NOAA's Recent Transition of Microwave Radar Water Level Sensors to Operations Results in Enhanced Storm Surge Monitoring Capability

The United States National Oceanic and Atmospheric Administration's (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) maintains real-time water level observations at more than 200 different coastal locations affected by varying combinations of meteorological and oceanographic conditions. These water level stations play a vital role in monitoring hazardous storm surges by providing real-time storm tides and tsunami detection, facilitating more timely and accurate warnings for coastal areas. Meanwhile, analysis of long-term observations provides information on frequency and elevation of extreme events, relative sea level trends, and subsidence of the local land. As was learned during the devastation of Hurricanes Katrina and Sandy, it is critical to know the correct water level and geodetic baseline datums for engineering and construction in the coastal areas.

Over the past several years, CO-OPS has been conducting a series of extensive laboratory and long-term field tests with several different brands of microwave radar range sensors to determine their suitability for use in the National Water Level Observation Network (NWLON) and other locations where CO-OPS requires long and short-term sea level measurements.

The 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, from above the sea surface. With no parts directly in contact with the water column, many problems typical of long-term subsurface ocean sensors, such as biological fouling and corrosion, can be avoided. Also, significant equipment cost savings and simpler deployments will result since a remote sensing setup requires significantly fewer hardware components for successful installation. These advantages support the potential to increase the spatial coverage of the water level measurements in an observation network, a key component to better resolving storm surge processes. Advantages include improvement of real-time emergency decision support and increased data coverage to support storm surge model validation and enhancement.

Field testing a new NWLON water level sensor must assess the impact of various environmental parameters on sensor performance so this new sensor can be used at all or most of the NWLON stations. For this reason, test microwave radar sensors have been installed alongside a series of accepted, operational water level sensors at several different NWLON field locations covering a range of coastal environment types. Analysis results from test data collected to date have shown that radar water level sensors meet CO-OPS operational requirements at all test sites located in semi-enclosed, fetch limited, low surface wave environments. Based on excellent performance of radar water level sensors observed at enclosed sites that are not directly exposed to open ocean coasts, CO-OPS is proceeding with a limited acceptance of radar water level sensors for operational use across a large subset of NWLON stations. Sensor performance continues to be analyzed in a broader range of intermediate to high surface wave energy regimes. Currently, CO-OPS is conducting extensive testing of the radar water level sensors in the following high and intermediate wave environments: Duck, NC; La Jolla, CA; Lake Worth, FL; and Monterey, CA.

In addition to the benefits of upgrading CO-OPS' existing NWLON network, radar water level measurement technology offers many opportunities to increase spatial coverage of the real-time network through establishment of new stations, in particular in regions with limited infrastructure that presents logistical and design challenges.

Most recently, NOAA employed radar water level technology in the establishment of a new, breakthrough Mobile Bay Storm Surge Monitoring Network (MBSSMN). In the spring of 2012, CO-OPS completed the establishment of the MBSSMN in partnership with the Mobile County Commission. 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, buoyancy, 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. Due to challenging station requirements and limited infrastructure in key locations, employment of radar water level sensors was paramount to the success of the endeavor.

Combined data from this project with the data provided by multiple stations in CO-OPS' existing Mobile Bay Physical Oceanographic Real Time System ( PORTS)® provide stakeholders with a unique offering of spatially densified water level, meteorological, and tidal current data. Mobile County now has a total of eight real time water level stations to provide full data coverage of its coastline. 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. The collected data will provide valuable information for validation and enhancement of storm surge models.

This presentation will include the latest field test results of radar water level sensors in the high wave environments and a summary of NOAA's long term goal for transitioning the new technology across NWLON. In addition, a summary of the MBSSMN storm surge monitoring network will be presented along with sample surge events that have been captured in records since establishment.