Editor's Note: News of this innovative use of the THREDDS Data Server in concert with GIS software came to us as a result of UPC staff participation at a GIS conference earlier this year. We'd love to hear about what other community members are doing with Unidata software and services as well — contact us at unidatanews@unidata.ucar.edu.
Although piracy has been around since nations have engaged in maritime trade, the scale and focus of attacks in and around the Horn of Africa has attracted significant attention over the past few years. The publicity reached a peak in April 2009 following the seizure of the Maersk Alabama and the direct involvement of the US Navy in the release of the ship's Captain. The extent of piracy in the Gulf of Aden and waters adjacent to Somalia led to the formation of Combined Task Force 151 (CTF151) to conduct anti-piracy operations.
Royal Australian Navy participation in CTF151 was the trigger for Navy HM Branch to analyse whether any weather dependent patterns could be identified in the timing and distribution of the attacks. The study commenced with accessing the NGA piracy database and overlaying the location of each attack on the long-term climate average for monthly mean significant wave height (a measure of the combined height of the locally wind driven sea and the underlying long wave swell) (Figure 1).
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Even when compared with a monthly mean climatology, the high correlation between the location and mean wave height was immediately apparent.
The next step was to use historical satellite wind and weather observations to determine the sea conditions at the time of each reported event. These were plotted by month against Significant Wave Height and distance offshore, consequently testing the hypothesis that attacks may occur in high sea states if closer to the coast (Figure 2). Attacks by month are highlighted in red and all attacks are shown as the transparent points.
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This analysis further emphasised the correlation between the location of each attack and the actual wave height at that location. Combining all months into a single plot (Figure 3), we see that no successful attack has occurred in a significant wave height above 2.2m and that attacks above 1.6m generally occur closer to the coast.
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The thresholds derived from the analysis of previous attacks are now applied to wave forecasts produced by the Australian Bureau of Meteorology. ArcGIS geoprocessing tools are used to generate traffic light images, animations and briefing slides every 12 hours, to show the risk of piracy attack, based on the historical patterns, at six hourly intervals out to five days. A sample plot is shown in Figure 4.
Areas in yellow are between 1.6m and 2.2m and areas in red, below 1.6m. It should be noted that these plots capture the environmental limitations only and do not take into account any other intelligence such as merchant or pirate ship locations.
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Today, a browser based map service is under development to enable on-demand analysis of environmental layers in real-time at a global scale. This development is based on THREDDS Data Server (TDS) to host the source data, ArcGIS Server (AGS) for the geoprocessing service and ArcGIS Server for Javascript for the user interface in a browser based client.
A Defence specific subset of the Australian Bureau of Meteorology's numerical weather prediction data is regularly subset via OPeNDAP into a Navy maintained TDS. This multidimensional array is exposed as OGC Web Map Service (WMS) and Web Coverage Service (WCS) via the TDS which become the inputs into Geoprocessing Services published in AGS. These GP Services contain the algorithms that define what environmental conditions make piracy likely or unlikely. Drop down lists allow a user to further define the threshold values that set the traffic light. As the TDS supports the publishing of a temporally varying WMS, the client is able to animate through the forecast time steps and determine not only where, but when piracy is likely based on the environment. While the piracy forecast products are developed exclusively for use by the Task Force, the METOC group uses similar methodology (THREDDS and ArcGIS) to produce other "traffic light" type products that highlight the environmental impacts on Boarding Operations, Replenishment at Sea, Clearance Diving, and other activities.
For more information on the piracy traffic light products, contact Paul Sliogeris at Navy HM Branch METOC Geospatial Services.
