Goal and Background
The main goal of this lab is to get basic knowledge of LiDAR data structure and processing. This includes the processing of numerous surface and terrain images and then processing and creation of intensity image and other products from point cloud.
This is our first time working with LiDAR data and getting to know our way around using it. LiDAR stand for light detection and ranging. This method takes light in the form of a pulsing laser the measure ranges to Earth. This data combined with other various data can help to generate 3D information about the shape of the Earth the characteristics of our planet.
Methods
Unlike our other labs, most of this lab was done in ArcMap instead of Erdas Imagine. For the first part of the lab we needed to do a quality check of the LAS dataset we are given. This entails checking the metadata and making sure everything looks correct. After doing so, I had to create a new LAS dataset, this keeps the data organized and easily accessible when working with it. Because we created a new dataset this means we need to build the statistics of the data. The data already has statistics associated with it, but the new area does not have this data unless we calculate it. Though, ArcCatalog does make this quite easier. With the push of the 'calculate' button, all of the statistics are now in the LAS file. The calculate button is sometimes too good to be true so we need to check the statistics to make sure they are correct. The best way to do so is to check the elevation. If the elevation is in the same range as the area the LiDAR data is taken of, then it's good to move onto the next step. Our statistics are good so it's onto the next step. Now we need to set the coordinate system for the data. No coordinate system was imported with the LAS files so we need to look at the original to see if one of those files has the coordinate system the data was taken in. It in fact does and now we need to transfer this to the new data. Everything is set in ArcCatalog and it's time to move into ArcMap to actually work with the data.
Once in ArcMap I imported the LAS dataset which is displayed in tiles until you zoom in to a certain extent and the LiDAR points are revealed. I also added a shapefile of Eau Claire county to get a better grasp of where everything is. Next I had to activate the LAS Dataset Toolbar in order to visualize the point clouds and generate different products for the next section of the lab. I explored the different options I could change the map to look like. For example, elevation, aspect, slope, and contour. I also changed the filters that were available. Here I couuld change which returns I wanted to see and which classes I wanted to see (ground, vegetation, building, water, etc). After playing around with those options for a while, I moved onto creating two different rasters. I created multiple DSMs and DTMs. Figures 1 and 2 were created using hillshade. Figure 1 shows the Eau Claire area with buildings and vegetation. Figure 2 takes away all of that and just shows what the ground looks like without it all. It was incredibly interesting to see what differences buildings and vegetation can make it a simple LiDAR image. Figure 3 shows a LiDAR intensity image. The intensity image shows the first return points from LiDAR.
Results
Below are the images I created using different tools throughout this lab.
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| Figure 1: Hillshaded image of the Eau Claire area. |
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| Figure 2: Hillshaded image of Eau Claire without buildings or vegetation |
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| Figure 3: LiDAR intensity image |
Conclusions
It was very interesting to see another side of remote sensing by learning about LiDAR. I didn't know how diverse this area of study could really be. I would like to learn more about LiDAR and all of it's capabilities. I would also like to see if there are any health risks involved with the LiDAR lasers that are being sent down. It will be interesting to see where LiDAR goes in the future and how it develops.
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