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The National Oceanic and Atmospheric Administration (NOAA) National Ocean Service Center for Operational Oceanographic Products and Services (CO-OPS) manages the National Current Observation Program (NCOP) and Physical Oceanographic Real-Time Systems (PORTS®). These programs provide tide and current predictions, as well as real-time current and meteorological information. Outdated current predictions, navigational support requirements, and incident response scenarios (e.g., oil spills, vessel accidents) have highlighted CO-OPS' need for a rapidly deployable system that provides near-surface current and meteorological observations. To address this, CO-OPS designed, developed, and tested a real-time system based on a surface buoy platform, hereinafter referred as CURrents BuoY (CURBY). This paper provides an overview of the system design, field test results, operational applications, and future plans.In 2018, CO-OPS completed the build, integration, and testing of the first prototype CURBY. A successful field test was completed during 2018 in the Chesapeake Bay, and the first operational deployment followed shortly on the Delaware River in 2019. Resulting measurements were used to improve tidal current predictions and to plan for a 2021 regional survey. Initial success with tidal current survey operations led to design enhancement and wider use. During 2020‐2021, CO-OPS partnered with the NOAA Office of Response and Restoration to build two new CURBYs to support emergency response applications in the Gulf of Mexico region. During 2022, two CURBY systems were deployed in the Columbia River, Oregon, to support additional NCOP operations. Future plans include establishing a long-term CURBY system for Kings Bay, Georgia, PORTS®.

The oceans play a key role in global issues such as climate change, food security, and human health. Given their vast dimensions and internal complexity, efficient monitoring and predicting of the planet’s ocean must be a collaborative effort of both regional and global scale. A first and foremost requirement for such collaborative ocean observing is the need to follow well-defined and reproducible methods across activities: from strategies for structuring observing systems, sensor deployment and usage, and the generation of data and information products, to ethical and governance aspects when executing ocean observing. To meet the urgent, planet-wide challenges we face, methods across all aspects of ocean observing should be broadly adopted by the ocean community and, where appropriate, should evolve into “Ocean Best Practices.” While many groups have created best practices, they are scattered across the Web or buried in local repositories and many have yet to be digitized. To reduce this fragmentation, we introduce a new open access, permanent, digital repository of best practices documentation (oceanbestpractices.org) that is part of the Ocean Best Practices System (OBPS). The new OBPS provides an opportunity space for the centralized and coordinated improvement of ocean observing methods. The OBPS repository employs user-friendly software to significantly improve discovery and access to methods. The software includes advanced semantic technologies for search capabilities to enhance repository operations. In addition to the repository, the OBPS also includes a peer reviewed journal research topic, a forum for community discussion and a training activity for use of best practices. Together, these components serve to realize a core objective of the OBPS, which is to enable the ocean community to create superior methods for every activity in ocean observing from research to operations to applications that are agreed upon and broadly adopted across communities. Using selected ocean observing examples, we show how the OBPS supports this objective. This paper lays out a future vision of ocean best practices and how OBPS will contribute to improving ocean observing in the decade to come.

The National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) and the Coastal Studies Institute (CSI) recently partnered to complete a successful 401 day field trial of a new subsurface ADCP buoy. The mooring system tested was new to CO-OPS, developed in response to several emerging current survey applications that require 6 to 12 months of current profile measurements in the topmost 30–50 m of a water column with depths ranging from 200-300m. Near surface current speeds at sites of interest reach 2–3 m/s. CSI has similar interest in measuring current profiles in the topmost, 50 m of the water column within the Gulf Stream, an area where currents may not be captured by bottom mounted ADCPs nor HF radar measurements. The mooring developed consists of commercial-off-the shelf (COTS) components. The topmost component is an ellipsoid, syntactic foam buoy, which houses an upward looking 300 kHz acoustic Doppler current profiler (ADCP). The ellipsoid buoy has lower drag than a spherical shaped buoy and significantly higher buoyancy than many COTS available streamlined buoys, allowing the ADCP to be positioned within the top 50 m of the water column when moored with adequate line length. CO-OPS and CSI completed a long-term field demonstration of the system off the coast of North Carolina near the Gulf Stream in approximately 325 m of water, from May 2017 - June 2018. The system was successfully recovered following a 401 day deployment. An overview of the mooring system and preliminary field results were presented in a 2018 conference proceedings paper, shorty after the field test conclusion (MTS/IEEE OCEANS18, Charleston). This second conference paper presents additional data and further analysis, including model results to help interpret observed buoy depth excursions. Plans for continuing work guided by initial field test results will also be discussed.

The United States National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) is responsible for maintenance and continued development of the National Water Level Observing Network (NWLON). NWLON consists of over 200 long-term stations that provide real-time water level observations throughout all U.S. coastal regions, including Atlantic, Pacific, and Arctic Ocean coasts, Gulf of Mexico, the Great Lakes, and Pacific and Caribbean island territories. One major challenge of maintaining and evolving NWLON is providing optimal spatial coverage to adequately resolve all water level processes of interest to a broad user group. Coastlines of the U.S. and its island territories cover a vast range of environment types resulting in many site specific NWLON system design and installation challenges. Meeting regional coverage needs involves establishing and maintaining a number of long-term stations where environmental conditions present significant challenges to delivery of high quality data and long-term station survivability. This paper provides an overview of CO-OPS existing long-term water level stations located in challenging environment types along with examples of latest measurement system research and development efforts to address future network expansion.

Currently the NOAA Center for Operational Oceanographic Products and Services (CO-OPS) is transitioning the primary water level sensor at most NWLON stations from an acoustic ranging system to microwave radar altimeters. The use of the microwave radars presents the potential to provide real-time wave information at NWLON sites in support of navigational safety and ocean research applications. Radar sensors at tide stations may offer a low cost, convenient way to increase nearshore wave observational coverage throughout the U.S. In a previous study, we examined the performance from a pulse microwave radar and continuous wave frequency modulated (CWFM) radars [1]. While both types of radars tracked significant wave height well, the pulse radar had less success resolving high frequency wind wave energy and aliased low frequency energy. The CWFM radars were more successful, though more costly in both expenses and power. Here we present the results of a continuation of that field study, focusing on the comparison of wave height measurements from two pulse microwave radar water level sensors, the WaterLOG H3611 and the Endress and Hauser Micropilot FMR240. A nearby bottom acoustic wave and current sensor (AWAC) is used as a reference. Significant wave height measurements from both radar water level sensors compared well to reference AWAC measurements over the test period, however the WaterLOG radar does not adequately resolve wind wave energy in high frequency bands (0.1 Hz and above) and aliases energy towards the low frequency end of the spectrum. WaterLOG radar limitations are most apparent during times of high winds and locally developing seas. The E+H radar demonstrates greater capability to resolve those higher frequency energies while avoiding the low frequency aliasing issue observed in the WaterLOG. An overview of field setup and sensors will be presented, along with an analysis of performance capabilities of each radar sensor.

A sea surface following buoy equipped with a wave sensor and acoustic Doppler current profiler (ADCP) may be a useful system design option for many different coastal ocean measurement applications. However, previous work has shown that surface buoy-mounted ADCP current profile data can be negatively impacted by buoy motion in dynamic coastal environments. Between 2014 and 2018, a series of three field experiments were conducted at a site in the south Chesapeake Bay to evaluate the performance of acoustic Doppler current profilers installed on small, dynamic surface buoy platforms (< 2 m). The focus of this paper is on results from the third, most recent field experiment conducted during December 2017 – January 2018. This third experiment evaluates potential improvements offered by a new Acoustic Doppler Current Profiler (ADCP) with an integrated Attitude and Heading Reference Sensor (AHRS) and a real-time motion compensation capability. The improved ADCP with ARHS was installed on a small surface buoy in a downward looking configuration. The test buoy system was deployed at the Chesapeake Bay field site alongside a second, nearby ADCP system in a bottom mount serving as a stable reference. Results comparing current profile measurements from buoy and bottom mount sensors indicate significant improvement in the buoy mounted ADCPs performance as compared to the previous two field tests. A summary of the new ADCP instrument employed, measurement methods, field observations, and initial performance evaluation will be presented, along with plans for continuing system development and testing.

The U.S. Integrated Ocean Observing System (IOOS) Quality Assurance / Quality Control of Oceanographic Data (QARTOD) project has produced a series of real-time quality control manuals for specific core variables and other variables of interest to the oceanographic community. Not all core variables warrant a QARTOD manual. We consider each remaining variable for which a QARTOD manual has not been produced and discuss the potential for development of a manual in the near term.QARTOD QC tests are presently being implemented by IOOS Regional Associations. We review the challenges anticipated and encountered in this process and provide an example of a successful effort. Manuals are updated to ensure they remain accurate and relevant; feedback following implementation is a key component of the update process.QARTOD manuals are used internationally, and we will continue to expand our global collaborative efforts. These include a review of the Global Ocean Observing System essential ocean variables to consider further candidates for a QC manual, and partnerships supportive of QC, QA, measurement uncertainty, and best practices. QARTOD manuals are also used by universities to train the individuals who will implement the next generation of advanced QC tests.

The present work focuses on improving motion compensation in current profile data from surface buoys by integration of an Attitude and Heading Reference Sensor (AHRS) to a state-of-the-art Acoustic Doppler Current Profiler (ADCP), thus expanding its use into applications where fine spatial and temporal resolutions are desired. Presently, the applicability of surface buoy-mounted ADCPs is generally limited to those applications where spatial and temporal averaging are acceptable methods to address motion concerns. However, the increasing demand from both the research and operational communities for ever finer resolution in space and time is rendering averaging as an unacceptable method for these type of deployments. But recent technological advances in miniature motion sensors (improved accuracy and resolution, and reduction in physical size, power consumption, and cost) promises to address some of the earlier concerns with surface buoy-mounted ADCPs by enabling realtime bin mapping at the individual ping level. Additionally, these advances allow for more precise validation of surface buoy-mounted ADCP data against static-mounted reference systems.

The critical need for real-time coastal oceanographic and meteorological measurements to support maritime forecasters, emergency managers, pilots, vessel operators, port authorities, coastal planners, and many other decision makers has rapidly grown, along with the variety of scientific research applications that rely on resulting long-term data records. To support the needs for such observations, the National Ocean Service Center for Operational Oceanographic Products and Services (CO-OPS) continues to maintain and develop the National Water Level Observation Network (NWLON) and Physical Oceanographic Real-Time Systems (PORTS®). Together, these networks consist of over 300 long-term, real-time observatories distributed across the nation's coasts.In situdata measured and disseminated in real time from NWLON and PORTS stations include water levels, ocean currents, waves, water temperature, conductivity, bridge clearance, visibility, and several meteorological parameters. CO-OPS invests heavily in analysis of emerging technologies to identify potential improvements in data quality and operating efficiency and to ensure that the evolving needs of its diverse user community are continuously met. Recent enhancements to the CO-OPS network include the transition to microwave radar water level sensors to increase accuracy and simplify installation and maintenance requirements; development and testing of nearshore wave measurement systems; development of standalone, bottom-mounted water level gauges for applications in remote Arctic areas; and expanding data communication capabilities to improve usage of the National Oceanic and Atmospheric Administration (NOAA) Geostationary Operational Environmental Satellites and to broaden use of the Iridium satellite system. An overview of the latest design features of typical CO-OPS real-time stations is presented, along with highlights of recent system developments and enhancements.

The National Oceanic and Atmospheric Administration (NOAA) is transitioning the primary water level sensor at the majority of tide stations in the National Water Level Observation Network (NWLON) from an acoustic ranging system to a microwave radar system. Field comparison of the acoustic and microwave systems finds statistically equivalent performance when temperature gradients between the acoustic sensor and water surface are small and when significant wave height is less than roughly 0.5 m. When significant wave height is greater than approximately 0.5–1 m, the acoustic system consistently reports lower water levels. An analysis of 2 months of acoustic and microwave water level data at Duck, North Carolina, finds that the majority of differences between the two sensors can be attributed to systemic errors in the acoustic system and that the microwave system captures water level variability with higher fidelity than the acoustic system. NWLON real-time data products include the water level standard deviation, a statistic that can serve as a proxy for significant wave height. This study identifies 29 coastal water level stations that are candidates for monitoring wave height based on water level standard deviation, potentially adding a significant source of data for the sparsely sampled coastal wave fields around the United States, and finds that the microwave sensor is better suited than the acoustic system for wave height estimates.

Current profiles collected using a Nortek Aquadopp profiler mounted in an AXYS Technologies TRIAXYS wave buoy are compared to coincident measurements from nearby bottom-mounted instruments. A 2014 experiment conducted in the Chesapeake Bay with 0 – 3 m waves and 0 – 1 m/s currents suggested that observed discrepancies of 200–400 mm/sec could be due to inadequate resolution of rapid buoy movements and subsequent improper transformation of acoustic Doppler beam data to geographic coordinates. A second, similar experiment was run in 2015–2015 with 4 Hz attitude/acceleration data provided in real time, and high frequency data logged for post-processing and analysis. Mean errors were reduced to ∼50 mm/sec, but showed a bias towards overestimating southward velocity. This bias was proportional to vertical shear and increased with depth; several possible explanations were detailed and discarded. While the substantial improvement in performance is notable and the implemented acceleration measurement improvementsshould be made operational, there is research remaining to understand the observed behavior.

The United States Boy Scouts of America (BSA) programs are designed to cover a range of different youth development activities. Central to the BSA program is the merit badge system. Merit badges provide an opportunity for scouts to learn about a specific topic, which may be focused on a hobby, physical activity, or prospective career field. There are more than 120 different merit badges that any Scout may earn, each with its own set of requirements. BSA introduced an oceanography merit badge in 1964. Very recently, a significant increase in demand for this particular merit badge throughout the Hampton Roads region of southeast Virginia was noticed by members of the National Oceanic and Atmospheric Administration's (NOAA) National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) Atlantic field office in Chesapeake, Virginia. CO-OPS also noted a limited number of opportunities to earn the badge, with some local events being booked beyond several years. In a pursuit to assist with the growing regional demand, a group of scientists, engineers, and marine technicians at the CO-OPS office in Chesapeake gathered to review merit badge requirements and then consulted with several contacts at Old Dominion University (ODU) that has recently been holding several different annual BSA merit badge events, including oceanography. The CO-OPS team designed a one day program that could be held at the Chesapeake field office and could meet all BSA badge requirements. The CO-OPS Chesapeake office is home to over 40 professionals in various fields of ocean science and marine technology and the facility houses a significant amount of oceanographic sensors, instrumentation, and a number of laboratory facilities. The first CO-OPS oceanography merit badge event was conducted during August 2011. Since, it has continued to be held on an annual basis, with five successful events completed to date. All five annual events reached the maximum registration limit of fifty scouts. An overview of the event program that CO-OPS has designed and continued to develop over the past 5 years will be presented along with examples of how interactive exhibits at the field office facility have been used to address BSA oceanography merit badge requirements.

The United States National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) is responsible for developing and maintaining the National Water Level Observation Network (NWLON) which consists of over 200 long term observatories throughout all U.S. coasts. CO-OPS continually pursues efforts to identify potential improvements to its observatory network. Many recent studies on global climate change have identified a significant increase in Arctic warming rates. Resulting trends of increased sea ice loss have led to Arctic waterways becoming more accessible during summer seasons. As a result, an increase in maritime transport throughout the region is anticipated for the near future. Presently, Artic waters within the U.S. Exclusive Economic Zone (EEZ) have very few navigational support products and services. NOAA, recognizing the changing conditions, anticipates a growing, critical need for real-time oceanographic and meteorological observations across the region. In support of long term modernization plans, CO-OPS has been working on the design, development, and testing of a standalone, real-time water level measurement system for use in remote Arctic coastal regions with very limited infrastructure. Two types of system designs have been identified, for short and long term applications. Both design types include a bottom mounted pressure gauge for the primary source of water level measurements. The long-term system design involves a cable run from an offshore bottom mounted pressure gauge to a small, shore station. The short term system design includes a surface buoy with satellite telemetry and acoustic modem; and a bottom unit consisting of a conductivity, temperature, pressure sensor and acoustic modem. The buoy based system is intended for real-time communications during ice-free periods. Details of the short-term version system design will be presented along with results from a recent field trial conducted in the lower Chesapeake Bay region near Virginia Beach, Virginia during 2014–2015. Plans for continuing system development and test will be discussed.

The National Oceanic and Atmospheric Administration’s (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) currently maintains twenty-two operational Physical Oceanographic Real- Time System (PORTS®) observatories throughout the United States’ coastal regions. Ocean current observations are among the multiple PORTS® data products that provide critical support for safe navigation and a variety of scientific and engineering applications. To ensure that its observing network provides the most accurate and up-to-date products available, CO-OPS routinely conducts test and evaluation of newly available oceanographic sensors and measurement systems. From October 10 – December 3, 2014, CO-OPS conducted a field test in the South Chesapeake Bay which included three acoustic current profiling and wave sensors deployed in bottom mounted, upward looking configuration 1) the TRDI 500 kHz Sentinel V, 2) the Nortek 600 kHz AWAC-AST, and 3) the Nortek 500 kHz Signature 500 AD2CP; and an AXYS Technologies TriAXYSTM Next Wave II Directional Wave Buoy with Currents provided with an integrated Nortek 600 kHz Aquadopp acoustic sensor. Also included in the deployment was a bottom mounted TRDI 600 kHz Workhorse Sentinel acoustic current profiling sensor. The test site was near the mouth of the bay where currents are predominantly tidal and the average water depth is approximately 15 meters (50 feet). During the test, currents at the site ranged in magnitude from approximately 0-0.75 m/s on a daily basis and reached as high as 1.2 m/s (2.3 knots) on one occasion. Three high-wind storm events passed through the region and significant wave heights exceeded 2 m on multiple occasions. Data results presented in this paper focus on comparison of wave measurements collected by the TriAXYSTM Next Wave II Directional Wave Buoy with Currents and the bottom-mounted TRDI 500 kHz Sentinel V. Currents measured by both devices are presented in [1]. Both instruments were deployed on 10 October, 2015; the Sentinel V operated until 2 November before ceasing data collection, possibly due to a faulty memory card. The TriAXYS buoy operated until recovery on 5 December 2015, transmitting wave data hourly and current data every 6 minutes via satellite in real time. Significant (Maximum) wave heights ranged from 0.15 (0.2) m to 2.5 (4.0) m and 5-7 second periods during the deployment, with the largest waves from the Northern quadrant, associated with strong northerly winds following cold front passages. In comparing bulk wave parameters, the two instruments agreed well on Maximum and Significant wave heigh and Peak period; in other measures of wave period (TMEAN and TZ), the Sentinel V showed a slight bias towards longer periods. Mean Wave Direction agreed well, to within 1 degree in the mean. Non-directional wave spectra were compared – the Sentinel V estimated these using two methods, Sea Surface Height and Velocity. The two were highly consistent and agreed well with the TriAXYS spectra, in spite of differences in methodology and frequency resolution. A notable feature of the non-directional spectra was the appearance of relative maxima of lower frequency waves (around 10 seconds) regularly appearing in the records of both instruments. Directional spectra also agreed quite well, and showed that the low frequency waves were primarily from the south, even in the presence of northerly winds, and likely from the open ocean 20 miles south at the mouth of the Chesapeake Bay. Of 12 identified QARTOD tests, 6 were applied. In general very few data points failed any of those tests; they did prove instructive on monitoring real-time data quality. The limited amount of time between instrument recovery and publication submission, combined with the significant processing required in analysis of these data sets, has resulted in limited analysis to this point. There are further data, in particular from the 5-beam Sentinel V, that need to be evaluated; there are features and inconsistencies in the data that need to be explored; we expect these will support significant further analysis and reporting.

The National Oceanic and Atmospheric Administration's (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) currently maintains twenty operational Physical Oceanographic Real-Time System (PORTS®) observatories throughout United States coastal regions. To expand its measurement capabilities, CO-OPS recently developed and tested a real-time wave measurement system featuring a Nortek 1-MHz Acoustic Waves and Current Profiler (AWAC). The test system consisted of a bottom platform assembly and a surface communications buoy. The bottom assembly contained the AWAC, a LinkQuest omnidirectional acoustic bottom modem, batteries, and a Benthos acoustic release with tethered pop-up float. The surface buoy supported a LinkQuest acoustic surface modem, an Iridium communication system, solar cells, battery, GPS receiver, and temperature and voltage sensors. A 35-day field test of this real-time wave system was conducted from June 16 through July 20, 2011, in shallow water (19 m) Atlantic Ocean region approximately 10 nautical miles off of the coast of Virginia. The site was in close proximity (approximately 190 m) to a Datawell Waverider buoy that is maintained by the Scripps Institute of Oceanography Coastal Data Information Program (CDIP). During the field test, bulk wave parameters, including significant wave height and average wave period, were transmitted real-time every 30 minutes. Raw data recorded internally on the AWAC included ‘burst’ samples of 2048, 2-Hz values, collected every half hour. After the AWAC was recovered at the end of the field test, raw data were downloaded and used to calculate half hourly power spectra, both non-directional and directional. The resulting field test data were used to compare measurements from the AWAC and Datawell Waverider. A description of the real-time AWAC waves system and field test performance is presented, along with a comparison of AWAC versus Datawell buoy measurements for both half hourly wave bulk parameters and frequency spectra.

In the spring of 2012, NOAA's Center for Operational Oceanographic Products and Services (CO-OPS), in partnership with the Mobile County Commission, established the first of it's kind Mobile Bay Storm Surge Monitoring Network (MBSSMN). The combination of Mobile Bay's long and narrow coastline boundaries, unique bathymetry, mouth opening to the Gulf of Mexico, and extensive tributary network results in a complex hydrodynamic system where water levels can vary significantly in space and time depending on the combined forcing from tides, winds, and pressure that may occur. The task of establishing a storm surge monitoring network involved installation of five new hurricane-hardened water level stations strategically located throughout coastal Mobile County. With permission from the Alabama State Port Authority, this project's data is combined with the data provided by multiple stations in CO-OPS' existing Mobile Physical Oceanographic Real Time System (PORTS)®. This provides stakeholders with a unique offering of spatially densified water level, meteorological, and tidal current data available on the Mobile PORTS® web page. Mobile County now has a total of eight real time water level observatories to provide full data coverage of its coastline from the Mississippi State line to Chickasaw in the Mobile River Delta at the north end of the county. MBSSMN is also the first local storm surge network in the country to have five of its monitoring stations elevated to Category Five modeled storm surge heights, ensuring the collection of data when it is needed most critically. The network will provide data and products that are critical for coastal resource management across the region on an ongoing basis, but most importantly supporting emergency management decisions before and during the passage of the most severe episodic storm events. Due to challenging station requirements and limited infrastructure in key locations, CO-OPS opted to employ remote radar range sensors to measure water level. Utilization of radar gauges for this purpose provided many operational advantages. After several years of testing, this radar sensor is being used operationally for the first time by CO-OPS, with excellent results after its first year of data collection. The first three MBSSMN stations were installed atop state highway bridges in southern Mobile County. This setup was possible due to the radar water level sensor's ability to measure the sea surface remotely from above, with no components in contact with the water column. Installation of the first three stations was completed in July 2011 and the first storm surge event to be captured was during the passage of Tropical Storm Lee in September 2011. The final two stations are elevated four pile structures that were constructed to raise the instrumentation above the maximum modeled Category Five hurricane storm surge height (22–25 feet above NAVD88). This paper will summarize the unique project requirements, committed stakeholder support, inventive problem resolution, and superb data quality that identify the MBSSMN as a template for future collaborative efforts of this type. A summary overview of the water level station designs will be presented along with observations collected during the passage of Tropical Storm Lee and other high wind surge events. Sample water level data that have been collected across the five network stations during storm events provide examples of temporal and spatial variability of a surge event in Mobile Bay.

The United States National Oceanic and Atmospheric Administration (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) is responsible for developing and maintaining the National Water Level Observation Network (NWLON), which consists of over 200 long-term observatories located across U.S. coasts, including the Great Lakes and U. S. island territories. CO-OPS continues to analyze state-of-the-art and emerging technologies to identify potential improvements in data quality and operating efficiency and to maintain core expertise for authorized missions. The international ocean observing community has recognized that microwave radar range sensors offer many potential benefits for long-term sea level monitoring. The most notable advantage of such sensors is the ability to measure water level remotely and from above the sea surface. Over the past 3.5 years, CO-OPS has conducted a series of extensive laboratory and long-term field tests with several different microwave radar range sensors to determine their suitability for use as water level sensors in NWLON and other CO-OPS measurements systems. Intermediate results from CO-OPS' extensive test efforts have been previously reported at various conferences and through several reports over the last three years. This paper provides a summary update on field test analysis conducted to date and reports a significant milestone to which most recent results have led: CO-OPS has recommended limited acceptance of radar water level sensors for use in its network of coastal observatories, and a transition of the new technology to operational applications is currently underway. In addition to a summary of most recent field test results, highlights from CO-OPS' plan to transition the microwave radar water level sensors to its network of operational coastal observatories will be presented, along with progress on initial operational installations. A summary of continued field testing to better understand microwave radar sensor performance capability and limitations in open ocean, large wave environments will also be presented.

The Center for Operational Oceanographie Products and Services (CO-OPS) of the National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, conducts thorough evaluations of new environmental measurement sensors through its Ocean Systems Test & Evaluation Program. New water level sensors that employ microwave (MW) radar technology are now being evaluated and compared with other devices including the Aquatrak acoustic (AC) sensor that presently serves as the operational standard for the National Water Level Observation Network (NWLON). While no part of a MW radar gage has contact with the water and radar transmission in the GHz range is insensitive to temperature and humidity change, the beam measuring distance to the water surface is allowed to transmit in open air with no confining hardware such as a wave guide or stilling well. Further study is therefore needed to fully understand the effect of a dynamic air-water interface on MW radar measurements. Four MW radar sensors (Sutron RLR-0002, Miros SM-094, Design Analysis H3611 and Ohmart/Vega Vegapuls 62) were mounted on the U.S. Army Corps of Engineers Field Research Facility (FRF) pier at Duck, NC where oceanographie and meteorological data were used to evaluate MW radar sensor performance under open ocean conditions. Water level 6-minute series from each MW sensor were compared with 6-minute series recorded by the NWLON AC sensor at Duck during September-October, 2008. MW-AC zero-mean difference series contained power (variance) at certain frequencies and cross-power (covariance) at these same frequencies with parameters such as wave height, wave steepness, longshore current speed, and air/water temperature ratio. MW-AC differences for all MW sensors showed noticeable change when Hmo wave heights exceeded 2 meters and marked change when Hmo wave heights exceeded 3 meters during storm events. Wave steepness increased abruptly at the onset of these events followed by a prolonged roll-off toward lower values. MW-AC differences for the Sutron and Mros sensors responded first negatively then positively to steepness episodes while the Design Analysis and Vegapuls sensors responded positively but with a noticeable lag during larger events. Coherence analyses for MW-AC difference versus wave height and wave steepness underscore similarities between the Sutron and Miros sensors in one group and between the Design Analysis and Vegapuls sensors in another group, each characterized by a set of distinctive frequencies. The same analyses involving longshore current speed and air/water temperature ratio hint at weaker associations at lunar diurnal and semidiurnal periods for the former and solar diurnal and semidiurnal periods for the latter.

The National Oceanic and Atmospheric Administration (NOAA) Center for Operational Oceanographic Products (CO-OPS) has been conducting a series of tests of several different types Microwave Water Level (MWWL) sensors in order to gain an understanding of sensor functions and performance capabilities and to assess the suitability for incorporation of these sensors into the NOAA National Water Level Observation Network (NWLON). On March 5-6, 2008, one particular laboratory test of four different microwave sensors was conducted with the following objectives: 1) determine the impact of surface gravity waves on the accuracy of measured water level and 2) collect a data set that can be used to develop techniques for removing high frequency surface wave induced noise from long term microwave water level records. The two day test was conducted at the Naval Surface Warfare Center (NSWC) Maneuvering and Sea Keeping Basin (MASK) in Carderock, Maryland. This facility includes a 110 m long, 73 m wide, 6.1 m deep indoor tank, with the capability to generate controlled, multi-directional surface waves. During the test, the four sensors measured water level in the tank from above, at four different sensor-to-water ranges, 3, 5, 7, and 9 meters. At each measurement height, a range of different surface wave conditions were generated in the tank, including regular controlled wavelength waves as well as irregular waves, simulating real ocean conditions. Results indicate that in some cases, continuously generated uniform wavelength waves caused offsets in measured water level for all sensors, and these offsets depend on the ratio between the width of the sensor footprint on the water surface and dominant wavelength of surface waves present. The impact of surface waves on measured water level varied across different sensors, due to different filtering and range tracking algorithms employed. Results will be used to gain a better understanding of sensors' processing capabilities and to ensure that each sensor's parameters are optimally configured for additional future field tests. A detailed overview of the setup and execution of this unique laboratory test will be presented along with analysis results summarizing the observed wave induced offsets. Recommendations on filtering methods for removing high frequency surface wave induced noise from long term MWWL measurements will also be discussed.

Surface waves are among several environmental parameters that significantly influence mid‐to‐high frequency (1–18 kHz) acoustic wave propagation. In coastal regions, surface waves are fetch limited with reduced spectral level at lower frequencies. In order to assess the detail of an acoustic signal interaction with the sea surface in such regions, a combined approach based on experimental observation and modeling of both surface waves and acoustic waves has been adopted. Data from two broadband shallow water acoustic experiments are presented. These data include simultaneous wind speed and acoustic propagation measurements. The experimental design allowed an examination of received signals corresponding to single surface bounced ray paths. Measured data analysis shows a high correlation between time–angle–intensity fluctuations of received signals and varying sea surface conditions. An empirical fetch‐limited ocean wave spectrum has been combined with an acoustic ray‐based model to study acoustic wave propagation. Rough sea surface realizations are generated and used as sea surface boundaries with the acoustic model. This combined sea surface/acoustic model predicts the variability of acoustic signal fluctuations as a function of varying sea surface. Modeled time–angle–intensity signal fluctuations compare excellently with field data at lower wind speeds.

Surface waves are among several environmental parameters that can influence broadband mid‐to‐high frequency (1–18 kHz) acoustic wave propagation. Understanding the interaction of sound waves at a rough surface requires a detailed description of the ocean wave spectrum. In shallow water regions, due to proximity to land, surface waves are usually fetch and duration limited with reduced spectral level and higher frequency components. A model that approximates the wave spectra for a fetch limited sea has been combined with acoustic ray‐based method for analysis of forward scattered acoustic signals in such a coastal environment. Numerical modeling is employed to investigate time‐frequency‐angle characteristics of ray paths reflected from a rough sea surface. Temporal variability of acoustic signal fluctuations has been examined as a function of varying sea surface. To validate this model, results are compared against a unique set of experimental data collected in a fetch limited region. The experimental desi...