This is a repost from the now defunct Whatever-Weather.com website.
Even though we are in summer, let’s look ahead and think about winter and snow. Research studies have been going on for at least a decade to use LiDAR for detailed snow measurements. Both airborne and ground tripod based LiDAR scanners have been used in various applications. Snow pack studies have been done in forested, mountainous, and arctic areas and are still ongoing. Airborne LiDAR for snowpack measurements are still in the research stage. The data from the airborne sensor offers detailed measurement and improves data under forest canopies, something that traditional NOAA RFC flights using gamma rays struggle with in collecting soil-water equivalent (SWE) data in dense forest canopy areas and during snowmelt (Hopkinson).
Airplane and tripod mounted LiDAR systems use returns from an infrared laser to collect many irregularly spaced elevation points. The numbers of points range from 1-2 per m2 down to a current 2pts/m2 for 0.5m spacing apart (Hopkinson) depending on the data density you want to acquire.
Once the flight planning was done for the required points/m^2, the airplane flies at a fixed altitude in S-patterns having around 50% overlap (Moreno) with a final flight track across the flight lines for calibration, it is processed to vertically and horizontally align, then scripts are run to do a rough automatic calibration. It is then sent to editors who do manual analysis to look for high points (like vegetation) and edges of slopes along cliff and hill faces to fix the classification. Then further scripts are run to produce other data products from the edited data like Digital Surface Models (DSMs) and Digital Elevation Models (DEMs). Some LiDAR systems collect photographic images during the same flight. This data is used for quality control (Moreno).
LiDAR snowpack requires two different flights as it uses map algebra to obtain the snowpack measurements. It first requires a flight without snow on the ground (and preferably with leaf off the trees in the spring or fall) as a base/control flight. Many states are collecting statewide LiDAR data through Departments of Transportation or Natural Resources for this data set. Be aware that some of this base data was flown during snowpack times so it will not be suitable for snowpack measurements as snow is already in the base data. Most of the data is without snowpack for a baseline database DSM. You then fly with snowpack on the ground to get a second DSM after which you then subtract the snow-free elevation data from the snowpack data to get your snowpack dataset.
Now that you have the snowpack, the next step is still in the research stage. It is to get the Snow-Water Equivalent (SWE) of the snow pack. The most recent research comes from 2010 from US Army Cold Regions Research and Engineering Laboratory in Ft. Wainwright, Alaska with Matthew Strum as the chief researcher of an international group doing a study to model it. They did a model that related snow bulk density to SWE using historical snow core data. The model took climate classes with location, day of year, and with snow depth to produce a local bulk density estimates. The study then used a continental scale data set to produce SWE estimates within +-8cm with many estimates falling much closer. It is a good start for producing SWE values with LiDAR data, more research will be needed to refine the process. The hope is to make it operational so LiDAR datasets can be used to complement gamma ray datasets.
Finally, if you have found this post interesting and something you want to follow up with, I want to refer the reader to a colleague of mine, James Young and his LiDAR blog. James has been in the LiDAR industry for 17 years and is a good contact if you are looking to do something with these applications of LiDAR that I am talking about. He is the LiDAR Solutions Manager at Aerometric, an aerial survey company out of Sheboygan, Wisconsin, and can assist you with planning or direct you to other colleagues if you want to do snow studies with airborne or ground-based LiDAR.
Keep checking in here at Whatever-Weather.com, my next topic will be talking about LiDAR and Precision Agriculture.
Banos et al; Assessment of Airborne LiDAR for snowpack depth modeling
Hopkinson et al; Mapping the Spatial Distribution of Snowpack Depth beneath a Variable Forest Canopy Using Airborne LiDAR Altimetry
Strum et al; Estimating Snow Water Equivalent using Snow Depth Data and Climate Classes
(c) 2012 Charles Schoeneberger
Chuck Schoeneberger is a University of North Dakota graduate in Atmospheric Sciences. He has his Masters in Geographic Information Systems from St Mary’s University of Minnesota in Winona, MN. He also has worked with LiDAR processing from a position at Aerometric, an aerial survey company based in Sheboygan, WI and ortho imagery from Aerometric and Airborne Data Systems of Redwood Falls, MN. He lives in the Twin Cities metropolitan area. One of his passions is learning about technologies that can be applied to disaster response for public safety before and after damaging weather events