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.
The diode laser is frequency modulated by a dual-pass acousto- optic modulation setup developed by the lidar group at Colorado State University in order to get the spectral information necessary to measure potassium temperature in the mesopause.
The receiver consists of an 800 mm diameter Cassegrain telescope that is fiber-optically coupled to receiver optics made up of an optical chopper to block low-altitude return, a narrow-band interference filter to reduce background, and an electronically gated GaAs photomultiplier detector.
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.
The laser output is wavelength locked using a pulsed wavemeter and software developed at the Arecibo Observatory in order to feed back to the dye laser's rotating grating.
As with the K lidar, the receiver consists of an 800 mm diameter Cassegrain telescope that is fiber-optically coupled to receiver optics made up of an optical chopper to block low-altitude return, a narrow-band interference filter to reduce background, and an electronically gated GaAs photomultiplier detector.
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.
The receiver is the same as above, except that, after exiting the fiber, the received light is split into two channels. The first goes directly to a photomultiplier, while the second passes through an I2 vapor cell before being detected by a PMT.
The ratio of filtered to unfiltered signal gives frequency information for measuring the winds. A Doppler shift is seen as an increase or decrease in absorption by the I2. Temperature profiles are gleaned from the unfiltered channel. This system works for altitudes above 20 km where the Mie scattering component of the signal is negligible. See our publications list for a reference to a more complete description of this system.
Arecibo Observatory 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).
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.