Skip to content. | Skip to navigation

Personal tools

You are here: Home

Search results

RSS Subscribe to an always-updated RSS feed.

2926 items matching your search terms.
Filter the results.
Item type



































New items since



Sort by relevance · date (newest first) · alphabetically
Article Reference Description of a new subspecies of Chicoreus (Triplex) cnissodus cnissodus (Euthyme, 1889) (Gastropoda, Muricidae) from Sri Lanka
Located in Library / RBINS Staff Publications
Article Reference Context-dependent specialization in colony defence in the red wood ant Formica rufa
Located in Library / RBINS Staff Publications
Article Reference Species-area relationships are modulated by trophic rank, habitat affinity, and dispersal ability
Located in Library / RBINS Staff Publications
Article Reference Annotated Checklist of the Terrestrial Gastropods of Nepal
Located in Library / RBINS Staff Publications
Article Reference Advantages of high quality SWIR bands for ocean colour processing: examples from Landsat-8
Located in Library / RBINS Staff Publications
Article Reference Comparison of three SeaWiFS atmospheric correction algorithms for turbid waters using AERONET-OC measurements
The use of satellites to monitor the color of the ocean requires effective removal of the atmospheric signal. This can be performed by extrapolating the aerosol optical properties in the visible from the near-infrared (NIR) spectral region assuming that the seawater is totally absorbant in this latter part of the spectrum. However, the non-negligible water-leaving radiance in the NIR which is characteristic of turbid waters may lead to an overestimate of the atmospheric radiance in the whole visible spectrum with increasing severity at shorter wavelengths. This may result in significant errors, if not complete failure, of various algorithms for the retrieval of chlorophyll-a concentration, inherent optical properties and biogeochemical parameters of surface waters. This paper presents results of an inter-comparison study of three methods that compensate for NIR water-leaving radiances and that are based on very different hypothesis: 1) the standard Sea WiFS algorithm (Stumpfet al., 2003; Bailey et al., 2010) based on a bio-optical model and an iterative process; 2) the algorithm developed by Ruddick et al. (2000) based on the spatial homogeneity of the NIR ratios of the aerosol and water-leaving radiances; and 3) the algorithm of Kuchinke et al. (2009) based on a fully coupled atmosphere-ocean spectral optimization inversion. They are compared using normalized water-leaving radiance nL(w) in the visible. The reference source for comparison is ground-based measurements from three AERONET-Ocean Color sites, one in the Adriatic Sea and two in the East Coast of USA. Based on the matchup exercise, the best overall estimates of the nL(w) are obtained with the latest SeaWiFS standard algorithm version with relative error varying from 14.97\% to 35.27\% for lambda = 490 nm and lambda = 670 nm respectively. The least accurate estimates are given by the algorithm of Ruddick, the relative errors being between 16.36\% and 42.92\% for lambda = 490 nm and lambda = 412 nm, respectively. The algorithm of Kuchinke appears to be the most accurate algorithm at 412 nm (30.02\%), 510 (15.54\%) and 670 nm (32.32\%) using its default optimization and bio-optical model coefficient settings. Similar conclusions are obtained for the aerosol optical properties (aerosol optical thickness tau(865) and the Angstrom exponent, alpha(510, 865)). Those parameters are retrieved more accurately with the SeaWiFS standard algorithm (relative error of 33\% and 54.15\% for tau(865) and alpha(510, 865)). A detailed analysis of the hypotheses of the methods is given for explaining the differences between the algorithms. The determination of the aerosol parameters is critical for the algorithm of Ruddick et al. (2000) while the bio-optical model is critical for the algorithm of Stumpf et al. (2003) utilized in the standard SeaWiFS atmospheric correction and both aerosol and bio-optical model for the coupled atmospheric-ocean algorithm of Kuchinke. The Kuchinke algorithm presents model aerosol-size distributions that differ from real aerosol-size distribution pertaining to the measurements. In conclusion, the results show that for the given atmospheric and oceanic conditions of this study, the SeaWiFS atmospheric correction algorithm is most appropriate for estimating the marine and aerosol parameters in the given turbid waters regions. (C) 2011 Elsevier Inc. All rights reserved.
Located in Library / RBINS Staff Publications
Article Reference Optical remote sensing of turbidity and total suspended matter in the Gulf of Gabes
Optical remote sensing was used to provide scientific information to support environmental management in the Gulf of Gabes that is located in the southeastern coast of Tunisia. This region is characterized by shallow continental shelf subjected to semi-diurnal tides. Industrial activities in this area since the early 1970s may have contributed to the degradation of the biodiversity of the ecosystem with eutrophication problems and disappearance of benthic and planktonic species. To assess the long-term effect of anthropogenic and natural discharges on the Gulf of Gabes, the optical environment of the coastal waters is assessed from in situ measurements of total suspended matter concentration (TSM), Secchi depth and turbidity (TU). This monitoring requires regular seaborne measurements (monthly), which is very expensive and difficult to obtain. The objective of the present study is the evaluation of the Moderate Resolution Imaging Spectrometer (MODIS) AQUA data compared with two sampling campaigns realized at the study area. To map turbidity data from MODIS images, a semi-empirical algorithm was applied at band 667 nm. This bio-optical algorithm has already been calibrated and validated on the Belgian coast. The validation of this algorithm on the Gulf of Gabes using in situ measurements of turbidity and remotely sensed turbidity obtained from MODIS imagery shows a correlation coefficient of 68.9\%. Seasonal and annual average maps for TSM and TU were then computed over the Gulf of Gabes using MODIS imagery. The obtained results of TSM and TU from remotely sensed data are conformable with those obtained through the analysis of in situ measurements. Therefore, remote sensing techniques offer a better and efficient tool for mapping and monitoring turbidity over the whole region.
Located in Library / RBINS Staff Publications
Article Reference Reconstruction of MODIS total suspended matter time series maps by DINEOF and validation with autonomous platform data
In situ measurements of total suspended matter (TSM) over the period 2003-2006, collected with two autonomous platforms from the Centre for Environment, Fisheries and Aquatic Sciences (Cefas) measuring the optical backscatter (OBS) in the southern North Sea, are used to assess the accuracy of TSM time series extracted from satellite data. Since there are gaps in the remote sensing (RS) data, due mainly to cloud cover, the Data Interpolating Empirical Orthogonal Functions (DINEOF) is used to fill in the TSM time series and build a continuous daily “recoloured” dataset. The RS datasets consist of TSM maps derived from MODIS imagery using the bio-optical model of Nechad et al. (Rem Sens Environ 114: 854-866, 2010). In this study, the DINEOF time series are compared to the in situ OBS measured in moderately to very turbid waters respectively in West Gabbard and Warp Anchorage, in the southern North Sea. The discrepancies between instantaneous RS, DINEOF-filled RS data and Cefas data are analysed in terms of TSM algorithm uncertainties, space-time variability and DINEOF reconstruction uncertainty.
Located in Library / RBINS Staff Publications
Article Reference Mapping total suspended matter from geostationary satellites: a feasibility study with SEVIRI in the Southern North Sea
Geostationary ocean colour sensors have not yet been launched into space, but are under consideration by a number of space agencies. This study provides a proof of concept for mapping of Total Suspended Matter (TSM) in turbid coastal waters from geostationary platforms with the existing SEVIRI (Spinning Enhanced Visible and InfraRed Imager) meteorological sensor on the METEOSAT Second Generation platform. Data are available in near real time every 15 minutes. SEVIRI lacks sufficient bands for chlorophyll remote sensing but its spectral resolution is sufficient for quantification of Total Suspended Matter (TSM) in turbid waters, using a single broad red band, combined with a suitable near infrared band. A test data set for mapping of TSM in the Southern North Sea was obtained covering 35 consecutive days from June 28 until July 31 2006. Atmospheric correction of SEVIRI images includes corrections for Rayleigh and aerosol scattering, absorption by atmospheric gases and atmospheric transmittances. The aerosol correction uses assumptions on the ratio of marine reflectances and aerosol reflectances in the red and near-infrared bands. A single band TSM retrieval algorithm, calibrated by non-linear regression of seaborne measurements of TSM and marine reflectance was applied. The effect of the above assumptions on the uncertainty of the marine reflectance and TSM products was analysed. Results show that (1) mapping of TSM in the Southern North Sea is feasible with SEVIRI for turbid waters, though with considerable uncertainties in clearer waters, (2) TSM maps are well correlated with TSM maps obtained from MODIS AQUA and (3) during cloud-free days, high frequency dynamics of TSM are detected. (C) 2009 Optical Society of America
Located in Library / RBINS Staff Publications
Article Reference Optimization and quality control of suspended particulate matter concentration measurement using turbidity measurements
The dry weight concentration of suspended particulate material, [SPM] (units: mg L-1), is measured by passing a known volume of seawater through a preweighed filter and reweighing the filter after drying. This is apparently a simple procedure, but accuracy and precision of [SPM] measurements vary widely depending on the measurement protocol and experience and skills of the person filtering. We show that measurements of turbidity, T (units: FNU), which are low cost, simple, and fast, can be used to optimally set the filtration volume, to detect problems with the mixing of the sample during subsampling, and to quality control [SPM]. A relationship between T and `optimal filtration volume', V opt, is established where V opt is the volume at which enough matter is retained by the filter for precise measurement, but not so much that the filter clogs. This relationship is based on an assessment of procedural uncertainties in the [SPM] measurement protocol, including salt retention, filter preparation, weighing, and handling, and on a value for minimum relative precision for replicates. The effect of filtration volume on the precision of [SPM] measurement is investigated by filtering volumes of seawater ranging between one fifth and twice V opt. It is shown that filtrations at V opt maximize precision and cost effectiveness of [SPM]. Finally, the 90\% prediction bounds of the T versus [SPM] regression allow the quality control of [SPM] determinations. In conclusion it is recommended that existing [SPM] gravimetric measurements be refined to include measurement of turbidity to improve their precision and quality control.
Located in Library / RBINS Staff Publications