Radio wave propagation over sea paths is influenced by the local meteorological condition at the atmospheric layer near the surface, especially during ducts. Duct condition can be determined by measurements of local meteorological parameters, by weather forecast models or by using inverse methods. In order to evaluate the feasibility of using inverse methods to retrieve the refractivity profiles a measurement of RF signals and meteorological parameters were carried out at a test site in the Baltic. During the measurements, signal power from two broadcast antennas, one at Visby and one at Vastervik, were received at Musko, an island south of Stockholm. The measurements were performed during the summer 2005 and the data was used to test the software package for inversion methods, SAGA (Seismo Acoustic inversion using Genetic Algorithms, by Peter Gerstoft UCSD, US). Refractivity profiles retrieved by SAGA were compared with the refractivity profiles calculated from measured parameters, during parts of the experiment, from rocket sounding, radio sounding, local meteorological measurements using bulk model calculations, and also obtained by the Swedish operational weather forecast model HIRLAM. Surface based duct height are predicted in relative many situations even though the number of frequencies or antennas height has to be increased to diminish the ambiguous of the refractive index profile.

The polarization characteristics of the water leaving radiance can provide information on bio-optical properties and composition of coastal water and can be used as well as a tool for the separation of chlorophyll fluorescence from elastic reflectance spectra. We report the results of simulations using a coupled ocean-atmosphere vector radiative transfer code (NASA GISS) to obtain the polarized reflectance for various water compositions typical for coastal zones, as function of wavelength and sun/sensor geometry. Results show that even for sensor orientations outside of the principal scattering plane, the polarization can nearly approach the maximum values observable in the principal scattering plane thereby minimizing undesirable sun glint effects. Simulations are complemented by laboratory and field measurements in Chesapeake Bay and near Sapelo Island, GA. We also report the results of the fluorescence retrieval from reflectance spectra using polarization discrimination as well as fluorescence line height (FLH) algorithms. Performance of these algorithms is analyzed in conjunction with the relationship between fluorescence magnitude and chlorophyll concentrations in the conditions typical for coastal waters.

The coastal zone is an extremely dynamic system. Variations in the concentration of its major constituents occur rapidly over space and time. This is in response to changes in bathymetry and tidal forces coupled with the influences of fronts, upwelling zones and river inflow. Today's research on the functioning of estuarine and coastal ecosystems, as well as attempts to quantify some of their biogeochemical fluxes are based on highly time consuming and costly sea campaigns and laboratory analyses. On September 2002, an airborne campaign using CASI sensor covered part of the Scheldt estuary (Belgium- Netherlands coastal zone). A 13 sampling stations field survey was realised in order to cover as quickly as possible the wide range of water quality encountered from the mouth of the estuary to the outer limit of the plume. Correlation was searched between classical ground truth measurements and the rich information provided by numerous CASI-SWIR spectral bands carefully chosen. These relations were not sufficient enough to derive synoptic view of the spatial distribution of many biogeochemical parameters in the Scheldt estuary and plume. In this research we found that some biogeochemical parameters of interest in estuaries and plumes that were retrieved using imaging spectroscopy techniques as the MF (Matched filtering) and the MTMF (Mixture Tuned Matched Filtering) are very encouraging. We showed that using those spectra based processing techniques we could accurately obtained the concentration distribution of suspended particulate matter (SPM) and particulate organic matter (POM), that we could not retrieved using the classical statistical techniques. Moreover, using the imaging spectroscopy techniques we significantly improved the coloured dissolved organic matter (CDOM) concentration classification, relatively to the results derived using the multiple regression technique.

An analytical model of infrared sea surface optical properties is developed to access to statistical radiative characteristics of a wind-roughened water surface. Any surface size, i.e. that contains or not all the statistical information of the stochastic process governing the sea surface, can be considered. This model deals with the problem of multi-resolution in a sensor field of view. Model validation has been conducted in 1D by comparison with a reference code and in 2D by comparisons with optical properties measurements and with validated 1D cross sections.

The purpose of this paper is to present simulation in order to compare a Hyperspectral Monte Carlo Model (MC) which generates synthetic images with realistic water wave surface to an iterative layered radiative transfer model used to generate hyperspectral synthetic images with realistic water wave surfaces. The MC model developed by Bostater and Gimond (2002) and Bostater and Chiang (2002) is divided into 5 steps: (1) Generation of the photons, (2) tracking of the photon optical path and simultaneously (3) recording of the photon's location within the water column, (4) then a tabulation of the sampling and its conversion to meaningful radiometric quantities and finally (5) a calculation and processing of the event probabilities between successive photons. This model will then be compared to the ILRT which is analytical and uses an iterative method to converge on the solution to a layered, iterative two flow radiative transfer model developed by (Bostater et al., 2002). The purpose of this research and the presentation will be to describe the effects of spectrally derived wave facets and the foam estimation coverage in order to assess the differences between the above modeling approaches, and to develop a better scientific understanding of the influence of water waves on the remote sensing signal from 400 to 750 nm, as well as the coupled influence of water waves and shallow bottom reflectance effects due to benthic aquatic habitat features such as submerged vegetation, corals, and other objects submerged within the water column as well as effects due to waves at the air-sea interface. The spectral wave models used include the wave (Phillips, Jonswap, Pierson-Moskowitz and TMA) that will help to simulate what a sensor sees from a low flying aircraft. In order to evaluate the wave models the Inverse Fast Fourier Transform (IFFT) is applied and results described.

Previous studies indicate that parallel computing for hyperspectral remote sensing image generation is feasible. However, due to the limitation of computing ability within single cluster, one can only generate three bands and a 1000*1000 pixels image in a reasonable time. In this paper, we discuss the capability of using Grid computing where the so-called eScience or cyberinfrastructure is utilized to integrate distributed computing resources to act as a single virtual computer with huge computational abilities and storage spaces. The technique demonstrated in this paper demonstrates the feasibility of a Grid-Enabled Monte Carlo Hyperspectral Synthetic Image Remote Sensing Model (GRID-MCHSIM) for coastal water quality algorithm.

Optical imaging of coral reefs and other benthic communities present below one attenuation depth, the limit of effective airborne and satellite remote sensing, requires the use of in situ platforms such as autonomous underwater vehicles (AUVs). The Seabed AUV, which was designed for high-resolution underwater optical and acoustic imaging, was used to characterize several deep insular shelf reefs of Puerto Rico and the US Virgin Islands using digital imagery. The digital photo transects obtained by the Seabed AUV provided quantitative data on living coral, sponge, gorgonian, and macroalgal cover as well as coral species richness and diversity. Rugosity, an index of structural complexity, was derived from the pencil-beam acoustic data. The AUV benthic assessments could provide the required information for selecting unique areas of high coral cover, biodiversity and structural complexity for habitat protection and ecosystem-based management. Data from Seabed sensors and related imaging technologies are being used to conduct multi-beam sonar surveys, 3-D image reconstruction from a single camera, photo mosaicking, image based navigation, and multi-sensor fusion of acoustic and optical data.

Remote sensing is increasingly being used as a tool to quantitatively assess the location, distribution and relative health of coral reefs and other shallow aquatic ecosystems. As the use of this technology continues to grow and the analysis products become more sophisticated, there is an increasing need for comprehensive ground truth data as a means to assess the algorithms being developed. The University of Puerto Rico at Mayaguez (UPRM), one of the core partners in the NSF sponsored Center for Subsurface Sensing and Imaging Systems (CenSSIS), is addressing this need through the development of a fully-characterized field test environment on Enrique Reef in southwestern Puerto Rico. This reef area contains a mixture of benthic habitats, including areas of seagrass, sand, algae and coral, and a range of water depths, from a shallow reef flat to a steeply sloping forereef. The objective behind the test environment is to collect multiple levels of image, field and laboratory data with which to validate physical models, inversion algorithms, feature extraction tools and classification methods for subsurface aquatic sensing. Data collected from Enrique Reef currently includes airborne, satellite and field-level hyperspectral and multispectral images, in situ spectral signatures, water bio-optical properties and information on habitat composition and benthic cover. We present a summary of the latest results from Enrique Reef, discuss our concept of an open testbed for the remote sensing community and solicit other users to utilize the data and participate in ongoing system development.

Benthic habitats are the different bottom environments as defined by distinct physical, geochemical, and biological characteristics. Remote sensing is increasingly being used to map and monitor the complex dynamics associated with estuarine and nearshore benthic habitats. Advantages of remote sensing technology include both the qualitative benefits derived from a visual overview, and more importantly, the quantitative abilities for systematic assessment and monitoring. Advancements in instrument capabilities and analysis methods are continuing to expand the accuracy and level of effectiveness of the resulting data products. Hyperspectral sensors in particular are rapidly emerging as a more complete solution, especially for the analysis of subsurface shallow aquatic systems. The spectral detail offered by hyperspectral instruments facilitates significant improvements in the capacity to differentiate and classify benthic habitats. This paper reviews two techniques for mapping shallow coastal ecosystems that both combine the retrieval of water optical properties with a linear unmixing model to obtain classifications of the seafloor. Example output using AVIRIS hyperspectral imagery of Kaneohe Bay, Hawaii is employed to demonstrate the application potential of the two approaches and compare their respective results.

Protocol development for science based mapping of submerged aquatic vegetation (SAV) requires comprehensive ground truth data describing the full range of variability observed in the target. The Indian River Lagoon, Florida, extends along 250 km of the east central Florida coast adjacent to the Atlantic Ocean. The lagoon crosses the transition zone between the Caribbean and Carolinian zoogeographic provinces making it highly diverse. For large scale mapping and management of SAV four common and three uncommon species of seagrass (Tracheophyta) and three broad groups of macroalgae; red algae (Rhodophyta), green algae (Chlorophyta), and brown algae (Phaeophyta) are recognized. Based on technical and cost limitations we established twenty, 7-10 km long flight transects for collection of 1.2 m² spatial resolution hyperspectral imagery covering the length of the lagoon. Emphasis was placed on the area near the Sebastian River and adjacent Sebastian Inlet. Twenty six 40 m long ground truth transects were established in the lagoon using 1 m² white panels to mark each transect end. Each transect target was located in the field using high precision GPS. Transects were positioned to cover a range of depths, SAV densities, mixed and monotypic species beds, water quality conditions and general sediment types. A 3 m wide by 30 m long grid was centered on each transect to avoid spectral influences of the white targets. Water depth, species of seagrasses, estimates of vegetation cover percentage, estimates of epiphytic density, and measured canopy height were made for each 1 m² (n=90). This target based grid arrangement allows for identification and extraction of pixel based hyperspectral signatures corresponding to individual ground truth grid cells without significant concern for rectification and registration error.

The primary measurement objective of the Advanced Scatterometer ASCAT, a spaceborne real aperture C band radar, is the determination of wind fields at the ocean surface. Unlike AMI instruments on-board ERS satellites, ASCAT uses long transmit pulses with linear frequency modulation (chirps) allowing the application of low peak transmission power while retaining a high SNR. A pulse-compression is performed on the received signal. This paper will focus on the impact of the use of pulse compression in particular on the location accuracy of the samples in presence of external perturbations. An eventual location error has important consequences on the normalization as well as on the geolocation of the measured data.

Within the Gavdos Project (Establishment of a European radar altimeter calibration and sea level monitoring site for Jason, Envisat and Euro-Gloss), a transponder has been used for an experimental work package. The instrument has been deployed on the island of Gavdos beneath the ascending pass of Envisat and was receiving the altimeter pulses, amplifying and retransmitting them back to the altimeter. The transponder could thus be easily identified in the altimeter data stream in the characteristic variation of the waveform power. Acting as a point target for the satellite radar altimeter, the range measurements from the satellite to the transponder are not subject of "speckle" effects, as it happens in the case of the sea surface when the multitude of scatters cause interference effects to the radar echo. The distance measurement has a resolution of < 1 cm [1]; provided that the atmospheric delays are properly modeled, the accuracy of a range measurement is estimated to 2 cm. The applications deriving from the use of the transponder in the altimetry context are based on the accurate determination of the transponder-satellite distance. These include the altimeter bias calibration, the measurement of the orbit radial errors especially in places where positioning systems are unavailable, determination of ice thickness, and height transfer between land and ocean or land and land.

SAR spaceborne capability to detect marine oil spills through damping of short gravity-capillary waves has been extensively demonstrated during past years. In contrast, it has not yet been found the optimal use of VIS/NIR imaging sensors for detection and monitoring of oil polluted areas. We propose the use of Modis images acquired in sun glint conditions to reveal smoothed regions such as those affected by oil pollution. According to Cox and Munk model, the physical mechanism that allows detection of oil slicks under sun glint imaging of clear sea surface is based on the modification of the wind-generated wave slopes distribution due the action of mineral oils. The methodology is demonstrated for a number of case studies occurred in the Mediterranean Sea and North Atlantic from 2001 to 2004. For each case, the oil slicks were detected by ERS SAR imaging and the corresponding Modis images were acquired within a few hours the SAR passage under sun glint conditions. The implemented procedure compares the water-leaving Cox and Munk sun glint reflectance with the reflectance measured by Modis at the top of the atmosphere (TOA). To accomplish the task, the Modis imaging parameters and an estimate of the wind vector are provided as input. The ECMWF analysis wind fields are considered for the purpose. It was found that the ratio between the TOA reflectance and the C&M reflectance enhances the capability to detect oil slicks. Moreover, an extensive analysis of the atmospheric effects on oil slick detection has been carried out by performing simulations using the 6S code. Preliminary results show that atmosphere contribution to the reflectance has little impact on oil slick detection, so that implementation of a surveillance procedure could be envisaged.

A sensitivity analysis of the irradiance reflectance calculated from the modified two-flow equations (Bostater, et al., and Bostater et al, 2002) to various model inputs is addressed. The modified two-flow equation approximate of the radiative transfer equation (RTE) with a collimated or specular component is used to calculate the sensitivity of the calculated irradiance reflectance on the inclusion of solar zenith angle, wind speed, shape factors, chlorophyll-a concentration, water depth, and bottom type.

GPS-Reflectometry studies the forward scattering of GPS reflections for the purposes of determining surface characteristics. This can be used for measuring sea states, soil humidity and polar ice age. Theoretical and experimental studies have been mainly carried out on ground and airborne platforms. A space-borne platform, however, would provide broader spatial and temporal coverage for Earth Observation and disaster monitoring. Currently UK-DMC represents the only Low Earth Orbit (LEO) satellite able to routinely schedule GPS reflection observations from ocean surfaces. Earlier research work has shown that Delay-Doppler Maps (DDMs) derived from reflections from space, although weak, will vary with geometry and sea state. In this work we extend these results by developing a modelling technique that derives relationships between wind conditions, sea roughness and GPS reflections received from a LEO satellite. We present simulation results and two-dimensional fitting of experimental data to compare DDMs. A novel technique is also proposed for reversing experimental DDMs obtained from GPS-R back to spatial energy maps. Preliminary data inversion results have been included to demonstrate the feasibility of this new methodology.

This paper describes a wavelet based approach to derivative spectroscopy. The approach is utilized to select, through optimization, optimal channels or bands to use as derivative based remote sensing algorithms. The approach is applied to airborne and modeled or synthetic reflectance signatures of environmental media and features or objects within such media, such as benthic submerged vegetation canopies. The technique can also applied to selected pixels identified within a hyperspectral image cube obtained from an board an airborne, ground based, or subsurface mobile imaging system. This wavelet based image processing technique is an extremely fast numerical method to conduct higher order derivative spectroscopy which includes nonlinear filter windows. Essentially, the wavelet filter scans a measured or synthetic signature in an automated sequential manner in order to develop a library of filtered spectra. The library is utilized in real time to select the optimal channels for direct algorithm application. The unique wavelet based derivative filtering technique makes us of a translating, and dilating derivative spectroscopy signal processing (TDDS-SP ^(R)) approach based upon remote sensing science and radiative transfer processes unlike other signal processing techniques applied to hyperspectral signatures.

Modern remote sensing systems used in repetitive environmental monitoring and surveillance applications are used on various platforms. These platforms can be categorized as stationary (fixed) or moving platforms. The sensing systems monitor the ambient environment which also may have inherent motion, such as the water surface with water waves. This is particularly the case for airborne or ship borne sensing of aquatic environments and is true for ground based walking or crawling systems. The time sequential comparison and spatial registration of sensor images, particularly "hyperspectral imagery" requires pixel to pixel registration for science based change and target (or medium) detection applications. These applications require sensor motion control combined with platform motion control. If the pixel sizes are small - on the order of 1 meter to less than 1 mm, then "nano-positioning accuracy" may be necessary for various aspects of the camera or surveillance sensor system, and/or related sensors used to control the moving platform. In this paper and presentation, an overview of converging technologies to sensor motion control and nano-positioning is discussed. The paper and presentation will demonstrate that the technologies converging on this aspect of remote sensing monitoring systems will require professionals with a combination of skills that are not readily available in today's workforce nor taught in educational programs today - especially at the undergraduate level. Thus there is a need to consider new avenues for educating professionals necessary to engineer and apply these converging technologies to important social environmental monitoring and surveillance needs.

On several occasions the sea surface has been measured with the mmW radar MEMPHIS in SAR geometry. This research was mainly aimed to investigate the ability of SAR for imaging of disturbances of the water surface at mm-wave radar bands and to gather data on the statistical properties of sea clutter. It can be suspected, that the probability density functions for the reflectivity of sea clutter is as well dependent on the radar wavelength as on resolution, as different scattering processes may significantly contribute. While most of the available millimeterwave data have been collected with a resolution of 75 cm, improvements of the MEMPHIS radar now allow a resolution of about 20 cm. The paper describes the measurement set-up, the evaluation methods and discusses the influence of resolution and radar frequency on sea clutter characteristics as found during the experiments.

A series of the Orbview-2/SeaWiFS (Sea-viewing Wide Field-of-view Sensor) images during the period from 1997 to 2003 is used to understand the spatial and temporal distribution of the chlorophyll-a concentration (Chl-a) in the Taiwan Strait (TS). It is found that the area with higher Chl-a is mainly along the western TS; it extends more offshore in cold seasons. The lowest Chl-a is always inside the deep Peng-Hu Channel, it can spread further northward in summer. From mode 1 results of the Empirical Orthogonal Function (EOF) analysis, we find the Chl-a in La Nina years (during the period from June 1998 to May 2001) showing greater variation than the other El Nino or normal years. The EOF1 results also indicate the highest Chl-a always in fall. Meanwhile, the peak in the 1997/1998 El Nino fall was the lowest maximum, while the lowest Chl-a is mainly in winter, but its interannual variation is not so clear.

Synthetic Aperture Radar (SAR) images from European Remote Sensing (ERS) satellites are used to investigate oil spill from ship navigations in the water adjacent to Taiwan. A total number of 136 images taken from 1993 to 1997 are used in this study. On the 136 images, only 46 images showing the possibility of oil spill which are based on the position and the shape of the discharge, the path of the ship, the sea characteristics of the area, and the weather conditions. The result shows that oil spill occurs most frequently in spring and least in winter. The sea area off eastern Taiwan has a probability which far surpassed other areas, followed by the middle sea area, the northern sea area, and the southern sea area. Regarding the oil spills at different areas with the distance to the shore, the oil spills at the middle area, with an average distance of 50 km (28 nautical miles), is closer than those at other areas. The statistical analysis demonstrates that the oil spill around Taiwan mostly occurs over 44 km (24 nautical miles) away from shore. Therefore, it is obvious that the probability of oil spills occurring as a ship leaves or enters the harbor is not high. Instead, the majority of oil spills takes place from middle to long distance navigating fishing boats as well as from oil and cargo freighters navigating international waterways.

Rapidly vanishing polar ice may be supplemented with extensive artificial ice in order to alleviate effects of global warming. Here we consider methods for creating such artificial ice by introducing synthetic polymer rafts or films to the supercooled topmost water layer near ice sheet borders in northern Arctic seas. Such films will have three major effects. They will reflect incoming solar radiation, reducing ice melting, ocean absorption of solar energy, and net heating rates. The films will also provide additional sites for nucleation of ice crystals. Finally, by decreasing wave amplitudes in their immediate vicinity, polymer films will allow ice crystals to aggregate into larger ice structures.