TIDE TOOL: Open-Source Sea-Level Monitoring Software for Tsunami Warning Systems Stuart A. Weinstein 1, Laura S. L. Kong 2, Dailin Wang 1, Nathan C. Becker 1 1. Pacific Tsunami Warning Center, USA, 2. International Tsunami Information Center/UNESCO-NOAA, USA, NH33A-1665 ABSTRACT: A tsunami warning center (TWC) typically decides to issue a tsunami warning bulletin when initial estimates of earthquake source parameters suggest it may be capable of generating a tsunami. A TWC, however, relies on sea-level data to provide prima facie evidence for the existence or non-existence of destructive tsunami waves and to constrain tsunami wave height forecast models In the aftermath of the 2004 Sumatra disaster, the International Tsunami Information Center asked the Pacific Tsunami Warning Center (PTWC) to develop a platform-independent, easy-to-use software package to give nascent TWCs the ability to process WMO Global Telecommunications System (GTS) sea-level messages and to analyze the resulting sea-level curves (marigrams). In response PTWC developed TIDE TOOL that has since steadily grown in sophistication to become PTWC’s operational sea-level processing system. TIDE TOOL has two main parts: a decoder that reads GTS sea-level message logs, and a graphical user interface (GUI) written in the open-source platform-independent graphical toolkit scripting language Tcl/Tk. This GUI consists of dynamic map-based clients that allow the user to select and analyze a single station or groups of stations by displaying their marigams in strip-chart or screen-tiled forms. TIDE TOOL also includes detail maps of each station to show each station’s geographical context and reverse tsunami travel time contours to each station. TIDE TOOL can also be coupled to the GEOWARE™ TTT program to plot tsunami travel times and to indicate the expected tsunami arrival time on the marigrams. Because sea-level messages are structured in a rich variety of formats TIDE TOOL includes a metadata file, COMP_META, that contains all of the information needed by TIDE TOOL to decode sea-level data as well as basic information such as the geographical coordinates of each station. TIDE TOOL can therefore continuously decode theses sea-level messages in real-time and display the time-series data in the GUI as well. This GUI also includes mouse-clickable functions such as zooming or expanding the time-series display, measuring tsunami signal characteristics (arrival time, wave period and amplitude, etc.), and removing the tide signal from the time series data. De-tiding of the time series is necessary to obtain accurate measurements of tsunami wave parameters and to maintain accurate historical tsunami databases. With TIDE TOOL, de-tiding is accomplished with a set of tide harmonic coefficients routinely computed and updated at PTWC for many of the stations in PTWC’s inventory (~570). PTWC also uses the decoded time series files (previous 3-5 days’ worth) to compute on-the-fly tide coefficients. The latter is useful in cases where the station is new and a long-term stable set of tide coefficients are not available or cannot be easily obtained due to various non-astronomical effects. The international tsunami warning system is coordinated globally by the UNESCO IOC, and a number of countries in the Pacific and Indian Ocean, and Caribbean depend on Tide Tool to monitor tsunamis in real time. Common Types of Sea-Level Stations Coastal Sea-Level Stations Typically Use GOES or BGAN DARTs USE IRIDIUM Rather than use a separate decoding function for each type of format, Tide Tool consists of a few generic Decoders that use Metadata describing the message format. What is Tide Tool? GTS Message Formats Correcting for the Effects of the Tide Tide Tool Uses Two Tide Correction Methods Computing the Tide Forecast Each Method Has Strengths and Weaknesses The Tide Tool GUI Basic Tide Tool Widgets Dynamic Map Interfaces (Clients) Tide Tool uses a Server – Client Architecture Strip Chart Widgets Tsunamis Observed With Tide Tool Strip Charts with Tsunami ETAs Indicated Ordered by Proximity To Crescent City Ordered by ETA Origins of Tide Tool