A number of spaceborne microwave sensors have been launched in the last decade, significantly increasing the quantity and quality of observations over the oceans that can be used to study air-sea interactions. These observations, when combined with conventional in-situ observations and model output, can be used to improve air-sea flux estimates and for model initialization and parameterization. However, because of the different characteristics, sampling frequency and resolution, and sensor accuracy, the calibration of satellite observations against in-situ observations is discussed. Special attention is paid to time, space, and scale transitions, and to formulating a velocity scale for use in large scale models. Specifically, the paper reviews recent observational and modeling studies that show that a considerable subgrid air-sea flux may be generated by directional variability in the near surface wind field. It then describes: (i) temporal-spatial conversion methods that allow proper calibration of satellite observations against in-situ data and synergistic use of heterogeneous data sets for estimating flux enhancement; and (ii) resolution dependent velocity scale terms that can be formulated from scatterometer observations and incorporate in General Circulation Models bulk formulas.

The usability of altimeter sea level data (TOPEX) and scatterometer wind data (QuikSCAT) in ENSO prediction is investigated with the latest version of the Lamont forecast model. The emphasis of this study is on the effectiveness of these data sets in initializing the model to forecast the 1999-2000 La Nina conditions. Both TOPEX and QuikSCAT observations seem to help the model to make better predictions in the tropical Pacific, with the former being more effective for this period. It is possible and extremely useful to apply these data to real-time ENSO forecasting. In principle, it is advisable to assimilate multiple data sets so that they can complement one another in providing the correct initial conditions for the model.

Two years of merged TOPEX-POSEIDON and ERS 1-2 altimeter data were used to investigate the evolution of gyres in the Gulf of Tehuantepec. Strong wind pulses named 'nortes' with typical structure of a jet with a fan-shaped and symmetric structure, extended from the coast to open-sea up to 200km, with its axis oriented mainly to N degree-S degree. They can reach maximum speeds of approximately 25 m/s. These 'nortes' generates a dipole-like structure in the Gulf of Tehuantepec, similar as the classical Ekman problem. The anticyclone gyre showed rotational periods of about 12 days and the cyclone 18 days. Only the anticyclone gyre can survive for more than 10 months. Annually average of more than 7 gyres are generated, mainly on winter an spring seasons. However, Sea Level Anomaly maps captured up to 25 gyres formed in the Gulfs of Tehuantepec and Papagayo. Center-gyre trajectories showed gyres traveled mainly south- westward, with translation speeds about 3-25 cm/s and diameters of 60 to 450 km. Some of these anticyclonic gyres intensify as they travel from the coast to open sea, by merging with other gyres, others decay, elongate and split or are absorbed by other gyres or the Mexican and Californian Current. The results presented in this study suggest that the generating-rate of gyres is larger than previously thought, and they can play a strong role in the exchange of properties between coast to open sea.

Satellite data have revealed the presence of an intens4e mesoscale anticyclonic eddy at the northern boundary of the Balearic Sea, which appeared in September 1998 and remained almost stationary until March 1999. Sea Surface Temperature (SST) images have allowed to investigate the formation of the eddy indicating an entrance of Atlantic Water through the Ibiza and Mallorca channels much stronger than normal conditions and following an anomalous path. Additional data form an oceanographic cruise on February 1999 confirmed the signature of Atlantic Water in the region. This structure produced a relevant inversion in the usual cyclonic circulation of the basis. The observed strong anticyclonic eddy induced anomalous northeastwards geostrophic velocities near the Catalan Coast reaching the maximums of about 50 cm/s, by contrast of the typical 20 cm/s in opposite sense. The three data-sets examined in this work are in good agreement in terms of the dimensions and intensity of the eddy. This suggests that remote sensing would be able to detect such kind of events in the future constituting a powerful tool providing a real-time monitoring of the Basin.

The evolution of an open-sea eddy, previously detected by IR imagery, is studied using Sea Level Anomalies (SLA) maps. This evolution is compared with the information given by surface drifters deployed along eddy diameter, during ALGERS98 cruise in western Mediterranean. Preliminary results show a good agreement between the structure observed form drifters trajectories and the velocity field obtained from SLA maps assuming a geostrophic balance. The center of the eddy is taken as the grid point of maximum SLA. Differences between this center and the center given by the drifters seen to be due to the precision of the grid used by altimetric maps. From the position of the centers the propagation velocity of the eddy is obtained. The mean velocity obtained from altimetry is 2.7 km/day which is coherent with previous studies.

This article explains a methodology to model the spatial structures present in sea surface temperature images, collected from oceanographic satellites, that allows the estimation of sea surface currents. An Eulerian velocity field is built under the assumption that the currents can be diagnosed by the geostrophic equation. The images are preprocessed using a multiresolution wavelet analysis that helps to extract the surface structures at a given scale. A first guess of the vector field is computed at isotherm edges and the whole map of vectors is reconstructed using vector spline interpolation techniques.

Sea surface salinity (SSS) has been recognized as a key parameter in climatological studies. SSS can be measured by passive microwave remote sensing at L band, where the sensitivity of the brightness temperatures shows a maximum and the atmosphere is almost transparent. To provide global coverage of this basic parameter with a 3-day revisit time, the SMOS mission was recently selected by ESA within the frame of the Earth Explorer Opportunity Missions. The SMOS mission will carry the MIRAS instrument, the first 2D L-band aperture synthesis interferometric radiometer. To address new challenges that this mission presents, such as incidence angle variation with pixel, polarization mixing, effect of wind and foam and others, a measurement campaign has been sponsored by ESA under the name of WISE 2000 and it is scheduled for October-November 2000. Two L-band radiometers, a video, a IR and a stereo-camera and four oceanographic and meteorological buoys will be installed in the oil platform 'Casablanca' located at 40 Km off the coast of Tarragona, where the sea conditions are representative of the Mediterranean open sea with periodic influence of the Ebro river fresh water plume.

An empirical method to estimate the solar incoming radiation has been improved using AVHRR-NOAA14 data in the framework of the ARTIST experiment. This method, using several bulk formulas, gives an estimation of the incoming solar radiation and results are compared with the surface-based and aircraft-based measurements. The first step of the method is the development of a cloud detection algorithm for the area and for the period of interest. The area is the Arctic Ocean near the Svalbard Islands and the period is from 15 March to 16 April 1998, the transition period form winter to sprint and in this particular case from the Polar Night to a period of quite normal insolation. Several bulk formulas, right for the Polar condition, are tested comparing the estimate insolation fluxes with the direct measurements made with a pyranometer mounted aboard the Polar2 aircraft and another pyranometer at the research base at Ny-Alesund. The comparison could define the best parameterization for the available data.

Many techniques have ben developed for the assessment and monitoring of sea suspended matter (SSM) by the two optical channels of the NOAA-AVHRR. However, they are useful only for cloudless conditions. In this work a new algorithm is proposed, which is based on the two AVHRR optical channels revealing SSM patterns also in hazy conditions or under thin clouds. It combines two indexes derived from the AVHRR optical bands in order to account for the effect of the atmosphere on albedo and moreover on the sea spatial patterns. A criterion based on the statistical comparison of the two indexes discriminates between clear areas and pixels belonging to one of two different classes of suspended sediments. The performance of the proposed algorithm has been tested on a set of NOAA-AVHRR imagery of the Adriatic sea acquired in the winter and summer 1997-98. The results showed spatial patterns steadily varying in time, which are recognized as inorganic sediments or chlorophyll.

Ecodynamics and the sea-air transfer of climate relevant trace gases are intimately coupled in the oceanic mixed layer. Ventilation of species such as dimethyl sulfide and methyl bromide constitutes a key linkage within the earth system. We are creating a research tool for the study of marine trace gas distributions by implementing coupled ecology-gas chemistry in the high resolution Parallel Ocean Program. The fundamental circulation model is eddy resolving, with cell sizes averaging 0.15 degree. Here we describe ecochemistry integration. Density dependent mortality and iron geochemistry have enhanced agreement with chlorophyll measurements. Indications are that dimethyl sulfide production rates must be adjusted for latitude dependence to match recent compilations. This may reflect the need for phytoplankton to conserve nitrogen by favoring sulfurous osmolytes. Global simulations are also available for carbonyl sulfide, the methyl halides and for nonmethane hydrocarbons. We discuss future applications including interaction with atmospheric chemistry models, high resolution biogeochemical snapshots and the study of open ocean fertilization.

DMS is a sulfur-compound produced naturally in the sea. Once in the atmosphere, it is photo oxidized to form a non-sea- salt sulfate aerosols which affect the radiative budget indirectly as cloud condensation nuclei (CCN). It has been postulated that the planet's climate may be modulated by variations in DMS production form changes of the sea surface temperature (SST). It is shown that surface seawater DMS concentrations can be diagnosed at a near global scale using (1) satellite observations of Chl a, (2) climatological SSTs, (3) a temperature dependent index of the marine community structure and (4), observational relationships based on cruise data. This procedure is used to characterize the spatio-temporal variations in marine DMS emissions to the atmosphere in the Southern Hemisphere for the spring and summer months. Some coherence is obtained between DMS emissions and the polarization measurements from the space borne POLDER instrument used to estimate the effective radius of liquid-phase clouds; higher are the DMS emissions lower is the cloud droplet radius. An inspection of the ISCCP-D products of low-cloud optical depth a d DMS emissions at Amsterdam Island and Cape Grim indicates that higher are the DMS emissions higher is the cloud optical depth. The IPSL ocean-atmosphere coupled model, which includes an explicitly representation of plankton dynamics and Chl a, predicts significant large-scale changes of DMS fluxes in response to a doubling of atmospheric CO₂. We envision that the decreased mass of sulfur in the tropical upper troposphere will lead to lower numbers of CCNs in the air subsiding back into the subtropical marine boundary layer. Hence, it is suggested that the sensitivity of mid- latitude clouds to local changes in DMS emissions will increase in the future.

Volatile organic sulfur compounds from an Atlantic Meridional Transect of the RRS James Clark Ros are presented together with optical data and upper ocean chlorophyl data. The latitudinal distribution of DMS and CH₃SH is consistent with a biological source with low values in oligotrophic areas and high values in coastal regions. The DMS/CH₃SH ratio shows systematic variation between oligotrophic and coastal areas and seems to correlate inversely with absorbance and fluorescence of colored dissolved organic matter. The latitudinal distribution of COS and CS₂ conform with existing models based on known sources and sinks of these compounds. A system of photochemical provinces is developed for these compounds based on a previously published scheme. An estimate of the global distribution of these provinces is made based on data archives and remotely sensed data.

The NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project has a worldwide, ongoing ocean color data collection program, as well as an operational data processing and analysis capability. SIMBIOS dat collection takes place via the SIMBIOS Science Team and the National Aeronautics and Space Administration (NASA) Aerosol Robotic Network. In addition, SIMBIOS has a calibration and product validation component. The primary purpose of these calibration and product validation activities are to (1) reduce measurement error by identifying and characterizing true error sources such as real changes in the satellite sensor or problems in the atmospheric correction algorithm, in order to differentiate these errors from natural variability in the marine light field; and (2) evaluate the various bio-optical algorithms being used by different ocean color missions. For each sensor, the SIMBIOS Project reviews the sensor design and processing algorithms being used by the particular ocean color project, compares the algorithms with alternate methods when possible, and provides the results to the appropriate project office.

A Mediterranean data set containing coincident in situ chlorophyll and Sea WiFS remote sensing reflectance was used to evaluate the performances of several ocean color empirical algorithms. The validation of the algorithms is based on a match up file of 63 coincident in situ and Sea WiFS measurements selected on the basis of a sequence of mask criteria that prevents the use of contaminated pixels. All the algorithms calibrated to global or non-Mediterranean data sets overestimate the chlorophyll concentration in the Mediterranean Sea for low values of chlorophyll-a concentration. A total pigment concentration algorithm based on a regression with Mediterranean data, proposed by Gitelson et al. For CZCS, gives good results for low chlorophyll concentrations but exhibits a scatter larger than OC2 for concentrations higher than 0.2 mg/m³. In this paper we propose a preliminary version of a new Mediterranean ocean color algorithm based on the OC2 functional form with coefficients estimated from a regression with our Mediterranean in situ data.

Through a combination of modeling and field work, we have investigated the possibilities of developing algorithms for the SeaWiFS and MERIS sensors which estimate the concentrations of chlorophyl a and phaeophytin a, dissolved yellow substances, and suspended particulate inorganic material in the upper water layer of Lakes Vaettern, and Vaenern the two largest lakes in Sweden. These concentrations are linked to the absorption and backscattering coefficients through a series of empirical relationships and ultimately radiance reflectance is estimated as a function of the ratio of backscattering to absorption. Model parameterization, i.e. the development of the empirical relationships linking the optically active substances to the inherent optical properties is based on both in situ measurements, and laboratory analyses specific to each lake. The frequency distributions of the optically active concentrations in each lake were estimated form long term monitoring data collected by the Swedish Environmental Protection Agency. Simulations which randomly varied the optically active substances based on their frequency distributions were used to generate synthetic data sets which could be used to examine possible remote sensing algorithms. The results of our modeling, suggest that both SeaWiFS and MERIS can provide useful estimates of yellow substances and SPIM in these two lakes. Accurate estimates of chlorophyll depend on measurements of radiance reflectance in the 660nm-680nm chlorophyll absorption band, in order to minimize interference from yellow substance absorption. As a result only the MERIS band 9: band 7 ratio was able to provide useful estimates of chlorophyll concentrations, and the accuracy of these estimates was influenced by variations in yellow substance absorption and variations in the shape of yellow substance absorption spectra measured in each lake.

Concerning with the ocean color remote sensing, the algorithm based on the empirical method is hard to apply to coastal regions, so-called case II water, since the constitution of water is optically complex. On the other hand, an inverse modeling using a neural network has a potential to retrieve the concentration of water constituents, such as chlorophyll a, inorganic suspended matter and colored dissolved organic matter, in case Ii water from remotely sensed data. As a representative area of Asian Case II water, Yellow Sea, which is known as a region with high SS and CDOM supplied form the Yellow River, was analyzed using ADEOS/OCTS data observed on 31.5.1997. Three different types of algorithm were examined: Alg. 1) Retrieval from nL_w using 670 and 865nm for the atmospheric correction bands; Alg. 2) Retrieval from nL_w using 765 and 865nm for the atmospheric correction bands; Alg. 3) Retrieval from atmosphere-ocean coupled simple radiative transfer model using all bands, where, nL_w is the normalized water leaving radiance. Although the best result was obtained by Alg. 2), Alg. 3) seems to be promising for case II water since reliable atmospheric correction can be carried out.

A remote sensing reflectance model, which describes the transfer of irradiant light within a homogeneous water column has previously been used to simulate the nadir viewing reflectance just above or below the water surface by Bostater, et al. Wavelength dependent features in the water surface reflectance depend upon the nature of the down welling irradiance, bottom reflectance and the water absorption and backscatter coefficients. The latter are very important coefficients, and depend upon the constituents in water and both vary as a function of the water depth and wavelength in actual water bodies. This paper describes a preliminary approach for the analytical solution of the radiative transfer equations in a two-stream representation of the irradiance field with variable coefficients due to the depth dependent water concentrations of substances such as chlorophyl pigments, dissolved organic matter and suspended particulate matter. The analytical model formulation makes use of analytically based solutions to the 2-flow equations. However, in this paper we describe the use of the unique Cauchy boundary conditions previously used, along with a matrix solution to allow for the prediction of the synthetic water surface reflectance signatures within a nonhomogeneous medium. Observed reflectance signatures as well as model derived 'synthetic signatures' are processed using efficient algorithms which demonstrate the error induced using the layered matrix approach is much less than 1 percent when compared to the analytical homogeneous water column solution. The influence of vertical gradients of water constituents may be extremely important in remote sensing of coastal water constituents as well as in remote sensing of submerged targets and different bottom types such as corals, sea grasses and sand.

A numerical study of scattering from 2D ocean-like surfaces is presented in this paper. Fist a new model for generating 2D fractal rough sea surface is introduced. This model incorprates the spectrum into fractal mode,, thus it can apply to any forms of sea spectrum. In this paper the Semi- Empirical Sea-Spectrum proposed by AK Fung is chosen for its simplicity. Afterwards, an improved composite surface model is developed to calculate the scattering coefficient. In this mode,, we calculate the value of slopes at each point of the large-scale roughness using numerical method, therefore avoid assuming the probability density distribution of slopes in the conventional composite surface mode. Afterwards, the ray-tracing method is adopted to predict the intensity of light scattered from rough sea surface, which helps to probe the sea surface's microstructure. Moreover, we make a study of the shadowing of each point on the surface by tracing the incident and scattered wave, and can get the ratio of the number of points unshadowed to the total number, i.e. the shadowing function. Finally an analysis of the amplitude characteristics and fractal characteristic of the scattered wave from sea surfaces is made, which are of great significance for distinguishing and detecting targets on the sea.

A normalized 2D band-limited Weierstrass fractal function s used for modeling the rough surface Based on Kirchhoff theory, an analytic solution of the average scattering field and the variance of scattering intensity are derived, the influence of fractal dimension, the patch size of the surface and the fundamental wavenumbers on the scattering field is discussed by theoretical analysis and numerical calculations. The fractal dimension D, which determines the surface roughness, will control the distribution of scattering pattern. Emphasis is also put on to examine the relation of fractal dimension with the variance of scattering intensity. The important conclusion is obtained that the diffracted envelope slopes of scattering pattern can be approximated to a slope of linear equation.

A good assessment of the information content of scatterometer winds is particular important to assimilate them in weather analysis. Besides retrieval problems in cases of a confused sea state, a particularly acute problem of Ku-band scatterometry is the sensitivity to rain. Elimination of poor quality data is therefore a prerequisite for the successful use of NSCAT or QuikSCAT winds. Following the quality control for the ERS and NSCAT scatterometers performed at KNMI, we further develop this methodology for QuikSCAT and define a quality indicator, called the normalized residual. In order to characterize and validate the normalized residual, we use collocated SSM/I rain and ECMWF wind data. The results how indeed correlation between Rn and data quality. A wind speed dependent Rn threshold is shown to be adequate in terms of rejecting poor quality data and keeping fair quality dat. This opens the way to a quantitative use of SeaWinds measurements in weather analysis.

A simple model which predicts radiance reflectance below the water surface as a function of the concentrations of chlorophyll, colored dissolved organic matter (CDOM), and suspended particulate material (SPIM) was applied in Garda lake, the largest freshwater basin in Italy and one of the most important of the European Union. The model is similar to others developed for oceanic and coastal waters predicting the radiance reflectance as a function of two inherent optical properties of water: the absorption coefficient and the backscattering coefficient. Three stations were sampled in January '98 in the southern part of Garda lake. Samples of water were collected just below the water surface to extract the optically active substances. Two underwater radiometers assembled on the same probe provided the measurement of downwelling irradiance and up welling radiance, respectively. At the same time the apparent optical properties were collected above the water volume by using a spectro radiometer. The simulated radiance reflectance spectra were compared to the ones measured and significant correlations were retrieved.

A homogeneous water column hyperspectral Monte Carlo modeling approach is compared to an analytical solution to a radiative transfer model system for irradiance. Both mathematical models and the solution approaches describe the transfer of irradiant light in a homogeneous medium. The analytical model has been previously used to describe the transfer of irradiant energy in a homogeneous water column, with and without fluorescence source terms as well as a direct specular or a collimated irradiance source term. The response of the water surface reflectance under solar irradiance or an artificial collimated light source is thus modeled. Synthetic reflectance signatures generated from the 2 mathematical models described the interaction of irradiant photon flux in terms of the 2 flow irradiance equations. The Monte Carlo model is used for creating synthetic coastal water color or reflectance signatures for clear waters with different bottom reflectance signatures using dat collected in the Caribbean Sea region. The analytical mode has suggested proportionality between the absorption and backscatter coefficients around 0.29. In this paper the proportionality factor for clear water using the Monte Carlo model or irradiance was found to vary, but averaged around 0.26. This compares to 0.33 form other published values used in simple remote sensing algorithms. Results suggest that the optical pathlength will be a dominant factor influencing the ability of the Monte Carlo model to accurately represent measured or known reflectance signatures. The hyperspectral Monte Carlo mathematical modeling results also suggest the value of the technique for calculating the backscattering coefficient in waters with varying suspended matter, dissolved organic matter and phytoplankton pigments.

An atmospheric mesoscale numerical model has been developed and applied to the marine atmospheric boundary layer in the vicinity of sharp sea-surface temperature (SST) gradients. The Gulf Stream offshore of Each Central Florida near Cape Canaveral is the region of interest. The model equations which govern atmospheric behavior are based on the basic conservation laws of mass, momentum, and energy. A 'primitive' equation formulation is used to produce preliminary predictions of horizontal velocity, potential temperature, and water vapor. The hydrostatic approximation is applied to the vertical momentum conservation equation and the anelastic form of the continuity equation is used to approximate mass conservation. Surface fluxes of momentum, heat, and moisture are estimated using high-resolution SST data obtained in near-real time from the AVHRR IR instrument. Interaction of the boundary layer flow with the nearby Central Florida peninsula is simulated by inducing a diurnal sea breeze circulation across the coastline. It is found through a series of simulations that the distribution of sea-surface temperatures influences the boundary layer flow field - especially over the region of the Gulf Stream front and the low level convergence field, which may be an important factor for initiating convective precipitation over the land-water margin and Gulf Stream. The importance of the air-sea or air-land interfaces are thus fully recognized as being crucial to parameterize via remote sensing data in order to proceed with further model developments of the newly developed sea-breeze model. Further examination of methods for estimating surface temperatures of the water and land as well as inclusion of surface gravity wave forcing due to the diurnal sea breeze over the complex land-water margin in the Indian River Lagoon will need to be included in order to utilize the model for future application.