I’m TAing a marine GIS/ocean mapping course this quarter, and will be teaching a lecture on some aspects of multibeam sonars and the data that you get from them. Which is fun since I haven’t really thought much about multibeam sonars since I worked at a sonar company about 6 years ago.
I was trying to figure out how to explain how a longer array means you can get a narrow beam. It’s all about interference patterns, right? So I wrote a little script in Python (you can access the script directly on my Github page).
Let’s say you have two elements spaced a half wavelength apart. You get something like this, with one main lobe:
Cool – there’s just one main lobe of higher amplitude. But then if you pull those elements just a bit further apart – I’m showing a 5 wavelength separation here – you can see a completely different pattern:
So: the wider separation made more beams and and those beams were narrower. Interesting…. What if we wanted to have just one main beam that we could maybe steer around? (ahem. maybe a little like a multibeam sonar??) The next picture shows a single beam produced by a line of 20 elements, all spaced at half a wavelength apart from each other. This time we’re zooming out a bit – showing 30m x 30m this time. Also this simulation shows what it would look like with a 200 kHz signal – which is a pretty common frequency for a shallow water multibeam sonar.
I am so very pleased to introduce my very first guest blogger: Emily T. Griffiths. I worked with Emily on the CalCurCEAS cruise earlier this month. We had adventures and misadventures and cookies. Lots of cookies. Emily’s background is in zoology and animal biology (undergrad) and marine biology (master’s). She worked as a research technician at the American Museum of Natural History and as a research analyst at Cornell’s Lab of Ornithology. For the last year, she’s been working with NOAA’s Southwest Fisheries Science Center as wildlife research biologist. And on top of that she is super awesome to hang out with. Just sayin’.
In the last post Michelle went over how we use towed hydrophone arrays to localize and track vocalizing marine mammals as the survey vessel moseys down the transect line. Historically, visual surveys have been the meat and potatoes of marine mammal survey estimates. However, adding an acoustic component to marine mammal surveys can greatly improve the chances of detecting species presence. Both methods have their strengths and weaknesses. The visual team can only see an animal if they come up for a breath, while acoustics can only detect an animal if they decide to clear their throat. That’s why the combination of both is key. In the case of sperm whales, for example, when you combine visual and acoustic efforts on surveys the science team has a 92% chance of finding an animal if they are in the study area. Not too shabby.
But here’s the thing: hydrophone arrays break, like, all of the time. The arrays I’ve been sent out with on CalCurCEAS are the current result of more than ten years of research and development, but they are still a work-in-progress. We are constantly making changes and improvements, or fixing issues that seemingly arise just because too much time has passed since the last issue. I’m on this ship with most of the tools I would need if an array did stop working and, in a pinch, crack open that sucker and attempt to fix it.
This is the reality when you’re depending on high-tech equipment to support your research: it’ll break so often that you’ll become convinced it’s because you looked at it funny. Or because it’s afraid of water. Or it just wanted to be held. All of these considerations about inanimate machinery parade through your mind as you’re running through your fifth deck test because the damn thing works in the lab but not in the open air.
Mechanical frustrations are not limited to hydrophone arrays. Oh no. Fresh out of college, I got a job in a academic research-based microscopy lab. I was charged with learning the ins and outs of the new environmental scanning election microscope, or ESEM, and the thing was a lemon. ESEMs were cutting edge because the specimen wasn’t destroyed in the imaging process, a hot ticket item when you want to look at the finer details of fossilized rodent teeth. Which we totally did. However, ‘cutting edge’ is frequently synonymous with ‘high-functioning prototype’. I spent my first six months crawling around that machine, guided by the manufacture’s technician because I had a smaller frame and fingers. A machine based on infant technology cannot really be returned, many times they’re made to order. If you did manage to return it, the replacement could have the same, or even woefully different issues. This is a clear ‘the devil you know’ situation, and though the ESEM was never perfect, after a time not only could I mostly fix it by myself, I also got to take some really amazing pictures in the name of research. Like of the dinosaur bone I broke, but that’s a different story.
Later in my career, I spent a year assisting in field tests of an autonomous biological recording device designed to be half the weight and cost of the current leader in the market. Rather than discuss the boring troubleshooting details, here’s a list of notes without context from my notebook to represent the plethora of issues we were dealing with. These notes are presented in the order that I find funniest with my [comments]:
We need access to all. [All your base are belong to us.]
Good ideas save issues. [Brilliant.]
The LED indicators → What are they? [I was having a slow day, let’s hope.]
Buy batteries, ask Anne how. [Do I not know how to buy batteries?]
Adam = Rob
Red hat fifth model, under-ware. [I have no actual idea what this note means.]
High power rifles are not common. [Useful.]
Analysis plan → bunch of SD cards in the mail, now what? [I’m a highly trained scientist.]
A doodle, after several failed field tests, of a tombstone inscribed with “She tried.” *
Towing a hydrophone array behind a ship is a silly idea for many reasons, outside of pulling a delicate instrument underwater at 10 knots while powering it with electricity and expecting not to die. Ships are incredibly noisy, and they interfere with our data collection. On CalCurCEAS we are deploying working autonomous free-floating recording prototypes known as DASBRs (Drifting Acoustic Spar Buoy Recorder). It’s very exciting technology. These devices have a higher chance of recording animals which are ship-shy (and therefore are little known), can record in deep waters (current bottom mounted devices are limited to the continental shelf), and allow us researchers to get a better understanding of ambient noise levels in the ocean.
I’ve been working on the DASBRs for about a year now, and though we’ve certainly had successful deployments, we’ve also had our fair share of “learning experiences.” Which is expected when you’re trying to do something new. In the field you make good with what you got because you can’t anticipate everything, you can only try. Sometimes this means spending hours trying to figure out why an instrument can’t hold a charge (only to realize you didn’t realize the plug-in charger has an on/off switch). Sometimes this means using a clamp and a thumbtack to replace a screw in a hole so small, narrow and deep it’s like throwing a dart and hitting a bull’s eye 6 thousand miles away (I am a leaf on the wind) **. Sometimes this means duct taping tennis balls to the bottom of a chair to prevent the chair from moving around because you’re bored and annoyed at the ocean swell pushing you and your chair around.
Even though it’s frequently discouraging and deadening, the embarrassing truth is that troubleshooting is one of my favorite parts of the job. Yes, you miss more than you hit when trying to find the origin of an issue, and by the time you hit you’re so exhausted that it’s more elating to chuck the equipment aside for the day than it is that the problem is solved. Besides you know, in your heart of hearts, that it isn’t. It’s just lurking. However, I still love a good puzzle and learning new things. Sometimes I learn things that make my job easier. Sometimes I learn that I’m really crappy at troubleshooting. It’s all valuable and puts me in a better position the next time something breaks. Because it’s not a question of if, only when.
* To my credit, I read Breakfast of Champions after making this doodle, and was simultaneously thrilled that I had organically made a joke that Vonnegut had also made, but disappointed that I couldn’t really claim it as my own.
** I know, I know. This is totally shoehorned in here. I may not be the Wash, but I’ll tell you what, it’s shiny.
As some of you may know, I’ve been learning about video editing lately. For the most part, it revolves around the online introductory oceanography class I’m helping develop, but there are a couple of other things I’m playing around with too.
My family is visiting from Canada, and my brother-in-law, Christian, has been showing me some cool tricks in Adobe After Effects. I often use a spectrogram to help describe how we “look at” sounds. It is pretty straightforward if you’ve seen them before but can be a bit strange the first time you see one.
In the past, I’ve showed a spectrogram and then included a separate sound file to show how they work, describing how they fit together in words. But I’ve finally figured out how to pull it all together in After Effects, and it’s surprisingly easy.
This video is pretty simple and is not much more than a couple of masks and a glow effect, with (of course) strategically placed keyframes. Here it is – enjoy!
According to John, the best thing about Sharknado is that they drive around in a Landcruiser, quite a lot like this one:
If you know John at all, you know that he LOVES that truck, and spends large chunks of his free time fixing it, taking it apart, restoring it, replacing parts, etc.
Here’s a sample of his Sharknado commentary:
The commentary continued even after the Landcruiser was obliterated, even if only to berate all other vehicles that turned up in the movie. Especially Hummers.
All in all, despite the filmmaker’s poor decision to destroy the world’s best truck, Sharknado was as epic as we ever could have hoped for in our wildest dreams. We encourage you all to enjoy it this holiday season.
Please welcome my next science+comics interview victim, Alexis!
Name: Alexis Rudd Job: PhD student in Zoology at the University of Hawaii Research: Alexis uses passive acoustic monitoring to study whales and dolphins off Hawaii
News Flash!! Whales and dolphins, a.k.a. cetaceans, hang out near the Hawaiian Islands! Okay, not a news flash at all, everyone knows that. But you may be surprised to learn that we don’t actually know much about them – what they’re doing, where they’re going, and why – especially once you get out to the deeper rougher waters further from shore. So why is it important to know about their hangout spots and behaviors? It’s because that kind of information can help us design and implement effective management and conservation strategies. Yes, cetaceans hang out near Hawaii, and we want to keep it that way!
Here’s the thing. Whales and dolphins (and loads of other animals) like to spend time where food is available. In the ocean, the big driver behind food abundance is primary productivity – phytoplankton, or plants that live in the sunlit upper layers of the ocean. And just like on land, different places in the ocean are more productive than others: some places are lush and green with plants and all the life they support, and other places are sort of like deserts – yes, animals live there, but it’s on a whole different scale. Here’s an image of productivity (actually, it’s an indicator of productivity – chlorophyll concentration, which satellites pick up by its color).
This picture shows green where there is a lot of productivity, and blue where there’s not much. So the deepest blues show where the ocean “deserts” are. The green places tend to be where nutrients are available – things like nitrogen and phosphate (yup, same stuff that’s in fertilizers for your garden), which might run off the land, or be brought up to the surface in upwelling zones.
But – not to worry! – it’s not exactly a dead zone around Hawaii. It just means that cetaceans might need to look for an oasis sometimes. One theory is that cold, nutrient-rich water gets pulled to the surface by cyclonic (counter-clockwise) eddies, triggering a cascade of activity up the food web – a very enticing fish/squid/zooplankton buffet indeed.
To address these kinds of theories, Alexis needs to figure out whether cetaceans are indeed seeking out certain environmental and oceanographic conditions. Often, studying cetaceans means getting on a boat and looking for them visually. This works reasonably well in calm waters, but it gets pretty tough to pick out a dolphin or a whale when the water is choppy. The prevailing winds are westerlies, and they come sweeping across the Pacific from California. Calm zones form on the leeward side of the islands, but the wind speeds up as it squeezes through the gaps, creating regions of high wind and rough seas.
Instead of looking for cetaceans visually, Alexis listens for the sounds they make. And here’s where the super creative part of her research comes in: she tags along on a tugboat that brings supplies to the different islands. Being the persistent scientist that she is, Alexis went out every two weeks for a year and a half, installing her underwater recording package (hydrophone) on the barge behind the tugboat. This setup was ideal in a lot of ways: first of all, people need their supplies all year round, so this vessel does regular trips. Second, having the hydrophone on a barge – separated from the loud tug engines – makes it easier to pick out cetacean sounds. Here’s what the basic setup looks like:
As the tugboat moves from island to island, it provides a great acoustic “view” of a very large area – the calm leeward side of the islands and also the windier regions between the islands. So Alexis is able to get a great “big-picture” idea of what’s going on.
She’s now collected hundreds of hours (!!) of recordings, and is going through the process of checking and documenting all of the identifiable cetacean calls. She links each call up to the location where the barge was at that time so that she can gather up all the data at the end and figure out whether there are correlations between the animals’ presence and environmental or oceanographic conditions.
“The second biggest animals in the world live in water. they make noise and I listen. Then I tell people where they might have been, where they might go next, and maybe even why.”
– Not a bad summary, really.