myneni
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ABSTRACT: The concept of canopy spectral invariants expresses the observation that simple algebraic combinations of leaf and canopy spectral transmittance and reflectance become wavelength independent and determine a small set of canopy structure specific variables. This set includes the canopy interceptance, the recollision and the escape probabilities. These variables specify an accurate relationship between the spectral response of a vegetation canopy to the incident solar radiation at the leaf and the canopy scale and allow for a simple and accurate parameterization for the partitioning of the incoming radiation into canopy transmission, reflection and absorption at any wavelength in the solar spectrum. This paper presents a solid theoretical basis for spectral invariant relationships reported in literature with an emphasis on their accuracies in describing the shortwave radiative properties of the three-dimensional vegetation canopies. The analysis of data on leaf and canopy spectral transmittance and reflectance collected during the international field campaign in Flakaliden, Sweden, June 25¿July 4, 2002 supports the proposed theory. The results presented here are essential to both modeling and remote sensing communities because they allow the separation of the structural and radiometric components of the measured/modeled signal. The canopy spectral invariants offer a simple and accurate parameterization for the shortwave radiation block in many global models of climate, hydrology, biogeochemistry, and ecology. In remote sensing applications, the information content of hyperspectral data can be fully exploited if the wavelength-independent variables can be retrieved, for they can be more directly related to structural characteristics of the three-dimensional vegetation canopy.
Remote Sensing of Environment 106 (2007) 1. 01/2007; 106:106-122.
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ABSTRACT: This paper presents a validation case study of Multi-angle Imaging SpectroRadiometer (MISR) surface products where its bidirectional reflectance (BRF) measurements during the Southern Africa Regional Science Initiative (SAFARI 2000) campaign are compared with those coincidently evaluated on the ground and from the air, using the Portable Apparatus for Rapid Acquisition of Bidirectional Observations of Land and Atmosphere (PARABOLA) and Cloud Absorption Radiometer observations, respectively. The presence of haze and smoke during the campaign provided a case study to evaluate the effect of atmospheric correction on MISR surface products. Two surface types were considered in the analyses: the bright desert-like surface of the Pan and the dark grassland that surrounds it. The results show that for the dark surface the BRF values retrieved from MISR are in good agreement, within 5%, with those obtained from field data. For the bright desert-like pan surface, better agreement, within ~10%, was found in all channels on the clear day but only in the forward scattering on the hazy day. A comparison of MISR aerosol retrievals to those obtained from three independent ground measurements suggests that, in the presence of a highly reflective surface, small uncertainties in the MISR aerosol retrievals become magnified at larger optical depths, causing errors in the surface BRF retrievals
IEEE Transactions on Geoscience and Remote Sensing 08/2006; · 2.89 Impact Factor
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Journal of Geophysical Research 01/2005; 110(D10S07). · 3.02 Impact Factor
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ABSTRACT: Most of the existing cloud radiation models and conventional techniques
of data processing assume that the mean number of drops with a given
radius varies proportionally to volume. The analysis of microphysical
data on liquid water drop sizes acquired during the First International
Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE),
July 1987, and the Atmosphere Radiation Measurements (ARM) Cloud
Intensive Operational Period (IOP), March, 2000, shows that, for
sufficiently small volumes, the number is proportional to the drop size
dependent power of the volume. The drop size dependent coefficient of
proportionality, or a generalized drop concentration, and the exponent
are determined solely by the smallest sampling volume; they are
independent of the volume drops occupy and differentiate spatial
distributions of drops with different sizes. For abundant small drops (r
> 14 μm) present, the exponent is 1 as assumed in the conventional
approach. However, for rarer large drops (r > 14 μm), the
exponents fall below unity for scales between the smallest sampling
volume and a "saturation" scale. At these scales, therefore, the mean
number of large drops decreases with volume at a slower rate than the
conventional approach assumes, suggesting more large drops at small
scales than conventional models account for; their impact is
consequently underestimated. The analysis presented here indicates that
depending on cloud size, the neglect of small-scale drop size
variability can result in a systematic underestimation of cloud
horizontal optical path.
AGU Spring Meeting Abstracts. 04/2004; -1:03.
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ABSTRACT: 1 ] Comparisons of the Multi-angle Imaging SpectroRadiometer (MISR) aerosol optical depths (AOD) with those of the AErosol RObotic NETwork (AERONET) were made at four desert sites, covering a two-year time period from December 2000 to November 2002. The two data sets show good correlation with no obvious systematic biases or trends, demonstrating MISR's ability to retrieve reliable visible and near infrared AOD over surfaces with relatively high reflectance. For MISR AOD obtained at 17.6 km spatial resolution, the estimated uncertainty is about 0.08. When the spatial resolution was degraded to 52.8 km, the estimated AOD uncertainty decreased to about 0.05. Year-long time-series comparisons of MISR and AERONET AOD at the four desert sites showed that MISR can quantitatively capture the temporal nature of strong dust activity in desert regions.
Geophys. Res. Lett. 01/2004; 31.
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Proc SPIE 01/2004; 5652:57-65.
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ABSTRACT: The Multi-angle Imaging SpectroRadiometer (MISR) is to be launched with the Earth Observing System EOS-AM1 spacecraft in 1999. Demanding specifications include a requirement that the instrument be calibrated, and placed on an accurate radiometric scale, to within 3% (1σ) uncertainty, for incident radiances near the upper end of a camera's dynamic range. Contributing factors to the uncertainty in radiance measurements include signal-to-noise ratio, goodness of fit of the calibration data to a quadratic equation, and quality of the experimental conditions (i.e. range and number of radiometric levels used to provide the calibration). These sources, as they are identified, are flagged as contributing to the absolute, relative band-to-band, relative camera-to-camera, or relative pixel-to-pixel radiance uncertainties. This paper summarizes the products and results from the uncertainty analysis of radiometric calibrations for the MISR. It also provides an example of a geophysical product retrieval that makes use of these data.
Metrologia 03/2003; 35(4):571. · 1.75 Impact Factor
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ABSTRACT: We explore a synergistic approach to use the complementary angular samplings from the Multi-angle Imaging SpectroRadiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) to improve MODIS surface bidirectional reflectance distribution function (BRDF) and albedo retrieval. Preliminary case studies show that MODIS and MISR surface bidirectional reflectance factors (BRFs) are generally comparable in the green, red, and near infrared. An information index is introduced to characterize the information content of directional samplings, and it is found that MISR angular observations can bring additional information to the MODIS retrieval, especially when the MISR observations are close to the principal plane. We use the BRDF parameters derived from the MISR surface BRFs as a priori information and derive a posteriori estimates of surface BRDF parameters with the MODIS observations. Results show that adding MISR angular samplings can reduce the relative BRF prediction error by up to 10% in the red and green, compared to the retrievals from MODIS-only observations which are close to the cross-principal plane.
IEEE Transactions on Geoscience and Remote Sensing 08/2002; · 2.89 Impact Factor
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ABSTRACT: A recent paper, J.V. Martonchik et al., IEEE Trans. Geosci. Remote Sensing, vol.36, p.1212-27 (1998), compared approximate radiative transfer results for top-of-atmosphere (TOA) radiance, using various algorithms published in the literature. We show that one of the algorithms was used incorrectly, resulting in its poor performance as stated in that paper. Correct usage produces results with errors typically less than 3%, which compares favorably to the other tested algorithms.
IEEE Transactions on Geoscience and Remote Sensing 08/2002; · 2.89 Impact Factor
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ABSTRACT: Examples of aerosol retrieval results, derived from the Multi-angle Imaging SpectroRadiometer (MISR) on the Earth Observation Science (EOS) Terra platform, are shown and the performance of the retrieval algorithms are discussed, following the first 18 months of operational data processing. A number of algorithm modifications were implemented, based on an analysis of aerosol retrieval results during this period, and these changes are described. Two cloud-screening algorithms, the angle-to-angle smoothness and angle-to-angle correlation tests, which were used in the preprocessing phase of the analyses are also described. The aerosol retrieval examples cover a wide variety of conditions, both over land and water. Particular aerosol types include dust clouds, forest fire and volcanic plumes, and localized dense haze. Finally, some ideas are discussed for additional improvement of the MISR aerosol data product, based on the experience gained in analyzing multiangle data and the associated geophysical products.
IEEE Transactions on Geoscience and Remote Sensing 08/2002; · 2.89 Impact Factor
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IEEE Transactions on Geoscience and Remote Sensing 08/2002; · 2.89 Impact Factor
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ABSTRACT: An advanced algorithm to characterize land surface properties on the basis of Meteosat-5 data has been developed and applied to year 1996 observations. Surface albedo values decontaminated from atmospheric effects and computed for a fixed Sun location have been derived for every day of 1996. A simple composite procedure has been applied over consecutive 10-day and 30-day periods to produce geographically complete maps of surface albedo. The sensitivity of Meteosat-5 observations to various land cover change scenarios has been assessed using models to simulate radiation transfer of solar radiation in soil-vegetation systems. The results suggest that the observed seasonal albedo changes cannot be explained by seasonally-driven phenological cycles of tropical vegetation so that a more complex set of mechanisms incorporating the effects of anthropogenic activities must be devised. Additional information derived from ATSR-2 measurements support the finding that the observed large and unexpected variations in surface albedo at a continental scale over Africa could be explained by intense biomass burning activities during the dry seasons
Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International; 02/2001
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Geophysical Research Letters 01/2001; 28. · 3.79 Impact Factor
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ABSTRACT: The multi-angle imaging spectroradiometer (MISR) instrument is
designed to provide global imagery at nine discrete viewing angles and
four visible/near-infrared spectral bands. The MISR standard products
include vegetation canopy green leaf area index (LAI) and fraction of
photosynthetically active radiation absorbed by vegetation (FPAR). These
products are produced using a peer-reviewed algorithm documented in the
EOS-AM1 (Terra) special issue of the Journal of Geophysical Research.
This paper presents results on spatial distributions of LAI and FPAR of
vegetated land surfaces derived from the MISR LAI/FPAR algorithm with
bidirectional reflectance data from the polarization and directionality
of the Earth's reflectance (POLDER) instrument over Africa. The results
indicate that the proposed algorithm reflects the physical relationships
between surface reflectances and biophysical parameters and demonstrates
the advantages of using multiangle data instead of single-angle data. A
new method for evaluating bihemispherical reflectance (BHR) from
multi-angle measurements of hemispherical directional reflectance factor
(HDRF) was developed to prototype the algorithm with POLDER data. The
accuracy of BHR evaluation and LAI/FPAR estimation is also presented. To
authors demonstrate the advantages of using multi-angle data over
single-angle data of surface reflectance
IEEE Transactions on Geoscience and Remote Sensing 10/2000; · 2.89 Impact Factor
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MISR/atbd-misr09. pdf. 01/1999;
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ABSTRACT: A family of surface bidirectional reflectance factor (BRF) models
is found suitable for representing the surface boundary condition and of
solving the problem of radiation transfer in the atmosphere. Optimal
input parameters for a wide variety of surface types are available. The
applicability of the models is analyzed with respect to (1) the
derivation of illumination independent reflection properties of the
surface, (2) the calculation of albedo, (3) the extrapolation of
reflectance factors to geometries other than those of the measurements.
Some of the models are linearly invertible. This family of models is
proposed as part of the land surface product algorithm of the
Multi-angle Imaging Spectro-Radiometer (MISR) of NASA/JPL, due to fly in
1998 on the EOS-AM platform
Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International; 08/1998
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ABSTRACT: Aerosols are believed to play a direct role in the radiation
budget of Earth, but their net radiative effect is not well established,
particularly on regional scales. Whether aerosols heat or cool a given
location depends on their composition and column amount and on the
surface albedo, information that is not routinely available, especially
over land. Obtaining global information on aerosol and surface radiative
characteristics, over both ocean and land, is a task of the Multi-angle
Imaging SpectroRadiometer (MISR), an instrument to be launched in 1998
on the Earth Observing System EOS-AM1 platform. Three algorithms are
described that will be implemented to retrieve aerosol properties
globally using MISR data. Because of the large volume of data to be
processed on a daily basis, these algorithms rely on lookup tables of
atmospheric radiative parameters and predetermined aerosol mixture
models to expedite the radiative transfer (RT) calculations. Over
oceans, the “dark water” algorithm is used, taking full
advantage of the nature of the MISR data. Over land, a choice of
algorithms is made, depending on the surface types within a scene-dark
water bodies, heavily vegetated areas, or high-contrast terrain. The
retrieval algorithms are tested on simulated MISR data, computed using
realistic aerosol and surface reflectance models. The results indicate
that aerosol optical depth can be retrieved with an accuracy of 0.05 or
10%, whichever is greater, and some information can be obtained about
the aerosol chemical and physical properties
IEEE Transactions on Geoscience and Remote Sensing 08/1998; · 2.89 Impact Factor
