The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Menghua Wang - One of the best experts on this subject based on the ideXlab platform.
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evaluation of sun Glint models using modis measurements
Journal of Quantitative Spectroscopy & Radiative Transfer, 2010Co-Authors: Hao Zhang, Menghua WangAbstract:Abstract To understand the performance of various sun Glint models, we have carried out comparison studies with measurements from Moderate Resolution Imaging Spectroradiometer (MODIS) for several popular sun glitter models, including the Cox–Munk models, Ebuchi–Kizu models, Breon–Henriot models, etc., over the open oceans using MODIS data at the near-infrared (NIR) (859 nm) and shortwave infrared (SWIR) bands (1240 and 2130 nm). Sun Glint models with and without a wind direction dependence were evaluated. To obtain the MODIS-measured Glint reflectance from the total reflectance at the top of the atmosphere, we performed atmospheric corrections to remove the effects of atmospheric absorption as well as radiance contributions from molecules (Rayleigh scattering) and aerosols. We have selected 12 MODIS sun Glint scenes over various open ocean regions for this study. Our results indicate that overall, the Cox–Munk [1] model with the wind direction dependence has the best performance in terms of correlation coefficients with the MODIS measurements. The Breon–Henriot [8] model performed similarly as from the Cox–Munk model as two models are in fact very close. Findings from these evaluations can improve our ability to accurately remove the sun Glint contamination in MODIS imagery and produce robust satellite ocean color and atmosphere products.
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correction of sun Glint contamination on the seawifs ocean and atmosphere products
Applied Optics, 2001Co-Authors: Menghua Wang, Sean W BaileyAbstract:For remote sensing of the ocean and atmosphere optical properties, the measurement of radiances affected by sun Glint has to be avoided and/or masked out. There are usually no meaningful retrievals in regions significantly contaminated by sun Glint. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) is capable of operationally tilting the sensor 20 degrees away from nadir to minimize sun Glint contamination. The sun Glint mask is computed from the Cox and Munk model [J. Opt. Soc. Am. 44, 838-850 (1954)] and applied to the SeaWiFS data. However, sun Glint is still a factor near the subsolar point. We present results that demonstrate the effect of sun Glint contamination on retrievals of ocean bio-optical and atmospheric products. We show that, although sun Glint contamination has a minor effect on retrieved ocean color products, the effect on retrieved atmospheric products, e.g., aerosol optical thickness, is significant. We describe a sun Glint correction scheme implemented in the SeaWiFS data-processing system and compare the results with and without sun Glint correction. With sun Glint correction the derived ocean and atmospheric products are improved. Also, the sun Glint masked area can be reduced and therefore can increase significantly the coverage area near the subsolar point.
Samantha Lavender - One of the best experts on this subject based on the ideXlab platform.
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sun Glint correction of high and low spatial resolution images of aquatic scenes a review of methods for visible and near infrared wavelengths
Remote Sensing, 2009Co-Authors: John D Hedley, Samantha LavenderAbstract:Sun Glint, the specular reflection of light from water surfaces, is a serious confounding factor for remote sensing of water column properties and benthos. This paper reviews current techniques to estimate and remove the Glint radiance component from imagery. Methods for processing of ocean color images use statistical sea surface models to predict the Glint from the sun and sensor positions and wind data. Methods for higher resolution imaging, used in coastal and shallow water mapping, estimate the Glint radiance from the near-infrared signal. The effects of some current methods are demonstrated and possibilities for future techniques are briefly addressed.
Carl J Legleiter - One of the best experts on this subject based on the ideXlab platform.
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removing sun Glint from optical remote sensing images of shallow rivers
Earth Surface Processes and Landforms, 2017Co-Authors: B T Overstreet, Carl J LegleiterAbstract:Sun Glint is the specular reflection of light from the water surface, which often causes unusually bright pixel values that can dominate fluvial remote sensing imagery and obscure the water-leaving radiance signal of interest for mapping bathymetry, bottom type, or water column optical characteristics. Although sun Glint is ubiquitous in fluvial remote sensing imagery, river-specific methods for removing sun Glint are not yet available. We show that existing sun Glint-removal methods developed for multispectral images of marine shallow water environments over-correct shallow portions of fluvial remote sensing imagery resulting in regions of unreliable data along channel margins. We build on existing marine Glint-removal methods to develop a river-specific technique that removes sun Glint from shallow areas of the channel without overcorrection by accounting for non-negligible water-leaving near-infrared radiance. This new sun Glint-removal method can improve the accuracy of spectrally-based depth retrieval in cases where sun Glint dominates the at-sensor radiance. For an example image of the gravel-bed Snake River, Wyoming, USA, observed-vs.-predicted R2 values for depth retrieval improved from 0.66 to 0.76 following sun Glint removal. The methodology presented here is straightforward to implement and could be incorporated into image processing workflows for multispectral images that include a near-infrared band. This article is protected by copyright. All rights reserved.
Hao Zhang - One of the best experts on this subject based on the ideXlab platform.
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evaluation of sun Glint models using modis measurements
Journal of Quantitative Spectroscopy & Radiative Transfer, 2010Co-Authors: Hao Zhang, Menghua WangAbstract:Abstract To understand the performance of various sun Glint models, we have carried out comparison studies with measurements from Moderate Resolution Imaging Spectroradiometer (MODIS) for several popular sun glitter models, including the Cox–Munk models, Ebuchi–Kizu models, Breon–Henriot models, etc., over the open oceans using MODIS data at the near-infrared (NIR) (859 nm) and shortwave infrared (SWIR) bands (1240 and 2130 nm). Sun Glint models with and without a wind direction dependence were evaluated. To obtain the MODIS-measured Glint reflectance from the total reflectance at the top of the atmosphere, we performed atmospheric corrections to remove the effects of atmospheric absorption as well as radiance contributions from molecules (Rayleigh scattering) and aerosols. We have selected 12 MODIS sun Glint scenes over various open ocean regions for this study. Our results indicate that overall, the Cox–Munk [1] model with the wind direction dependence has the best performance in terms of correlation coefficients with the MODIS measurements. The Breon–Henriot [8] model performed similarly as from the Cox–Munk model as two models are in fact very close. Findings from these evaluations can improve our ability to accurately remove the sun Glint contamination in MODIS imagery and produce robust satellite ocean color and atmosphere products.
Tyler D Robinson - One of the best experts on this subject based on the ideXlab platform.
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detecting ocean Glint on exoplanets using multiphase mapping
The Astronomical Journal, 2018Co-Authors: Jacob Lustigyaeger, Victoria S Meadows, Tyler D Robinson, Guadalupe Tovar Mendoza, Edward W Schwieterman, Yuka Fujii, Rodrigo LugerAbstract:Rotational mapping and Glint are two proposed methods to directly detect liquid water on the surface of habitable exoplanets. However, false positives for both methods may prevent the unambiguous detection of exoplanet oceans. We use simulations of Earth as an exoplanet to introduce a combination of multiwavelength, multiphase, time-series direct-imaging observations and accompanying analyses that may improve the robustness of exoplanet ocean detection by spatially mapping the ocean Glint signal. As the planet rotates, the Glint spot appears to "blink" as Lambertian scattering continents interrupt the specular reflection from the ocean. This manifests itself as a strong source of periodic variability in crescent-phase reflected light curves. We invert these light curves to constrain the longitudinal slice maps and apparent albedo of two surfaces at both quadrature and crescent phase. At crescent phase, the retrieved apparent albedo of ocean-bearing longitudinal slices is increased by a factor of 5, compared to the albedo at quadrature phase, due to the contribution from Glint. The land-bearing slices exhibit no significant change in apparent albedo with phase. The presence of forward-scattering clouds in our simulated observation increases the overall reflectivity toward crescent, but clouds do not correlate with any specific surfaces, thereby allowing for the phase-dependent Glint effect to be interpreted as distinct from cloud scattering. Retrieving the same longitudinal map at quadrature and crescent phases may be used to tie changes in the apparent albedo with phase back to specific geographic surfaces, although this requires ideal geometries. We estimate that crescent-phase time-dependent Glint detections are feasible for between 1-10 habitable zone exoplanets orbiting the nearest G, K, and M dwarfs using a space-based, high-contrast, direct-imaging telescope with a diameter >6 m.
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detecting oceans on extrasolar planets using the Glint effect
The Astrophysical Journal, 2010Co-Authors: Victoria S Meadows, Tyler D Robinson, David CrispAbstract:Glint, the specular reflection of sunlight off Earth's oceans, may reveal the presence of oceans on an extrasolar planet. As an Earth-like planet nears crescent phases, the size of the ocean Glint spot increases relative to the fraction of the illuminated disk, while the reflectivity of this spot increases. Both effects change the planet's visible reflectivity as a function of phase. However, strong forward scattering of radiation by clouds can also produce increases in a planet's reflectivity as it approaches crescent phases, and surface Glint can be obscured by Rayleigh scattering and atmospheric absorption. Here, we explore the detectability of Glint in the presence of an atmosphere and realistic phase-dependent scattering from oceans and clouds. We use the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional line-by-line, multiple-scattering spectral Earth model to simulate Earth's broadband visible brightness and reflectivity over an orbit. Our validated simulations successfully reproduce phase-dependent Earthshine observations. We find that the Glinting Earth can be as much as 100% brighter at crescent phases than simulations that do not include Glint, and that the effect is dependent on both orbital inclination and wavelength, where the latter dependence is caused by Rayleigh scattering limiting sensitivity to the surface. We show that this phenomenon may be observable using the James Webb Space Telescope paired with an external occulter.
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detecting oceans on extrasolar planets using the Glint effect
arXiv: Earth and Planetary Astrophysics, 2010Co-Authors: Victoria S Meadows, Tyler D Robinson, David CrispAbstract:Glint, the specular reflection of sunlight off Earth's oceans, may reveal the presence of oceans on an extrasolar planet. As an Earth-like planet nears crescent phases, the size of the ocean Glint spot increases relative to the fraction of illuminated disk, while the reflectivity of this spot increases. Both effects change the planet's visible reflectivity as a function of phase. However, strong forward scattering of radiation by clouds can also produce increases in a planet's reflectivity as it approaches crescent phases, and surface Glint can be obscured by Rayleigh scattering and atmospheric absorption. Here we explore the detectability of Glint in the presence of an atmosphere and realistic phase-dependent scattering from oceans and clouds. We use the NASA Astrobiology Institute's Virtual Planetary Laboratory 3-D line-by-line, multiple-scattering spectral Earth model to simulate Earth's broadband visible brightness and reflectivity over an orbit. Our validated simulations successfully reproduce phase-dependent Earthshine observations. We find that the Glinting Earth can be as much as 100% brighter at crescent phases than simulations that do not include Glint, and that the effect is dependent on both orbital inclination and wavelength, where the latter dependence is caused by Rayleigh scattering limiting sensitivity to the surface. We show that this phenomenon may be observable using the James Webb Space Telescope (JWST) paired with an external occulter.
