LIDAR, once dubbed ladar
LIDAR stands for LIght Detection and Ranging and was initially referred to as ladar when it was first created due to its similarity to radar, it's radio-wave brethren. Much like radar uses radio waves to detect the position of vehicles and terrain, lidar uses infrared, visible, and ultraviolet light waves to detect the position of objects or particles.
Lidar is used to directly study the atmosphere by transmitting pulses of laser light into the atmosphere and detecting the backscattered light. Lidar systems measure the intensity of this backscattered light to determine the relative density of the matter at all altitudes with the system's range. The laser beam from the lidar propagates upward through the atmosphere, hits clouds or particulate matter, comes back down into the system's receiver, and is then calculated as the intensity of the light from a certain altitude. From this, we can measure the height and thickness of clouds, the relative density of pollen or other solid aerosols, and the height and structure of aerosols in the atmosphere. Most lidar systems are designed and specially built by scientists to satisfy specific interests, such as to study the canopy height of rainforests or to study the amount of carbon dioxide in the lower atmosphere.
The PEARL system (Portable Eye-safe Atmospheric Research Lidar) is an elastic micropulse lidar, meaning it has a single-frequency, low-powered laser that makes the system safe to view, so students do not need to have laser training in order to operate it by themselves. This low-powered laser also restricts the height of how far up our lidar can see. Currently, we know we can see up to 5 km, and we are hoping to see up to 10 km before the end of 2013. The term "elastic lidar" indicates that our lidar uses only one laser wavelength rather than two or three wavelengths, as is common in Differential Absorption Lidar (DIAL). By the summer of 2013, we also hope to add depolarization capability to our lidar, which will allow us to determine the texture/orientation of the particulate matter that our lidar detects. Cirrus clouds contain ice particles, which return light polarized differently than low-lying clouds with solely liquid water. Pollen would show the same depolarization as ice clouds, while most normal air would show the same polarization as liquid clouds.