Zsolt Volent

Kelp forest mapping by use of airborne hyperspectral imager

We present an easy and efficient approach for remote sensing of ocean color, relevant for monitoring and management of kelp forest and bottom substrate with a cheap custom made hyperspectral imager. Remote sensing of ocean color was performed in the Kongsfjord, Spitsbergen (79 deg N and 12 deg E) from an airplane (2950 m altitude) equipped with a hyperspectral imager, giving monochromatic images (425-825 nm) using the push broom technique, captured with custom designed software in 5 nm steps. Synchronously in situ measurements of upwelling spectral irradiance, (E u(λ))(λ = 350-950 nm) measured at 30 cm depth were performed as a reference for the remotely sensed images. Surface water samples were taken for enumeration and identification of organic (plankton), inorganic particles, and colored dissolved organic matter. For identification and classification of kelp and bottom substrate, Bayesian supervised classification and a differential histogram equalization technique were used and compared. Both techniques gave successful discrimination between kelp and bottom substrate in shallow water above the Secchi depth (<19 m). The imager could easily be implemented for other applications such as detection and monitoring of phytoplankton blooms, suspended matter, and colored dissolved organic matter in surface waters, especially in connection with environmental and aquaculture management.

Improved monitoring of phytoplankton bloom dynamics in a Norwegian fjord by integrating satellite data, pigment analysis, and Ferrybox data with a coastal observation network

Monitoring of the coastal environment is vitally important as these areas are of economic value and at the same time highly exposed to anthropogenic influence, in addition to variation of environmental variables. In this paper we show how the combination of bio-optical data from satellites, analysis of water samples, and a ship-mounted automatic flow-through sensor system (Ferrybox) can be used to detect and monitor phytoplankton blooms both spatially and temporally. Chlorophyll a (Chl a) data and turbidity from Ferrybox are combined with remotely sensed Chl a and total suspended matter from the MERIS instrument aboard the satellite ENVISAT (ENVIronmental SATellite) European Space Agency. Data from phytoplankton speciation and enumeration obtained by a national coastal observation network consisting of fish farms and the Norwegian Food Safety Authority are supplemented with data on phytoplankton pigments. All the data sets are then integrated in order to describe phytoplankton bloom dynamics in a Norwegian fjord over a growth season, with particular focus on Emiliania huxleyi. The approach represents a case example of how coastal environmental monitoring can be improved with existing instrument platforms. The objectives of the paper is to present the operative phytoplankton monitoring scheme in Norway, and to present an improved model of how such a scheme can be designed for a large part of the worlds coastal areas.

Microscopic hyperspectral imaging used as a bio-optical taxonomic tool for micro- and macroalgae

In the presented study a hyperspectral imager (400-700 nm) mounted on a stereo-microscope was used to separate differences in in vivo optical signatures identifying different pigment groups of bloom-forming phytoplankton and macroalgae by comparing spectral absorption, transmittance, and reflectance from 400-700 nm. The results show that the hyperspectral imager could be used to detect spectral characteristics on the microm level to calibrate, validate, identify, and separate objects with differences in color (optical fingerprinting). This information can be used for pigment group specific taxonomy (bio-optical taxonomy), eco-physiological information (e.g., health status), monitoring, and mapping applications.

Drag Forces on, and Deformation of, Closed Flexible Bags

The use of closed flexible bags is among the suggestions considered as a potential way to expand the salmon production in Norway. Few ocean structures exist with large, heavily compliant submerged components, and there is presently limited existing knowledge about how aquaculture systems with flexible closed cages will respond to external sea loads. The flexibility and deformation of the bag are coupled to the hydrodynamic forces, and the forces and deformation will be dependent on the filling level of the bag. In order to get a better understanding of the drag forces on, and deformation of, such bags, experiments were conducted with a series of closed flexible bags. The bags were towed in a towing tank in order to simulate uniform current. Four different geometries were investigated, cylindrical, cubical, conical, and pyramidal, and the filling levels were varied between 70% and 120%. The main findings from the experiments were that the drag force was highly dependent on the filling level, and that the drag force increases with decreasing filling level. Comparing the drag force on a deflated bag with an inflated one showed an increase of up to 2.5 times.

Modelling of Drag Forces on a Closed Flexible Fish Cage

Abstract To cope with ecological challenges in the aquaculture industry, Closed Flexible Fish Cages (CFC) are proposed used in the sea. However, the existing knowledge about how the CFC will respond to external sea loads are limited. More knowledge is needed to understand the response of the cage if this technology is to be utilized in an industrial scale. In this paper a new method for mathematical modelling of the increase in drag, for decreasing filling level of a CFC is proposed. A model for a filling-level-dependent drag coefficient is presented. Experimental data are analysed related to forces and deformations on the bag for different filling levels. The analysed bag showed an increased tendency to deform for decreasing filling levels, leading to an increase in drag coefficient.

Presentation of the optical sensor OPTISENS designed for Eulerian measurements of phytoplankton on a moored buoy

Since 1988 a newly designed transmissometer (OPTISENS) has been used along the southern Norwegian coast to monitor phytoplankton blooms. The instrument has been suspended on a buoy equipped with an ARGOS PTT for satellite transmission of data. The OPTISENS is a light beam transmissometer with 3 different colors of the light, i.e. red, green and blue with peak wavelengths at 650 nm, 555 nm and 470 nm, respectively. Long-term measurements in the sea and laboratory experiments of in vivo absorption- and fluorescence excitation spectra, have demonstrated that it not only can distinguish between different particles but also identify of different groups of bloom-forming phytoplankton, some of which are toxic. The attenuation coefficient ratios between the colors blue, green, yellow and red will be discussed for different phytoplankton groups.

Closed Flexible Fish Cages: Modelling and Control of Deformations

Closed Flexible Fish Cages are proposed used in the sea, to meet with ecological challenges in the aquaculture industry. Earlier experiences with structural collapse of a similar concept have shown that it is crucial to secure the cage against rifts and escapes. To ensure this, a method to detect leakages and pump failure at an early stage must be developed. To detect leakages it is important to know how the bag deforms under static conditions for lower filling levels. In this paper a new method for modelling the deformed shape of the bag for decreasing filling level is proposed. Experimental data are analysed related to deformations on the bag for different filling levels, under static conditions.Copyright

Wave Response of Closed Flexible Bags

Recent environmental considerations, as salmon lice, escape of farmed fish and release of nutrients, have prompted the aquaculture industry to consider the use of closed fish production systems. The use of such systems is considered as one potential way of expanding the salmon production in Norway. To better understand the response in waves of such bags, experiments were conducted with a series of 1:30 scaled models of closed flexible bags. The bags and floater were moored in a wave tank and subjected to series of regular waves (wave period between 0.5 and 1.5s and wave