Altimetric LiDAR primarily uses the range measured by the laser ranger. To realise accurate and long range measurement the laser pulse should have the following characteristics:
· High power: So reflectance is available at receiver
· Short pulse length: Less uncertainty in time measurement
· High collimation: Less uncertainty due to smaller footprint
· Narrow optical spectrum: Small bandpass filter to reduce noise
· Eye safety: The lasers are more dangerous as wavelength reduces
· Spectral reflectivity of laser from terrain features: So reflectance (signal) is available.