R. A. Richter

High-Resolution Doppler Lidar for Boundary Layer and Cloud Research

Abstract The high-resolution Doppler lidar (HRDL) was developed to provide higher spatial, temporal, and velocity resolution and more reliable performance than was previously obtainable with CO2-laser-based technology. The improved performance is needed to support continued advancement of boundary layer simulation models and to facilitate high-resolution turbulent flux measurements. HRDL combines a unique, eye-safe, near-IR-wavelength, solid-state laser transmitter with advanced signal processing and a high-speed scanner to achieve 30-m range resolution and a velocity precision of ∼10 cm s−1 under a variety of marine and continental boundary layer conditions, depending on atmospheric and operating conditions. An attitude-compensating scanner has been developed to facilitate shipboard marine boundary layer observations. Vertical velocities, fine details of the wind profile near the surface, turbulence kinetic energy profiles, and momentum flux are measurable with HRDL. The system is also useful for cloud s...

Characteristics of coherent lidar returns from calibration targets and aerosols

A CO(2) heterodyne lidar system and high speed digitizer were used to examine properties of returns from disk and belt-type calibration targets and atmospheric aerosols. Amplitude statistics of the returns from the targets examined corresponded to those of the Rayleigh phasor predicted by theory. Returns from a belt sander fluctuated at a much slower rate than those from the disks or aerosols, requiring longer averaging times for accurate power measurement. At very close focal lengths returns from single large particles often domier nated the backscattered aerosol signal.

Feasibility studies for a global wind measuring satellite system (Windsat): analysis of simulated performance.

A detailed computer simulation of the Windsat global wind measuring process has been developed and used to establish error limits as a function of design parameters. Studies were conducted for a Windsat research system in a 300- and an 800-km orbit. Wind measuring errors were <2 m sec−1 in the troposphere for the recommended set of parameters. Our study results indicate the feasibility of measuring global winds from a space platform using a coherent laser radar.

Aerosol backscattering profiles at λ = 10.6 μm

A systematic program of observing atmospheric backscatter beta profiles from 4 to 16-km above sea level is described. Initial monthly averages indicating a lognormal distribution are presented. Cirrus prevalence, volcanic layers in the stratosphere, diurnal effects, convection, calibration, and absorption effects are discussed as well.

Calibration of coherent lidar targets

We determine the backscatter reflectance (more properly the bidirectional reflectance distribution function at a 45 degrees angle of incidence and observation) for circularly polarized radiation of lambda = 10.6 microm for 120-grit aluminum oxide sandcloth (1.5 x 10(-2) sr(-1)) and 400-grit silicon carbide sandpaper (1.1 x 10(-2) sr(-1)) with respect to sublimed flowers of sulfur (1.8 x 10(-1) sr(-1)). The effect of range and the atmospheric effect of turbulence-induced beam wander are discussed for both rotating disks and linearly translated belts. The advantages of large slowly rotating disks for field calibrations are presented.

Scanning tropospheric ozone and aerosol lidar with double-gated photomultipliers

The Ozone Profiling Atmospheric Lidar is a scanning four-wavelength ultraviolet differential absorption lidar that measures tropospheric ozone and aerosols. Derived profiles from the lidar data include ozone concentration, aerosol extinction, and calibrated aerosol backscatter. Aerosol calibrations assume a clear air region aloft. Other products include cloud base heights, aerosol layer heights, and scans of particulate plumes from aircraft. The aerosol data range from 280 m to 12 km with 5 m range resolution, while the ozone data ranges from 280 m to about 1.2 km with 100 m resolution. In horizontally homogeneous atmospheres, data from multiple-elevation angles is combined to reduce the minimum altitude of the aerosol and ozone profiles to about 20 m. The lidar design, the characterization of the photomultiplier tubes, ozone and aerosol analysis techniques, and sample data are described. Also discussed is a double-gating technique to shorten the gated turn-on time of the photomultiplier tubes, and thereby reduce the detection of background light and the outgoing laser pulse.

Ground-Based Coherent Lidar Measurement Of Tropospheric And Stratospheric Parameters

During 1982 we used the NOAA pulsed Doppler lidar as part of experimental programs to measure precisely lidar system performance and extend the instruments demonstrated atmospheric monitoring capabilities. Key system characteristics such as pulse shape, chirp, alignment stability, telescope efficiency, and pulse-to-pulse variability were studied and their effect on measurement accuracy quantified. The field experiments also demonstrated the systems capabilities and limitations in monitoring winds, backscatter, turbulence, and moisture. By scanning the wind field at low scan elevation angles, we have observed such small-scale meteorological events as thunderstorm gust fronts, downbursts, and cold front passage. Scans at higher elevation angles enable us to monitor upper level winds, such as those in the vicinity of the polar-front jet. We also monitor backscatter coefficient (β) over both the short and long term. Daily observations show a noticeable decrease in tropospheric β during the winter months. The stratospheric aerosol layer resulting from the El Chichon volcano eruption was easily observed during fall 1982.

National Oceanic and Atmospheric Administration's (NOAA) Pulsed, Coherent, Infrared Doppler lidar - Characteristics And Data

We describe detailed performance characteristics of NOAAs pulsed, coherent, hybrid TEA, CO2 Doppler lidar. Included are acoustically generated inter-pulse frequency jitter of the hybrid cavity, on-line center and off-line center plasma-generated intra-pulse chirp, and transmitter-receiver feed-through isolation. Data processing and display are discussed. Data taken in the clear atmosphere into the stratosphere, including VAD scans For mesoscale convergence, are presented, as well as calibration procedures.

Feasibility And Design Considerations Of A Global Wind Sensing Coherent Infrared Radar (WINDSAT)

Since 1977, NOAA has been investigating the feasibility of a global wind-sensing lidar in response to the need for altitude profiles of the wind vector to serve as input to global circulation models. The lidar technique obtains the wind information by assessing the Doppler information contained in CO2 laser radiation backscattered from the atmospheric aerosol (particulates, droplets, etc.). The results of studies undertaken to define the proposed system concept and hardware for a space-shuttle-borne demonstration flight are presented. Resulting from considerations of wind vector accuracy, area coverage and sampling density, signal detectability and space shuttle compatibility requirements were a continuous conical scan of the telescope with a half cone angle of 62° centered on nadir, telescope diameter (1.25 m), laser pulse energy (10 J), pulse repetition frequency (8 Hz), pulse duration (6 ins) and laser wavelength (9.11 pm). Requirements that the concept imposes on platform stability, navigation and attitude determination, line-of-sight pointing and lag angle compensation, on-board Doppler processing, prime power and thermal dissipation are discussed. The system configuration intended for a hardware design study is presented.