Thomas G. McRae

Backscatter absorption gas imaging: a new technique for gas visualization

This paper presents a new laser-based method of gas detection that permits real-time television images of gases to be produced. The principle of this technique [which is called backscatter absorption gas imaging (BAGI)] and the operation of two instruments used to implement it are described. These instruments use 5-W and 20-W CO(2) lasers to achieve gas imaging at ranges of approximately 30 and 125 m, respectively. Derivations of relevant BAGI signal equations that can be used to predict the performance of a gas imager are provided. The predictions of this model and the measured range performance of an extended-range gas imager are compared. Finally, the results of gas sensitivity measurements and imaging tests on flowing gases are presented. These can be used to generate a realistic estimate of the BAGI sensitivity expected in detecting leaks of many different vapors.

Current Status Of The NAVSEA Synchronous Scanning Laser Imaging System

This paper constitutes an update on our efforts to develop an underwater laser-based imaging system (UWLIS). The work is being performed under contract from the Naval Sea Systems Command Office of Salvage and Diving (NAUSEA/00C) in order to provide instrumentation that will improve the visibility range available to deep-ocean (1500-6000 m) submersible vehicles during ocean-floor search-and-salvage operations. In general, these submersibles are remotely operated vehicles (ROV) that currently employ high-intensity floodlights and low-light-level TV cameras to produce video images of the seafloor, which are relayed to the mother ship to allow target identification. Often, these floodlight-based systems require that the ROV come within 6 to 10 m of the target in order to positively identify it. This poses both a risk of damaging the vehicle on outcropping seafloor terrain features and an increase in mission cost due to the time lost on maneuvering to identify false targets. Given that salvage-operation costs typically range from

State of the art and future plans for IR imaging of gaseous fugitive emissions

1000 to

Desian And Preliminary Evaluation Of An Underwater Laser-Based Imaging System

3000 per hour, a system that would improve the visibility range from 10 to 100 m would save thousands of dollars and greatly increase the probability of success of these missions.

Results of 40-m3 LNG Spills onto Water

The means to detect, visualize and survey different kinds of gases within industrial and energy processes, technical infrastructure, landfill bodies, indoor and outdoor environment are discussed. The current status and future plans for IR imaging technologies in the U.S. and in Sweden are described. Primary consideration is given to mobile and airborne remote sensing systems, such as current laser-based imaging technologies, advanced IR systems with and without filter techniques, and two-dimensional gas-correlation techniques, being used or under development. Results of recent laboratory and field experiments involving the imaging of natural gas leaks under both controlled and actual conditions are presented and discussed. Plans for future field testing and technology improvements are described.

Refinery Evaluation of Optical Imaging to Locate Fugitive Emissions

The design and preliminary evaluation of an underwater laser-based imaging system (UWLIS) being developed by the Lawrence Livermore National Laboratory for the Naval Sea Systems Command is described. The system is composed of a synchronously scanning argon-ion laser beam and a very narrow (4 milliradian) field-of-view detector. The laser beam and detector field of view are separated at the imaging system, but converge at the target to reduce the common optical scattering volume. The system produces a standard real-time TV image and has a predicted range of 100 m for 5 watts of laser power. The results of evaluations conducted in a 15-m deep tank at the Naval Coastal Systems Center are presented and discussed. The performance of the UWLIS in various turbid water conditions is compared to typical low-light-level underwater TV systems.

PPLN-OPO-based backscatter absorption gas imaging (BAGI) system and its application to the visualization of fugitive gas emissions

Lawrence Livermore National Laboratory (LLNL) is conducting safety research under the sponsorship of the U.S. Department of Energy (DOE) to determine the possible consequences of liquefied natural gas (LNG) spills. The LLNL program includes both the collection of data from various size experiments and development of an ensemble of computer models to make predictions for conditions under which tests cannot be performed. In spills of 40 cubic metres (m3) of LNG onto water done at the Naval Weapons Center (NWC), China Lake, California in 1980 and 1981, data was collected on gas cloud dispersion and combustion and rapid phase transition (RPT) explosions. Analysis of the data from these tests, including comparisons between the predictions of various models and the data, are presented. The results suggest that largescale spills may be more hazardous than would have been predicted based on earlier small-scale tests. Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.

Development of a compact gas imaging sensor employing a cw fiber-amp-pumped PPLN OPO

Abstract Fugitive emissions account for approximately 50% of total hydrocarbon emissions from process plants. Federal and state regulations aiming at controlling these emissions require refineries and petrochemical plants in the United States to implement a Leak Detection and Repair Program (LDAR). The current regulatory work practice, U.S. Environment Protection Agency Method 21, requires designated components to be monitored individually at regular intervals. The annual costs of these LDAR programs in a typical refinery can exceed US

Application of backscatter absorption gas imaging to the detection of chemicals related to drug production

1,000,000. Previous studies have shown that a majority of controllable fugitive emissions come from a very small fraction of components. The Smart LDAR program aims to find cost-effective methods to monitor and reduce emissions from these large leakers. Optical gas imaging has been identified as one such technology that can help achieve this objective. This paper discusses a refinery evaluation of an instrument based on backscatter absorption gas imaging technology. This portable camera allows an operator to scan components more quickly and image gas leaks in real time. During the evaluation, the instrument was able to identify leaking components that were the source of 97% of the total mass emissions from leaks detected. More than 27,000 components were monitored. This was achieved in far less time than it would have taken using Method 21. In addition, the instrument was able to find leaks from components that are not required to be monitored by the current LDAR regulations. The technology principles and the parameters that affect instrument performance are also discussed in the paper.

The development and application of a short range, real-time active imaging system

We report on a laser active imager suitable for the visualization of natural gas leaks and volatile organic compounds emitted by oil refineries. The described backscatter-absorption gas-imaging (BAGI) system employs a raster scanner in conjunction with a tunable continuous wave (cw) laser source. The imager creates real-time video imagery of a scene, while illuminating it with infrared laser light at a wavelength that is absorbed by the gas to be detected. Thus, gas plumes that otherwise cannot be seen by the human eye appear in BAGI images as dark clouds. In order to produce the high intensity infrared light that is needed to image natural gas and refinery by-products, we used a nonlinear frequency-conversion technique that employs the quasi-phase-matched crystal periodically poled LiNbO3. The crystal serves as the active medium in a cw optical parametric oscillator (OPO) that is pumped by a diode-pumped Nd:YAG laser. The output frequencies were selected to coincide with absorption features of general aliphatic species (2935 and 2968 cm-1), aromatics, such as benzene and toluene (3033 cm-1), and methane (3018 cm-1). The crystal was engineered to cover the desired spectral range using a fan-out design. This allows tuning of the OPO between 2832 and 3145 cm-1 in idler wavelength by simply translating the crystal at a fixed temperature. Presented data demonstrate the performance of this system for imaging species of interest at relevant concentrations and ranges up to about 30 m.