Mobile Differential Absorption Lidar Research Articles

Calibration and field test of mobile lidar for remote sensing of atmospheric methane

Subject of study. Methane concentration in near-the-surface tropospheric sensing paths was investigated under background conditions using a mobile differential absorption lidar. Aim of study. A mobile differential absorption lidar for remote sensing of atmospheric methane in the mid-infrared spectral range was designed, calibrated, and tested in natural field experiments. Method. The designed lidar enables investigation in the atmosphere using the differential absorption method. This method is based on the effect of resonant absorption of laser emission by gases. The emission source of the lidar has two operating wavelengths, one (on-line) in the center of the methane absorption line and the other (off-line) on the wing of the absorption line. The lidar signals obtained at on- and off-line wavelengths enable retrieval of the methane concentration under background conditions. Main results. The designed mobile IR differential absorption lidar for investigation of atmospheric methane is described. The mobile IR emission source of the differential absorption lidar was calibrated in the informative range of methane sensing near 3400 nm. The results of a natural field test of the mobile IR lidar for detection of atmospheric response at the calibrated sensing wavelengths and retrieval of methane background concentrations of approximately 2.0 ppm in horizontal surface atmospheric sensing paths are presented. Practical significance. The technical solutions for the design of the mobile lidar for remote methane sensing proposed in this paper enable formulation of the requirements on its further improvement aiming to increase the measurement range, design a vertical configuration for remote sensing from an aircraft, and use it at arctic latitudes.

Mercury as a Geophysical Tracer Gas - Emissions from the Emperor Qin Tomb in Xi\xb4an Studied by Laser Radar

Mercury is, because of its high vapor pressure and its prevalence in the atmosphere as atoms, an interesting geophysical tracer gas, also with potential archaeological applications. According to historical records dating back 2200 years, the mausoleum chamber of the “Terracotta Army Emperor” Qin in Xi´an, China, contains large amounts of liquid mercury, considered as an elixir of life at the time. We here report on measurements of the atmospheric contents of atomic mercury above the tomb mound performed with a mobile differential absorption lidar (light detection and ranging) system. Our measurements, which were performed from three different locations around the mound, indeed indicate elevated atmospheric mercury levels, with localizations, which correlate with previous in situ soil sampling results. Concentrations up to 27 ng/m3 were observed, significantly higher than the typical general pollutant level in the area which was found to be around 5–10 ng/m3. An out-flux of about 5×10−8 kg/s was estimated. Highly volatile mercury may be escaping through cracks, which developed in the structure over time, and our investigation supports ancient chronicle records on the tomb, which is believed never to have been opened/looted. Our findings also have bearings on the proposed use of mercury as a tracer gas for valuable ores and geothermal resource exploration, and also bring problematics around reliable nuclear waste long-term underground storage to mind.

A mobile differential absorption lidar for simultaneous observations of tropospheric and stratospheric ozone over Tibet.

We developed a mobile ozone differential absorption lidar system to simultaneously measure the vertical profiles of tropospheric and stratospheric ozone from an altitude of ~5 to 50 km. The system emits four laser beams at wavelength of 289 nm, 299 nm, 308 nm and 355 nm and receives their corresponding Mie/Rayleigh backscattering return signals, and two N2 Raman return signals at 332 nm and 387 nm shifted from 308 nm and 355 nm, respectively. An assembled telescope array with four 1.25-m telescopes (effective diameter > 2 m) collects the Rayleigh and Raman backscattering signals at 308/332 and 355/387 nm. This system is currently deployed at the Yangbajing Observatory in Tibet (~4300 m elevation) and has begun observations in regular campaign mode since October 2017. The lidar results agree very well with those observed by the Aura/MLS satellite. This novel ozone lidar system operates at the highest elevation of any such system in the world. The higher elevation and larger receiver aperture of this system yield a higher signal-to-noise ratio and lower statistical uncertainty.

Volcanic Plumes: Impacts on the Atmosphere and Insights into Volcanic Processes

Here we introduce a Special Issue of Geosciences focused on the scientific research field of ‘Volcanic Plumes: Impacts on the atmosphere and insights into volcanic processes’ [...]

Volcanic Plume CO2 Flux Measurements at Mount Etna by Mobile Differential Absorption Lidar

Volcanic eruptions are often preceded by precursory increases in the volcanic carbon dioxide (CO2) flux. Unfortunately, the traditional techniques used to measure volcanic CO2 require near-vent, in situ plume measurements that are potentially hazardous for operators and expose instruments to extreme conditions. To overcome these limitations, the project BRIDGE (BRIDging the gap between Gas Emissions and geophysical observations at active volcanoes) received funding from the European Research Council, with the objective to develop a new generation of volcanic gas sensing instruments, including a novel DIAL-Lidar (Differential Absorption Light Detection and Ranging) for remote (e.g., distal) CO2 observations. Here we report on the results of a field campaign carried out at Mt. Etna from 28 July 2016 to 1 August 2016, during which we used this novel DIAL-Lidar to retrieve spatially and temporally resolved profiles of excess CO2 concentrations inside the volcanic plume. By vertically scanning the volcanic plume at different elevation angles and distances, an excess CO2 concentration of tens of ppm (up to 30% above the atmospheric background of 400 ppm) was resolved from up to a 4 km distance from the plume itself. From this, the first remotely sensed volcanic CO2 flux estimation from Etna’s northeast crater was derived at ≈2850–3900 tons/day. This Lidar-based CO2 flux is in fair agreement with that (≈2750 tons/day) obtained using conventional techniques requiring the in situ measurement of volcanic gas composition.

A mobile differential absorption lidar to measure sub-hourly fluctuation of tropospheric ozone profiles in the Baltimore–Washington, D.C. region

Abstract. Tropospheric ozone profiles have been retrieved from the new ground-based National Aeronautics and Space Administration (NASA) Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL) in Greenbelt, MD (38.99° N, 76.84° W, 57 m a.s.l.), from 400 m to 12 km a.g.l. Current atmospheric satellite instruments cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, the Tropospheric Ozone Lidar Network (TOLNet) has been developed, which currently consists of five stations across the US. The GSFC TROPOZ DIAL is based on the DIAL technique, which currently detects two wavelengths, 289 and 299 nm, with multiple receivers. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman cells, filled with high-pressure hydrogen and deuterium, using helium as buffer gas. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range-resolved number density can be derived. An interesting atmospheric case study involving the stratospheric–tropospheric exchange (STE) of ozone is shown, to emphasize the regional importance of this instrument as well as to assess the validation and calibration of data. There was a low amount of aerosol aloft, and an iterative aerosol correction has been performed on the retrieved data, which resulted in less than a 3 ppb correction to the final ozone concentration. The retrieval yields an uncertainty of 16–19% from 0 to 1.5 km, 10–18% from 1.5 to 3 km, and 11–25% from 3 to 12 km according to the relevant aerosol concentration aloft. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make routine tropospheric ozone profile measurements in the Baltimore–Washington, D.C. area.

First measurements of a carbon dioxide plume from an industrial source using a ground based mobile differential absorption lidar.

The emission of carbon dioxide (CO2) from industrial sources is one of the main anthropogenic contributors to the greenhouse effect. Direct remote sensing of CO2 emissions using optical methods offers the potential for the identification and quantification of CO2 emissions. We report the development and demonstration of a ground based mobile differential absorption lidar (DIAL) able to measure the mass emission rate of CO2 in the plume from a power station. To our knowledge DIAL has not previously been successfully applied to the measurement of emission plumes of CO2 from industrial sources. A significant challenge in observing industrial CO2 emission plumes is the ability to discriminate and observe localised concentrations of CO2 above the locally observed background level. The objectives of the study were to modify our existing mobile infrared DIAL system to enable CO2 measurements and to demonstrate the system at a power plant to assess the feasibility of the technique for the identification and quantification of CO2 emissions. The results of this preliminary study showed very good agreement with the expected emissions calculated by the site. The detection limit obtained from the measurements, however, requires further improvement to provide quantification of smaller emitters of CO2, for example for the detection of fugitive emissions. This study has shown that in principle, remote optical sensing technology will have the potential to provide useful direct data on CO2 mass emission rates.

A TEA CO2 laser with a peak radiation power of 100 MW

A high-power pulse-periodic TEA CO2 laser is used as a component of a long-range mobile differential absorption lidar. In order to reach the ultimate peak generation power, a system for laser excitation with a supply voltage of ±40 kV and efficient preionization was developed, allowing the laser to operate at high pressures of gas mixtures of various compositions. Energy, time, and spatial characteristics of laser radiation were studied. Laser pulses with an energy of >10 J and FWHM duration of ≈30 ns were obtained. The ultimate peak laser radiation power is 100 MW, and the maximum efficiency with respect to the discharge-consumed energy is 12.6%.

Industrial Emission Control Using Lidar Techniques

A mobile DIAL (differential absorption lidar) remote sensing system has been employed in the monitoring of industrial pollutant emissions. Measurements of sulfur dioxide and mercury vapor were performed at nine different Swedish industrial plants within the framework of a control program commissioned by the Swedish Environmental Protection Agency. Total atmospheric fluxes of these species could be determined by combining wind data with a mapping of the concentration distribution downwind from the sources. The emission values obtained were compared with in situ measurements made by the companies themselves. The values from single point sources correlate well, whereas the DIAL system normally measures a higher total flux from several distributed sources including diffuse emissions. The results are used to discuss the applicability and limitation of the DIAL technique for remote surveillance of industrial emissions. (Less)

Comparative study of nitric oxide immission in the cities of Lyon, Geneva, and Stuttgart using a mobile differential absorption LIDAR system

The immission load of nitric oxide due to traffic is investigated in the cities of Lyon, Geneva, and Stuttgart using a mobile differential absorption LIDAR system (DIAL). Horizontal and vertical maps of the NO mixing ratio, as well as 24 hour records are presented. It is shown that street canyons favor high immission values, whereas broad main axes are efficiently ventilated (Lyon); inversion conditions rise the average immission load within a city mainly independent of traffic (Geneva and Stuttgart), whereas highly frequented intersections favor high immission values regardless of weather conditions (Geneva); the observed maximum immission loads also depend on the traffic density during rush hours (Stuttgart).

STROZ LITE: Stratospheric Ozone Lidar Trailer Experiment

As a part of the international Network for the Detection of Stratospheric Change, Goddard Space Flight Center has developed a mobile differential absorption lidar capable of making precise and accurate measurements in the stratosphere between 20 and 45 km. We present in this paper a description of the instrument, a discussion of the data analysis, and some results from an intercomparison held at JPL's Table Mountain Observatory in California during October and November 1988.

Lidar Measurements Of Tropospheric Gases

Measurements of pollutants and water vapor in the troposphere using the differential absorption lidar (DIAL) technique are described. Measurements are made of sulfur dioxide in power plant plumes with a mobile DIAL system operated near 300 nm. Comparisons of sulfur dioxide concentrations determined with the DIAL system and in-stack monitors are found to be in agreement to within 18%. Vertical water vapor profiles with a ground-based lidar system are measured using the water vapor absorption line at 724.3 nm. Rawinsonde and DIAL water vapor profile data are shown to agree within 10% to an altitude of 2.5 km. Simulations are discussed for airborne DIAL measurements of sulfur dioxide, water vapor, and nitrogen dioxide.