West Coast/Alaska Tsunami Warning Center

Operations Manual

NOAA/NWS/WCATWC

910 South Felton Street

Palmer, Alaska 99645

http://wcatwc.arh.noaa.gov

Section 4.2: Sea Level Processing System

Last Updated: 10/2011

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Program Description:

The WCATWC accesses sea level data from approximately 500 locations throughout the Pacific, Indian, and Atlantic basins. These gages are owned and operated by several different agencies, such as the National Ocean Service (NOS), the University of Hawaii, the Australian National Tidal Facility, the Japanese Metrological Agency, and others. Sea level data transmission into and through the WCATWC is described by the figure in Section 3.3.

Sea level data arrive at the WCATWC in a variety of formats and sample rates. WCATWC maintains a number of recording stations throughout Alaska and data from these stations are transmitted in digital form via VSAT or dedicated circuits with a 15 second sample rate. These data are received directly at WCATWC and routed to the appropriate processing computer. Most of the other monitored sea level data are transmitted digitally via GOES satellite at sample rates varying from 1 minute to 15 minutes.

Data sent via GOES satellite are downloaded at the NOAA Command and Data Acquisition Station at Wallops Island, VA and sent to the National Weather Service Telecommunications Gateway (NWSTG) in Maryland for dissemination. The data are then sent to the WCATWC over two independent communication paths. The first path is a dedicated communications line. Data arriving over this line is routed to the TIDE1 PC. The second path arrives via a direct internet socket connection with the NWSTG. This data is routed to the TIDE2 PC. The dual path, dual computer configuration provides for system redundancy.

Data arriving at both processing computers are passed through an ingesting program that decodes the data into station specific data files that are logged to disk in a consistent format on each system (example here).

The program TideView is the graphical user interface to the sea level data files. Tideview can display multiple stations in a single window or alternatively, display the PlotView window to investigate individual stations with greater accuracy.

TideView options include the capability of selecting all or a selected subset of stations from a specific ocean basin, displaying stations selected directly from the EarthVu GIS system, and displaying the tsunami ETAs calculated from the WCATWC travel time models.

For more detailed station analysis, PlotView can display stations selected from the TideView display.   Predicted tides are computed and the observed tide, predicted tide, and the detided series can be displayed and scaled as the analyst desires. Additionally, the data can be low-pass filtered to remove high frequency noise, or high-pass filtered to remove the tide. When filtering data, it is often advantageous to use the de-spike option to prepare the data. From within PlotView, tools are available to measure tsunami amplitudes and periods that can, optionally, be directly input into tsunami center messages. As well as displaying real-time data, the program can recall older data to re-examine past events. In addition to invoking PlotView from the Tideview display, an analyst can see the current tide information at a site by invoking PlotView by double-clicking the desired tidestation in the EarthVu GIS system.

Data from the deep-ocean tsunami recorders, or DART buoys, are also processed by PlotView and TideView. In addition to the normal processing described above, trigger data from these buoys activate the WCATWC alarm system.