Cloud Detection from the Spaceborne POLDER Instrument and Validation against Surface Synoptic Observations

Bréon, François‐Marie; Colzy, Stéphane

doi:10.1175/1520-0450(1999)038<0777:cdftsp>2.0.co;2

Cited by 92 publications

(69 citation statements)

References 10 publications

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“…POLDER-3 cloud microphysical properties retrievals have a 36 km × 36 km spatial resolution. Cloud top pressure is derived from the cloud oxygen pressure (Bréon and Colzy, 1999). Cloud top pressure retrieved by POLDER-3 appears to be a better proxy for low-level cloud height than MODIS cloud top pressure derived using a thermal signature assuming a given temperature profile (Buriez et al, 1997;Weisz et al, 2007;Tietze et al, 2011;Desmons et al, 2013).…”

Section: Satellite Cloud Property Retrievalsmentioning

confidence: 99%

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

et al. 2016

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Abstract. The properties of low-level liquid clouds in the Arctic can be altered by long-range pollution transport to the region. Satellite, tracer transport model, and meteorological data sets are used here to determine a net aerosol-cloud interaction (ACI net ) parameter that expresses the ratio of relative changes in cloud microphysical properties to relative variations in pollution concentrations while accounting for dry or wet scavenging of aerosols en route to the Arctic. For a period between 2008 and 2010, ACI net is calculated as a function of the cloud liquid water path, temperature, altitude, specific humidity, and lower tropospheric stability. For all data, ACI net averages 0.12±0.02 for cloud-droplet effective radius and 0.16±0.02 for cloud optical depth. It increases with specific humidity and lower tropospheric stability and is highest when pollution concentrations are low. Carefully controlling for meteorological conditions we find that the liquid water path of arctic clouds does not respond strongly to aerosols within pollution plumes. Or, not stratifying the data according to meteorological state can lead to artificially exaggerated calculations of the magnitude of the impacts of pollution on arctic clouds.

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Section: Satellite Cloud Property Retrievalsmentioning

confidence: 99%

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

et al. 2016

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“…The AOT is retrieved at the 670 nm and 865 nm channels equipped with polarized filters. Only cloud-free pixels selected according to the cloud-screening algorithm of Bréon and Colzy (1999) are processed. The surface contribution is modelled as a semi-empirical bidirectional polarized distribution function that depends on the normalized difference vegetation index (NDVI) and the geo-type of the pixel according to the IGBP classification (Nadal and Bréon, 1999).…”

Section: Evaluation Of the Polder-2 Aerosol Optical Thicknessmentioning

confidence: 99%

Characterization of aerosol pollution events in France using ground-based and POLDER-2 satellite data

et al. 2006

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Abstract. We analyze the relationship between daily fine particle mass concentration (PM2.5) and columnar aerosol optical thickness derived from the Polarization and Directionality of Earth's Reflectances (POLDER) satellite sensor. The study is focused over France during the POLDER-2 lifetime between April and October 2003. We have first compared the POLDER derived aerosol optical thickness (AOT) with integrated volume size distribution derived from ground-based Sun Photometer observations. The good correlation (R=0.72) with sub-micron volume fraction indicates that POLDER derived AOT is sensitive to the fine aerosol mass concentration. Considering 1974 match-up data points over 28 fine particle monitoring sites, the POLDER-2 derived AOT is fairly well correlated with collocated PM2.5 measurements, with a correlation coefficient of 0.55. The correlation coefficient reaches a maximum of 0.80 for particular sites. We have analyzed the probability to find an appropriate air quality category (AQC) as defined by U.S. Environmental Protection Agency (EPA) from POLDER-2 AOT measurements. The probability can be up to 88.8% (±3.7%) for the "Good" AQC and 89.1% (±3.6%) for the "Moderate" AQC.

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“…This pixel is also observed from a number of other sequences/directions and we identified the one closest to nadir viewing. A simple test on the reflectance in the blue channel was used to eliminate cloud contaminated pixels [Bréon and Colzy, 1999]. Water covered pixels were also discarded, based on the spectral signature of the reflectance at 670 and 865 nm.…”

Section: Data Processingmentioning

confidence: 99%

Analysis of hot spot directional signatures measured from space

Bréon

2002

J. Geophys. Res.

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[1] Reflectance measurements from the spaceborne Polarization and Directionality of Earth Reflectances (POLDER) instrument are used to analyze the so-called hot spot directional signature in the backscattering direction. The hot spot is measured with an angular resolution better than half a degree using the directional capabilities of the radiometer, with some assumptions on the spatial homogeneity of the surface. The analysis yields the first quantitative observation of the hot spot signature of vegetated surfaces, with such angular resolution. The measurements show that the hot spot reflectance is a function of the phase angle x rather than a function of a parameter Á, often used in hot spot modeling, that quantifies the horizontal distance between Sun and view directions. The observed directional signature is very accurately fitted by a linear ratio of the phase angle, as predicted by a simple theory of radiative transfer within the canopy foliage. Most of the measured hot spot half widths are between 1°and 2°. Some dispersion occurs for the cases belonging to the forest and desert International Geosphere-Biosphere Program (IGBP) classes, in the range 1°to 5°. Theory predicts that the width is independent of wavelength. Our measurements indicate that the widths at 670 and 865 nm are very close, but with a significant scatter in regards to the rather small variability. The distribution of the width as a function of the IGBP surface classification shows a variability within the classes that is larger than between the classes, except for the ''evergreen broadleaf'' class. The hot spot reflectance amplitude is generally on the order of 0.10-0.20 at 865 nm and 0.03-0.18 at 670 nm, although the full range of values is wider. For thick canopies, it may be interpreted in terms of foliage element (leaf ) reflectance. Retrieved values are on the order of 0.4 in the near infrared and in the range 0.05-0.20 at 670 nm. At 440 nm, the amplitude of the signature is very small, as is expected from the small surface reflectance. This confirms that the atmospheric contribution to the reflectance increase at the backscattering direction is negligible.

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Cloud Detection from the Spaceborne POLDER Instrument and Validation against Surface Synoptic Observations

Cited by 92 publications

References 10 publications

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

Characterization of aerosol pollution events in France using ground-based and POLDER-2 satellite data

Analysis of hot spot directional signatures measured from space

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