Inversion of Reflectance Spectra of Nonchlorophyllous Turbid Coastal Waters

Forget, Philippe; Ouillon, Sylvain; Lahet, Florence; Broche, P.

doi:10.1016/s0034-4257(98)00117-5

Cited by 63 publications

(23 citation statements)

References 24 publications

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“…As examples, the above-water measurements of Han and Rundquist (1997), Forget et al (1999), and Doxaran et al (2002) all show spectra with a common shape in the NIR, as do the underwater measurements of Malthus and Dekker (1995). However, a precise assessment of the NIR spectral shape was not the objective of these studies, and the measurement protocols used were not well-adapted for this purpose, notably regarding the viewing geometry and sky reflectance correction for the above-water measurements.…”

Section: Acknowledgmentsmentioning

confidence: 99%

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: Acknowledgmentsmentioning

confidence: 99%

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

et al. 2006

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“…Nevertheless, such data are limited to surface waters. Forget et al (1999Forget et al ( , 2001 studied the sensitivity of water reflectance to variations in SPM concentration with depth. They developed an inversion method for a radiative transfer model restricted to the simple case of a two-layer ocean and tested it on various documented experimental data, also from the Rhône (also see Ouillon 2003).…”

Section: Existing Challenges In Spm Assessmentsmentioning

confidence: 99%

Daily and seasonal dynamics of suspended particles in the Rhône River plume based on remote sensing and field optical measurements

2012

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Satellite ocean colour remote sensing can serve as a powerful tool to assess river plume characteristics because it provides daily mapping of surface suspended particulate matter (SPM) concentration at high spatial resolution. This study's ultimate objective was to better understand daily and seasonal particle dynamics in a coastal area strongly influenced by freshwater discharge and wind-the Rhône River (France), this being the major source of terrestrial input to the Mediterranean Sea. SPM concentrations and biogenic composition (chlorophyll a, organic carbon) were investigated during several bio-optical field campaigns conducted in spring-autumn of 2010 both from aboard a research vessel and by means of an autonomous profiling float. Freshwater discharge and wind velocities varied significantly during the year, associated with marked fluctuations in surface SPM (upper 1 m), even within hours and not restricted to any specific season. Thus, the range was ca. 12-25 g m -3 (dry mass basis) on 9 April (spring), and ca. 3-39 g m -3 on 4-5 November (late autumn). Short-term variations were observed also in SPM composition in terms of POC (albeit not chl a), with POC/SPM ratios ranging between ca. 3 and 11% over ca. 3 weeks in spring. Nevertheless, the particulate backscattering coefficient (b bp ) proved to be a robust proxy of SPM concentration in the river plume (b bp (770)00.0076×SPM, R 2 00.80, N056). It has recently been demonstrated that 80% of the Rhône's terrestrial discharge occurs during flood events. The results of the present study revealed that, under these conditions, SPM is constrained largely within surface waters (i.e. at depths <5 m), with only weak daily vertical variability. By implication, ocean colour satellite data are highly suitable in meaningfully estimating the overall SPM load exported by the Rhône River to the Mediterranean. These findings make a solid contribution to future improvements of three-dimensional sediment transport models for the region and similar settings.

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“…It has also been used as an easily measured proxy to describe the quantity of light availability in the aquatic environment [2]. Through measuring the degree of attenuation of sunlight that is caused by both scattering and absorption of all optically active components, i.e., pure water, suspended sediment, colored dissolved organic matter (CDOM), and phytoplankton, water transparency provides information on incident sunlight penetration depth through the water column [3][4][5][6][7]. Although more sophisticated instruments are commercially available, Secchi disks are still being widely and regularly utilized to measure water transparency for oceanography and limnology.…”

Section: Introductionmentioning

confidence: 99%

MODIS-Based Mapping of Secchi Disk Depth Using a Qualitative Algorithm in the Shallow Arabian Gulf

Kaabi¹,

Zhao²,

Ghedira³

2016

Remote Sensing

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Abstract:Regionally calibrated algorithms for water quality are strongly needed, especially for optically complex waters such as coastal areas in the Arabian Gulf. In this study, a regional qualitative algorithm was proposed to retrieve seawater transparency, with Secchi disk depth (SDD) as a surrogate, in the Arabian Gulf. A two-step process was carried out, first estimating the diffuse attenuation coefficient of downwelling irradiance at 490 nm (K d _490) from MODIS/Aqua imagery and then SDD based on empirical correlations with K d _490. Three satellite derived K d products were tested and assessed against a set of in situ measurements, and one from a semi-analytical algorithm based on inherent optical properties gave the best performance with a R 2 of 0.62. Comparisons between the performances of SDD models developed in this study and those established in other regions indicated higher accuracy of our proposed model for the Gulf region. The potential factors causing uncertainties of the proposed algorithm were also discussed. Seasonal and inter-annual variations of SDD over the entire Gulf were demonstrated using a 14-year time series of MODIS/Aqua data from 2002 to 2015. High SDD values were generally observed in summer while low values were found in winter. Inter-annual variations of SDD did not shown any significant trend with exceptions during algal bloom outbreaks that resulted in low SDD.

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Inversion of Reflectance Spectra of Nonchlorophyllous Turbid Coastal Waters

Cited by 63 publications

References 24 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

Daily and seasonal dynamics of suspended particles in the Rhône River plume based on remote sensing and field optical measurements

MODIS-Based Mapping of Secchi Disk Depth Using a Qualitative Algorithm in the Shallow Arabian Gulf

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