Articles

The Soil Moisture and Ocean Salinity (SMOS) mission is ESA’s second Earth Explorer ‘opportunity mission’, scheduled for launch in early 2006. Selected for an extended feasibility (Phase-A) study in 1999, which was completed in December 2001, SMOS is currently in the design and development phase (Phase-B). SMOS will exploit an innovative instrument designed as a two- dimensional interferometer for acquiring brightness temperatures at L-band (1.4 GHz) to retrieve soil moisture and ocean salinity. Both are key variables used in weather, climate and extreme-event forecasting. As a secondary objective, data acquired by SMOS over ice/snow regions may be used to characterise the ice and snow layers and thus complement other satellite observations to advance the science of the cryosphere*.

The US Salinity Temperature and Roughness Remote Scanner (STARRS) was exploited during an European campaign in 2001 (EuroSTARRS) supporting the scientific preparation of the Soil Moisture and Ocean Salinity (SMOS) mission. This paper is intended to introduce the EuroSTARRS experiment set-up and to provide an overview of all activities performed during this campaign.

The WISE campaigns were sponsored by the European Space Agency (ESA) to gather experimental data to improve the knowledge of the L-band brightness temperature dependence with wind speed at different incidence angles and azimuth angles. The goal is to help the development of sea surface salinity retrieval algorithms for ESA’s SMOS Earth Explorer Mission. The UPC L-band AUtomatic RAdiometer (LAURA) plus other sensors to characterize the sea surface state were installed at the Casablanca oil rig (Spain) during approximately 2 months in 2000 and 2001. The derived wind speed sensitivity at vertical and horizontal polarizations and different incidence angles is presented.

Keywords: Emissivity, microwave radiometry, sea measure- ments, sea surface electromagnetic emission.

Sea surface salinity can be measured by passive mi- crowave remote sensing at L-band. In May 1999, the European Space Agency (ESA) selected the Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission to provide global coverage of soil moisture and ocean salinity. To determine the ef- fect of wind on the sea surface emissivity, ESA sponsored the Wind and Salinity Experiment (WISE 2000). This paper describes the field campaign, the measurements acquired with emphasis in the radiometric measurements at L-band, their comparison with nu- merical models, and the implications for the remote sensing of sea salinity.

In May 1999, the European Space Agency (ESA) selected SMOS as the second Earth Explorer Opportunity mission, with a launch date in June 2005. One of its goals is the generation of global SSS maps with 10 to 30 day revisit time. The sensor embarked on SMOS is an L-band dualpolarization radiometer with full polarimetric capability called MIRAS (Microwave Imaging Radiometer by Aperture Synthesis). The retrieval of sea surface salinity (SSS) from microwave radiometric measurements is based on the fact that the dielectric constant of seawater is a function of the salinity and the temperature. The sensitivity of TB to SSS is maximum at low microwave frequencies and the optimum conditions for salinity retrieval are found at L-band, where there is a band protected for passive observations (1400-1427 MHz). However, even at this frequency the sensitivity of TB to SSS is low: 0.5 K per psu for an SST of 20°C, decreasing to 0.25 K per psu for an SST of 0°. Since other variables influence the brightness temperature (TB) signal (sea surface temperature, roughness and foam), unless they are properly accounted for, the SSS determination will be erroneous. The objective of the ESA-sponsored WISE (WInd and Salinity Experiment) 2000 and 2001 field campaigns is to improve our understanding on the effects of the sea surface roughness and foam on TB at different incidence angles and polarizations, so as to help the development of sea surface emissivity models that may be used in the SSS retrieval algorithms. This paper summarizes the main results of WISE 2000 and presents the first preliminary results of WISE 2001.

The final aim of the Wind and Salinity Experiment (WISE) is to obtain the salinity from L-band sea surface emissivity with a precision of +- 0.1 psu. This supposes a temperature precision of at least +- 0.3 K and our paper demostrates that it is a feasible and reliable objective. Thus, using a therminal infrared radiometer (CE 312), the sea surface temperature (SST) is determined with a precision of +- 0.13 K.

Two campaigns were conducted in November 2001 to measure the brightness temperature of the sea in L-band and the sea surface environmental parameters. The first results are presented below, especially an example of airborne radiometer measurements made during an abrupt change in the wind speed.

The European Space Agency SMOS (Soil Moisture and Ocean Salinity) mission is scheduled for launch in 2006. SMOS will exploit an innovative instrument designed as a 2-D interferometer acquiring globally brightness temperatures at L-band (1.4 GHz) to retrieve soil moisture fields over the land surfaces and ocean salinity fields over the oceans. Considering the exploratory nature of the salinity measurement with SMOS, the GODAE open ocean requirement (0.1 psu over 200km every 10 days) represents a technically challenging objective that has been set as a goal for the mission.

Keywords: Ocean mesoscale, SAR, Alboran Sea, western Mediterranean Sea, surface layer circulation

In autumn 1992 the entire Alboran Sea (western Mediterranean) was sampled by the Spanish R/V Garc ́ıa del Cid. The incoming jet of Atlantic water, its associated meandering front, and the two big anticyclonic gyres were described from conductivity-temperature- depth (CTD) and acoustic Doppler current profiler (ADCP) data. Smaller-scale eddies were also observed. Additionally, 36 ERS-1 synthetic aperture radar (SAR) scenes were obtained from mid-September to mid-October. The SAR images capture these features when wind conditions are suitable. The current shear is mainly depicted as narrow lines of low backscatter because of the damping of waves by natural surface films. These lines delineate the northern border of both gyres and the beginning of the alongslope Algerian current at the eastern limit of the Alboran Sea. ADCP observations confirm that lines on SAR imagery follow the direction of the surface currents. The two gyres present high backscatter values in their center, while their frontal boundaries appear modulated by the variation of the marine atmospheric boundary layer stratification due to the surface thermal front. SAR has observed small spiral eddies that were not evidenced by the almost contemporaneous but too coarse CTD in situ sampling. Good spatial correspondence between radar-detected and in situ-measured structures occurs when comparing SAR images to the surface dynamic topography, rather than strictly surface water characteristics. INDEX TERMS: 0933 Exploration Geophysics: Remote sensing; 4223 Oceanography: General: Descriptive and regional oceanography; 4520 Oceanography: Physical: Eddies and mesoscale processes; 4528 Oceanography: Physical: Fronts and jets; 4572 Oceanography: Physical: Upper ocean processes.

In May 1999, the European Space Agency (ESA) selected SMOS as an Earth Explorer Opportunity (Kerr, 1998). One of its goals is the generation of global Sea Surface Salinity (SSS) maps. The sensor embarked is an L-band interferometric radiometer with full-polarimetric capability called MIRAS. The retrieval of SSS from microwave measurements is based on the fact that the brightness temperature Tb) of seawater is a function of the dielectric constant, temperature and sea surface state (roughness, foam,...). The sensitivity of Tb to SSS is maximum at L-band, but it is necessary to quantify the other effects to have a reliable SSS retrieval. In order to improve the present understanding of these effects on Tm, ESA sponsored the WISE (Wind and Salinity Experiment) 2000 and 2001 field campaigns. These experimental results are of great importance for the development of sea surface emissivity models on the derived SSS from the data obtained in both campaigns. It also presents the impact of using in-situ measured or satellite-derived wind information, or even compute simultaneously the wind speed (from the measured multi-angular Tb), on the retrieved SSS.

Although temporary cyst stages are common in dinoflagellates, their role remains unclear. Every year Alexandrium taylori (Dinophyceae) forms dense patches (106 cells l−1) along La Fosca beach (Spain, northwest Mediterranean), which last for 2 months (July, August). One of the characteristics of the life history of A. taylori is the shift from a vegetative motile stage to non-motile temporary cysts. Here we present the temporal changes in the abundance of temporary cysts in sediments and their in situ encystment and excystment rates. The in situ encystment rate of temporary cysts from the water column to the sediment ranged from 1.8 × 106 to 4.4 × 106 cysts m−2 day−1, whereas the excystment rate was between 0.9 × 106 to 2.7 × 106 cysts m−2 day−1 during the bloom period. Some of the temporary cysts in the sediment took more than 1 day to produce vegetative cells and remained viable for at least 4 days. We propose that temporary cyst formation in this species is a tool for reducing population losses. The production of temporary cysts can be an advantage since part of the population is stored in the sediments.

Keywords: Partial differential equations (PDE); Boundary problems; Spectral methods; Analytical solution

Tau spectral methods and Adomian’s decomposition can be fruitfully combined to quickly approximate the analytical solution of any time-dependent partial differential equation with boundary conditions defined on the four sides of a rectangle. In this work, combinations of Legendre polynomials have been used to generate orthogonal two-dimensional polynomials on a rectangular domain. The time evolution of the solution is condensed in a set of nonlinear differential equations for the polynomial coefficients. This system can be integrated by using Adomian’s decomposition method with analytic extension or, alternatively, successive approximations, which generate a time series that can be truncated at the required precision order. The result is an analytic approximation to the final solution which can be easily obtained by using any commercial symbolic processor.

The purpose of GODAE is carry out global oceanic data assimilation and ocean forecasts in order to provide regular and comprehensive descriptions of ocean fields such as temperature, salinity and currents at high temporal and spatial resolution. GODAE will develop assimilation capability for a range of in situ ocean observations, including salinity, and existing satellite observations such as sea level, sea surface temperature (SST) and vector wind. Satellite measurements for sea surface salinity (SSS) will not become available for several more years. Until then, the analyzed salinity fields from the assimilation experiments will be based largely on more sparse in situ salinity data and indirect estimates derived from other measurements such as temperature and sea level. Two new satellite missions to map SSS globally are now being planned or developed for launch in the 2006 time frame. These will come after the GODAE demonstration phase from 2003 to 2005. Nevertheless, GODAE is the pilot program for operational and research ocean assimilation activities that will extend into the indefinite future. At the end of the demonstration phase, GODAE will have developed the capability to apply such data sets, and the community will be prepared to use the satellite SSS data as soon as they become available. The first of these satellites to be approved is the European Space Agency Soil Moisture Ocean Salinity (SMOS) missions. This is a dual land/ocean science mission, as the nameimplies, using the 1.4 GHz passive microwave channel suitable to measuring both parameters. The sensor is a technically complex two-dimensional phased-array system designed principally for soil moisture retrievals. The SMOS program includes a focused effort to retrieve salinity data over the ocean. The observatory will provide global coverage every 3 days and ~50 km resolution for a 3-5 year mission. The salinity data will need to be averaged over broader scales to reduce measurement error. The eventual salinity retrieval accuracy remains an open issue under investigation. Aquarius is a dedicated salinity mapping mission proposal presently being reviewed by NASA. The decision will be made by the end of June 2002 of whether it will be approved for further definition studies, leading to eventual construction and launch. Aquarius will employ a high-precision 1.4 GHz radiometer system plus radar backscatter measurements to correct the large effects of surface wind roughness. The focus of the Aquarius design is to optimize the salinity retrieval accuracy for global climate studies. Aquarius will provide global maps every 8 days at 100 km resolution. A rigorous error analysis shows that the measurements will have an rms uncertainty <0.2 psu on monthly time scales globally and closer to 0.1 psu in the tropics. A strong collaboration exists between the SMOS and Aquarius projects. Once both missions are fully approved, plans call for the formation of a joint international salinity remote sensing working team which will be open to GODAE and the broader community.

The EuroSTARRS campaign of the European Space Agency (ESA) is an aircraft campaign designed to help scientists to prepare the SMOS (Soil Moisture and Ocean Salinity) Mission, which will be launched early in 2006 (Figure 1), to acquire global measurements of soil moisture and ocean salinity which are two parameters that play a key role in the determination of climate. Besides getting data of these two quantities, scientists will be able to incorporate these measurements in Numerical Prediction Models and Climate Models in order to significantly improve their analyses and predictions.

Keywords: eddies, Balearic Sea, Mediterranean Sea, altimetry, AVHRR, hydrography

Sea surface topography from TOPEX/Poseidon and ERS satellites, SST images derived from advanced very high resolution radiometer (AVHRR) sensors, and conductivity-temperature-depth (CTD) data collected during an oceanographic survey are examined to investigate an intense mesoscale anticyclonic eddy observed at the northern boundary of the Balearic Sea (western Mediterranean). This eddy, which constitutes the strongest signal detected in the Balearic basin since altimetric data are available, appeared in September 1998 to the northwest of Menorca Island and remained almost in the same location until its disappearance in March 1999. The paper focuses mainly on identifying the conditions that led to the eddy formation and on the description of its evolution and sudden disappearance. Derived variables such as geostrophic velocity or vorticity are computed to complement the hydrographic and dynamical information provided by observed variables. Also, meteorological data are examined related to the main hypothesis made for the origin of the eddy.

Keywords: Mesoscale eddies; Hydrographic measurements; Lagrangian buoys; ADCP; Altimetry; Deep circulation; Mediterranean Sea; Algerian Basin

The Algerian Basin dynamics is dominated by the presence of very energetic mesoscale structures. Deep open sea eddies are key features that influence the regional circulation of water masses at all depths. In May 1998, an open sea eddy was sampled near 38ºN 2ºE by means of CTD, Acoustic Doppler Current Profiler (ADCP) and surface Lagrangian drifters. For the first time, it has been possible to characterise one of these mesoscale structures in its full depth, down to 2800 m. The density distribution indicated the presence of lighter water in the centre of the eddy from the surface to the bottom. The direct velocity measurements in the surface layer, plus the determination of the baroclinic shear from CTD data, evidenced that the anticyclonic motion was present in the whole water depth.

Keywords: ADCP, heading, horizontal currents, Alboran Sea.

Traditionally the horizontal orientation in a ship (heading) has been obtained from a gyrocompass. This instrument is still used on research vessels but has an estimated error of about 2-3 degrees, inducing a systematic error in the cross-track velocity measured by an Acoustic Doppler Current Profiler (ADCP). The three-dimensional positioning system (GPS 3DF) provides an independent heading measurement with accuracy better than 0.1 degree. The Spanish research vessel BIO Hespérides has been operating with this new system since 1996. For the first time on this vessel, the data from this new instrument are used to estimate gyrocompass error. The methodology we use follows the scheme developed by Griffiths (1994), which compares data from the gyrocompass and the GPS system in order to obtain an interpolated error function. In the present work we apply this methodology on mesoscale surveys performed during the observational phase of the OMEGA project, in the Alboran Sea. The heading-dependent gyrocompass error dominated. Errors in gyrocompass heading of 1.4-3.4 degrees have been found, which give a maximum error in measured cross-track ADCP velocity of 24 cm s-1.

Keywords: Mesoscale eddies; Coastal current instability; Lagrangian current measurement; Infrared imagery; Mediterranean Sea; Algerian basin

During the autumn–winter of 1996–1997, drifting buoy trajectories and infrared satellite images provided new information on the characteristics of several mesoscale phenomena generated by the Algerian Current (AC) in the western Mediterranean Sea. A mesoscale event, as defined by previous studies, consists of a meander of the current associated with a surface anticyclonic eddy inside its crest, a transitory surface cyclonic eddy (Ec) upstream from the crest, and a deep anticyclonic eddy just below the meander. Most events propagate eastward along the coast at a few km per day until they are forced, mainly by the topography at the entrance to the channel of Sardinia, to detach from the coast and propagate seaward. They thus become open-sea anticyclonic eddies and generally complete an anticlockwise circuit in the Algerian basin. Surface buoys were launched upstream from an event and across it near 11E. They made it possible to characterise the anticyclonic and cyclonic surface eddy features, and for the first time clearly showed the meander, which is in general not well depicted with images. It has thus been definitely demonstrated that most of the AC (speeds of several tens of cm/s) crosses the relatively slowly propagating events. As usual, the event we sampled reached a mature stage characterised by a vanishing of the Ec, and increased up to B100 km. Its arrest and decrease before it reached the channel of Sardinia, which is not so usual, was contemporaneous to the reappearance of the Ec and could be related to the growing of another coastal eddy upstream. At the entrance to the channel of Sardinia (near 7–81E), the trajectories and images also documented another event which was larger (up to B120 km) and in the phase of detachment. Since the buoys drifted alternately to the west and to the east between this event and the coast, it is clear that an event can detach only temporarily and allow part of the AC to flow eastward directly. As indicated by infrared images, the definitive detachment occurred after all the buoys escaped from the event. The whole in situ and satellite data set is fully consistent with all the previous observations of the AC mesoscale variability, and quantitatively supports the proposed hypotheses for the event structure. It is consistent with laboratory experiments and some results of numerical models of coastal instability processes

Keywords: Seasonal variations; Shelf edge dynamics; Water masses; Water exchange; Nutrients; Chlorophyll; Western Mediterranean; Ebro river shel

Among several field efforts undertaken in the framework of the EU MAST-III FANS project, three oceanographic cruises covering the Ebro shelf and slope regions (NW Mediterranean) were carried out on board R/V Garc!ıa del Cid between November 1996 and July 1997. A major aim of these three cruises was to provide insight into the seasonal variability of the distribution of physico-chemical oceanographic parameters and the shelf/slope circulation. In this paper we discuss the observed changes in the hydrographic structure, the spatial distribution of nutrients, chlorophyll and suspended particulate matter and the local circulation in relationship to the seasonal variability of the Ebro river discharge rates and the water column stratification. The added effects of mesoscale circulation structures and of the exchanges across the shelf edge are also addressed.

Keywords: Food ratio; Enzyme; Growth; Cephalopod; Octopus; Larvae

Experiments were conducted to investigate growth and proteolytic activity of the common octopus Octopus vulgaris, reared with different diets and ration levels during first feeding. Four ration levels were tested, 0.2, 2, 4 and 10 Artemia nauplii ml
1 day
1 and co-feeding techniques were tested using 10 Artemia nauplii ml
1 day
1 plus three different compound millicapsules. Total proteolytic activity, trypsin and chymotrypsin levels were recorded from eggs, hatchlings and during the first month of paralarval rearing. Five days after hatching, paralarval weight and proteolytic activity was dependent on food ration. The low-food treatment did not lead to an increase in hatchling weight, in contrast with the positive increase of the other treatments. After 20 days, best survival was observed in treatments fed 2 and 4 nauplii ml
1 day
1. High nauplii rations of 10 nauplii ml
1 day
1 plus millicapsule diet treatments produced higher growth and higher proteolytic, trypsin and chymotrypsin levels, but poor survival. Total proteolytic activity was correlated with paralarval weight, whereas trypsin and chymotrypsin were maintained at hatchling levels only for the high food and co-feeding treatments, and decreased in the others. The trypsin activity in the high-food treatment showed a sharp increase after 15 days and 880 mg of the mean dry weight (2.5 times hatchling weight). Millicapsules were ingested by the paralarvae after 5 days but did not lead to a significant increase in weight. Enriched Artemia nauplii seem to be useful only as an initial diet until a doubling in hatchling weight is achieved. This period can extend from 11 to 14 days at 20 C, after which a larger prey and/or suitable microdiet is required. D 2002 Elsevier Science B.V. All rights reserved.

The systematics of the deep-sea cirrate octopod genus Opisthoteuthis Verrill in the Atlantic Ocean is reviewed. Comparisons, based on examination of all extant type material and new, reported and unreported material collected in recent years from the Atlantic, show the presence of five species: Opisthoteuthis agassizii Verrill 1883, O. grimaldii (Joubin, 1903), O. massyae (Grimpe, 1920) and two new species, O. calypso and O. hardyi, which are described. Opisthoteuthis agassizii, distributed only in the western North Atlantic, is redescribed, and a neotype is designated for the presumed lost holotype. Opisthoteuthis grimaldii, distributed in the East Atlantic and possibly also in the western North Atlantic, and O. massyae, distributed in the East Atlantic are also redescribed and junior synonyms listed. Opisthoteuthis calypso, found in the East Atlantic and O. hardyi, known only from a single specimen from the SW Atlantic are described. New morphometric data for O. agassizii, O. massyae and O. grimaldii are given. Illustrations, geographical distributions and a review of the biological information for all five species are provided.