Objectives

• The goal is for you to become familiar with practical applications of LIDAR calculations as well as elevation information extraction from LIDAR masspoints. Specific LIDAR principles that will be explored are LIDAR range and instantaneous laser footprint. In this exercise you will also use the ArcMap Spatial Analyst extension to interpolate the USC campus elevation LIDAR point data to a raster grid.

Part I. LIDAR Image Calculations

A. LIDAR Range

1. The LIDAR Range () is determined by the following equation,, where t is the traveling time, and c is the speed of light.

    a. How many meters would  be if the traveling time were 6600 nanoseconds (10^-9 seconds)?

    b. How many meters would the airplane travel at the same time if the airplane speed is 200 mph (89.4 m/s)?

B. Instantaneous Laser Footprint

2. The Diameter of the instantaneous laser footprint () on the ground is computed by , where  is the altitude of the aircraft AGL,  is the instantaneous scan angle under investigation, and  is the divergence of the laser beam. A LIDAR system with AGL = 750m,  = 15º and  = 1mrad is used to obtain LIDAR imagery.

a. According to the   equation, the instantaneous laser footprint  is how many meters?

b. How many meters would  be if AGL were 1000 meters?

c. How many meters would  be if the instantaneous scan angle were 30 degrees?

Part II. LIDAR Questions

1. What are the four major technologies used to obtain elevation information? Describe the advantages and disadvantages of each technology.

2. It is very important to know the exact location of the LIDAR laser at all times during data collection. In LIDAR, what technology is used to accomplish this? Describe this technology.

3. It is necessary to have accurate LIDAR antenna orientation information (roll, pitch, and heading) at all times during data collection. What instrument is used to measure the orientation information?

Part III. Spatial Interpolation of LIDAR Point Data Using IDW Model

Inverse distance weighted methods are based on the assumption that the interpolating surface should be influenced most by the nearby points and less by the more distant points. The interpolating surface is a weighted average of the scatter points and the weight assigned to each scatter point diminishes as the distance from the interpolation point to the scatter point increases.

MATERIALS

    The LIDAR datasets you will be working with for ArcGIS are: 

•  USCcampus.img          Aerial photography of USC campus

•  Lidar_USC.shp           LIDAR data of USC campus

    1.  Open ArcMap with a new Data Frame. Add the following data: USCcampus.img and Lidar_USC.shp

    2.  Load the Spatial Analyst Extension

• Tools - Extensions: Select Spatial Analyst (make sure Spatial Analyst is selected).
• Tools -Customize: Select Spatial Analyst Toolbar.

    3.  Set the Extent of the grid and the cell size of the grid

• Spatial Analysis - Options, click on the Extent tab
• Choose "Analysis Extent:" same as USCcampus.img.
• Then click the Cell Size tab; Set the cell size as 5 feet. Click OK.

    4.  Creating a surface using IDW model

• Click the Spatial Analyst dropdown arrow, point to Interpolate to Raster, and click Inverse Distance Weighted.
• Click the Input points dropdown arrow and click the point dataset Lidar_usc.shp.
• Click the Z value field parameter dropdown arrow and click ELEV.
• Change the Power value to 3.
• Give the output file a name as IDW_USC, and save it in your working directory.
• Leave other parameters as default, and click OK.

    5.  Create a shaded-relief map based on the generated IDW_USC file.

The LIDAR derived IDW can be made even easier to interpret by applying a shaded-relief algorithm that highlights the terrain as if it were illuminated by the Sun from a specific direction.

• Click the Spatial Analyst dropdown arrow, point to Surface Analysis, and click Hillshade.
• Click the Input surface dropdown arrow and click IDW_USC.
• Specify the azimuth value you want to use. Use the default is 315 degrees.
• Specify an altitude value. Use the default is 45 degrees.
• Give the output a name as Hillshade_USC, and save it in your working directory.
• Leave other parameters as default, and click OK.

    6. Create Contours

    Sometimes it is valuable to extract contours (lines of equal elevation) from DSMs or DTMs to highlight subtle differences in the terrain and to identify depressions.

• Click the Spatial Analyst dropdown arrow, point to Surface Analysis, and click Contour.
• Click the Input surface dropdown arrow and click IDW_USC.
• Type a Contour interval to specify the distance between contours, Use the default value 10.
• Give the output file a name as Contour_USC, and save it in your working directory.
• Leave other parameters as default, and click OK.

    7. Create a map of your final results, including IDW, Hillshade, and Contour. Your map should include the following information:

• Title
• Short description of your map
• Your name

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