Naval Oceanographic Office Research Articles

Evaluation of the relative performance of sea surface temperature measurements from different types of drifting and moored buoys using satellite‐derived reference products

Sea surface temperature (SST) measurements from drifting and moored buoys have been used extensively to validate satellite SST products. Previous efforts explored overall uncertainties in the buoy measurements, but did not quantify differences in the performance of different buoy types. Here, drifting and moored buoys stratified into open‐ocean and coastal, were evaluated by manufacturer (drifters) and buoy program (moorings) to identify significant deviations in their suitability for satellite validation. Biases and standard deviations were computed for differences between the buoy SST measurements and two satellite references: the Advanced Microwave Scanning Radiometer SST product from Remote Sensing Systems and the U.S. Naval Oceanographic Office K10 analysis. No significant differences were found among the various drifting and tropical moored buoys, regardless of the manufacturer/program. The largest deviations were observed for the non‐tropical moored buoys possibly in part due to calibration differences. In general, coastal buoys exhibited greater standard deviations associated with increased physical variability within the coastal regions. Tropical moored buoys showed smaller standard deviations than for the drifters resulting from better quality measurements or reduced variability in the tropics. Large deviations between the coastal moorings and the SST references appeared linked to coastal currents with upwelling, rather than buoy performance. Coastal moorings provided sampling of small‐scale coastal variability, not resolved in satellite products, offering the potential for improving poorly parameterized coastal SSTs. Differences due to diurnal warming were largely eliminated by constraining collocations between the satellite and the buoy to ±1 h. Overall, most buoy types appear suitable for satellite SST validation.

High frequency bottom loss database generation at the naval oceanographic office

The Naval Oceanographic Office (NAVOCEANO) generates the low- and high-frequency bottom loss databases (LFBL and HFBL). In support of these upgrades, NAVOCEANO carries out survey operations to make acoustic and geophysical measurements. From these measurements, bottom loss parameters are extracted via numerical inversions. The HFBL database describes acoustic bottom loss over the range 1.5-4 kHz and is based on a set of nine bottom-loss curves derived from the Marine Geological Survey carried out by NAVOCEANO (1965–1968). The optimum curve at a given location is derived from a process of brute force inversion using measured transmission loss (TL) data. Curves are interpolated to the nearest 1/10th; they are then input to the CASS model to determine which curve optimizes the fit between the CASS prediction and the measured TL data. Optimal curves are determined independently at each of the 1/3 octave frequencies over the HFBL range. Studies of the derived curve values in a recent upgrade area have indicated very high variability. This variability does not tend to correlate with bottom sediment type, and the variability tends to be highest in the higher frequency bands. An implication is that scattering caused by roughness at the water/sediment interface may be driving variability.

Experience with geoacoustic inversion of transmission loss

This presentation will discuss recent experience with geoacoustic inversion of transmission loss (TL) data from 50 to 5000 Hz from both deep and shallow water regions. For shallow water, a multi-layered geoacoustic profile with range dependent layer thicknesses is used. Layer thickness is not an inversion parameter but is known from ancillary data such as seismic profiling and chirp sonar. Issues related to range dependent sound speed profiles (SVPs) will be discussed as will observation of the time spread of multipath arrivals. For deep water, a single layer geoacoustic profile is assumed. Quality of inversion is assessed using comparison of measured and modeled TL and the estimation error. The estimation error is the dependence of the total rms error—summed over range, frequency, and receivers—on the values of a geoacoustic parameter within the bounds used to constrain inversion. The estimation error identifies geoacoustic parameters that are well constrained or poorly constrained by the TL data. Inversion was carried out using a genetic algorithm model [D. Harvey et al., Oceans '02 MTS/IEEE, 1, 358–362 (2002)]. Acoustic and environmental data were provided by the Naval Oceanographic Office. [Work funded by the Ocean Bottom Characterization Initiative through PEO C4I, PWM 120.]

A bottom-sediments province database and derived products, Naval Oceanographic Office

The Naval Oceanographic Office maintains a bottom-sediment province database at three levels of resolution: (1) a low-resolution legacy data set derived from secondary sources for the low- and mid-latitude ocean basins; (2) medium-resolution, actively maintained ``Regional Sediments'' data sets covering most of the continental margins of Eurasia and North America; and (3) high-resolution, limited-extent data sets derived from acoustic imagery. Sediment provinces are categorized via an ``Enhanced'' sediment classification consisting of seven locational, ten compositional, and 97 textural components. The resultant large number of categories allows for retention of source-data nomenclature but can be unwieldy and redundant. To provide accessibility and consistency to a variety of users, the Enhanced categories are reclassified into simplified or specialized sediment category sets. These include the High Frequency Environmental Acoustics categories for performance prediction, a mean grain-size set, a non-technical littoral set, as well as other bottom characteristics such as burial potential and bottom type. The Enhanced categories have also been assigned a limited number of geoacoustic and physical properties. Although the province approach and the reclassification schemes produce useful inputs for models and other predictions, users must recognize that they are subject to inherent limitations and ambiguities.

Operational sea surface temperature bias adjustment using AATSR data

One objective of the sea surface temperature (SST) component of the Global Monitoring for the Environment and Security (GMES) MERSEA project was to define the combined use of all SST products in an optimal interpolation scheme. Most SST products are now available in a common format but show regional differences between datasets that must be removed before use. We have defined a simple method using the SST derived from the Advanced Along Track Scanning Radiometer (AATSR) onboard the European Space Agency (ESA) ENVISAT platform as a common reference for all SST products. This method is based on an analysis of the differences between a given dataset and the AATSR SST over the 10 preceding days and over a 5° regular grid. These space–time characteristics have been defined empirically in a preliminary experiment. The efficiency of the method has been evaluated on a daily basis for a two year period (2007–2008) based on two SST products from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT): the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) derived SST over the Atlantic and the Advanced Very High Resolution Radiometer (AVHRR) SST derived at fine scale over the North-East Atlantic. They have been compared to the AATSR and buoy SSTs and to the Naval Oceanographic Office (NAVOCEANO) AVHRR global SST product. The SEVIRI SST bias, which was reduced from −0.40K to −0.02K for the 0–20N latitude band by this approach provides a good example of the performance of the method. Reductions in the bias are also demonstrated for the North Atlantic, where cloudiness related problems were expected.

Lightweight Autonomous Underwater Vehicles (AUVs) performing coastal survey operations in REP 10A

Lightweight Autonomous Underwater Vehicles (AUVs) were developed for Naval Special Warfare (NSW) Group 4 search and survey missions from a commercial AUV baseline (Iver 2) through integration of commercial off-the-shelf (COTS) hardware components, and through software development for enhanced on-board Command and Control functions. The development period was 1 year under a project sponsored by the Office of Naval Research TechSolutions Program Office. Hardware integration was completed by the commercial AUV vendor, OceanServer Technology, Inc., and software development was conducted by the Naval Undersea Warfare Center, Naval Oceanographic Office, and U MASS Dartmouth, with support from hardware and software application providers (YSI, Inc., Imagenex Technology Corp., and CARIS). At the conclusion of the integration and development period, an at-sea performance evaluation was scheduled for the Lightweight NSW AUVs with NSWG-4 personnel. The venue for this evaluation was the NATO exercise Recognized Environmental Picture 10A (REP 10A), hosted by Marinha Portuguesa, and coordinated by the Faculdade de Engenharia–Universidade do Porto. REP 10A offered an opportunity to evaluate the performance of the new AUVs and to explore the Concept of Operations (CONOPS) for employing them in military survey operations in shallow coastal waters. Shore- and ship-launched scenarios with launch/recovery by a single operator in a one-to-many coordinated survey, on-scene data product generation and visualization, data push to Reach Back Cells for product integration and enhancement, and survey optimization to streamline survey effort and timelines were included in the CONOPS review. Opportunities to explore employment of hybrid AUV fleets in Combined Force scenarios were also utilized. The Naval Undersea Warfare Center, Marinha Portuguesa, the Faculdade de Engenharia–Universidade do Porto, and OceanServer Technology, Inc., were the primary participants bringing in-water resources to REP 10A. Technical support and products were provided by the Naval Research Laboratory–Stennis Space Center, Naval Oceanographic Office, NATO Undersea Research Centre, University of Massachusetts–Dartmouth, and YSI, Inc. REP 10A proved to be a very effective exercise in meeting each of the critical goals. Results of the performance evaluation guided final development and Independent Verification and Validation (IV&V) for the Lightweight NSW AUV, leading to on-time, successful Factory Acceptance Testing and delivery of the three contracted vehicles to NSWG-4 in September, 2010.

Comparison of two and three spatial dimensional solutions of a parabolic approximation of the wave equation at ocean-basin scales in the presence of internal waves: 200–250 Hz.

Numerical solutions are given for a parabolic approximation to the acoustic wave equation at 200 and 250 Hz in two and three spatial dimensions to determine if azimuthal coupling in the horizontal coordinate significantly affects horizontal correlation in the presence of internal gravity waves in the sea. Coupling is a small effect at distances of 4000 km or less. This implies that accurate solutions are possible using computations from uncoupled vertical slices. Shapes of horizontal correlation are not far from shapes given by several theories. Estimates of horizontal correlation at 4000 km and 200 and 250 Hz are about 0.4 and 0.3 km, respectively. [Work supported by the Office of Naval Research Contract Nos. N00014-06-C-0031 and N00014-10-C-0480 and by a grant of computer time from the DOD High Performance Computing Modernization Program at the Naval Oceanographic Office.]

In Memoriam: Larry Hsu

He was a member of the American Geophysical Union. Larry received a B.S. in Mechanical Engineering from National Taiwan University in 1969, an M.S. in Mechanical Engineering from Duke University in 1971, and a Ph.D. in Marine Studies from the University of Delaware in 1981. For his dissertation, he investigated turbulent heat transfers in the atmospheric surface layer. Larry began his career in the Navy with the Mapping, Charting, and Geodesy Branch in the Marine Geosciences Division of the Naval Ocean Research and Development Activity NORDA at the Stennis Space Center, MS in 1987. He worked at the Magnetic Observatory for several years investigating ocean processes using laser technology. He developed the Tidal Atlas Software TAS , a PC-based application that allowed users to retrieve and display global tidal characteristics for any region or location. Graphical outputs included tidal data, cotidal and tidal height plots. The application was transitioned to the Naval Oceanographic Office in 1993. Larry served as an active member of the

Optimal Linear Fitting for Objective Determination of Ocean Mixed Layer Depth from Glider Profiles

Abstract A new optimal linear fitting method has been developed to determine mixed layer depth from profile data. This methodology includes three steps: 1) fitting the profile data from the first point near the surface to a depth using a linear polynomial, 2) computing the error ratio of absolute bias of few data points below that depth versus the root-mean-square error of data points from the surface to that depth between observed and fitted data, and 3) finding the depth (i.e., the mixed layer depth) with maximum error ratio. Temperature profiles in the western North Atlantic Ocean over 14 November–5 December 2007, collected from two gliders (Seagliders) deployed by the Naval Oceanographic Office, are used to demonstrate the capability of this method. The mean quality index (1.0 for perfect determination) for determining mixed layer depth is greater than 0.97, which is much higher than the critical value of 0.8 for well-defined mixed layer depth with that index.

US GODAE: Global Ocean Prediction with the HYbrid Coordinate Ocean Model (HYCOM)

Abstract : The main objective is to use the HYbrid Coordinate Ocean Model (HYCOM) with data assimilation in an eddy-resolving, fully global ocean prediction system with transition to the Naval Oceanographic Office (NAVOCEANO) at .08 deg equatorial (~7 km mid-latitude) resolution in 2007 and .04 deg resolution by 2011. The model will include shallow water to a minimum depth of 5 m and provide boundary conditions to finer resolution coastal and regional models that may use HYCOM or a different model. In addition, HYCOM will be coupled to atmospheric, ice and bio-chemical models, with transition to the Fleet Numerical Meteorology and Oceanography Center (FNMOC) for the coupled ocean-atmosphere prediction. Basin-scale configurations will also form the backbone of the NOAA/NCEP/MMAB Ocean Forecast System. All the systems will be transitioned with assimilation of sea surface height (SSH) from satellite altimeters, sea surface temperature (SST) and temperature (T)/salinity (S) profiles, including profiles from ARGO floats. In addition, 30-day forecasts are planned once a week. The global system will include two-way coupling to an ice model and a version with two-way coupling to an atmospheric model for transition to FNMOC. The project will ensure that an accurate and generalized ocean model nesting capability is in place to support regional and littoral applications when global HYCOM becomes operational. This will include the capability to provide boundary conditions to nested models with fixed depth z-level coordinates, terrain following coordinates, generalized coordinates (HYCOM), and unstructured grids. To facilitate this goal, HYCOM will be developed into a full-featured coastal ocean model in collaboration with a partnering project. The project will participate in the multinational Global Ocean Data Assimilation Experiment (GODAE) and international GODAE-related ocean prediction system intercomparison projects.

Environmental acoustic recording system (EARS) buoys for marine animal acoustics.

EARS buoys were developed as autonomous, moored, underwater recording systems by the Naval Oceanographic Office (NAVOCEANO) to make long-term ocean ambient noise measurements. When the Littoral Acoustic Demonstration Center (LADC) was formed as a consortium of university and U.S. Navy scientists in 2001, the buoys were capable of measuring up to 1000 Hz for 1 yr. LADC added listening to sperm whales to its noise and propagation measurements. NAVOCEANO quickly modified the buoys to measure up to 5859 Hz for 36 days. The buoys, moored at depths from 550 to 950 m in the Gulf of Mexico, produced exceptionally clear recordings of sperm whale echolocation and coda clicks and recordings of other whales. EARS Generation 2 buoys are now capable of recording one channel to 96 kHz, or four channels to 25 kHz, for more than 13 days on four 120 Gbyte notebook disk drives. Experiments in the Gulf of Mexico and the Ligurian Sea have targeted both sperm and beaked whales. Audio results and visualizations of these recordings reveal rich detail of Odontocete clicks and enable new analyses, such as the identification of individual whales from the properties of their clicks. [Research supported by ONR and SPAWAR.]

Overview of U.S. Navy Operational Oceanographic Models in Support of Acoustic Applications

The Naval Oceanographic Office operational global 1/8° Navy Coastal Ocean Model assimilates satellite and in‐situ data to produce daily 72‐hr forecasts. Output includes 3D fields of temperature, salinity, u‐ and v‐components of ocean currents at standard depth levels, and these support derived fields including sound speed and sonic layer depth. The global model provides initial/boundary conditions for nested regional models, primarily relocatable NCOM. The relocatable NCOM modeling system can be set up quickly for areas of interest, includes river and tidal forcing, and is forced with a high‐resolution atmospheric mesoscale model. Local and remote observations are incorporated into the models through the Navy Coupled Ocean Data Assimilation system, which assimilates sea surface temperature data from satellite, ships and buoys, profile data from floats and gliders, xbt's, CTD's, fixed and drifting buoys as well as altimeter‐derived sea surface heights and ice concentration. In this presentation we will discuss how the operational ocean models feed into acoustic prediction models and tactical decision aids, the role glider observations will play in the modeling strategy, the use of ensembles to provide improved prediction error estimates and guide new observations, and future plans.

High Resolution Modeling of Coastal Inundation: User Requirements and Current Practice, a Navy Perspective

The impact of coastal flooding and inundation on Navy operational missions and the existing Navy requirements for resolution and accuracy relevant to coastal inundation are presented. High resolution (less than 500 m) coastal models exercised operationally at the Naval Oceanographic Office are reviewed, summarizing the advantages, disadvantages and typical spatial resolutions of each. The present state of Navy coastal inundation modeling from a research and development perspective is presented along with highlights of planned advances in the near-future. Lastly, the gaps between users, products, data and research and development are illuminated. Fine-scale bathymetry and topography as well as in situ currents for validation are required for accurate, high resolution inundation modeling. Gaps between the needs of Navy users and the type and form of operationally available inundation products are identified and discussed. The need for usability, relocateability, and expediency in the operational setting contribute in large part to the delay in transitioning model capabilities from research and development to operations.

1/32° real-time global ocean prediction and value-added over 1/16° resolution

A 1/32° global ocean nowcast/forecast system has been developed by the Naval Research Laboratory at the Stennis Space Center. It started running at the Naval Oceanographic Office in near real-time on 1 Nov. 2003 and has been running daily in real-time since 1 Mar. 2005. It became an operational system on 6 March 2006, replacing the existing 1/16° system which ceased operation on 12 March 2006. Both systems use the NRL Layered Ocean Model (NLOM) with assimilation of sea surface height from satellite altimeters and sea surface temperature from multi-channel satellite infrared radiometers. Real-time and archived results are available online at http://www.ocean.nrlssc.navy.mil/global_nlom. The 1/32° system has improvements over the earlier system that can be grouped into two categories: (1) better resolution and representation of dynamical processes and (2) design modifications. The design modifications are the result of accrued knowledge since the development of the earlier 1/16° system. The improved horizontal resolution of the 1/32° system has significant dynamical benefits which increase the ability of the model to accurately nowcast and skillfully forecast. At the finer resolution, current pathways and their transports become more accurate, the sea surface height (SSH) variability increases and becomes more realistic and even the global ocean circulation experiences some changes (including inter-basin exchange). These improvements make the 1/32° system a better dynamical interpolator of assimilated satellite altimeter track data, using a one-day model forecast as the first guess. The result is quantitatively more accurate nowcasts, as is illustrated by several model-data comparisons. Based on comparisons with ocean color imagery in the northwestern Arabian Sea and the Gulf of Oman, the 1/32° system has even demonstrated the ability to map small eddies, 25–75 km in diameter, with 70% reliability and a median eddy center location error of 22.5 km, a surprising and unanticipated result from assimilation of altimeter track data. For all of the eddies (50% small eddies), the reliability was 80% and the median eddy center location error was 29 km. The 1/32° system also exhibits improved forecast skill in relation to the 1/16° system. This is due to ( a) a more accurate initial condition for the forecast and ( b) better resolution and representation of critical dynamical processes (such as upper ocean – topographic coupling via mesoscale flow instabilities) which allow the model to more accurately evolve these features in time while running in forecast mode (forecast atmospheric forcing for the first 5 days, then gradually reverting toward climatology for the remainder of the 30-day forecast period). At 1/32° resolution, forecast SSH generally compares better with unassimilated observations and the anomaly correlation of the forecast SSH exceeds that from persistence by a larger amount than found in the 1/16° system.

A Variable Buoyancy Control System for a Large AUV

A large autonomous undersea vehicle (AUV), the Seahorse, has been designed, constructed, and tested by the Applied Research Laboratory at Pennsylvania State University (ARL/PSU, University Park, PA) for the U.S. Naval Oceanographic Office (NAVOCEANO, Stennis Space Center, MS). The vehicle is required to launch in shallow water (<10 m) and to hover without propulsion. Additionally, due to the very large size of the vehicle, low operating speeds and very long missions, small changes in vehicle trim resulting from battery replacement, sensor exchanges, and water temperature variations can result in significant drag-induced energy penalties over the duration of a mission. It is, therefore, important to continually maintain the AUV in fore-aft trim over the course of the mission. The vehicle is equipped with a two tank variable buoyancy system (VBS) to meet these requirements. The resulting control problem is one where the control variable, pump rate, is proportional to the third derivative of the sensed variable, depth; there are significant delays, and forces are nonlinear (including discontinuous) and highly uncertain. This paper describes the design of the VBS and the control software operating in two modes: depth control mode and trim control mode. In-water test data and simulation results are presented to illustrate the performance of the VBS controller. The benefits of the presented approach lie in the intuitiveness and simplicity of the design and the robustness as evidenced by the performance in both fresh and salt water. This paper provides practical insight into the operation of a VBS with an AUV and discusses actual operational experience. To our knowledge, no previous work considers the significance of an observed surface capture phenomenon to the design of a VBS control system, especially in very shallow water.

The contourite depositional system of the Gulf of Cádiz: A sedimentary model related to the bottom current activity of the Mediterranean outflow water and its interaction with the continental margin

The present paper is mostly a synthesis of work conducted on the continental margin of the Gulf of Cadiz using a broad database collected by several cruises and projects supported by the Spanish Research Council and the NRL and Naval Oceanographic Office (USA), including: bathymetry, sidescan sonar imagery, seismic profiles, sediment cores, submarine photographs and physical oceanographic data. These data have enabled us to establish a detailed understanding of the morphologic development of the margin, its Pliocene and Quaternary stratigraphy, and a full characterization of the contourite depositional system (CDS) generated by the Mediterranean outflow water (MOW). The northern margin of the Gulf of Cadiz shows the following distinct features: (a) an active compressive framework where the “Cadiz Allocthonous Unit” provides an unstable substratum for Late Miocene, Pliocene and Quaternary sedimentation; (b) a relative lack of submarine canyons, except in the western area of the Algarve margin; (c) a very broad continental slope that lacks a marked continental rise; (d) a middle slope dominated by along-slope processes driven by the MOW, which has generated a complex CDS during the Pliocene and Quaternary; and (e) an irregular lower slope and abyssal plain region dominated by down-slope processes that is partly detached from an upper slope source region. The CDS is composed of both depositional and erosive features. The main depositional features are characterised by sedimentary wave fields, sedimentary lobes, mixed drifts, plastered drifts, elongated mounded, and separated drifts and sheeted drifts. The main erosive features are contourite channels, furrows, marginal valleys and moats. These various depositional and erosive features have a specific location along the margin, and their detailed distribution is essential to understand the present (and past) interaction of the MOW with the middle slope. Based on this distribution, five morphosedimentary sectors have been identified within the CDS, which from east to west are: (1) proximal scour and sand ribbons; (2) overflow sedimentary lobe; (3) channels and ridges; (4) active contourite drifts; and (5) submarine canyons. The development of the CDS has been controlled in general by the Pliocene and Quaternary environmental and paleoceanographic changes and by the morphology of the margin, but in detail the development of each of these sectors is related to systematic deceleration of the MOW as it flows westwards, to the interaction with the margin bathymetry, and to the effects of Coriolis force. Our comprehensive sedimentary model for the CDS defines the Gulf of Cadiz margin as a mixed contourite-turbidite system with a detached combined drift-fan morphology. This is different from many other contourite influenced margins, where the contourite processes are dominant on the middle slope, and separated from the down-slope processes, which are characteristic on the lower slope and abyssal plains.

Airborne Lidar and Integrated Technologies for Coastal Mapping and Nautical Charting

The state-of-the-art in airborne coastal mapping and charting technology is the Compact Hydrographic Airborne Rapid Total Survey (CHARTS) system. CHARTS is the U.S. Naval Oceanographic Office program name for an Optech, Inc. SHOALS 3000T20-E. CHARTS comprises a 3 kHz bathymetric lidar, a 20 kHz topographic lidar, a DuncanTech DT4000 high-resolution digital camera, and a Compact Airborne Spectrographic Imager(CASI)-1500. The integrated sensor suite has the capability to collect lidar bathymetry, lidar topography, RGB imagery, and hyperspectral imagery. Beyond these products, the diffuse attenuation coefficient and seafloor reflectance at multiple wavelengths may be estimated by combining information from the bathymetric lidar waveform and the hyperspectral imagery.The Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) specified development of the CHARTS system and currently manages its operations for Department of Defense customers. CHARTS data collection rate of 21 square nautical miles per survey hour enables rapid completion of large nautical charting work for the U.S. Naval Oceanographic Office. The U.S. Army Corps of Engineers National Coastal Mapping Program uses CHARTS to collect engineering scale data for the entire U.S. coastline. JALBTCX continues to lead development in the field of airborne lidar and integrated technologies for coastal mapping and charting. Future research efforts include mining the individual data sets collected by CHARTS for information beyond elevation, combining data sets to further identify physical and environmental characteristics of the coastal zone, and integrating additional complementary sensors with CHARTS.

Sea Surface Height Predictions from the Global Navy Coastal Ocean Model during 1998–2001*

Abstract A ⅛° global version of the Navy Coastal Ocean Model (NCOM), operational at the Naval Oceanographic Office (NAVOCEANO), is used for prediction of sea surface height (SSH) on daily and monthly time scales during 1998–2001. Model simulations that use 3-hourly wind and thermal forcing obtained from the Navy Operational Global Atmospheric Prediction System (NOGAPS) are performed with/without data assimilation to examine indirect/direct effects of atmospheric forcing in predicting SSH. Model–data evaluations are performed using the extensive database of daily averaged SSH values from tide gauges in the Atlantic, Pacific, and Indian Oceans obtained from the Joint Archive for Sea Level (JASL) center during 1998–2001. Model–data comparisons are based on observations from 282 tide gauge locations. An inverse barometer correction was applied to SSH time series from tide gauges for model–data comparisons, and a sensitivity study is undertaken to assess the impact of the inverse barometer correction on the SSH validation. A set of statistical metrics that includes conditional bias (Bcond), root-mean-square (rms) difference, correlation coefficient (R), and nondimensional skill score (SS) is used to evaluate the model performance. It is shown that global NCOM has skill in representing SSH even in a free-running simulation, with general improvement when SSH from satellite altimetry and sea surface temperature (SST) from satellite IR are assimilated via synthetic temperature and salinity profiles derived from climatological correlations. When the model was run from 1998 to 2001 with NOGAPS forcing, daily model SSH comparisons from 612 yearlong daily tide gauge time series gave a median rms difference of 5.98 cm (5.77 cm), an R value of 0.72 (0.76), and an SS value of 0.45 (0.51) for the ⅛° free-running (assimilative) NCOM. Similarly, error statistics based on the 30-day running averages of SSH time series for 591 yearlong daily tide gauge time series over the time frame 1998–2001 give a median rms difference of 3.63 cm (3.36 cm), an R value of 0.83 (0.85), and an SS value of 0.60 (0.64) for the ⅛° free-running (assimilated) NCOM. Model– data comparisons show that skill in 30-day running average SSH time series is as much as 30% higher than skill for daily SSH. Finally, SSH predictions from the free-running and assimilative ⅛° NCOM simulations are validated against sea level data from the tide gauges in two different ways: 1) using original detided sea level time series from tide gauges and 2) using the detided data with an inverse barometer correction derived using daily mean sea level pressure extracted from NOGAPS at each location. Based on comparisons with 612 yearlong daily tide gauge time series during 1998–2001, the inverse barometer correction lowered the median rms difference by about 1 cm (15%–20%). Results presented in this paper reveal that NCOM is able to predict SSH with reasonable accuracies, as evidenced by model simulations performed during 1998–2001. In an extension of the validation over broader ocean regions, the authors find good agreement in amplitude and distribution of SSH variability between NCOM and other operational model products.

Geophysicists Honored by AGU

The American Geophysical Union has announced the winners of its medals and awards for 2003.The William Bowie Medal, AGU’s most prestigious prize, goes this year to Donald L. Turcotte, professor of geology at the University of California, Davis. He was honored for his “outstanding contributions in many areas of geophysics and his unselfish cooperation,” according to the award citation. Gerard C. Bond, Doherty Senior Scholar at the Lamont-Doherty Earth Observatory of Columbia University, received the Maurice Ewing Medal for his “fundamental contributions to the understanding of tectonophysics, climate, and sea-level changes.”The John Adam Fleming medalist, Christopher T. Russell, was recognized for his “numerous original and significant contributions to a broad range of space sciences.” Russell is a professor of geophysics and space physics in the department of Earth and space sciences and the Institute of Geophysics and Planetary Physics at UCLA.The Harry H. Hess Medal recipient is David L. Kohlstedt, professor of geology and geophysics at the University of Minnesota, Twin Cities. Kohlstedt was honored for his “fundamental contributions to understanding the Earth’s upper mantle rheology.” Shlomo P. Neuman received the Robert E. Horton Medal for his “theoretical and applied concepts leading to major advances in conceptual understanding of groundwater flow and transport processes.” Neuman is the Regents’ Professor in the department of hydrology and water resources at the University of Arizona, Tucson. Francis A. Dahlen Jr, chair of the geosciences department at Princeton University, is the recipient of the Inge Lehmann Medal for his “fundamental theoretical advances laying the foundations of modern global seismology.” Kurt M. Cuffey, Guido Salvucci, and Lianxing Wen each earned a James B. Macelwane Medal, given to recognize significant contributions to the geophysical sciences by outstanding young scientists. Cuffey is a professor of geography at the University of California, Berkeley, Salvucci is a professor with joint appointments in the Earth sciences and geography departments at Boston University and Wen is an assistant professor of geophysics at SUNY, Stony Brook. Jean Jouzel, director of the Institut Pierre-Simon Laplace in Paris, collected the Roger Revelle Medal for his “pioneering and fundamental work in the field of geochemistry as applied to glaciology and climatology.”“His unselfish efforts to provide unclassified information to scientists in efforts to create new knowledge” garnered the Edward A. Flinn III Award for Robert H. Higgs, retired director of the geophysics department at the Naval Oceanographic Office in Stennis Space Center, Mississippi.The Excellence in Geophysical Education Award was granted to Jacob Bear for his “outstanding support for both undergraduate and graduate education in hydrogeology through seminal textbooks” and for his “impact on many young professionals worldwide.” Bear is a professor emeritus in the department of civil and environmental engineering at the Technion-Israel Institute of Technology in Haifa, Israel.© 2003 American Institute of Physics.

Physical oceanography and acoustic propagation during LADC experiment in the Gulf of Mexico in 2001

The Littoral Acoustic Demonstration Center (LADC) deployed three environmental and acoustic moorings in a downslope line just off the Mississippi River Delta in the northern Gulf of Mexico in an area of a large concentration of sperm whales in July 2001. The measurement of whale vocalizations and, more generally, ambient noise, were the objectives of the experiment. Each mooring had a single hydrophone autonomously recording Environmental Acoustic Recording System (EARS) obtained from the U.S. Naval Oceanographic Office and modified to recorded signals up to 5859 Hz continuously for 36 days. Also, self-recording, environmental sensors were attached to the moorings to obtain profiles of time series data of temperature and salinity. Satellite imagery and NOAA mooring data were gathered for an analysis of eddy formations and movement in the Gulf. This paper will discuss the possible environmental impact of two events that occurred during the experiment: the passage of Tropical Storm Barry and the movement of the remnants of an eddy in the area. Discussed also will be the expected effects of these events on acoustic propagation based on modeling, which are carried out for long range and low frequency (300 km and 500 Hz) using the normal-mode acoustic model SWAMP (Shallow Water Acoustic Modal Propagation by M. F. Werby and N. A. Sidorovskaia) and for short range and high frequency (10 km and 5000 Hz) using the parabolic-equation acoustic model RAM (Range-dependent Acoustic model by M. Collins). [Work supported by ONR.]