First Return

First Return is a critical term used in the context of LiDAR (Light Detection and Ranging) and 3D geospatial data processing. It stands for the first substantial reflection detected upon interaction of a LiDAR laser pulse with objects on or above the Earth's surface. Due to the nature of the first return, which typically reflects off the highest encountered objects, it can detect tree canopies, vegetation, buildings, towers, power lines, and other elevated objects.

In the case of an airborne LiDAR survey, a laser pulse can produce several returns after passing through vegetation and reaching the ground surface. Consequently, first returns can provide useful information regarding the surfaces that are higher than others within a certain surveyed area. The information gained with the help of LiDAR first returns is frequently utilized in 3D mapping, canopy analysis, vegetation mapping, building detection, terrain modeling, and elevation analysis.

Comprehension of first returns is helpful in understanding LiDAR point cloud interpretation and distinction between elevated objects and ground surfaces. When coupled with last returns and intermediate returns, first returns provide useful information for 3D geospatial analysis and surface modeling.