We report the progress in the development of a compact mid-infrared differential absorption lidar (DIAL) for ground-based and airborne monitoring of leaks in natural gas pipeline systems. This sensor, named Lidar II, weighs approximately 30 kg (70 lbs) and occupies a volume of 0.08 m3 (3.5 ft3). Lidar II can be used on the ground in a topographic mode or in a look-down mode from a helicopter platform. The 10-Hz pulse repetition rate and burst-mode averaging currently limit the airborne inspection speed to 30 km/h. The Lidar II laser transmitter employs an intracavity optical parametric oscillator. Wavelength tuning is accomplished through two mechanisms: a servo-controlled crystal rotation for slow and broad-band tuning and a fast piezo-activated wavelength shifter for on-line/off-line switching in less than 10 ms. The sensor operates in the 3.2-3.5-μm band with the primary focus on hydrocarbons and volatile organics. In the pipeline inspection work, the two main targets are methane and ethane, the latter chemical being important in preventing false positives. Initial results of Lidar II testing on actual pipeline leaks are reported. To supplement the mapping capabilities of Lidar II with range-resolved information, a short-range (less than 300 m) aerosol backscatter lidar is currently under development.
LaSen, Inc. is continuing development of compact and rugged lidar systems for ground-based and airborne detection of volatile organic components (VOC) in the mid-infrared spectral region. The first-generation ground-based sensor (Lidar I) measures 0.19 m3 and weighs 55 kg. Throughout 2001, Lidar I is undergoing a series of field tests in south-central New Mexico, USA. The tests completed to date include measuring methane level at rural dumpsites and monitoring emissions from contaminated soil at a diesel fuel spill site. To support the lidar programs, LaSen developed a compact tunable mid-infrared laser source based on an intracavity optical parametric oscillator. The laser source delivers up to 1.3 mJ of mid-infrared energy per pulse and is angular tuned in the 3-5 micrometers band through a servo- controlled loop. A piezo-driven tuner for fast switching between on and off lines is available as an option. Lidar I performance characteristics relevant to detection of various VOC are discussed. The second-generation sensor (Lidar II) is undergoing development and is scheduled for tests in the fourth quarter of 2001. Lidar II is a re-packaged version of Lidar I, with a significant decrease in both weight and size. Although not specifically designed for an airborne platform, Lidar II will be capable of demonstration flights on board a helicopter operating in a look-down topographic mode.
A compact (2'6' X 2'5' X 1'1') 3.30 - 3.47-micrometers DIAL lidar has been constructed for base remediation and chemical monitoring. The lidar system is designed for short range (0.5 km maximum) aerosol backscatter detection of light hydrocarbons with sensitivities at parts-per-million level in a 30-m ranging bin. The system can also operate in the topographic mode. The on-line and off-line wavelengths are produced sequentially using a dual crystal intra-cavity KTA OPO. Detection is by means of an 8-in Newtonian telescope coupled to a Stirling cycle cooled InSb detector. The system incorporates an onboard digital signal processor and controller, operator's interface is furnished by a laptop PC. Results of initial tests using diesel fuel and a solvent are presented.
Differential absorption lidars (DIAL) in the mid-infrared (2 - 5 micrometers ) are used to monitor various chemical species. Two wavelengths are required to perform the differential absorption measurement: an `on' line and an `off' line. Previously, the measurement has been made by sequentially tuning between the two lines. However, this can produce errors in the measured differential absorption, especially when a DIAL is used in a `look down' reflector mode from a high speed aircraft, because of variations in the Earth's reflectivity between laser pulses. To avoid this problem and to construct a high speed DIAL system, LaSen, Inc. has developed an intra-cavity `stacked' optical parametric oscillator/laser (OPOL), which is capable of producing simultaneous tunable outputs in the 2 - 5 micrometers region. This laser system utilizes a compact diode pumping scheme and an overlapped laser/OPO resonator design that produces multiple wavelength outputs and minimizes the number of optical components and optical path length. The decreased size of the OPOL system and increased ruggedness makes it ideal for man-portable and airborne operation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.