University of the Littoral Opal Coast

About: University of the Littoral Opal Coast is a education organization based out in Dunkirk, France. It is known for research contribution in the topics: Catalysis & Dielectric. The organization has 1242 authors who have published 2383 publications receiving 46230 citations. The organization is also known as: ULCO.

Incoherent broadband cavity enhanced absorption spectroscopy for in situ measurements of NO(2) with a blue light emitting diode

Abstract: We report on the development of Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) using a blue light emitting diode (LED) for the detection of NO2 in laboratory ambient air. Absorption of the oxygen collisional pair in the atmosphere was also detected in the same spectral range. The mirror reflectivity was determined using a standard gas sample mixture of NO2, and calibrated with the help of the absorption spectrum of the oxygen collisional pair in pure oxygen at atmospheric pressure. Optimization of the experimental parameters was investigated and is discussed in detail. For the first time in IBBCEAS involving broadband absorption spectra, averaging time for signal-to-noise ratio enhancement has been optimized using Allan variance plot. 18.1 ppbv NO2 in laboratory ambient air has been retrieved from the absorption spectra using differential fitting method over a 40 nm spectral region centered at 470 nm. A minimum detection sensitivity of about 2.2 ppbv (1σ) for NO2 at atmospheric pressure has been achieved using the optimal averaging time of 100 s by means of a high finesse optical cavity formed with two moderate reflectivity (∼99.55%) mirrors. No purging of the cavity mirrors by high purity He or N2 gas streams was necessary to prevent contamination of the mirror faces for the in situ measurements.

Hyperspectral and multispectral ocean color inversions to detect Phaeocystis globosa blooms in coastal waters

Abstract: Identification of phytoplankton groups from space is essential to map and monitor algal blooms in coastal waters, but remains a challenge due to the presence of suspended sediments and dissolved organic matter which interfere with phytoplankton signal. On the basis of field measurements of remote sensing reflectance (Rrs(λ)), bio-optical parameters, and phytoplankton cells enumerations, we assess the feasibility of using multispectral and hyperspectral approaches for detecting spring blooms of Phaeocystis globosa (P. globosa). The two reflectance ratios (Rrs(490) /Rrs(510) and Rrs(442.5) /Rrs(490)), used in the multispectral inversion, suggest that detection of P. globosa blooms are possible from current ocean color sensors. The effects of chlorophyll concentration, colored dissolved organic matter (CDOM), and particulate matter composition on the performance of this multispectral approach are investigated via sensitivity analysis. This analysis indicates that the development of a remote sensing algorithm, based on the values of these two ratios, should include information about CDOM concentration. The hyperspectral inversion is based on the analysis of the second derivative of Rrs(λ) (dλ2 Rrs). Two criteria, based on the position of the maxima and minima of dλ2Rrs, are established to discriminate the P. globosa blooms from diatoms blooms. We show that the position of these extremes is related to the specific absorption spectrum of P. globosa and is significantly correlated with the relative biomass of P. globosa. This result confirms the advantage of a hyperspectral over multispectral inversion for species identification and enumeration from satellite observations of ocean color. Copyright 2008 by the American Geophysical Union.

Vertical migrations of fish larvae: Eulerian and Lagrangian observations in the Eastern English Channel

Abstract: The Eastern English Channel is known for its strong hydrodynamics. Tidal and residual currents are reinforced by the south-western dominant wind and drift waters from the English Channel to the North Sea. Previous spatial studies have shown that the advection of larvae could differ from one species to another. Flounder (Pleuronectes flesus) larvae were found offshore, drifting to the north until the fins were formed; then they were found near the coast. However, sole (Solea solea) larvae remained in coastal waters during their development. The difference in larval spatial distribution is assumed to be related to the interaction between vertical migration and advection by alternative tidal currents, leading to a selective tidal stream transport. To describe the vertical distribution of these larvae, two strategies were used. First, a Eulerian study was carried out with samples taken at the same geographical location every 1.5 h for 41 h. Ichthyoplankton were collected in the water mass using a Bongo net and with a suprabenthic multi-net sledge, at four layers above the sea bed, between 0.1 and 1.4 m. Secondly, to enable water movement to be disregarded, a Lagrangian study was carried out by using a Bongo net every 3 h, following a drifting buoy for 3 days. The results show that even during the youngest stages, sole larvae are able to perform tidal and diel vertical migration. We assume that they may limit their advection to the North Sea because of their upward migration during ebb and at night, which may enable them to remain in the same area dealing with the currents. Flounder larvae begin their vertical migration at the stage of notochord flexion, which ends their drift to the north. The larvae reach the bottom of the water column, particularly during ebb when they are concentrated in the first 40 cm above the bottom. This behaviour favours their advection during flow, leading to efficient and fast transport towards the coast.

Sedimentation in a fluvially infilling, barrier‐bound estuary on a wave‐dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa

Abstract: The Oueme River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km2 circular central basin, Lake Nokoue, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km2). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood-tidal delta sand deposited in association with non-preserved transgressive sand barriers. The change in estuary-mouth sedimentation from a transgressive barrier-inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross-barrier tidal flux associated with barrier-inlet systems. As barrier formation west of the Oueme River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Oueme embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoue has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary-mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave-dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co-existing highstand sediment suites, with limited admixture, the marine-derived, estuary-mouth barrier and upland-derived back-barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial-marine sediment mixing and facies interfingering.