Lidar

1. INTRODUCTION

LIDAR is an acronym for light direction and ranging, and is a laser remote sensing technique used in both science and industry. It is the optical equivalent of the microwave radar, and so is often referred to as laser radar. In the Atmospheric-Optics Laboratory we use LIDAR for atmospheric research, and obtain measurements of aerosol particulates, clouds, temperatures and water-vapor. The measurements are used for studies of trans boundary pollution transport and Arctic climate change.

1.1 LIDAR

LIDAR is similar in principle to Radar (Radio Detection and Ranging). It is a very helpful instrument to observe the Earth’s atmosphere. A LIDAR transmits light to a target (the atmosphere), which scatters a small portion of the light back along the line of sight. The LIDAR is able to infer several characteristics of the target, which subtly alters the incident light. A light may be in the form of short pulses (“pulsed”) or continuously (“continuous-wave”). For the case of pulsed LIDAR, the range to the target may be measured by timing the flight of the pulse from the laser to the target and back. To construct a LIDAR system we need a laser to send out powerful light pulses, a telescope to receive the backscattered light, a sensitive detector to measure the intensity, a bunch of electronics, etc. Using LIDAR we measure where, how and how much light was scattered back.

In radar, radio waves are transmitted into the atmosphere, which scatters some of the power back to radar’s receiver. A LIDAR also transmits and receives electromagnetic radiation, but at a higher frequency. LIDAR operates in the ultraviolet, visible and infrared region of the electromagnetic spectrum.

Long wavelengths Short wavelengths

Fig.1.1: Electromagnetic spectrum

Different types of physical processes in the atmosphere are...