LIDAR

Science & Atmospheric Sciences


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LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. It measures distance to a target by illuminating that target with a pulsed laser light, and measuring the reflected pulses with a sensor. Differences in laser return times and wavelengths can then be used to make digital representations of the target. The name lidar, sometimes considered an acronym of Light Detection And Ranging (sometimes Light Imaging, Detection, And Ranging), was originally a portmanteau of light and radar. LIDAR is popularly used to make high-resolution maps, with applications in geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. The technology is also used for control and navigation for some autonomous cars. Lidar sometimes is called laser scanning and 3D scanning, with terrestrial, airborne, and mobile applications.


Capabilities

Potassium Doppler-Resonance Lidar

The transmitter is a pulsed Alexandrite Ring Laser injection seeded by an external cavity Diode Laser. The diode laser is locked to the central cross-over feature of the Doppler-free spectrum from the K D1 spectral line.

Multi-metal Resonance Lidar

This lidar uses a pulsed dye laser pumped by a Nd:YAG laser for its transmitter. The fundamental output can operate in the yellow to near-IR in order to measure Na or K densities. This output can be doubled or mixed with residual IR from the Nd:YAG laser at 1064 nm in order to reach wavelengths for Fe, Ca, Ca+, or for DIAL studies of O3 near 310 nm.

Doppler Rayleigh-Mie Lidar

The Rayleigh-Mie transmitter is an injection- seeded pulsed Nd:YAG laser. The PRF is 40 Hz, and the average power is 24 W. The seed laser is frequency locked to the edge of an absorption line in I2.


Lidar Projects


Doppler Resonance Lidar

Mesopause Climatology: Long-term seasonal studies of the climatology of the mesopause. This study is presently underway with nighttime temperature profiling between 85 and 100 km. At a later date we will add line-of-sight winds and, using an ultra- narrow-band filter to cut out the solar background, daytime measurements.

Dynamics and Chemistry of Atomic Layer Enhancements: The study of neutral atomic layer enhancements, sometimes called "sporadic" or "sudden" layers. Doppler measurements will make temperature profiles of the layers and look for wind shears or other dynamics which may lead to their formation. Working in combination with the multi-metals lidar (see below), we can also gain clues to the chemical reactions taking place within the layers.

Tides and Gravity Waves: Short-term (during one or several consecutive nights) observations of the temperature (and wind) structure of the mesopause gives valuable information on the gravity wave spectrum, wave-breaking, and tidal motions.

Multi-Metal Resonance Lidar

Meteor Composition Studies: Meteors burn up in the upper atmosphere, between 80 and 120 km, leaving behind a trail of ions, atoms, molecules, and dust. Using resonance lidar, the increase in the quantity of a given atomic species due to a meteor can be detected. By observing two or more metals, some idea of meteor composition and ablation sequence can be determined.

Simultaneous observation of a metal and its ion: By switching between wavelengths, near-simultaneous observations of Ca and Ca+ can be made. This is especially useful to the study of layer chemistry and the formation of atomic layer enhancements (ALEs).

Doppler-Rayleigh Lidar

Stratospheric and Mesospheric Climatology, Waves, and Tides: The Rayleigh lidar can profile atmospheric temperatures in the altitude range from 30 to 80 km. It can also profile winds to above 50 km. This makes it a powerful instrument in the study of middle atmospheric dynamics.