Monday, August 11, 2014

What the heck is LiDAR?

By Sandi Funke, Education Director

Land cover map courtesy of Tukman Geospatial LLC.
I was at a staff meeting recently where our research and preserve management staff got all starry eyed while waxing poetic about the new topographic maps produced of Pepperwood using “LiDAR.” LiDAR stands for Light Detection and Ranging, and it’s basically a way of measuring the surface of the ground using an airplane-mounted laser. Our scientists talked about how wonderful these maps are and how lucky we are to have access to this ground-breaking technology. This is not the first time I have seen technical folks get all giddy over LiDAR, so why is it so special? Our Preserve Ecologist explained it was “technology and science, hand in hand” that got her excited. The tremendous range of LiDAR data applications for research ecologists and land managers is certainly cause for excitement.

Sonoma County has LiDAR data thanks to our friends at the Sonoma County Agricultural Preservation and Open Space District (SCAPOSD), and a new partnership with NASA. The data was produced as part of the Sonoma Veg Map project, a collaboration between SCAPOSD and the Sonoma County Water Agency and others. “The countywide LiDAR data is allowing us to accurately map the diverse habitats that exist in Sonoma County,” said Tom Robinson, SCAPOSD Conservation Planner. “Such an inventory will significantly increase our ability to protect and preserve the county’s biodiversity and natural landscapes, and the ecosystem services they provide for the community.”

LiDAR can record multiple distance points in the same relative
area, essentially creating a cross-section of vegetation.
Image courtesy of SCAPOSD.
As explained by the National Oceanic and Atmospheric Administration, LiDAR is a “remote sensing method which uses pulsed laser light to determine the surface of the Earth.” Light pulses emitted from equipment on an aircraft are reflected by the surface they encounter. A sensor records this reflected light to produce a range of distances. When this laser range data is combined with other data including position information from GPS, the result is a dense, detail rich group of elevation points and accurate, three dimensional information about the shape of the Earth and surface characteristics from forest canopy down to the ground level.

LiDAR can produce incredibly high-resolution “digital elevation models,” or DEMs, which are basically detailed topographic maps that can be used for many purposes. In Sonoma County, LiDAR light pulse measurements were spaced only 3” apart. This means the resulting images reveal very fine features, like the shape of trees and shrubs, the outline of streams, and even individual fence posts.

This graphic demonstrates the difference in resolution between the new LiDAR data 
and existing methods. Image courtesy of SCAPOSD.
Here at Pepperwood, we will use the data for modeling our hydrology, determining where erosion may be occurring, identifying potential restoration sites, monitoring forest structure and vegetation community succession, and a multitude of other uses we have not even explored yet. We are currently using these detailed elevation maps to delineate drainages so we can improve our hydrologic modeling along and to establish “grazing monitoring units” defined by geological features.

Land cover map courtesy of Tukman Geospatial LLC.
LiDAR greatly reduces the amount of time researchers have to spend surveying on the ground. Data which could otherwise take months to collect can be gathered using LiDAR in an afternoon. Though there is no replacement for the long-term, on-the-ground monitoring we employ to record how our landscapes and their inhabitants are changing over time, LiDAR is an excellent addition to our toolbox. It will help us better manage our preserve for resiliency under climate change pressures and develop protocols that can be used by other preserves and open spaces in our region.

A special thank you to Tom Robinson and the Sonoma County Agricultural Preservation and Open Space District for sharing the above images! Read more about LiDAR on the SCAPOSD website here.

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