Reaping Unexpected Benefits from Geiger-mode LiDAR Data
About a year and a half ago, the Channel Island Regional GIS (CIRGIS) cooperative launched an initiative to update elevation and topographic contour information for a large swath of Southern California. CIRGIS is a non-profit public benefit cooperation founded in 2004, and part of its mission is to empower government and private agencies in Santa Barbara and Ventura counties through collaborative data acquisition projects and data sharing. True to its mission, CIRGIS organized a cooperative purchase for the LiDAR elevation data needed for the area.
After sending out proposals to numerous agencies in the region, nine cities, one university, and a water district signed on to the effort. “Existing data for these counties was 10 to 20 years old, and there were large areas where data was incomplete, non-existent, or out of date,” according to Hassan Kasraie, the CIRGIS LiDAR Project Manager. After narrowing the list of potential vendors, CIRGIS ultimately went with Harris because of its Geiger-mode LiDAR sensor. “Geiger-mode LiDAR technology offered a wide-area collect at high-resolution, and with the cooperative purchase, the price per square foot was approximately half of what it would have been with independent buys,” said Kasraie.
Participating cities and agencies intend to use this LiDAR data for planning and operations including:
- Evaluating slopes for development
- Calculating hydraulic pressures for sewer and storm water flows
- Managing emergencies, flood control and planning
- Visualizing and evaluation of bridges, buildings and vegetation in 3-D
Leveraging Geiger-mode LiDAR Beyond Initial Plans
The data was only recently delivered, and one city has already identified several ways to leverage it for projects outside of their initial plans. Fillmore knew that City Planning needed LiDAR to extract building foot prints and to calculate impervious surfaces. David Burkhart, a consultant for the city who also happens to be the Chief Financial Officer for CIRGIS, had some plans of his own for the data. Burkhart manages the contractor who operates the city’s sewage treatment plant, the sewage collection system, and the recycled water distribution system. “Parts of the city’s sewage collection system are overloaded, so we’re using the elevation contours to try to come up with some solutions,” said Burkhart.
“We’re in the process of determining the ground surface elevation of manholes from the LiDAR data. Then we're using a simple and crude method of putting a long pole down the manhole to measure the depth,” explained Burkhart. They will use that information to model the existing system, determine sewage loads on existing pipes, and identify problem areas. From there, a number of alternative solutions can be explored to determine what is most cost effective.
“We’ll also use the model by adding General Plan buildout of the City to determine future sewage loads and identify any future problems,” added Burkhart.
Geiger-mode LiDAR Data Helps City Save Money
By using the Geiger-mode LiDAR data for the project, Burkhart says the city is saving money it would have otherwise had to spend on an engineering consultant. He also plans to use the data to create a Digital Elevation Model of the sewer system pipe inverts to identify the areas where it intersects the groundwater table. “The City has a problem with infiltration of groundwater into a low lying portion of the sewer system that may add as much as 30 percent to the sewage flow during wet weather,” Burkhart explained. “That hasn’t been a problem for a while, but could be if it ever rains again in California."
Harris collected the Geiger-mode LiDAR data at a very high resolution, but licensed it to participating agencies at USGS Level 1 (eight points per square meter). Harris provided professional surveyor certification that this resolution exceeds FEMA guidelines and can be used to apply for recovery funds in declared emergencies. Higher resolution data is available if needed for extracting building outlines or providing information about facilities and potential hazards to first responders.