The State of North Carolina ( where I reside) has a lot of GIS data. I am , in particular, intrigued by the statewide lidar data set. Lidar , for the uninformed, stands for Light Detection And Ranging. You basically find out how far away things are by shooting a laser pulse at them and measuring the amount of time it takes to hit the thing and bounce back.
This can be very useful if you mount your laser in an airplane and shoot it at the ground. You can then measure the distance between the plane and the ground. If you know the exact location of the plane via GPS, then you know the elevation of the ground at that point. Take points continuously as you fly the plane and you get a pretty good picture of what the ground surface looks like. The ground surface can be mapped to within 6″-9″ in vertical accuracy.
Why does the state of North Carolina have statewide lidar data? Well it’s because of Floyd. Not Floyd the barber from the
Andy Griffith Show
I’m talking about Floyd the hurricane, a tropical cyclone that came ashore in North Carolina in 1999.
Floyd dropped a lot of rain (> 18 inches) on coastal North Carolina a few weeks after hurricane Dennis dropped 15 inches of rain on the same areas. The floods that followed caused a lot of damage, and highlighted the inaccuracy of the existing paper floodplain maps.
In response, the State of North Carolina set up the North Carolina Floodplain Mapping Program with the purpose of accurately mapping the floodplains. The program chose lidar as the method of obtaining a land surface to model the hydrology of each watershed to determine the floodplain extent. Lidar data was collected for the entire state over the course of about 5 years 2001-2006. How much data is that? Quite a bit, but I’ll save that for my next post…