Lab 5 LiDAR remote sensing

GEOG 338

Charlie Krueger

Lab 5: LiDAR remote sensing

Goal and Background:

The goal of this lab is to have the class gain the knowledge about LiDAR data and what can be done with the data. LiDAR stands for light detection and ranging and it uses the light from a laser pulse to measure ranges to the Earth. These laser pulses help gather information about the shape of the Earth and the characteristics of the Earth’s surface. Using LiDAR systems scientists are able to examine both the natural and manmade things in the environment like building and bridges. LiDAR uses two different types of lasers that work better for different surfaces. LiDAR uses near-infrared laser to map land, while it uses green light to measure seafloors and riverbeds because it can penetrate the water. In this lab there were two specific objectives that were given to the class and the first was processing and retrieving different surface and terrain models. The second was using the models to create intensity images and other products that come from using point cloud. The data that the class used in this lab was Lidar point clouds in a LAS file format. LiDAR is an expanding part of the remote sensing field and is sure to produce many jobs in the future so it was good for the class to become familiar with using it.

Methods:

The first part of this lab was point cloud visualization in Erdas Imagine which is a program that is used to look at data and make corrections to images in it. The lab instructed to copy the Lab 5 folder and move it into a different section were students could use the data. This data was then opened in ArcMap another program that is used to examine data and used to make changes to the data.

The second part of the lab was to generate a LAS dataset and explore lidar point clouds with ArcGIS/ArcMap. To start in ArcMap, the students had to create a new LAS dataset in the folder that represented lab 5. Next all of the data that was viewed in Erdas Imagine was copied and moved into the LAS dataset. The statistics of the added data was then calculated and examined in the lab. The coordinate system of this data was also looked at and it had valuable information for the lab in it. Then the actual coordinate system that would be used was set. The LAS dataset was then placed onto the screen of ArcMap so the data could be examined. The properties of the data were changed so that the information would come up on the screen and be viewed. The LAS dataset toolbar was very useful during this lab because it allowed for quick viewing changes of the data. Changing this like filters from elevation, aspect, slope, and contour was simple with this toolbar. The layer properties of the data set could also be used to transform the data into what the user wanted to view. Here the data filter could be customized even more and the way that was done was changing the classification codes and the returns. Another interesting tool was the LAS dataset profile which allowed for a 3D type of image to be created from a selected area from the map.

The final section of this lab was generation of Lidar derivative products. Here different views of the data would be created using different tool through ArcMap. The following maps were made in this section Digital surface model (DSM) with first return, Digital terrain model (DTM), Hillshade of your DSM, and Hillshade of your DTM.  The first tool that was used was LAS dataset to Raster and this tool took a while because of the large dataset that it was processing. With the outcome of this tool another tool was used on it and that was a tool call Hillshade. Also in this part the lab instructed to create a map by deriving Lidar Intensity image from point cloud. The same tools were used in this process just the set up was a bit different by changes the dataset to Points instead of elevation like the last map and first return everything else was the same. The map image was then saved over to a different file type so that it could be viewed in ERDAS Imagine.

Results:

Digital Surface Model (DSM) First Return

Digital Terrain Model (DTM) First Return

DSM Hill shade tool applied

DTM Hill shade tool applied

Intensity Image Created

Sources:

Lidar point cloud and Tile Index are from Eau Claire County, 2013.  Eau Claire County Shapefile is from Mastering ArcGIS 6th Edition data by Margaret Price, 2014.