After receiving a significant amount of response for our metadata blog, we decided to discuss one of the most important aspects of any mapping project, ground control. Ground control refers to pre-marked or photo identifiable points on the Earth’s surface with known positions that is used either to process and rectify the raw geospatial data or to verify the accuracy of the final mapping products. Ground control networks are usually field surveyed in order to determine accurately their positions. However, other sources of accurate ground points can be used to verify and validate the accuracy of geospatial data products. Airborne LiDAR is excellent example of such sources as it provides highly accurate ground points that can be used in some instances as ground controls.
In GeoSAR mapping we typically use two types of ground control; a LiDAR profiler on the aircraft, and corner reflectors on the ground. As we fly over an area, our LiDAR profiler collects millions of 3-dimentional points (X,Y,Z) with high fidelity. These points provide a highly accurate dataset to compare and validate the GeoSAR products. Corner Reflectors, on the other hand, are deployed in the project area prior to our data collection. Corner Reflectors are targets constructed of material that is highly reflective to the radar signal. These reflectors are surveyed with a high level of accuracy and then imaged by the radar as we fly over them. They provide an easily identifiable known location in the radar data. Reflector data are used in the least-squares adjustment, removing slight offsets in the data between bands, and as another source of validation. The image below shows a radar reflector used during one of our mapping projects. You will notice that there are four sides to the reflector, allowing the reflector to be imaged from multiple sides during a single collection.
Ground control points are just one attribute of our unique GeoSAR mapping solution. If you would like to continue the conversation or receive more information please leave a comment. Stay tuned for more GeoSAR capabilities and updates!