Results of Hong Kong trial

The installation of the Professor Ridzwan Fish Blast Detection Station at the WWF Marine Life Centre in Hoi Ha Wan was successful in allowing Teng Hoi to check the detection system and upgrade its blast detection software.

The detector is designed to handle noisy environments whilst remaining sensitive to the sounds of distant blast events.  Sources of noise local to the detector include WWF's glass bottomed boat, nearby fishing boats and snapping shrimp.  Snapping shrimp are only a few centimeters in length and are common in tropical and subtropical seas.  They generate a lot of reef noise by using a specially adapted claw to create a clicking sound (http://en.wikipedia.org/wiki/Snapping_shrimp).  Remarkably, the shrimp's claw creates a small underwater explosion and when a shrimp clicks close to the detector, Teng Hoi's software must analyse the sound and determine if it was a nearby shrimp or a distant blast event.  Typically the sofware detects 3-5000 shrimp clicks per day. By using a number of analytical techniques, the software has proven very reliable in distinguishing blast events from shrimp clicks.  For the human ear, the difference seems quite obvious: take a listen to the sounds of shrimp and blasts for yourself by clicking the pictures below.
     
       

The shrimp click above was a big one isolated from the background sound.  Take a listen to the background reef sound (1.6 MB) so you can appreciate just how many shrimp there are and how noisy the environment is in Hoi Ha Wan.  The shrimp clicks combine to give an effect that sounds like radio static.

Over the course of three months of continuous monitoring, eight blast events were recorded.  The detection station uses an array of three hydrophones to determine the direction of the blast sound.  However, because there is only one detection station, we cannot determine the location of the blast.  We only know that it occurred somewhere along the direction line.  See the map below for details.

 
   
       
 

The vertical scale of the map is about 20 km.