Platform and Environmental Effects on Above-Water Determinations of Water-Leaving Radiances

Hooker, SB; Morel, A.

doi:10.1175/1520-0426(2003)020<0187:paeeoa>2.0.co;2

Cited by 44 publications

(44 citation statements)

References 15 publications

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“…Zenith angles of the sea-and skyviewing radiance sensors were 40Њ. The frame was fixed to the prow of the ship, facing forward to minimize ship shadow and reflection (Hooker and Morel 2003). The ship was maneuvered on station to point the radiance sensors at a relative azimuth angle of 135Њ away from the sun.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

et al. 2006

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Theory and seaborne measurements are presented for the near infrared (NIR: 700-900 nm) water-leaving reflectance in turbid waters. According to theory, the shape of the NIR spectrum is determined largely by pure water absorption and is thus almost invariant. A ''similarity'' NIR reflectance spectrum is defined by normalization at 780 nm. This spectrum is calculated from seaborne reflectance measurements and is compared with that derived from laboratory water absorption measurements. Factors influencing the shape of the similarity spectrum are analyzed theoretically and by radiative transfer simulations. These simulations show that the similarity spectrum is valid for waters ranging from moderately turbid (e.g., water-leaving reflectance at 780 nm of order 10 Ϫ4 or total suspended matter concentration of order 0.3 g m Ϫ3 ) to extremely turbid (e.g., reflectance at 780 nm of order 10 Ϫ1or total suspended matter of order 200 g m Ϫ3). Measurement uncertainties are analyzed, and the air-sea interface correction is shown to be critical for low reflectances. Applications of the NIR similarity spectrum to atmospheric correction of ocean color data and to the quality control of seaborne, airborne, and spaceborne reflectance measurements in turbid waters are outlined.Although ocean color remote sensing has focused primarily on visible wavelengths (400-700 nm) where photosynthetic pigments have detectable absorption features, there is a growing interest in water-leaving reflectances at near infrared (NIR) wavelengths, usually taken as the range 700-1,000 nm. There are essentially three reasons for this. First, although for atmospheric correction over clear waters the NIR water-leaving reflectance can usually be taken as zero (Gordon and Wang 1994), for turbid waters it is essential to model or estimate NIR water-leaving reflectance in order to 1 Corresponding author (K.Ruddick@mumm.ac.be). 2 Present address: Polytechnic of Namibia, P/Bag 13388, Windhoek, Namibia. AcknowledgmentsThis study was funded by the Belgian Science Policy Office's STEREO program in the framework of the BELCOLOUR project SR/00/03, by the European Union under the REVAMP project EVG1-CT-2001-00049, and by PRODEX contract 15190/01. The captains, crews, and support staff of the research vessels Belgica and Zeeleeuw are thanked for their enthusiastic help with the seaborne measurements. Jean-Paul Huot and the scientists of the RE-VAMP project and the MERIS Validation Team are especially thanked for the many discussions that have helped to improve and control the quality of the seaborne measurements. Wolfgang Cordes of GKSS is acknowledged for the tests on polarization and droplet sensitivity of spectroradiometers. Rudiger Heuermann of TriOS and Jean-Pierre De Blauwe and André Pollentier of MUMM-Oostende are thanked for help with system design; Barbara Van Mol for help with figure preparation; Bouchra Nechad for discussions on the use of the near infrared (NIR) range for total suspended matter (TSM) retrieval; and Arnold Dekker for discussion of op...

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Section: Experimental Methodsmentioning

confidence: 99%

“…Band number (center wavelength in nm) NIR band ratio 1985) or quality control of above-water reflectance measurements (e.g., to detect contamination by ship shadow or reflection; Hooker and Morel 2003). For more reflective waters such a hypothesis is no longer valid.…”

Section: Sensormentioning

confidence: 99%

Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

et al. 2006

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“…From its data, the water-leaving radiance L À u just beneath the sea surface and hence the so-called remote sensing reflectance R À rs l ð Þcan be estimated (see, e.g. Hooker and Morel 2003). Data are available during daylight and can be used in clear sky or homogeneous cloud conditions only.…”

Section: Meteorological and Remote Sensing Instrumentsmentioning

confidence: 99%

A hydrographic time series station in the Wadden Sea (southern North Sea)

et al. 2009

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In the tidal inlet between the East Frisian islands of Langeoog and Spiekeroog, southern North Sea, a timeseries station was set up in autumn 2002 as part of the research programme BioGeoChemistry of Tidal Flats run by the University of Oldenburg. The purpose of the station is to provide continuous data on physical, biological and chemical parameters. In addition to instruments recording basic hydrographic and meteorological parameters, the time-series station is equipped with acoustic Doppler profilers for measuring surface waves and current profiles. Compact optical spectrometers are being used for spectral measurements of seawater transmission and for daylight reflectance. Additional sensors were installed for measuring oxygen, nutrients and methane in the seawater. The data shall help to quantify the flux of dissolved and suspended matter between the backbarrier tidal flat and the open sea and to characterise the material transformation in the tidal flat area by biogeochemical processes over the tidal cycle. Due to its novel design, operation of the station is also possible during winter and under extreme weather conditions (gales, storm surges, and sea ice) when data sampling with conventional platforms such as research vessels, buoys, or smaller poles could not be performed in the past. In this way, time series of data are obtained, which include events that are most relevant to the evolution of this coastal area. The performance of the station and its equipment are presented with data covering 6 years of operation. Time series of air and water temperature as well as seawater salinity demonstrate the multiyear dynamics of these parameters in the East Frisian Wadden Sea. Hydrographic data collected under specific meteorological conditions such as gales and storm surges exemplify the all-weather capabilities of the station and its value for studying hydrographic processes in the Wadden Sea.

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“…This will influence the value of L w . The problem has been discussed by Hooker and Morel (2003) and Hooker and Zibordi (2005). In our case we find that this reflectance was included in the ship-shading effect determined by .…”

Section: Processing Of L Uw Measurementsmentioning

confidence: 49%

“…Under an overcast sky the ranges were 1.0-1.6 at both wavelengths. All of these factors constitute a challenge with regard to a quantitative analysis of the recordings (Bissett et al, 2004;Garaba and Zielinski, 2013;Hooker and Morel, 2003;Mueller et al, 2003;Simis and Olsson, 2013).…”

Section: Introductionmentioning

confidence: 99%

Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements

et al. 2015

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Abstract. During 4 field days in the years [2009][2010][2011] 22 data sets of measurements were collected in the inner Oslofjord, Norway. The data consist of recordings of spectral nadir radiances in air and water as well as spectral downward irradiance in air. The studied wavelengths are 351, 400, 413, 443, 490, 510, 560, 620, 665, 681, 709 and 754 nm.The water-leaving radiance and the reflected radiance at the sea surface have been obtained from the measured nadir radiances in air and water, where the latter radiance has been extrapolated upwards to the surface. For comparison we present a simpler and much faster method that determines the water-leaving and reflected radiances solely from abovesurface measurements of upward nadir radiance and downward irradiance. This new method is based on an assumption about similarity in spectral shape of the radiance reflected at the surface, and it makes use of the small ratio between water-leaving and reflected radiances at 351 and 754 nm in the Oslofjord.A comparison between the quantities determined by the two mentioned methods shows that the average relative deviations between their results are less than or equal to 15 % for the reflected radiance, at the studied wavelengths. The average relative deviation of the water-leaving radiance at 560 nm is 24 %. These results are obtained for a cloudiness range of 1-8 oktas (12.5-100 %) and solar zenith angles between 37 and 51 • . We consider these to be acceptable uncertainties for a first check of satellite products in the inner Oslofjord.

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Platform and Environmental Effects on Above-Water Determinations of Water-Leaving Radiances

Cited by 44 publications

References 15 publications

Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

A hydrographic time series station in the Wadden Sea (southern North Sea)

Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements

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