The system and mechanical design of a four-wavelength lidar system is described. The system is designed to be maximally adaptive to deployment scenario in terms of both size/weight/power and detection application. The wavelengths included in the system are 266 nm, 355 nm, 1064 nm, and 1574 nm – all generated from Nd:YAG based pump laser sources. The system is designed to have a useful range from 400 meters to 5,000 meters, depending on the wavelength and atmospheric conditions.
Dugway Proving Grounds (DPG) plays a key role in the open-air field-testing of systems used in defense against chemical and biological threats. The performance of systems under test are benchmarked against a suite of wellcharacterized point and standoff instrumentation. Elastic-backscatter lidar systems with large power-apertures operating at 1.06 μm provide standoff detection, quantification, and location of aerosol plumes. The accuracy and sensitivity these systems provide comes at the cost of a large NOHD (>5 km) which limits their utility. To this end, Space Dynamics Lab (SDL) developed an eye-safe system following system requirements from DPG. The system provides a standoff capability for field tests where a NOHZ and required PPE would be an undue burden. CELiS (Compact Eye-Safe Lidar System) is an elastic-backscatter lidar that operates at 1.57 μm, using a commercial 30 Hz Nd:YAG laser and OPO combination. The short pulse length and low repetition rate give the system an advantage in range resolution and daytime operation over a similarly sized system based on a fiber laser. CELiS uses LidarView, an SDL-developed lidar display package, for data acquisition and hardware control. The Joint Ambient Breeze Tunnel (JABT) is used to perform calibration and sensitivity measurements of the various lidar systems at DPG. The JABT provides confinement of an aerosol plume and allows for comparison of TSI APS (Aerodynamic Particle Sizer) concentrations to the lidar backscatter values over an extended period. CELiS was used to support a recent JABT test and the data analysis and performance results from the test are described.
KEYWORDS: LIDAR, Imaging systems, Sensors, 3D image processing, 3D acquisition, Cameras, Control systems, Stereoscopic cameras, Process control, Image processing
The Space Dynamics Laboratory (SDL), working with Naval Research Laboratory (NRL) and industry leaders Advanced Scientific Concepts (ASC) and Hood Technology Corporation, has developed a small SWAP (size, weight, and power) 3D imaging flash ladar (LAser Detection And Ranging) sensor system concept design for small tactical unmanned air systems (STUAS). The design utilizes an ASC 3D flash ladar camera and laser in a Hood Technology gyro-stabilized gimbal system. The design is an autonomous, intelligent, geo-aware sensor system that supplies real-time 3D terrain and target images. Flash ladar and visible camera data are processed at the sensor using a custom digitizer/frame grabber with compression. Mounted in the aft housing are power, controls, processing computers, and GPS/INS. The onboard processor controls pointing and handles image data, detection algorithms and queuing. The small SWAP 3D imaging flash ladar sensor system generates georeferenced terrain and target images with a low probability of false return and <10 cm range accuracy through foliage in real-time. The 3D imaging flash ladar is designed for a STUAS with a complete system SWAP estimate of <9 kg, <0.2 m3 and <350 W power. The system is modeled using LadarSIM, a MATLAB® and Simulink®- based ladar system simulator designed and developed by the Center for Advanced Imaging Ladar (CAIL) at Utah State University. We will present the concept design and modeled performance predictions.
CELiS (Compact Eyesafe Lidar System) is an elastic backscatter light detection and ranging (lidar) system developed for monitoring air quality environmental compliance regarding particulate matter (PMk) generated from off-road use of wheeled and tracked vehicles as part of the SERDP (Strategic Environmental Research and Development Program) Measurement and Modeling of Fugitive Dust Emission from Off-Road DoD Activities program. CELiS is small, lightweight and easily transportable for quick setup and measurement of PMk concentration and emissions. CELiS operates in a biaxial configuration at the 1.5μm eyesafe wavelength with a working range of better than 6 km and range resolution of 5 m. In this paper, we describe an algorithm that allows for semi-quantitative PMk determination under a set of guiding assumptions using a single wavelength lidar. Meteorological and particle measurements are used to estimate the total extinction (α) and backscatter (β) at a calibration point located at the end range of the lidar. These α and β values are used in conjunction with the Klett inversion to estimate α and β over the lidar beam path. A relationship between β, α and PMk mass concentrations at calibration points is developed, which then allows the β and α values derived to be converted to PMk at each lidar bin over the lidar beam path. CELiS can be used to investigate PMk concentrations and emissions over a large volume, a task that is very difficult to accomplish with typical PMk sensors.
Rapid expansion of the oil and gas industry in Alberta, including the oil sands, has challenged the Alberta Government to keep pace in its efforts to monitor and mitigate the environmental impacts of development. The limitations of current monitoring systems has pushed the provincial government to seek out advanced sensing technologies such as satellite imagery and laser based sensors. The Space Dynamics Laboratory (SDL) of Utah State University, in cooperation with Alberta Environmental Monitoring, Evaluation and Reporting Agency (AEMERA), has developed North America’s first mobile differential absorption lidar (DIAL) system designed specifically for emissions measurement. This instrument is housed inside a 36’ trailer which allows for mobility to travel across Alberta to characterize source emissions and to locate fugitive leaks. DIAL is capable of measuring concentrations for carbon dioxide (CO2) and methane (CH4) at ranges of up to 3 km with a spatial resolution of 10 meters. DIAL can map both CO2 and CH4, as well as particulate matter (PM) in a linear fashion; by scanning the laser beam in both azimuth and elevation DIAL can create images of emissions in two dimensions. DIAL imagery may be used to understand and control production practices, characterize source emissions, determine emission factors, locate fugitive leaks, assess plume dispersion, and confirm air dispersion modeling. A system overview of the DIAL instrument and some representative results will be discussed.
Kori Moore, Michael Wojcik, Randal Martin, Christian Marchant, Derek Jones, William Bradford, Gail Bingham, Richard Pfeiffer, John Prueger, Jerry Hatfield
Particulate-matter (PM) emissions from a typical spring agricultural tillage sequence and a strip–till conservation tillage sequence in California’s San Joaquin Valley were estimated to calculate the emissions control efficiency (η) of the strip–till conservation management practice (CMP). Filter-based PM samplers, PM-calibrated optical particle counters (OPCs), and a PM-calibrated light detection and ranging (LIDAR) system were used to monitored upwind and downwind PM concentrations during May and June 2008. Emission rates were estimated through inverse modeling coupled with the filter and OPC measurements and through applying a mass balance to the PM concentrations derived from LIDAR data. Sampling irregularities and errors prevented the estimation of emissions from 42% of the sample periods based on filter samples. OPC and LIDAR datasets were sufficiently complete to estimate emissions and the strip–till CMP η, which were ∼90% for all size fractions in both datasets. Tillage time was also reduced by 84%. Calculated emissions for some operations were within the range of values found in published studies, while other estimates were significantly higher than literature values. The results demonstrate that both PM emissions and tillage time may be reduced by an order of magnitude through the use of a strip–till conservation tillage CMP when compared to spring tillage activities.
Ground based remote sensing technologies such as scanning lidar systems (light detection and ranging) are increasingly
being used to characterize ambient aerosols due to key advantages (i.e., wide area of regard (10 km2), fast response time,
high spatial resolution (<10 m) and high sensitivity). Scanning lidar allows for 3D imaging of atmospheric motion and
aerosol variability. Space Dynamics Laboratory at Utah State University, in conjunction with the USDA-ARS, has
developed and successfully deployed a three-wavelength lidar system called Aglite to characterize particles in diverse
settings. Aglite generates near real-time imagery of particle size distribution and size-segregated mass concentration in
addition to the ability to calculate whole facility emission rates. Based on over nine years of field and laboratory
experience, we present concentration and emission rate results from various measurements in military and civilian
deployments.
CELiS (Compact Eyesafe Lidar System) is a tactical elastic lidar system commissioned by the Strategic Environmental
Research and Development Program (SERDP) for the purpose of air quality environmental compliance issues
surrounding the offroad use of wheeled and tracked vehicles. A complete CELiS instrument weighs less than 300 lbs., is
less than 2 cubic meters in volume and uses 700 W of 120V AC power. CELiS has a working range of better than 2km
and a range resolution of 5m.
Here, we demonstrate and characterize a high-energy, eye-safe, spectrally narrow, and frequency-agile near-IR optical parametric oscillator (OPO). The injection-seeded, noncritical phase-matched (NCPM) potassium titanyle arsenate (KTA) and ring-cavity OPO was pumped in single longitudinal mode (SLM) at 7 ns full width at half maximum FWHM and 30 Hz, neodymium-doped yttrium aluminum garnet (Nd:YAG), generating 243 mJ per pulse OPO signal output with a conversion efficiency of 27%, spectral linewidth of 157 MHz, and approximately M2 of 29. Also, we demonstrate a nonmechanical method to switch the frequency of the OPO at a rate of 2 Hz from 1535.036 to 1535.195 nm, which represents the on/off resonances of carbon dioxide, respectively. However, the switching rate can be extended into the MHz range and is limited by the electronics driving the diode laser. Given the performance results of our frequency-agile OPO, this transmitter has great potential as a source in DIAL applications.
We have demonstrated a 243mJ, eye-safe, injection seeded,
non-critically phase-matched (NCPM), singly resonant
oscillator (SRO), KTA ring-cavity optical parametric oscillator (OPO). The OPO was pumped with a single mode 7ns
FWHM, 30Hz, Q-switched, Nd:YAG at a wavelength of 1064.162nm. The OPO was injection-seeded utilizing a single
longitudinal (SLM) distributed feedback (DFB) diode laser. As a result, the KTA OPO generated an eye-safe signal
wavelength of 1535.200nm with a maximum energy of 243mJ, a conversion efficiency of 27%, a cavity mode seed
range of 853MHz FWHM, and a maximum M2=30. This high energy,
eye-safe OPO could potentially increase the
sensitivity and range capabilities of elastic LIDAR and DIAL systems which are used for remote sensing applications.
KEYWORDS: Quantum cascade lasers, Black bodies, Copper, Temperature metrology, Sensors, Signal detection, Mid-IR, Infrared radiation, Environmental sensing, Surgery
Continuous improvements of quantum cascade laser (QCL) technology have extended the applications in environmental
trace gas monitoring, mid-infrared spectroscopy in medicine and life science, law enforcement and homeland security
and satellite sensor systems. We present the QCL based emissivity monitor for the CORSAIR blackbody. The emissivity
of the blackbody was designed to be better than 0.9999 for the spectral range between 5 to 50μm. To actively monitor
changes in blackbody emissivity we employ a QCL-based infrared illumination source. The illumination source
consisted of a QCL and thermoelectric cooler (TEC) unit mounted on a copper fixture. The stability of the QCL was
measured for 30, 60, and 90s operation time at 1.5A driving current. The temperature distribution along the laser
mounting fixture and time dependent system heat dispersion were analyzed. The results were compared to radiative and
conductive heat transfer models to define the potential laser operating time and required waiting time to return to initial
temperature of the laser mount. The observed cooling behaviour is consistent with a primarily conductive heat transfer
mechanism.
A high output power, eye-safe, lidar transmitter based on a KTA optical parametric oscillator (OPO) was
demonstrated. The OPO was based on a two crystal, doubly resonant, non-critically phase-matched, KTA ring
cavity. An injection seeded, 7ns, 30Hz, flashlamp-pumped, Q-switched Nd:YAG laser was used to pump the
OPO. The OPO converted the 1064nm pump beam into a 1533nm signal wave and 3475nm idler wave. In
addition to demonstrating a high power OPO system, we investigated the effects of seeding the pump laser on
the OPO's conversion efficiency, oscillation threshold, maximum signal power, and beam quality. The power
conversion efficiency between the signal and the injection seeded pump was 22% with an oscillation threshold
of 104MW/cm2 (500mJ) and a maximum signal power of 6.44W (215mJ). The power conversion efficiency
between the signal and the unseeded pump was 24% with an oscillation threshold of 77MW/cm2 (367mJ) and a
maximum signal power of >7W (243mJ). When the pump laser was seeded, the full angle divergence improved
by nearly a factor of five.
Agriculture, through wind erosion, tillage and harvest operations, burning, diesel-powered machinery and animal production operations, is a source of particulate matter emissions. Agricultural sources vary both temporally and spatially due to daily and seasonal activities and inhomogeneous area sources. Conventional
point sampling methods originally designed for regional, well mixed aerosols are challenged by the disrupted wind flow and by the small mobile source of the emission encountered in this study. Atmospheric
lidar (LIght Detection And Ranging) technology provides a means to derive quantitative information of particulate spatial and temporal distribution. In situ point measurements of particulate physical and
chemical properties are used to characterize aerosol physical parameters and calibrate lidar data for unambiguous lidar data processing. Atmospheric profiling with scanning lidar allows estimation of temporal and 2D/3D spatial variations of mass concentration fields for different particulate fractions (PM1,
PM2.5, PM10, and TSP) applicable for USEPA regulations. This study used this advanced measurement technology to map PM emissions at high spatial and temporal resolutions, allowing for accurate
comparisons of the Conservation Management Practice (CMP) under test. The purpose of this field study was to determine whether and how much particulate emission differs from the conventional method of
agricultural fall tillage and combined CMP operations.
Use of ground based remote sensing technologies such as scanning lidar systems (light detection and ranging)
has gained traction in characterizing ambient aerosols due to some key advantages such as wide area of regard
(10 km2), fast response time, high spatial resolution (<10 m) and high sensitivity. Energy Dynamics Laboratory
and Utah State University, in conjunction with the USDA-ARS, has developed a three-wavelength scanning
lidar system called Aglite that has been successfully deployed to characterize particle motion, concentration, and
size distribution at both point and diffuse area sources in agricultural and industrial settings. A suite of massbased
and size distribution point sensors are used to locally calibrate the lidar. Generating meaningful particle
size distribution, mass concentration, and emission rate results based on lidar data is dependent on strategic
onsite deployment of these point sensors with successful local meteorological measurements. Deployment
strategies learned from field use of this entire measurement system over five years include the characterization
of local meteorology and its predictability prior to deployment, the placement of point sensors to prevent
contamination and overloading, the positioning of the lidar and beam plane to avoid hard target interferences,
and the usefulness of photographic and written observational data.
A high output power, eye-safe, LIDAR transmitter based on a KTA optical parametric oscillator (OPO) was
demonstrated. The OPO was based on a two crystal, NCPM, KTA ring cavity which was doubly resonant.
A 7ns, 30Hz, flashlamp-pumped, Q-switched Nd:YAG laser was injection seeded and used to pump the
OPO. The OPO converted the 1064 nm pump beam into a 1533 nm signal wave and 3475 nm idler wave.
In addition to demonstrating a high power OPO system, we investigated the effects of seeding the pump
laser on the OPO's conversion efficiency, oscillation threshold, maximum signal power, and beam quality.
The power conversion efficiency between the signal and the injection seeded pump was 22% with an
oscillation threshold of 104 MW/cm2 (500 mJ) and a maximum signal power of 6.44 W (215 mJ). The
power conversion efficiency between the signal and the unseeded pump was 24% with an oscillation
threshold of 77 MW/cm2 (367mJ) and a maximum signal power of 7 W (233 mJ). The beam quality of the
signal beam was produced an M2 =15. When the pump laser was seeded, the full angle divergence improved
by nearly a factor of five.
The NASA climate science mission Climate Absolute Radiance and Refractivity Observatory (CLARREO), which is to
measure Earth's emitted spectral radiance from orbit for 5 years, has an absolute accuracy requirement of 0.1 K (3σ) at
220 K over most of the thermal infrared. To meet this requirement, CLARREO needs highly accurate on-board
blackbodies which remain accurate over the life of the mission. Space Dynamics Laboratory is developing a prototype
blackbody that demonstrates the ability to meet the needs of CLARREO. This prototype is based on a blackbody design
currently in use, which is relatively simple to build, was developed for use on the ground or on-orbit, and is readily
scalable for aperture size and required performance. We expect the CLARREO prototype to have emissivity of ~0.9999
from 1.5 to 50 μm, temperature uncertainties of ~25 mK (3σ), and radiance uncertainties of ~10 mK due to temperature
gradients. The high emissivity and low thermal gradient uncertainties are achieved through cavity design, while the SItraceable
temperature uncertainty is attained through the use of phase change materials (mercury, gallium, and water) in
the blackbody. Blackbody temperature sensor calibration is maintained over time by comparing sensor readings to the
known melt temperatures of these materials, which are observed by heating through their melt points. Since blackbody
emissivity can potentially change over time due to changes in surface emissivity (especially for an on-orbit blackbody)
an on-board means of detecting emissivity change is desired. The prototype blackbody will include an emissivity
monitor based on a quantum cascade laser to demonstrate the concept.
Infrared radiometers and spectrometers generally use blackbodies for calibration, and with the high accuracy needs of
upcoming missions, blackbodies capable of meeting strict accuracy requirements are needed. One such mission, the
NASA climate science mission Climate Absolute Radiance and Refractivity Observatory (CLARREO), which will
measure Earth's emitted spectral radiance from orbit, has an absolute accuracy requirement of 0.1 K (3σ) at 220 K over
most of the thermal infrared. Space Dynamics Laboratory (SDL) has a blackbody design capable of meeting strict
modern accuracy requirements. This design is relatively simple to build, was developed for use on the ground or onorbit,
and is readily scalable for aperture size and required performance. These-high accuracy blackbodies are currently
in use as a ground calibration unit and with a high-altitude balloon instrument. SDL is currently building a prototype
blackbody to demonstrate the ability to achieve very high accuracy, and we expect it to have emissivity of ~0.9999 from
1.5 to 50 μm, temperature uncertainties of ~25 mK, and radiance uncertainties of ~10 mK due to temperature gradients.
The high emissivity and low thermal gradient uncertainties are achieved through cavity design, while the low
temperature uncertainty is attained by including phase change materials such as mercury, gallium, and water in the
blackbody. Blackbody temperature sensors are calibrated at the melt points of these materials, which are determined by
heating through their melt point. This allows absolute temperature calibration traceable to the SI temperature scale.
Principal Component Analysis (PCA) has proven to be a valuable tool for remote sensing data compression, pattern
recognition, and for filtering out measurement noise. In this paper, we present preliminary results on the application of
PCA technique to reduce random noise present in lidar observations. Typically, the SNR at a given range can be
improved either by increasing the integration time of the measurements or by applying spatial averaging. This procedure,
however, improves the SNR at the expense of the instrument's temporal and spatial resolution. The number of range bins
needed to characterize backscatter features is far less than the number of components needed to characterize the
distribution of these features in the atmosphere. The higher-order PCA components, which mainly serve to characterize
noise, can be eliminated along with the noise that they characterize. The results of PCA noise filtering of lidar
observations strongly depend on the variability of aerosol plumes. To avoid loss of information in the presence of highly
variable aerosol plumes, it is necessary to use a conservative number of principal components higher then optimum for
maximum noise reduction. Nevertheless, noise reduction factors of 2-8, depending on the lidar range and atmospheric
variability, can still be achieved.
In this paper we present design considerations, thermal and optical modeling results, and device performance for a
ruggedized, compact laser transmitter that utilizes a room temperature quantum cascade (QC) laser source. The QC laser
transmitter is intended for portable mid-infrared spectroscopy applications, where the 3 to 5 μm and 8 to 12 μm
atmospheric transmission window is relatively free of water vapor interference and where the molecular rotational
vibration absorption features can be used to detect and uniquely identify chemical compounds of interest. Initial QC
laser-based sensor development efforts were constrained by the complications of cryogenic operation. However,
improvements in both QC laser designs and fabrication processes have provided room-temperature devices that now
enable significant miniaturization and integration potential for national security, environmental monitoring, atmospheric
science, and industrial safety applications.
We demonstrate the use of a tunable external cavity quantum cascade laser system for measurement of broad absorption
features in the mid-infrared spectral region. The thermoelectrically cooled external cavity laser was tuned over a 65 cm-1range centered at 8.7 microns using stepper motor control. Pulsing the laser at a high duty cycle provided 2-4.5 mW
average output power over the tuning range, and enabled phase-sensitive detection of amplitude-modulated signals. We
used the laser system to measure the absorption spectra of Freon-125 using a Herriott cell. In addition, the absorption
spectrum of water in the laboratory air was measured. The measurements showed excellent agreement with reference
spectra, in both wavelength and amplitude. The measured scan resolution of 0.14 cm-1 is suitable for measurement of the
absorption features of complex molecules as well as simple molecules with atmospherically broadened lines. We
discuss the limits to the scan resolution due to effects of spectral chirp and mode-hops during pulsed operation.
We demonstrate the performance of a novel long-wave infrared photoacoustic laser absorbance
spectrometer for gas-phase species using an amplitude modulated (AM) quantum cascade (QC) laser and a
quartz tuning fork microphone. Photoacoustic signal was generated by focusing the output of a Fabry-Perot
QC laser operating at 8.41 μm between the legs of a quartz tuning fork which served as a transducer for the
transient acoustic pressure wave. The QC laser was modulated at the resonant frequency of the tuning fork
(32.8 kHz). This sensor was calibrated using the infrared absorber Freon-134a by performing a
simultaneous absorption measurement using a 35 cm absorption cell. The NEAS of this instrument was
determined to be 2 x 10-8 W • cm / √Hz, and the fundamental sensitivity of this technique is limited by the
noise floor of the tuning fork itself.
We demonstrate the performance of a novel long-wave infrared photoacoustic laser absorbance spectrometer for gas-phase species using an amplitude modulated (AM) quantum cascade (QC) laser and a quartz tuning fork microphone. Photoacoustic signal was generated by focusing the output of a Fabry-Perot QC laser operating at 8.41 μm between the legs of a quartz tuning fork which served as a transducer for the transient acoustic pressure wave. The QC laser was modulated at the resonant frequency of the tuning fork (32.8 kHz). This sensor was calibrated using the infrared absorber Freon-134a by performing a simultaneous absorption measurement using a 35 cm absorption cell. The NEAS of this instrument was determined to be (see equation in manuscript), and the fundamental sensitivity of this technique is limited by the noise floor of the tuning fork itself.
Quantum cascade laser (QCL) offer many desirable attributes as mid-infrared laser sources for chemical and remote sensing. Some key advantages are a narrow linewidth, wide bandwidth current modulation characteristics and moderate tunability (15 cm-1). Combined, these characteristics allow for applications to a wide variety of chemical and remote sensing techniques such as wavelength and frequency modulation based detection techniques, cavity enhanced point sensors as well as techniques such as LIDAR and DIAL. This paper will describe laser development efforts to enhance QCL frequency stabilization and QCL injection locking and to develop robust external cavity QCL designs.
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