Monthly Archives: March 2009

Acoustics Blooper in NCIS

I saw the NCIS episode “One Shot, One Kill” and noticed a blooper in the show. Maybe that’s not that cool, but this particular blooper requires knowing something about acoustic localization. This is the technology that is being used to let marine mammal researchers place the position of whales who are vocalizing and also lets police departments know about where gunshots have been fired. The basic idea is that one places a bunch of sound transducers in known positions, and one can — with the aid of a bunch of math and computer power — estimate where a sound originated.

In the case of marine mammal researchers, Whitlow Au and the research group at the University of Hawaii have had a four-hydrophone array, where the hydrophones are arranged in a tetrahedral shaped, and the whole thing is a bit over a meter across, IIRC. With a sufficiently fast simultaneous-sampling data recorder, they can get a reasonably good bearing and range estimate on a whale or dolphin.

For the police, there have been installations of microphones in several cities. First, a microphone detects a gunshot. Second, another program delivers a localization estimate. Some of these are claimed to be accurate to about 80 feet. Given the reverberant qualities of sound propagation in the urban environment that’s either a testament to amazing skill on the part of the engineers, or amazing BS on the part of the marketers.

So if gunshots can be acoustically localized, what was the problem with NCIS showing use of the technology? It came in the form of having the goth forensics guru character, Abby Sciuto (played by Pauley Perrette), showing a graphic on a computer monitor supposedly giving the result of the localization for a gunshot. The graphic showed a linear array of three microphones and three straight lines running through the estimated shooter’s position and each of the microphones. Nice, simple to grasp, and wrong. First, acoustic localization will give you a half of a hyperboloid as a solution for a time-of-arrival difference between any pair of sound transducers. The estimated location is going to be at places where multiple hyperboloids intersect. Even if one simplifies things to being more-or-less restricted to a 2D solution, there isn’t much call for showing a straight line when graphing an acoustic localization. Second, anyone worth a flip doing acoustic localization for a known sniper situation isn’t going to deploy just three microphones relatively close to each other, and certainly not with with them in a linear array. The best situation to have for acoustic localization is to have the sound source within one’s array of microphones. If you have to deploy a small number of microphones, and can’t get a long baseline, staggering them so there is not a straight line through the positions is going to help. With a symmetrical situation like the line of three microphones, one has poorer localization the closer a source is to being on that line. (On the line, there is no localization of a source outside the microphones; time of arrival will tell you on which side of the array the source is, but whether it is eight feet or 800 yards from the outside microphone isn’t going to be determined by time of arrival differences.) Using a triangle when in a 2D situation or a tetrahedron for 3D is going to work out better.

It makes for an interesting question of what the best placement would be if one were planning
to do acoustic localization of a sniper and one only had three mics, but knew where the target was, and that the only distant approach came from one side of the building where the target was. Offhand, I’d put one mic on the line normal to the target’s building, either on the building or 50 to 100 yards to the front of the building. The other two would go out to either side about 300 yards and a total of about 1,200 yards from the building. That would help make it more likely that a sniper spot is within the triangle formed by the three mics.

Sirenian International Goes Sociable

Sirenian International, a manatee conservation and public outreach organization, now has a Facebook group.

SI also has a field course in Belize that one can sign up for:

Ecology, Behavior & Conservation of Manatees & Dolphins
A Unique Field Course in the Drowned Cayes, Belize
Host: Caryn Self-Sullivan
Type: Education – Class
Network: Global
Start Time: Saturday, May 30, 2009 at 12:00am
End Time: Friday, June 12, 2009 at 5:00pm
Location: Spanish Bay Conservation & Research Center
Street: Drowned Cayes
City/Town: Belize, Belize


Want to be a Marine Mammal Biologist? Want to be a Behavioral Ecologist?

Here’s your chance to join our research team for two intense weeks of total immersion into the world of Animal Behavior, Antillean manatees, and bottlenose dolphins in Belize!


Become totally immersed into island living, behavioral ecology and marine biology through lectures and learning activities, literature review, debate, projects, and field research. This unique field course combines an overview of the ecology, behavior, and conservation of sirenians and cetaceans with hands-on manatee & dolphin research in the Drowned Cayes, Belize.

Get out of the classroom! You’ll spend 3-4 hours on the water each day learning about the environment as we explore a labyrinth of mangrove islands, seagrass beds, and coral patches searching for elusive manatees and charismatic dolphins. You’ll collect behavioral and environmental data and learn about photo-id techniques; you’ll develop a Fact Sheet or Activity Booklet about a related topic to be published by the Hugh Parkey Foundation for Marine Awareness & Education and/or Sirenian International. Extra-curricular activities include diving or snorkeling at Turneffe Atoll, and exploring an ancient Maya City.

That just sounds cool.

Dr. Self-Sullivan was one of my fellow grad students back when Diane and I were at Texas A&M University. She’s terrific and has years of experience with the marine mammal populations in Belize, so if you have the time and inclination, I’d suggest signing up pronto.

Dembski, “Weasel”, and Video-Level Evidence

A post over at Uncommon Descent with a long-running series of comments resulted in a link to a video segment that bears on a stance taken by William Dembski and others that Richard Dawkins’ “weasel” program somehow worked by locking-in correct characters, protecting those from further mutation. The video shows that no such protection was given to correct characters. I’ve sent an email to Dembski and Robert Marks to bring this directly to their attention. I’ll share it with you here.

“David Kellogg” on Uncommon Descent linked to a YouTube video of a 1987 BBC Horizons program on Richard Dawkins’ “The Blind Watchmaker”. It includes video closeups of Dawkins’ “weasel” program in operation. The video also plainly shows that letters that match the target string are not locked or latched, just as I informed you some time ago (2000/10/09 for Dr. Dembski and 2007/10/11 for Dr. Marks).

View the following video:

The relevant part begins at 6:15 into the video. The camera is close enough to the screen to show the letters in the evolutionary computation clearly, and it plainly shows that there is no latching of any character in any position.

You have continued to present Dawkins’ “weasel” program as incorporating a latching mechanism for correct characters, and have gone so far as to term “weasel” a partitioned search. You concluded in drafts of papers that “weasel”‘s performance advantage over blind search was due to it having a partitioned search as its mechanism.

I previously laid out the evidence that the description of “weasel” provided by you was incorrect, without apparent effect. I have a further blog post that plots the performance of the partitioned search as you described it, and an accurately implemented version of the “weasel” program.


While actual “weasel” is slightly less efficient than Dembski-partitioned-search, both are dramatically better than blind search. This is at variance with several of the claims that you have made.

Given that now the evidence is as clear that Dawkins’ did not use a partitioned search as it always has been that he never described a partitioned search, I would hope that you each and jointly will take steps to remove the inaccurate descriptions and invalidated conclusions that were made on an incorrect premise.

Wesley R. Elsberry

Why pay attention to persistent antievolutionist error over a toy pedagogical example from 23 years ago? Because the antievolutionists don’t seem to be able to understand even the simplest sort of illustration of evolutionary computation, and that implies that understanding the basics of the principles behind “weasel” is also far from them. The incorrect description of “weasel” is propagated in the text of a paper that Dembski has claimed has been accepted for publication somewhere, though the correction was brought to Dembski’s attention over eight years ago, and to his co-author’s attention in 2007. Not only is the description incorrect, but the incorrect elements of the description were the ones that were the subject of analysis and the basis for the erroneous conclusions that they drew. Further, the tenacity with which this error has been clung to has resulted in the incorrect description and conclusion being used by others in the religious antievolution movement, as may be seen in Meyer’s Hopeless Monster. Error this basic whose effects have been so protracted needs to be exposed assiduously.

NYT References Panda’s Thumb Blogger Tara Smith

An op-ed column by Nicholas Kristof in the New York Times referenced Panda’s Thumb blogger Tara Smith. The op-ed is about the incidental evolution of a superbug in hogs given antibiotics and the health risks that now entails.

Since then, that strain of MRSA has spread rapidly through the Netherlands especially in swine-producing areas. A small Dutch study found pig farmers there were 760 times more likely than the general population to carry MRSA (without necessarily showing symptoms), and Scientific American reports that this strain of MRSA has turned up in 12 percent of Dutch retail pork samples.

Now this same strain of MRSA has also been found in the United States. A new study by Tara Smith, a University of Iowa epidemiologist, found that 45 percent of pig farmers she sampled carried MRSA, as did 49 percent of the hogs tested.

Minimal Protection for Images

I’ve already had at least one image of mine pirated for derivative work sold on CafePress. I like sharing my photography with others, but I’d also like to get my fair share when it comes to profits made from my work.

Something that isn’t a whole lot of work turns out to be adding a plaintext comment to a JPEG format image. I’m using the “jhead” utility that is available for many different platforms. (Anybody else remember the king of multi-platform applications, the Kermit terminal and file transfer utility?) In any case, replacing a current comment in a JPEG file with something specified in a command-line string is simple:

jhead -cl ‘Copyright 2009 by Wesley R. Elsberry. All rights reserved.’ picture.jpg

That would set the “picture.jpg” comment field to be the copyright statement in single quotes.

I just wrote a short Perl script that is trundling through the images directory I have for this blog and adding the comment line to all of them. I’ll be adding that to my regular processing workflow on my file server, so in the future every JPEG file going out should have my copyright statement included.

It is pretty easy to strip comments, too, but at least for casual thieves the comment field should give me an opportunity to find my work when it strays.