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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Airborne water vapor DIAL system and measurements of water and aerosol profiles

The Lidar Applications Group at NASA Langley Research Center has developed a differential absorption lidar (DIAL) system for the remote measurement of atmospheric water vapor (H2O) and aerosols from an aircraft. The airborne H2O DIAL system is designed for extended flights to perform mesoscale investigations of H2O and aerosol distributions. 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. The dye laser has an oscillator/amplifier configuration which incorporates a grating and prism in the oscillator cavity to narrow the output linewidth to approximately 15 pm. This linewidth can be maintained over the wavelength range of 725 to 730 nm, and it is sufficiently narrow to satisfy the off-line spectral requirements. In the Alexandrite laser, three intracavity tuning elements combine to produce an output linewidth of 1.1 pm. These spectral devices include a five-plate birefringent tuner, a 1-mm thick solid etalon and a 1-cm air-spaced etalon. A wavelength stability of +/- 0.35 pm is achieved by active feedback control of the two Fabry-Perot etalons using a frequency stabilized He-Ne laser as a wavelength reference. The three tuning elements can be synchronously scanned over a 150 pm range with microprocessor-based scanning electronics. Other aspects of the DIAL system are discussed.

Higdon, Noah S.↗
NASA NTRS1993

Comparison of ozone profiles obtained with NIES DIAL and SAGE II measurements

Ozone profiles obtained with the Differential Absorption Lidar (DIAL) system at the National Institute for Environmental Studies (NIES) (Tsukuba, Japan) were compared with data provided by the satellite sensor SAGE II. The SAGE II data were selected based on criteria of spatial and temporal differences between the DIAL and the SAGE II measurements: five degrees in latitude and 15 degrees in longitude, within a latitudinal band from 31 deg to 41 deg N, and within one, three and five days after or before the DIAL measurements. Results show very good agreement for the individual and the zonal-mean profiles. The average mean difference between the DIAL and the SAGE II measurements over the altitudes 15-50 km was about 10 percent.

Nakane, Hideaki↗
NASA NTRS1998

Two Wavelength Ti:sapphire Laser for Ozone DIAL Measurements from Aircraft

Laser remote sensing of ozone from aircraft has proven to be a valuable technique for understanding the distribution and dynamics of ozone in the atmosphere. Presently the differential absorption lidar (DIAL) technique, using dual ND:YAG lasers that are doubled to pump dye lasers which in turn are doubled into the UV for the "on" and "off' line lasers, is used on either the NASA DC-8 or P-3 aircraft. Typically, the laser output for each line is 40-mJ and this is split into two beams, one looking up and the other downward, each beam having about 20-mJ. The residual ND:YAG (1.06 micron) and dye laser energies are also transmitted to obtain information on the atmospheric aerosols. While this system has operated well, there are several system characteristics that make the system less than ideal for aircraft operations. The system, which uses separate "on" and "off" line lasers, is quite large and massive requiring valuable aircraft volume and weight. The dye slowly degrades with time requiring replacement. The laser complexity requires a number of technical people to maintain the system performance. There is also the future interest in deploying an ozone DIAL system in an Unpiloted Atmospheric Vehicle (UAV) which would require a total payload mass of less than 150 kg and power requirement of less than 1500 W. A laser technology has emerged that could potentially provide significant enhancements over the present ozone DIAL system. The flashlamp pumped Ti:sapphire laser system is an emerging technology that could reduce the mass and volume over the present system and also provide a system with fewer conversion steps, reducing system complexity. This paper will discuss preliminary results from a flashlamp-pumped Ti:sapphire laser constructed as a radiation source for a UV DIAL system to measure ozone.

Situ, Wen↗
NASA NTRS1998

Correlative Stratospheric Ozone Measurements with the Airborne UV DIAL System during TOTE/VOTE

The airborne UV differential absorption lidar (DIAL) system participated in the Tropical Ozone Transport Experiment/Vortex Ozone Transport Experiment (TOTE/VOTE) in late 1995/early 1996. This mission afforded the opportunity to compare the DIAL system's stratospheric ozone measuring capability with other remote-sensing instruments through correlative measurements over a latitude range from the tropics to the Arctic. These instruments included ground-based DIAL and space-based stratospheric instruments: HALOE; MLS; and SAGE II. The ozone profiles generally agreed within random error estimates for the various instruments in the middle of the profiles in the tropics, but regions of significant systematic differences, especially near or below the tropopause or at the higher altitudes were also found. The comparisons strongly suggest that the airborne UV DIAL system can play a valuable role as a mobile lower-stratospheric ozone validation instrument.

Grant, William B.↗
NASA NTRS2008

Development and Evaluation of a High Sensitivity DIAL System for Profiling Atmospheric CO2

A ground-based 2-micron Differential Absorption Lidar (DIAL) CO2 profiling system for atmospheric boundary layer studies and validation of space-based CO2 sensors is being developed and tested at NASA Langley Research Center as part of the NASA Instrument Incubator Program. To capture the variability of CO2 in the lower troposphere a precision of 1-2 ppm of CO2 (less than 0.5%) with 0.5 to 1 km vertical resolution from near surface to free troposphere (4-5 km) is one of the goals of this program. In addition, a 1% (3 ppm) absolute accuracy with a 1 km resolution over 0.5 km to free troposphere (4-5 km) is also a goal of the program. This DIAL system leverages 2-micron laser technology developed under NASA's Laser Risk Reduction Program (LRRP) and other NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO2 absorption lines suitable for profiling of lower tropospheric CO2. It also incorporates new high quantum efficiency, high gain, and relatively low noise phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. This presentation describes the capabilities of this system for atmospheric CO2 and aerosol profiling. Examples of atmospheric measurements in the lidar and DIAL mode will be presented.

Ismail, Syed↗
DOE OSTI2021

Development of a Framework for Data Integration, Assimilation, and Learning for Geological Carbon Sequestration (DIAL-GCS) (Final Report)

This project aimed to develop and demonstrate a Data Integration, Assimilation, and Learning framework for geologic carbon sequestration projects (DIAL-GCS). DIAL-GCS is an intelligence monitoring system (IMS) for automating GCS closed-loop management by leveraging recent developments in machine learning technologies, complex event processing (CEP), and reduced-order modeling. The safe and efficient operation of GCS repositories requires integrated monitoring to track the injected CO¬2 as it moves within a storage reservoir. GCS projects are data intensive, as a result of proliferation of digital instrumentation and smart-sensing technologies. GCS projects are also resource intensive, often requiring multidisciplinary teams performing different monitoring, verification, accounting (MVA) tasks throughout the lifecycle of a project to ensure secure containment of injected CO2. The success of GCS thus depends in a large part on our ability to access, assimilate, and analyze heterogeneous data and information sources in a timely manner. This project included a number of meaningful and necessary tasks to transform the human domain knowledge into machine-interpretable rules for automating knowledge extraction and discovery in GCS. The specific technical objectives of the proposed DIAL-GCS project were to develop an ontology-driven GCS data management module for storing, querying, and exchanging GCS data (both historic and live sensor data) from multiple sources and in heterogeneous formats. Incorporate a CEP engine for detecting abnormal situations by seamlessly combining expert knowledge, rule-based reasoning, and machine learning. Enable uncertainty quantification and predictive analytics using a combination of coupled-process modeling, AI/ML methods, and reduced-order modeling, and integrate and demonstrate the system’s capabilities with both real and simulated data. As far as we know, this is one of the first projects aimed to develop intelligent monitoring systems (IMS) targeting the GCS. Under this project, the team had developed a large number of web applications and scientific algorithms that contribute the main theme of intelligent monitoring. The team has published more than a dozen peer reviewed papers and disseminated the research results at multiple technical meetings.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1981

Remote probing of the atmosphere using a CO2 DIAL system

An overview of our laser remote sensing effort is presented. Using both fundamental and frequency-doubled CO2 laser radiation in a differential absorption LIDAR (DIAL) system, background concentrations of CO, NO, and C2H4 in the atmosphere as well as increases due to localized emission sources have been measured. These species have been detected using the backscattered laser radiation from topographic targets at ranges to 2.7 km with a sensitivity of plus or minus 10 ppb. In addition, using a dual-laser DIAL system, the effect of induced correlation of the LIDAR returns due to atmospheric turbulence has been investigated. These results have been used to help quantify the accuracy of the DIAL measurements and are shown to be consistent with theory.

Killinger, D. K.↗
NASA NTRS1982

Effect of differential spectral reflectance on DIAL measurements using topographic targets

Differential absorption lidar (DIAL) measurements of atmospheric gases and temperature made using topographic targets to provide the backscattered signal are subject to errors from the differential spectral reflectance of the target materials. The magnitude of this effect is estimated for a number of DIAL measurements reported in the literature. Calculations are presented for several topographic targets. In general the effect on a DIAL measurement increases directly with increasing wavelength and laser line separation, and inversely with differential absorption coefficient and distance to the target. The effect can be minimized by using tunable or isotope lasers to reduce the laser line separation or by using additional reference wavelengths to determine the surface differential spectral reflectance.

Grant, W. B.↗
NASA NTRS1983

Terminal area automatic navigation, guidance and control research using the Microwave Landing System (MLS). Part 5: Design and development of a Digital Integrated Automatic Landing System (DIALS) for steep final approach using modern control techniques

The design and development of a 3-D Digital Integrated Automatic Landing System (DIALS) for the Terminal Configured Vehicle (TCV) Research Aircraft, a B-737-100 is described. The system was designed using sampled data Linear Quadratic Gaussian (LOG) methods, resulting in a direct digital design with a modern control structure which consists of a Kalman filter followed by a control gain matrix, all operating at 10 Hz. DIALS uses Microwave Landing System (MLS) position, body-mounted accelerometers, as well as on-board sensors usually available on commercial aircraft, but does not use inertial platforms. The phases of the final approach considered are the localizer and glideslope capture which may be performed simultaneously, localizer and steep glideslope track or hold, crab/decrab and flare to touchdown. DIALS captures, tracks and flares from steep glideslopes ranging from 2.5 deg to 5.5 deg, selected prior to glideslope capture. Digital Integrated Automatic Landing System is the first modern control design automatic landing system successfully flight tested. The results of an initial nonlinear simulation are presented here.

Halyo, N.↗
NASA NTRS1986

Development of a high-altitude airborne dial system: The Lidar Atmospheric Sensing Experiment (LASE)

The ability of a Differential Absorption Lidar (DIAL) system to measure vertical profiles of H2O in the lower atmosphere was demonstrated both in ground-based and airborne experiments. In these experiments, tunable lasers were used that required real-time experimenter control to locate and lock onto the atmospheric H2O absorption line for the DIAL measurements. The Lidar Atmospheric Sensing Experiment (LASE) is the first step in a long-range effort to develop and demonstrate an autonomous DIAL system for airborne and spaceborne flight experiments. The LASE instrument is being developed to measure H2O, aerosol, and cloud profiles from a high-altitude ER-2 (extended range U-2) aircraft. The science of the LASE program, the LASE system design, and the expected measurement capability of the system are discussed.

Browell, E. V.↗
NASA NTRS1986

Assesment of dial data collection and analysis techniques

The key issues in all areas of Differential Absorption Lidar (DIAL) data collection and analysis techniques were examined. This included consideration of the practical and theoretical limitations of DIAL and the range of possible DIAL measurements.

Browell, E. V.↗
NASA NTRS1986

Nd:Glass-Raman laser for water vapor dial

A tunable solid-state Raman shifted laser which was used in a water vapor Differential Absorption Lidar (DIAL) system at 9400 A is described. The DIAL transmitter is based on a tunable glass laser operating at 1.06 microns, a hydrogen Raman cell to shift the radiation to 1.88 microns, and a frequency doubling crystal. The results of measurements which characterize the output of the laser with respect to optimization of optical configuration and of Raman parameters were reported. The DIAL system was also described and preliminary atmospheric returns shown.

Kagann, R. H.↗
NASA NTRS1992

Comparison of eye-safe solid state laser DIAL with passive gas filter correlation measurements from aircraft and spacecraft

Differential Absorption Lidar (DIAL) using solid state Ti:sapphire lasers finds current application in the NASA/LASE Project for H2O vapor measurements in the approximately = 0.820 micron region for the lower and mid-troposphere and in potential future applications in planned measurements of the approximately = 0.940 micron region where both strong and weak absorption lines enables measurements throughout the troposphere and lower stratosphere. The challenge exists to perform measurements in the eye-safe greater than 1.5 micron region. A comparison between DIAL and passive Gas Filter Correlation Radiometer (GFCR) measurements is made. The essence of the differences in signal to noise ratio for DIAL and passive GFCR measurements is examined. The state of the art of lasers and optical parametric oscillators (OPO's) is discussed.

Hess, Robert V.↗
NASA NTRS1995

Line-center/side-line diode laser seeding for DIAL measurements of the atmosphere

The ability of DIAL systems to probe deeply into the atmosphere is enhanced if the pulsed laser is capable of sequentially operating at different wavelengths, each wavelength corresponding to a different absorption cross-section of the gas of interest. Such wavelength versatility is particularly important for airborne or spaceborne DIAL measurements of H2O(v) due to its strong vertical gradient (several orders of magnitude). Strong H2O(v) cross-sections are necessary to retrieve H2O(v) data from high altitudes while the use of weaker cross sections enables penetration of the DIAL laser pulses to lower altitudes.

Sachse, Glen↗
NASA NTRS1995

Linear operating region in the ozone dial photon counting system

Ozone is a relatively unstable molecule found in Earth's atmosphere. An ozone molecule is made up of three atoms of oxygen. Depending on where ozone resides, it can protect or harm life on Earth. High in the atmosphere, about 15 miles up, ozone acts as a shield to protect Earth's surface from the sun's harmful ultraviolet radiation. Without this shield, we would be more susceptible to skin cancer, cataracts, and impaired immune systems. Closer to Earth, in the air we breathe, ozone is a harmful pollutant that causes damage to lung tissue and plants. Since the early 1980's, airborne lidar systems have been used for making measurements of ozone. The differential absorption lidar (DIAL) technique is used in the remote measurement of O3. This system allows the O3 to be measured as function of the range in the atmosphere. Two frequency-doubled Nd:YAG lasers are used to pump tunable dye lasers. The lasers are operating at 289 nm for the DIAL on-line wavelength of O3, and the other one is operated at 300 nm for the off-line wavelength. The DIAL wavelengths are produced in sequential laser pulses with a time separation of 300 micro s. The backscattered laser energy is collected by telescopes and measured using photon counting systems. The photon counting system measures the light signal by making use of the photon nature of light. The output pulse from the Photo-Multiplier Tube (PE), caused by a photon striking the PMT photo-cathode, is amplified and passed to a pulse height discriminator. The peak value of the pulse is compared to a reference voltage (discrimination level). If the pulse amplitude exceeds the discrimination level, the discriminator generates a standard pulse which is counted by the digital counter. Non-linearity in the system is caused by the overlapping of pulses and the finite response time of the electronics. At low count rates one expects the system to register one event for each output pulse from the PMT corresponding to a photon incident upon the photocathode, however, at higher rates the limitations of the discrimination/counting system will cause the observed count rate to be non-linear with respect to the true count rate. Depending on the pulse height distribution and the discriminator level, the overlapping of pulses (pulse pile-up) can cause count loss or even an additional apparent count gain as the signal levels increase. Characterization of the system, including the pulse height distribution, the signal to noise ratio, and the effect of the discriminator threshold level, is critical in maximizing the linear operating region of the system, thus greatly increasing the useful dynamic range of the system.

Andrawis, Madeleine↗
NASA NTRS2000

Advanced Atmospheric Water Vapor DIAL Detection System

Measurement of atmospheric water vapor is very important for understanding the Earth's climate and water cycle. The remote sensing Differential Absorption Lidar (DIAL) technique is a powerful method to perform such measurement from aircraft and space. This thesis describes a new advanced detection system, which incorporates major improvements regarding sensitivity and size. These improvements include a low noise advanced avalanche photodiode detector, a custom analog circuit, a 14-bit digitizer, a microcontroller for on board averaging and finally a fast computer interface. This thesis describes the design and validation of this new water vapor DIAL detection system which was integrated onto a small Printed Circuit Board (PCB) with minimal weight and power consumption. Comparing its measurements to an existing DIAL system for aerosol and water vapor profiling validated the detection system.

Refaat, Tamer F.↗
NASA NTRS2000

Airborne UV DIAL Measurements of Ozone and Aerosols

The NASA Langley Research Center's airborne UV Differential Absorption Lidar (DIAL) system measures vertical profiles of ozone and aerosols above and below the aircraft along its flight track. This system has been used in over 20 airborne field missions designed to study the troposphere and stratosphere since 1980. Four of these missions involved tropospheric measurement programs in the Pacific Ocean with two in the western North Pacific and two in the South Pacific. The UV DIAL system has been used in these missions to study such things as pollution outflow, long-range transport, and stratospheric intrusions; categorize the air masses encountered; and to guide the aircraft to altitudes where interesting features can be studied using the in situ instruments. This paper will highlight the findings with the UV DIAL system in the Pacific Ocean field programs and introduce the mission planned for the western North Pacific for February-April 2001. This will be an excellent opportunity for collaboration between the NASA airborne mission and those with ground-based War systems in Asia Pacific Rim countries to make a more complete determination of the transport of air from Asia to the western Pacific.

Grant, William B.↗
NASA NTRS2000

Tunable Single-Frequency Near IR Lasers for DIAL Applications

Tunable single-frequency sources in the 2-4 micron wavelength region are useful for remote DIAL measurements of chemicals and pollutants. We are developing tunable single-frequency transmitters and receivers for both direct and coherent detection lidar measurement applications. We have demonstrated a direct-diode-pumped PPLN-based OPO that operates single frequency, produces greater than 10 mW cw and is tunable over the 2.5 - 3.9 micron wavelength region. This laser has been used to injection seed a pulsed PPLN OPO, pumped by a 1.064 micron Nd:YAG laser, producing 50-100 microJoule single-frequency pulses at 100 Hz PRF near 3.6 micron wavelength. In addition, we have demonstrated a cw Cr:ZnSe laser that is tunable over the 2.1 - 2.8 micron wavelength region. This laser is pumped by a cw diode-pumped Tm:YALO laser and has produced over 1.8 W cw. Tm- and Tm, Ho-doped single-frequency solid-state lasers that produce over 50 mW cw and are tunable over approximately 10 nm in the 2 -2.1 micron band with fast PZT tuning have also been demonstrated. A fast PZT-tunable Tm, Ho:YLF laser was used for a direct-detection column content DIAL measurement of atmospheric CO2. Modeling shows that that all these cw and pulsed sources are useful for column-content coherent DIAL measurements at several km range using topographic targets.

Henderson, Sammy W.↗