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Sky lasers for plant measuring

If you’re like me, you’ve wondered how lasers might have a practical application in your life. Luckily, I think lasers could be very useful for researching some of the things I am interested in. Specifically, using laser technology to measure vegetation with a tool called LIDAR.

LIDAR

LIDAR is a remote sensing tool. Remote sensing is any way of measuring something from afar, like using satellite or aerial images to measure things on the ground, or analyzing the heat or colors of things on the ground. Depending on who you ask, LIDAR is either shorthand for Light Detection and Ranging, or a derivative of light and radar. It can be written as LIDAR, Lidar, or LiDAR.

Essentially, a laser is mounted on an aircraft or satellite, and laser pulses are emitted towards the earth. The light reflects off of whatever it hits, be it ground, tree, building, whatever, and returns to the aircraft. The time it takes for the light to bounce back is recorded, and since we know how fast light travels, we can use this data to figure out the distance the light travelled, and therefore, where that object is in relation to the aircraft. It does this a gazillion times, always recording the location and length of time for the light to return. This results in a “point cloud,” which is a 3D set of points that can be converted into latitude (Y), longitude (X), and elevation or height (Z). A common application of this data is high-resolution elevation maps (see some examples here).

Vegetation

LIDAR could be very useful for measuring vegetation. There are many different ways to analyze the “point cloud” to learn different things about what’s on the ground, and two of those ways are deriving vegetation canopy height and vegetation density. I’m particularly interested in vegetation as it relates to wildlife habitat, and changes in vegetation over space and time due to invasive plant infestations. LIDAR could be a very useful tool for investigating these things!

Vegetation canopy height: With LIDAR, so many laser pulses are emitted and measured, some will inevitably hit the tops of plants and also the gaps between plants, even if the gaps are very small. We can use a computer program to decide which points are ground points and which are plant-top points. From these two types of points, ground and top, we can estimate the height of the plants. 

A depiction of how LIDAR can estimate the height of a forest canopy. Image credit: Alena Warren

A depiction of how LIDAR can estimate the height of a forest canopy. Image credit: Alena Warren

Vegetation density: Similarly, if we know which points are hitting plants and which ones are hitting the ground, and where these points are, we can make a map showing where the plants are closer together, or further apart.

This tool is becoming increasingly common and comprehensive, and I believe it will have many applications to ecology, so I am learning more about it and how to use it. I’m trying to make plant height maps to help me figure out where there are likely patches of New England cottontail habitat; this type of habitat is typically shrublands around 2-3 meters tall. Some LIDAR data that FEMA has collected is available for anyone to use, so I have the data, but not quite the skills (yet). 

For more information about New England cottontail habitat, check out my post about it, or the NH Department of Fish and Game page.

And if you are interested in other tools and technology, check out our Tools of the Trade Series! 

References and further reading:

NOAA LIDAR

NOAA Remote Sensing

University of New Hampshire LIDAR site

ArcGIS Forest Canopy and Density Info

 

For more on New England cottontail habitat...

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Winter is Coming: Bunny Edition

Now we know what happens to the treesgreensmicrobeshumans and intertidal zones in the cold winter. I bet you're dying to know, what happens to bunnies in the winter? Well, winter is hard on the bunnies. Here I'll discuss a few of things I've learned while researching New England cottontail habitat.