IGAC: LiDAR processing and its use in modeling of flooding in urban zones

UN-SPIDER's Regional Support Office in Colombia, the Agustin Codazzi Geographic Institute (IGAC) is doing a research project about LiDAR (Light Detection and Ranging Laser). LiDAR is a type of active remote sensor whose processing is not yet very common neither in Colombia nor in the countries of our region. These sensors emit millions of laser pulses which then backscatter to the sensor. The information of these laser pulses can then be used to create Digital Terrain Models (DTM) and Digital Elevation Models (DEM) for large land extents with the best spatial resolution available at the moment.

DTMs and DEMs of LiDAR generate more accurate flooding models than any other remote sensing application. These flooding models also have the best spatial resolution, less than 1 meter, allowing for a very precise identification of risk areas. This is a necessary characteristic of flooding models of urban areas because in these places the differences in centimeters define significant affectation grades.

Most software used to process LiDAR data has expensive licenses; therefore their use is restricted to some specific users. IGAC's expert have developed two methodologies to generate DTMs and DEMs using freeware: The first methodology filters the impulses based on radiometric characteristics and interpolates the filtered pulses using the Kriging analysis. The second methodology filters the impulses based on geometric characteristics and generates DTMs and DEMs using an iterative TIN (triangulated irregular network) algorithm. In addition IGAC develop a tool for ArcToolBox of ArcGIS to get directly files .LAS. This tool allows to visualize the files .LAS, filter pulses, and generate DTMs and DEMs.