Processing and presentation of high-resolution DART° data for recent significant tsunami events

The National Geophysical Data Center (NGDC) in Boulder, Colorado, is an integral part of the U.S. National Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite, Data, and Information Service. One of three NOAA data centers, NGDC hosts the long-term archive and management of tsunami data for research and mitigation of tsunami hazards under collaborative development between the National Weather Service, the Pacific Marine Environmental Laboratory, and the National Data Buoy Center. Archive responsibilities include the global historic tsunami event and run-up database, the Deep-ocean Assessment and Reporting of Tsunami (DART°) event and native bottom pressure and temperature observations, coastal tide-gauge data from US/NOAA operated stations, historic marigrams, and other hazards-related data and information. In terms of tsunami observations, NGDC currently process and archives all recovered native or 15 seconds high-resolution DART° bottom pressure observation time series. Tsunami signal-to-noise ratios in the deep-ocean are such that de-tiding based on a combination of tidal harmonic predictions and carefully constructed filters are necessary to obtain clean tsunami records. The processing includes removing tides using a customized version of the IOS tidal package of Mike Foreman. Additional processing is applied for parts of the records with registered tsunami events where the noise from the intra-gravity waves and components representing larger scale oceanic processes are removed by band-pass Kaiser-Bessel filters. The NGDC tsunami archive contains processed full record high-resolution observations for the period 2002-2010. An event-specific archive of real-time and native high-resolution observations recorded during recent significant tsunamis, including the March 2011 Japan Tohoku event are now available through new event pages that have been integrated with the NOAA Global Historical Tsunami Event Database. Event pages are developed to deliver comprehensive summaries of each tsunami event, including socio-economic impacts, tsunami travel time maps, raw observations, de-tided residuals, spectra of the tsunami signal compared to the energy of the background noise, and wavelets. These data are invaluable to tsunami researchers and educators as they are essential to providing a more thorough understanding of tsunamis and their propagation in the open ocean and subsequent inundation of coastal communities. All tsunami data are accessible at http://ngdc.noaa.gov/hazard/recenttsunamis.shtml. Details of filtering and tide removal techniques applied during the processing of all tsunami time series are discussed and spatial distribution and density of the observations along with general statistics are presented. Results obtained from analysis of all recently recovered 15-second high-resolution DART observations for the 11 March 2011 Japan Tohoku tsunami after application of the described processing techniques are presented and show the historic nature of this event; the largest deep-ocean tsunami amplitude in recorded history.