STEM

STEM is Science, Technology, Engineering, and Math

Bats_smithsonian_video
Tracking Bat Colonies With High-Speed Cameras

All of the STEM disciplines play a role in Hristov and Allen’s research on bats. Here you can learn about:

  • high-speed imaging
  • laser scanning
  • thermography

Check back to learn more about:

  • acoustics

For an overview, check out this Science Friday video.

Over time we hope to highlight other scientists’ research too, for example, what changes are there day to day, season to season, year to year in the cave climate?

High-Speed Video

By recording and analyzing high-speed video scientists can study bat movement in great detail.

BatsGridp10_3printWhat is high-speed video?

High-speed video makes use of very high frame rates during recording in order to slow down during playback the action of fast events.  The technique allows the viewer to study in detail fast actions and movements.  Because of limitations in human perception, frame rates as low as 12 fps are interpreted as moving pictures, however, most video that we watch is at least twice as fast.  If you watch the evening news on your television you will view the footage at 30 fps, and when you watch a movie at the theatre you will be viewing it at 24 fps. High-speed cameras record hundreds to thousands, and some advanced cameras even over a million frames per second.  So although the technology has advanced and video can be recorded on devices as small as a smartphone, high-speed videography lets scientists, broadcasters and artists alike slow down fast moving action for more detailed interpretations.  The cameras that scientists use to study fast moving wild animals and humans are similar to those used on the sidelines during the Superbowl and by makers of action movies.

Why do bat scientists use high-speed video?

Bats move fast and often interact with other members in large groups. Highs-speed video allows scientists to see how the wings of flying bats move, whether individuals crash into each other or their environment (cave, branches etc.); how predators attempt to capture and bats avoid them.

How do scientists use high-speed video?

Traditionally scientists have used high-speed video in the laboratory setting. Animals are often brought in from the wild and trained to perform a specific behavior in front of the camera(s). Because of advances in technology and increases in portability, scientists are now leaving the confines of the laboratory and recording natural behaviors in the animals’ natural habitat. The Center For Design Innovation’s current system of high-speed cameras consists of five units, capable of recording images with up to 2560 × 1600 pixels at rates as high as 3250 fps.  These cameras make it possible to “stop” a kernel of corn mid-pop or a bat in flight. Each camera can function on its own without a connection to a computer or in combination with other cameras permitting flexible deployment in a range of circumstances. Most such cameras weigh ~10 pounds – that’s equivalent to two 5-lb bags of flour, or 4 traditional cameras, so high-speed cameras generally need a tripod for steady operation.

Benefits

  • High frame rate and resolution permit detailed analysis in space and time
  • Modern cameras are more portable, boast sensors with high light sensitivity, and have advanced solutions for data storage, transfer, and backup.

Challenges

  • High-speed cameras require a lot of light – example?
  • High-speed cameras are quiet expensive. Advanced ones can cost as much as a medium-sized house.
  • Most high-speed cameras are rather bulky and complicated to operate.

Questions scientists have answered by filming bats in high-speed:

  • How do individual bats move within a group?
  • How bats use their wings to fly?
  • What is the speed of a group of bats?
  • Do bats hit or touch each other in a group
  • How close are bats when they emerge from a cave?

 

Long-Range Laser Scanning

By recording and analyzing 3D Laser scanning scientists can make accurate, distant and non-invasive surveys of complex physical environments.

Carlsbad_FAROScan_AmphitheaterTwilight_v1What is long-range laser scanning?

Long-range laser scanning is a new technology that uses laser light to survey complex environments. Sometimes referred to as LIDAR, 3D scanning, or time-of-flight range finding, the technology is used by scientists, engineers and architects. Here we use the term 3D laser scanner as the most general form of the technology but refer specifically to a low-power, laser-based device that uses a noncontact method of collecting distance measurements. Imagine you want to map out the Big Room at CAVE, how would you take accurate measurements of the topography and features? Traditional methods might include a tape measure or more recently a range finder that can be purchased at a local hardware store. The principle advantage of 3D laser scanning is the speed and accuracy with which these recordings can be made. This method can collect up to 1,000,000 data points every second, and can make measurements as close as 1/16in (2mm) at 300ft (150m). 3D laser scanners use a vertically revolving mirror in combination with a horizontally panning base to steer a laser beam and estimate the distance between features in the environment and the device. This creates a “point cloud” of data, a virtual reality model of the recorded setting, that can be used for direct distance, area, or volume measurements, or the data can be converted to other formats to generate models for further manipulation.

Why do bat scientists use long-range laser scanning?

Bats do not exist in isolation but instead are immersed and interact with objects in their environment at different scales. 3D laser scanning makes the reality of bats’ environment more understandable by capturing and representing it in virtual reality.

How do scientists use 3D laser scanning?

The Center For Design Innovation’s current system includes a pair of FARO Focus 3D® laser scanners to quantify the 3D environment, including cave dimensions and topography. The scanners are also used to survey large arrays of scientific equipment in the wild including camera and microphone arrays. The 3D laser scanner uses a line of sight to make measurements and cannot see through opaque objects.  Therefore, a single scan is rarely sufficient to capture all the information of a three-dimensional environment. Multiple scans resolve this limitation and often scientists make numerous acquisitions from various vantage points to get a more accurate representation of the setting. Whether 2 or 200 scans are collected, they need to be “stitched” together by either a computer program or a human. Once recorded and processed, laser scans produce an image that can be manipulated and viewed from different perspectives for further investigation.

Benefits

  • High accuracy
  • Fast data collection.
  • Intuitive interpretation from a virtual reality “point-cloud”

Challenges

  • Cluttered environments require more time and more scans
  • Instrumentation is sensitive and demanding to operate

Questions about bat environments scientists have answered by laser scanning

  • How large are the caves that bats use for homes?
  • How much surface does a colony of bats cover?
  • How much poop do bats produce?

More detail on cave mapping techniques from Mark Joop, Interpreter and Caver

I don’t know about you, but I was really wowed today by the laser scanner demonstration. What an incredible machine! It’s so smart! I have done a lot of cave survey in my day, but never did we produce a final map that provided as much information as a laser scan.

In cave survey, the data is collected by the use of a compass, an inclinometer, a fiberglass tape measure, and in the last decade or so, a Disto laser distance finder (there are other brands, but at the time not as accurate or shoot as far). The latter was used mainly to measure LRUDs (left, right, up, down) at each station, but some cave surveyors also used it to replace the tape measure. The problem with using the Disto to produce your line plot through the cave was that you had to hold it very steady. The longer the shot, the more that the slightest movements would cause the red dot to move far from the chosen station, which you are trying to hit in the dark. There are tricks to help mitigate this dilemma, such as holding up a yellow field notebook in the plane of the station as a target. But still, to avoid errors, we would shoot the distance at least 3 times and take the mode value. It is faster to just stretch the tape! The advantage of shooting LRUDs with the Disto was that you did not have to guess anymore, nor disturb parts of the cave that could now remain undisturbed. So while this new fangle devise added accuracy to the map, it still does not compare to the laser scanner, which can replicate every detail of the floor, walls, and ceiling throughout the cave. And on top of that, you can later move through the cave as a virtual tour at home!

Thermal imaging Bats_thermalimage_web

Using thermal imaging scientists can observe organisms in complete darkness without artificial lights and can make inferences about thermal patterns in individuals and groups.

What is thermal imaging?

Thermal video makes use of the heat that emanates from objects (both living and non-living) in the environment. Energy is lost from the surface of objects as waves of heat and is known as radiation. Unlike traditional cameras that capture light reflected from the surfaces of objects, or infrared cameras that require a source of IR light, true thermal cameras can capture this thermal energy and can translate it into an image. Thermal video can record differences in temperature as small as 1/100th of a degree from distances of several hundred feet. Some advanced cameras can capture video at up to 125 fps.

Why do bat scientists use thermal imaging?

Bats are nocturnal; most of their activity is at night, and they reside and raise young in dark environments (e.g. caves, attics, tree hollows). Most bats show fluctuations in metabolic rate and body temperature (torpor and hibernation) and by observing the surface temperature of their bodies with thermal imaging scientists can monitor these changes.

How do scientists use thermal imaging?

Thermal cameras are now easier to set up in the field. Cameras can be moved around between sites, or they can also be installed permanently to observe long-term trends and behavior at a single site. A single camera can record the size of an entire colony.  Several cameras working together can reconstruct the emergence or return of a group of bats in 3D.

Benefits

  • Cameras do not need artificial or introduced light to capture natural behavior
  • Cameras can record in complete darkness
  • Thermal readings visualize the organisms and their environments, and the temperature values have meaning.

Challenges

  • There is not a one-size-fits all approach. There are two types of cameras with thermal imaging sensors — one kind is smaller, lighter and more portable but less accurate; the other is larger, more expensive; it is harder to install and maintain in the field but captures better images and more accurate readings.

Questions about bats scientists have answered by using thermal imaging

  • How many bats reside in a particular colony
  • How do groups of bats use the space in the cave (roost)?
  • How closely do groups of bats group together inside the cave?
  • What are the light patterns as groups of bats leave the cave to feed?
  • How do bats regulate their body temperatures?

 

Motion Capture

What is motion capture?

Motion capture is a way to record patterns of movement, like how a person walks.

Researchers place dots on the body and then video cameras track these markers. Computer programs can translate the video into specs for a 3-D model.Modeling

Motion capture technology came into play in the 1970s and 1980s as a tool for biomechanics research. Coaches use mo-cap to sports performance. Motion capture makes it possible to give cartoon characters movements that are human.

In The Hobbit and The Lord of the Rings films, the Gollum’s appearance was completely computer animated, but all of his movements were based on the actor’s movements. Serkis wore markers on his joints during his performance. After the video shoot, computer software translated the video into specs that animators used to bring the character to life.

Why do bat researchers use motion capture?

Training a bat to fly in a lab, where conditions can be controlled, makes it easier to study night-flying, fast-moving creatures.  However, even then researchers are limited on how much they can learn because they cannot do everything to a live bat they think up. With mo-cap, they can make a 3D model that has complex movements. Even tiny details of motion, can be quickly and accurately recreated physically. They can see the effects of movement in one joint on the rest of the body.

 How do scientists use motion capture?

Once researchers get a 3-D virtual model of a bat, they can change the perspective, speed of motion, zoom in or out, make drawings based on the movement and study the patterns.

What do bat researchers learn by using motion capture?

The bat model moves exactly how a real bat would, and gives researchers a fresh way to “see” and study bat movement.

Researchers have already used motion capture to study the physiology of bat flight. For example, the motion and range of a bat’s wings in flight varies according to speed and species. Researchers learn how bats propel themselves, how they maneuver and land, and how they adapt to changes in wind speed or air pressure. Fruit bats and insect-eating bats, for example, have different flying styles that seem well-suited to their different needs.

 Why is motion capture used?

Motion capture does not hurt bats! No physical harm occurs to the bats by flying in the lab.  Bats are then released back into the wild.

Benefits

Accurate model

Models can be manipulated to answer researchers’ questions

No need to harm a live bat

Challenges

It takes time to train bats to fly in a lab environment in order to capture the motion. The hardware and software are expensive.  Additionally, people need training to operate the technology.

Resources

The resources below can be a starting point for learning more about bats and motion capture.

http://web.mit.edu/comm-forum/papers/furniss.html

http://en.wikipedia.org/wiki/Motion_capture

http://www.mit.edu/~djwillis/FlappingFlight/BatFlight.html

http://news.brown.edu/pressreleases/2009/03/bats

Contributed by Ellen Rohn