What distinguishes first return LiDAR data from second return LiDAR data?

First return LiDAR data and second return LiDAR data are distinguished by the types of surfaces they capture during the scanning process. First return data primarily reflects the highest point that the laser pulse hits, which is often the treetops or other tall features in the landscape. This allows for the creation of a digital surface model that shows the locations of vegetation and buildings.

In contrast, second return data is created when the laser pulse penetrates through the canopy and reflects off the ground or other lower surfaces. As a result, second return data is particularly valuable for understanding the terrain and ground surface beneath vegetation, providing insights into ground elevation and surface contours that are not visible in the first return data alone.

This distinction between the two returns is crucial in applications such as forestry, where understanding both the vegetation structure (first return) and the underlying terrain (second return) is necessary for effective management and analysis. The correct choice highlights this difference in data capture functions, making it essential for any GIS professional to comprehend how these returns contribute to spatial analysis.