A Lidar bare earth model, often constructed from last returns, displays the lowest elevation points in a landscape, effectively stripping away vegetation and buildings to reveal the terrain surface. These returns represent the final pulse reflection, making them ideal for creating Digital Terrain Models (DTMs) to analyze ground contours, slopes, and hidden surface features.
Key Aspects of Last Return Data:
Ground Representation: Last returns hit the ground or the lowest object (like low brush) when a laser pulse passes through canopy gaps.
Terrain Modeling: They are primary data sources for producing Digital Terrain Models (DTMs) and Digital Elevation Models (DEMs).
Feature Removal: By filtering out intermediate and first returns (which hit tree tops/buildings), the last return highlights only the "bare earth".
Limitations: In areas of extremely dense vegetation, the laser may not reach the ground, causing the last return to represent low vegetation rather than the true ground surface.