Recall that it is not the magnitude of the earthquake that dictates tsunami intensity; it is related to the nature of the plate motions. In these events, coastal tide gages recorded maxima less than a meter, and at the radar sites, only tens of centimeters. This was seen by the 13 MHz SeaSonde at Padang, Indonesia and two 5 MHz SeaSondes in the Andaman Islands belonging to India. A paper submitted August 2012 to Remote Sensing journal offers details of these detections3.
Is this the end of our tsunami algorithm development? No. As with other tsunami sensors, analysis algorithms, and their mutual data fusion, they are in a state of flux and optimization. Our algorithm will see improvements in the following areas:
– The tradeoff between probability of detection and false alarms. You want the former to be as big as possible and the latter to be small. There is a "cost function" that describes this tradeoff. Never a false alarm carries a high cost of missing "the big event" and is unnecessary because other information (e.g., seismic) in a national tsunami fusion center will cull relevant alerts.
– The large velocity associated with the incoming tsunami is sensed by the radar. This will be converted to height through the spatio-temporal relations we developed, because height is the real killer.
– Although our recent experience shows the tsunami is detected before it arrives at the coast, we must refine this alert time more precisely. Again, the spatio-temporal tools to do this exist; we will develop and test them based on our past data observations.
|1- Barrick, D.E. "A Coastal Radar System for Tsunami Warning." Remote Sensing of Environment, Vol. 8, 353-358 (1979).
2- Lipa, B., D. Barrick, S. I. Saitoh, Y. Ishikawa, T. Awaji, J. Largier, and N. Garfield. "Japan Tsunami Current Flows Observed by HF Radars on Two Continents." Remote Sensing, Vol. 3,1-17 (2011).
3- Lipa, B. J., D.E. Barrick, S. Diposaptono, J. Isaacson, B.K. Jena, B.B. Nyden, K. Rajesh, T. Srinivasa Kumar. “High Frequency Radar Detection of the Weak 2012 Indonesia Tsunamis.”
Submitted to Remote Sensing in August 2012.