KEYWORDS: LIDAR, Aerosols, Backscatter, Analog electronics, Signal to noise ratio, Linear filtering, Sensors, Motion estimation, Digital filtering, Receivers
The performance of two direct-detection atmospheric lidar systems with very different methods of generating and detecting laser radiation is compared as the result of a field experiment held in March 2015, in Chico, California. During the noncontinuous, 11-day test period, in which the systems operated side by side, the micropulse lidar was operated at its maximum pulse repetition frequency (15 kHz) and integrated elastic backscatter over the interpulse period of the analog direct-detection lidar (0.1 s). Operation at the high pulse repetition frequency resulted in second-trip echoes that contaminated portions of the data. The performance of the micropulse lidar varied with background brightness—as expected with a photon-counting receiver—yet showed equal or larger backscatter intensity signal-to-noise ratio throughout the experiment. Examples of wind fields and time series of wind vectors from both systems during the Chico experiment are presented. In addition, scans over the ocean that were collected by the micropulse lidar during a subsequent deployment on the northern California coast are presented. We conclude by reviewing the advantages and disadvantages of each system and make some suggestions to improve the design and performance of future systems.
Although operating at the same near-infrared 1.5- m wavelength, the Raman-shifted Eye-safe Aerosol Lidar (REAL) and the Scanning Aerosol Micro-Pulse Lidar-Eye-safe (SAMPLE) are very different in how they generate and detect laser radiation. We present results from an experiment where the REAL and the SAMPLE were operated side-by-side in Chico, California, in March of 2015. During the non-continuous, eleven day test period, the SAMPLE instrument was operated at maximum pulse repetition frequency (15 kHz) and integrated over the interpulse period of the REAL (0.1 s). Operation at the high pulse repetition frequency resulted in second trip echoes which contaminated portions of the data. The performance of the SAMPLE instrument varied with background brightness--as expected with a photon counting receiver|--yet showed equal or larger backscatter intensity signal to noise ratio throughout the intercomparison experiment. We show that a modest low-pass filter or smooth applied to the REAL raw waveforms (that have 5x higher range resolution) results in significant increases in raw signal-to-noise ratio and image signal-to-noise ratio--a measure of coherent aerosol feature content in the images resulting from the scans. Examples of wind fields and time series of wind estimates from both systems are presented. We conclude by reviewing the advantages and disadvantages of each system and sketch a plan for future research and development activities to optimize the design of future systems.
Laser Interrogation of Surface Agents (LISA) is a UV-Raman technique that provides short-range standoff detection and identification of surface-deposited chemical agents. ITT Industries, Advanced
Engineering and Sciences Division, is currently developing and expanding the LISA technology under several programs that span a variety of missions for homeland defense. We will present and discuss some of these applications, while putting in perspective the overall evolution undergone by the technique within the last years. These applications include LISA-Recon (now called the Joint Contaminated Surface Detector--JCSD) which was developed under a cost-sharing arrangement with the U.S. Army Soldier and Biological Chemical Command (SBCCOM) for incorporation on the Army’s future reconnaissance
vehicles, and designed to demonstrate single-shot on-the-move measurements of chemical contaminants at concentration levels below the Army's requirements. In parallel, LISA-Shipboard is being developed to optimize the sensor technique for detection of surface contaminants in the operational environment of a ship. The most recently started activity is LISA-Inspector that is being developed to provide a transportable sensor in a 'cart-like' configuration.
Laser Interrogation of Surface Agents (LISA) is a new technique which exploits Raman scattering to provide standoff detection and identification of surface-deposited chemical agents. ITT Industries, Advanced Engineering and Sciences Division is developing the LISA technology under a cost-sharing arrangement with the US Army Soldier and Biological Chemical Command for incorporation on the Army's future reconnaissance vehicles. A field-engineered prototype LISA-Recon system is being designed to demonstrate on-the- move measurements of chemical contaminants. In this article, we will describe the LISA technique, data form proof-of- concept measurements, the LISA-Recon design, and some of the future realizations envisioned for military sensing applications.
The application of a novel mini-Raman Lidar to the standoff detection and identification of chemical spills is discussed. The new chemical sensor combines the spectral fingerprintign of solar-blind UV Raman spectroscopy with the principles of lidar to open a new venue of short-range, non- contact detection and identification of unknown substances on surfaces. In addition to discussing experimental result collected with a 'proof-of-principle' system, a next generation system, currently under development, is also presented.
Dale Richter, N. Higdon, Patrick Ponsardin, David Sanchez, Thomas Chyba, Doyle Temple, Wei Gong, Russell Battle, Mika Edmondson, Anne Futrell, David Harper, Lincoln Haughton, Demetra Johnson, Kyle Lewis, Renee Payne-Baggott
ITTs Advanced Engineering and Sciences Division and the Hampton University Center for Lidar and Atmospheric Sciences Students (CLASS) team have worked closely to design, fabricate and test an eye-safe, scanning aerosol-lidar system that can be safely deployed and used by students form a variety of disciplines. CLASS is a 5-year undergraduate- research training program funded by NASA to provide hands-on atmospheric-science and lidar-technology education. The system is based on a 1.5 micron, 125 mJ, 20 Hz eye-safe optical parametric oscillator (OPO) and will be used by the HU researchers and students to evaluate the biological impact of aerosols, clouds, and pollution a variety of systems issues. The system design tasks we addressed include the development of software to calculate eye-safety levels and to model lidar performance, implementation of eye-safety features in the lidar transmitter, optimization of the receiver using optical ray tracing software, evaluation of detectors and amplifiers in the near RI, test of OPO and receiver technology, development of hardware and software for laser and scanner control and video display of the scan region.
The need for high resolution spatial and temporal measurements of tropospheric ozone is discussed. Tropospheric ozone is globally increasing due to anthropogenic sources such as industrialization and biomass burning. In addition to its hazardous effects during pollution episodes, elevated levels of tropospheric ozone may have additional detrimental environmental effects due to ozone's crucial role in tropospheric chemistry and in global climate. Ground-based lidar instruments can play an important role in meeting this measurement need. We present test results for a prototype compact, minimal-cost ozone lidar. The instrument is designed to be as reliable and simple as possible but still be capable of routinely measuring ozone profiles with less than 10% relative error from the ground up into the lower stratosphere. In addition to local pollution monitoring, this lidar satisfies the basic requirements necessary for future global monitoring projects requiring multi-instrument networks, such as that proposed for the Global Tropospheric Ozone Project (GTOP). GTOP is currently being formulated by a scientific panel of the International Global Atmospheric Chemistry Project to meet its goal to better understand the processes that control the global sources, sinks, and transformation mechanisms of tropospheric ozone.
KEYWORDS: Absorption, Receivers, Heterodyning, Carbon dioxide lasers, Sensors, Chemical analysis, LIDAR, Chemical detection, Carbon dioxide, Control systems
The Air Force Research Laboratory (AFRL) Active Remote Sensing Branch has developed the Laser Airborne Remote Sensing (LARS) system for long standoff range chemical detection using the differential absorption lidar (DIAL) technique. The system is based on a high-power CO2 laser which uses either the 12C16O2 or the 13C16O2 carbon dioxide isotopes as the lasing medium, and has output energies of up to 5 J on the stronger laser transitions. The lidar system is mounted on a flight-qualified optical breadboard designed for installation in the AFRL Argus C-135E optical testbed aircraft. This paper will present chemical detection results and issues arising from ground tests of the system performed from September to December 1998. Recent advances in implementing a frequency-agile heterodyne receiver to further increase the standoff range of the DIAL system will also be presented.
The Air Force Research Laboratory (AFRL) Active Remote Sensing Branch has developed the Laser Airborne Remote Sensing (LARS) system for chemical detection using the differential absorption lidar technique. The system is based on a high-power CO2 laser which can use either the standard 12C16O2 or the 13C16O2 carbon dioxide isotopes as the lasing medium, and has output energies of up to 5 J on the stronger laser transitions. The lidar system is mounted on a flight-qualified optical breadboard designed for installation into the AFRL Argus C- 135E optical testbed aircraft. The Phase I ground tests were conducted at Kirtland AFB in 1997, prior to the LARS flight tests performed in September 1997 at Kirtland AFB and the Idaho National Engineering and Environmental Laboratory. The Phase II ground tests were conducted in 1998 to determine the optimum performance of the LARS systems, after the incorporation of modifications and improvements suggested by the flight test results. This paper will present some of the chemical detection and radiometric results obtained during the Phase II ground tests. Following the presentation of the direct detection results, a summary of current work on a heterodyne DIAL system is given.
Current results from laboratory testing of an eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar measurements in the troposphere are presented. This compact prototype instrument is intended to be a prototype for operation at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar to be widely deployed, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. To achieve these goals, the system incorporates (1) an all- solid state compact OPO transmitter, (2) a highly efficient, narrow bandpass grating-based receiver, (3) dual analog and photon-counting detector channels, and (4) a PC-based data acquisition system.
KEYWORDS: Data acquisition, Control systems, Computing systems, LIDAR, Chemical analysis, Absorption, Control systems design, Pulsed laser operation, Data processing, Chemometrics
The Air Force Research Laboratory (AFRL) Laser Remote Optical Sensing (LROS) program has developed the Laser Airborne Remote Sensing (LARS) system for chemical detection using the differential absorption lidar (DIAL) technique. Airborne tests during the last year resulted in chemical detection at a slant range of 30 km. As the next step in the development process, concepts for a compact, semi-autonomous DIAL system are being considered. This paper describes the conceptual design and external interfaces of the acquisition, processing, and control system computers required to operate a semi-autonomous DIAL system. The conceptual design of the VME-based real-time computer system uses three CPUs: (1) a data acquisition and control CPU which synchronizes experiment timing and pulsed CO2 laser operation while controlling lidar subsystem components such as pointing and tracking, wavelength sequencing, and optical alignment; (2) a data reduction CPU which serves as the semi-autonomous controller and performs real-time data reduction; and (3) a data analysis CPU which performs chemometric analysis including chemical identification and concentration. The triple-CPU and multi-layered software decouple time-critical and non-critical tasks allowing great flexibility in flight-time display and processing.
KEYWORDS: Ozone, Receivers, LIDAR, Transmitters, Optical parametric oscillators, Mirrors, Analog electronics, Near field optics, Data acquisition, Camera shutters
The development of a portable, eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar (DIAL) measurements in the troposphere is presented. This compact prototype instrument is intended to operate at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar technology to be widely deployed in networks, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. The chosen laser transmitter for the system is an all-solid state tunable frequency-doubled OPO which produces 25 mJ uv pulses. Progress with alternative solid-state uv laser sources based upon an IR-pumped OPO and based upon stimulated Raman scattering in barium nitrate will be discussed. The receiver incorporates highly efficient dielectric coatings, a parabolic primary and a narrow- bandpass grating-based filter. Dual analog and photon-counting detector channels are incorporated to extend the measurement range. All data acquisition and control hardware is incorporated in an industrial PC-based system. A flexible, user-friendly graphical user interface is written in LabVIEW for data acquisition and online processing and display.
The Air Force Research Laboratory (AFRL) Active Remote Sensing Branch has developed the Laser Airborne Remote Sensing (LARS) system for chemical detection using the differential absorption lidar (DIAL) technique. The system is based on a high-power CO2 laser which can use either the standard 12C16O2 or the 13C16O2 carbon dioxide isotopes as the lasing medium, and has output energies of up to 5 J on the stronger laser transitions. The lidar system is mounted on a flight-qualified optical breadboard designed for installation into the AFRL Argus C- 135E optical testbed aircraft. The Phase I ground tests were conducted at Kirtland AFB in 1997, prior to the LARS flight tests performed in September 1997 at Kirtland AFB and the Idaho National Engineering and Environmental Laboratory (INEEL). The Phase II ground tests were conducted in 1998 to determine the optimum performance of the LARS system, after the incorporation of modification and improvements suggested by the flight test results. This paper will present some of the chemical detection and radiometric results obtained during the Phase II ground tests.
The Air Force Research Laboratory has developed and tested an airborne CO2 differential absorption lidar system for the remote detection of chemicals. The Laser Airborne Remote Sensing DIAL system uses topographic backscatter to provide a long-range measurement of the column-content absorption of chemical plumes in the path of the laser beam. A high-power CO2 laser, capable of operation on multiple isotopes, and a Mersenne telescope constitute the major transceiver components. In addition to the laser, telescope, and transceiver optics, several onboard diagnostic instruments were mounted on the flight bench to monitor and optimize the system performance during airborne operation. The flight bench, electronics racks, and data acquisition and experiment control stations were designed to be integrated onto the AFRL C-135E research aircraft, and to utilize the existing pointing and tracking system on the aircraft.
The Air Force Research Laboratory has developed and operated an airborne CO2 DIAL system for chemical detection of trace gases in the atmosphere'. This system, designated Laser Atmospheric Remote Sensing (LARS), is used for chemical detection of trace gases in the column content, topographical backscatter mode wherein detection of trace chemicals is performed by ratioing the backscattered signal strengths of combinations of transmitted CO2 laser lines absorbed by the trace chemical(s) to the backscattered signal produced by non-absorbed laser lines. Identification and quantification of trace chemical signatures sampled at multiple discrete CO2 laser frequencies is dependent upon isolation of the chemical signature from the absorption spectrum of the multi-kilometer atmospheric slant path over which measurements are made. Ambient atmospheric concentrations of C02, H20, and 03 contribute discrete line absorptions in the 9 im —11 tm spectral region in which the LARS system operates. The detailed form of the atmospheric absorption spectrum depends upon the concentration of each absorber and its variation with altitude along the slant measurement path. In addition to discrete atmospheric line absorption that must be accounted for in the DIAL measurements, a weaker continuum (smooth, slowly wavelength-varying) absorption due to water vapor must also be taken into account.
The U.S. Air Force Phillips Laboratory is evaluating the feasibility of long-standoff-range remote sensing of gaseous species present in trace amounts in the atmosphere. To date, the Phillips Laboratory program has been concerned with the preliminary design and performance analysis of a commercially available CO2 laser-based DIAL system operating from mountain-top-observatory and airborne platform and more recently with long-range ground testing using a 21.8 km slant path from 3.05 km ASL to sea level as the initial steps in the design and development of an airborne system capability. Straightforward scaling of the performance of a near-term technology direct-detection LIDAR system with propagation range to a topographic target and with the average atmospheric absorption coefficient along the path has been performed. Results indicate that useful airborne operation of such a system should be possible for slant path ranges between 20 km and 50 km, depending upon atmospheric transmission at the operating wavelengths of the 13C16O2 source. This paper describes the design of the airborne system which will be deployed on the Phillips Laboratory NC-135 research aircraft for DIAL system performance tests at slant ranges of 20 km to 50 km, scheduled for the near future. Performance simulations for the airborne tests will be presented and related to performance obtained during initial ground-based tests.
Development of a wavelength-stabilized laser diode injection-seeded alexandrite laser for differential absorption lidar (DIAL) measurements of atmospheric water vapor in the 727 nm region is described.
The spectral characteristics of an alexandrite laser used for making water vapor DIAL measurements are evaluated. The optical servo-system used to lock the laser wavelength on a water vapor absorption line is described. A brief description of the DIAL system is given and the data obtained with this lidar during flight tests in March 1990 are also presented.
An overview of some of the developments completed on an alexandrite laser for making water vapor DIAL measurements is presented in this paper. A computer control for active stabilization of the two intracavity etalons has been implemented and recently tested in an aircraft environment. Long-term frequency drift (i.e., 2 hours) of less than 0.7 pm has been observed in the laboratory. An alignment technique to get the optimum free spectral range ratio for the two etalons is also developed.
A differential absorption lidar (DIAL) system developed at NASA Langley Research Center for the remote measurement of atmospheric H2O and aerosols from an aircraft is briefly discussed. This DIAL system utilizes a Nd:YAG laser-pumped dye laser as the off-line transmitter and a narrowband, tunable Alexandrite laser as the on-line transmitter. A 1-m monochromator and a multipass absorption cell are used to position the on-line laser to the center of the H2O line. The receiver system has a 14-in. diameter, f/7 Celestron telescope to collect the backscattered laser light and focus in into the detector optics. Return signals are converted to electrical signals by the optical detector and are digitalized and stored on magnetic tape. The results of fligh tests of the system are shown.
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