Christian J. Grund

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...

The 27-28 October 1986 FIRE IFO cirrus case study - Cloud optical properties determined by High Spectral Resolution Lidar

Abstract During the FIRE cirrus IFO, the High Spectral Resolution Lidar (HSRL) was operated from a roof top site on the University of Wisconsin–Madison campus. Because the HSRL technique separately measures the molecular and cloud particle backscatter components of the lidar return, the optical thickness is determined independent of particle backscatter. This is accomplished by comparing the known molecular density distribution to the observed decrease in molecular backscatter signal with altitude. The particle to molecular backscatter ratio yields calibrated measurements of backscatter cross section that can be plotted to reveal cloud morphology without distortion due to attenuation. Changes in cloud particle size shape and phase affect the backscatter to extinction ratio (backscatter-phase function). The HSRL independently measures cloud particle backscatter phase function. This paper presents a quantitative analysis of the HSRL cirrus cloud data acquired over an ∼33 hour period of continuous near-zenit...

Observations of Pinatubo ejecta over Boulder, Colorado by lidars of three different wavelengths

NOAA lidars at wavelengths of 0.574, 0.694, and 10.591 μm have observed ejecta from the eruption of Mt. Pinatubo both in the troposphere and stratosphere over Boulder, Colorado, since July 27, 1991. Multilayered clouds have been highly variable on time scales of minutes to days. Measurements at multiple wavelengths provide valuable information on size distribution and the wavelength dependence of backscatter and optical depth.

Comparison of Mount Pinatubo and El Chichon volcanic events: Lidar observations at 10.6 and 0.69 μm

Analyses of a dense set of lidar observations of the volcanic clouds from Mount Pinatubo and El Chichon, primarily over Boulder, Colorado, and at a wavelength of 10.59 μm, reveal notable similarities and differences. The importance of tropopause folding events for purging stratospheric debris into the troposphere is confirmed, as well as the role of gravitational settling to bring debris into the grasp of the folding mechanism. Seasonal influences appear more important than time after eruption in both poleward transport and in purging stratospheric material downward. We discuss the lengthening of the decay process for the Mount Pinatubo clouds by either an equatorial reservoir of debris or by eruptions of Mount Spurr. Simultaneous observations at 0.69 and 10.59 μm help monitor aerosol effective radii versus altitude with good temporal and vertical resolution.

Depolarization and Backscatter Lidar for Unattended Operation

A depolarization and backscatter lidar for unattended, stand-alone eye safe operation has been developed and is undergoing tests at NOAA ETL. The system operates with a frequency doubled Nd:YLF micro-Joule pulse laser transmitter and employs a narrow field-of-view and narrow bandpass photon counting receiver. Monitoring, control, display, and data archiving are achieved through a network connection to a remote computer.

Fiber-optic scrambler reduces the bandpass range dependence of Fabry–Perot étalons used for spectral analysis of lidar backscatter

Lidar systems that analyze backscatter with Fabry-Perot étalons exhibit range-dependent spectral transmission functions. A fiber-optic scrambler is described that reduces this range dependence.

Optical Autocovariance Direct Detection Lidar for Simultaneous Wind, Aerosol, and Chemistry Profiling from Ground, Air, and Space Platforms

Optical Autocovariance Wind Lidar (OAWL) is a new direct-detection interferometric Doppler lidar approach that inherently enables simultaneous acquisition of multiple-wavelength High Spectral Resolution Lidar calibrated aerosol profiles (OA-HSRL). Unlike other coherent and direct detection Doppler systems, the receiver is self referencing; no specific optical frequency lock is required between the receiver and transmitter. This property facilitates frequency-agile modalities such as DIAL. Because UV laser wavelengths are accommodated, a single transmitter can simultaneously support winds, Raman, fluorescence, DIAL, and HSRL receiver channels, each sampling identical spatial and temporal volumes. LOS species flux measurements are acquired without the usual spatial and temporal sampling errors (or cost, volume, mass, power, and logistical issues) incurred by separate lidar systems, or lidars in combination with other remote or in-situ sensors. A proof of concept (POC) OAWL system has been built and demonstrated at Ball, and OAHSRL POC is in progress. A robust multi-wavelength, field-widened OAWL/OA-HSRL system is under development with planned airborne demonstration from a WB-57 in late 2010. Detailed radiometric and dynamic models have been developed to predict performance in both airborne and space borne scenarios. OA theory, development, demonstration status, advantages, limitations, space and airborne performance, and combined measurement synergies are discussed.

High Resolution Doppler Lidar Measurements of Wind and Turbulence

The Environmental Technology Laboratory (ETL) High Resolution Doppler Lidar (HRDL) was developed to provide higher spatial, temporal, and velocity resolution, and more reliable performance, than was previously obtainable with C02 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 recently operated from a ship during the Marine Boundary Layer Experiment and demonstrated simultaneously 5 cm/s velocity resolution and 30 m range resolution. Program objectives, technology and performance are discussed.

Proposed Compact, Eye-Safe Lidar for Measuring Atmospheric Water Vapor

A thorough understanding of tropospheric water vapor is essential for forecasting weather and modeling radiative transfer. This project focuses on the development of an automated, ground-based, compact, eye-safe and inexpensive differential absorption lidar (DIAL) to profile tropospheric water vapor. Such a system could be widely deployed to supplement twice-daily radiosonde profiles or used in arrays to measure water vapor transport variability with a continuous datastream from a known location. Instrument features will include daytime measurement capabilities, a detection range of 3–6 km, a spatial resolution of 100 m, a temporal resolution of ~15 minutes, and an error of less than 1 g/kg. This paper discusses the results of a lidar simulation and solid-state laser options for use in a low-cost water vapor lidar.

Compact diode laser homodyne vibrometers

We discuss the architecture and performance of compact, robust, alignment-free, homodyne vibrometers using telecom diode lasers as the illumination source. The technical challenges and performance of implementations using conventional macroscopic optical components are compared with ultra-miniature micro-bench components and assembly methods. Focused sensitivity exceeding 4.6 pm/SQRT(Hz) at 1m range, 23 pm/SQRT(Hz) at 5m range, and useful operation to >20m have been demonstrated with COTS 1550 nm sources, 1.5 cm transmit/receive beam diameter and 32 mW transmitted power. Vibrometer measurement bandwidth exceeds 100 kHz with current electronics. Demonstrated performance is suitable for a variety of defense, security, and inspection applications.