Chris Shannon, P.E., CFM
Division Manager - Geographic Information Systems
Geographic Information Systems (GIS) provide the ability to build and maintain an inventory of anything on the earth or any information that is tied to a location. One may ask the question – Why is GIS important? Simply put, because location matters.
Jack Dangermond, co-founder of the Environmental Systems Research Institute (ESRI), said – “When you put it on a map, people get it”.
Any location on the earth has massive amounts of data tied to it, which not only include physical features, but political, economic and social data, as well. GIS facilitates the process by which we can visualize, analyze and understand this data.
Remote sensing is one of the methods commonly used for collecting physical data to be integrated into GIS. Remote sensors collect data from objects on the earth without any direct contact. They do this by detecting energy reflected from the earth, and are typically mounted on satellites or aircraft. Remote sensing technology has become much more prevalent, accurate and accessible in recent years, and covers a wide range of engineering applications.
First, engineers use remote sensing to help them determine the topography of our earth. Three-dimensional images of the earth’s surface (shown in Figure 1) can be generated using LiDAR, which stands for Light Detection and Ranging.
LiDAR sensors use pulsed lasers combined with position and orientation data to collect dense groups of elevation points called point clouds. These point clouds can then be processed into contours and digital elevation models (DEMs) representing the shape of the earth. Engineers can use a DEM to calculate a very quick and fairly accurate estimate of the volume of earth-moving necessary to develop a tract of land.
Remote sensing is also used to monitor land use, which aids engineers and planners in making decisions during the course of a design project. Optical sensors measure the solar radiation reflected from the surface of the earth. The different wavelengths detected are combined, resulting in an image that resembles a photograph taken by a camera of the earth’s surface.
Figure 2 shows the progress of development over a 14-year period around Katy, Texas.
Finally, remote sensing is used in hydrologic applications such as measuring the area of impervious surfaces. Impervious surface datasets are generated by classifying different bands in images collected by optical sensors. This can be done since different materials reflect visible and infrared light in different ways.
Houston’s rapid increase in population over the recent years has brought with it an explosion in the amount of roads, rooftops and parking lots that drape the landscape. This puts increased pressure on the environment by adding to the pollution of Houston’s bayous and further exacerbating urban flooding.
Engineers utilize impervious surface datasets, such as the example shown in Figure 3, to help monitor this growing issue.
As computing technology advances, so does the quality and quantity of data available to engineers. GIS has become an integral tool in many industries as a way to utilize this data to its fullest potential.