Range-resolved Differential Absorption Lidar Research Articles

Simulation and analysis of the CO2 range-resolved differential absorption lidar system at 2 μm

The range-resolved differential absorption lidar is a high-precision device to measure the concentration of carbon dioxide. This paper provides a system-wide theoretical analysis method for the performance analysis and parameter optimization of the lidar system using the given parameter range. The scattered echo signal, signal-to-noise ratio, and detection sensitivity were simulated by setting assumed parameters with the HITRAN 2020 database and the US 1976 standard atmosphere model to analyze the detection distance and concentration resolution of the lidar system. The effects of the laser energy, repetition frequency, and photodetector noise were also discussed. The wavelength selection near the absorption line is critical because it controls the height region of the highest sensitivity and the demands on frequency stability. Recommendations for the selection of absorption lines are provided in this paper. A quantitative analysis of each error source provided reasonable error ranges.

Multi-Frequency Differential Absorption LIDAR (DIAL) System for Aerosol and Cloud Retrievals of CO2/H2O and CH4/H2O

We discuss a remote sensing system that is used to simultaneously detect range-resolved differential absorption LIDAR (light detection and ranging; DIAL) signals and integrated path differential absorption LIDAR signals (IPDA LIDAR) from aerosol targets for ranges up to 22 km. The DIAL/IPDA LIDAR frequency converter consists of an OPO pumped at 1064 nm to produce light at 1.6 μm and operates at 100 Hz pulse repetition frequency. The probe light is free space coupled to a movable platform that contains one transmitter and two receiver telescopes. Hybrid photon counting/current systems increase the dynamic range for detection by two orders of magnitude. Range resolved and column integrated dry-air CO2 and CH4 mixing ratios are obtained from line shape fits of CO2 and CH4 centered at 1602.2 nm and 1645.5 nm, respectively, and measured at 10 different frequencies over ≈1.3 cm−1 bandwidth. The signal-to-noise ratios (SNRs) of the IPDA LIDAR returns from cloud aerosols approach 1000:1 and the uncertainties in the mixing ratios weighted according to the integrated counts over the cloud segments range from 0.1% to 1%. The range-averaged DIAL mixing ratios are in good agreement with the IPDA LIDAR mixing ratios at the 1% to 2% level for both CO2 and CH4. These results can serve as a validation method for future active and passive satellite observational systems.

Case study on the influence of synoptic-scale processes on the paired H2O–O3 distribution in the UTLS across a North Atlantic jet stream

Abstract. During a research flight of the Wave-driven ISentropic Exchange (WISE) campaign, which was conducted over the eastern North Atlantic on 1 October 2017, the composition of the upper troposphere and lower stratosphere (UTLS) across the North Atlantic jet stream was observed by airborne, range-resolved differential absorption lidar (DIAL) profiles. We investigate how the high variability in the paired H2O and O3 distribution along the two-dimensional lidar cross section is affected by synoptic-scale weather systems, as revealed by the Lagrangian history of the observed air masses. To this aim, the lidar observations are combined with 10 d backward trajectories along which meteorological parameters and derived turbulence diagnostics are traced. The transport and mixing characteristics are then projected to the vertical cross sections of the lidar measurements and to the H2O–O3 phase space to explore linkages with the evolution of synoptic-scale weather systems and their interaction. Tropical, midlatitude, and arctic weather systems in the region of the jet stream and the related transport and mixing explain the complex H2O and O3 distribution to a large extent: O3-rich stratospheric air from the high Arctic interacts with midlatitude air from the North Pacific in a northward-deflected jet stream associated with an anticyclone over the US and forms a filament extending into the tropopause fold beneath the jet stream. In the troposphere, lifting related to convection in the intertropical convergence zone (ITCZ) and two tropical cyclones that continuously injected H2O into dry descending air from the tropical Atlantic and Pacific form filamentary H2O structures. One tropical cyclone that transitioned into a midlatitude cyclone lifted moist boundary layer air, explaining the highest tropospheric H2O values. During the two days before the observations, the air with mixed tropospheric and stratospheric characteristics experienced frequent turbulence along the North Atlantic jet stream, indicating a strong influence of turbulence on the formation of the extratropical transition layer (ExTL). This investigation highlights the complexity of stirring and mixing processes and their close connection to interacting tropospheric weather systems from the tropics to the polar regions, which strongly influenced the observed fine-scale H2O and O3 distributions. The identified non-local character of mixing should be kept in mind when interpreting mixing lines in tracer–tracer phase space diagrams.

Range-resolved detection of boundary layer stable water vapor isotopologues using a ground-based 1.98 µm differential absorption LIDAR.

This paper presents a first demonstration of range-resolved differential absorption LIDAR (DIAL) measurements of the water vapor main isotopologue H2 16O and the less abundant semi-heavy water isotopologue HD16O with the aim of determining the isotopic ratio. The presented Water Vapor and Isotope Lidar (WaVIL) instrument is based on a parametric laser source emitting nanosecond pulses at 1.98 µm and a direct-detection receiver utilizing a commercial InGaAs PIN photodiode. Vertical profiles of H2 16O and HD16O were acquired in the planetary boundary layer in the suburban Paris region up to a range of 1.5 km. For time averaging over 25 min, the achieved precision in the retrieved water vapor mixing ratio is 0.1 g kg-1 (2.5% relative error) at 0.4 km above ground level (a.g.l.) and 0.6 g kg-1 (20%) at 1 km a.g.l. for 150 m range bins along the LIDAR line of sight. For HD16O, weaker absorption has to be balanced with coarser vertical resolution (600 m range bins) in order to achieve similar relative precision. From the DIAL measurements of H2 16O and HD16O, the isotopic abundance δD was estimated as -51‰ at 0.4 km above the ground and -119‰ in the upper part of the boundary layer at 1.3 km a.g.l. Random and systematic errors are discussed in the form of an error budget, which shows that further instrumental improvements are required on the challenging path towards DIAL-profiling of the isotopic abundance with range resolution and precision suitable for water cycle studies.

Upconversion detector for range-resolved DIAL measurement of atmospheric CH4.

We demonstrate a robust, compact, portable and efficient upconversion detector (UCD) for a differential absorption lidar (DIAL) system designed for range-resolved methane (CH4) atmospheric sensing. The UCD is built on an intracavity pump system that mixes a 1064 nm pump laser with the lidar backscatter signal at 1646 nm in a 25-mm long periodically poled lithium niobate crystal. The upconverted signal at 646 nm is detected by a photomultiplier tube (PMT). The UCD with a noise equivalent power around 127 fW/Hz1/2 outperforms a conventional InGaAs based avalanche photodetector when both are used for DIAL measurements. Using the UCD, CH4 DIAL measurements have been performed yielding differential absorption optical depths with relative errors of less than 11% at ranges between 3 km and 9 km.

Performance evaluation of a 16-µm methane DIAL system from ground, aircraft and UAV platforms

Methane is an efficient absorber of infrared radiation and a potent greenhouse gas with a warming potential 72 times greater than carbon dioxide on a per molecule basis. Development of methane active remote sensing capability using the differential absorption lidar (DIAL) technique enables scientific assessments of the gas emission and impacts on the climate. A performance evaluation of a pulsed DIAL system for monitoring atmospheric methane is presented. This system leverages a robust injection-seeded pulsed Nd:YAG pumped Optical Parametric Oscillator (OPO) laser technology operating in the 1.645 µm spectral band. The system also leverages an efficient low noise, commercially available, InGaAs avalanche photo-detector (APD). Lidar signals and error budget are analyzed for system operation on ground in the range-resolved DIAL mode and from airborne platforms in the integrated path DIAL (IPDA) mode. Results indicate system capability of measuring methane concentration profiles with <1.0% total error up to 4.5 km range with 5 minute averaging from ground. For airborne IPDA, the total error in the column dry mixing ratio is less than 0.3% with 0.1 sec average using ground returns. This system has a unique capability of combining signals from the atmospheric scattering from layers above the surface with ground return signals, which provides methane column measurement between the atmospheric scattering layer and the ground directly. In such case 0.5% and 1.2% total errors are achieved with 10 sec average from airborne platforms at 8 km and 15.24 km altitudes, respectively. Due to the pulsed nature of the transmitter, the system is relatively insensitive to aerosol and cloud interferences. Such DIAL system would be ideal for investigating high latitude methane releases over polar ice sheets, permafrost regions, wetlands, and over ocean during day and night. This system would have commercial potential for fossil fuel leaks detection and industrial monitoring applications.

Direct measurement of the total reaction rate of OH in the atmosphere

A new method to investigate atmospheric chemical kinetics is presented. It is based on the pump and probe principle. Preliminary measurements are described on the decay rate of OH in the planetary boundary layer its concentration has been raised by laser flash photolysis of background ozone and subsequent reaction of the O(1D) with atmospheric water vapor. The measured OH disappearance kinetics are compared with model calculations yielding information on the fast reaction of OH. The presented point measurements can be extended to a range resolved differential absorption LIDAR technique.

Injection-seeded optical parametric oscillator for range-resolved DIAL measurements of atmospheric methane

A pulsed injection-seeded optical parametric oscillator (OPO) has been studied and its suitability for applications requiring dual-wavelength operation has been demonstrated. Single-mode operation was achieved by injection seeding the OPO with radiation from a tunable diode laser. The OPO was tuned over a range of 90 nm (1490.6–1580.3 nm) with an average output energy of 5 mJ (7% conversion efficiency) and a linewidth of 140 MHz. The inherent stability of the travelling-wave cavity design has enabled stable operation to be achieved without active stabilisation of the cavity. Dual-wavelength operation has been achieved by injecting two seed frequencies simultaneously. The suitability of the OPO for infrared Differential Absorption Lidar (DIAL) measurements has been demonstrated by making a range-resolved measurement of atmospheric methane.

Differential Absorption Lidars for Measuring Atmospheric Minor Constituents Related to Earth Warming.

Atmospheric minor constituents related to earth warming have many absorption lines in the IR region. Recent progress in high power IR tunable lasers makes the detection of these species possible by the differential absorption lidar (DIAL). This paper describes the theoretical analysis of the detection range of the IR range-resolved DIALs. At first, the detection ranges are generally calculated over a wavelength range from 200 nm to 16μm. For the ideal absorption line strength, the typical detection range in IR is 3-4 km in the vertical distribution measurement, but it increases to 10 km in the horizontal distribution measurement. Based on the HITRAN database, we surveyed useful absorption lines for DIAL measurement in the 1-5μm range, and found that CO2, CH4, N2O and CO were detectable besides H2O. Detailed simulation of the DIAL measurement was made for each of the absorption lines of these molecules, and it was shown that the range-resolved DIAL method was useful for the detection of these four species.

Simulation of range-resolved DIAL measurements on in-flight rocket plumes

Feasibility studies were carried out for a ground-based experiment using the differential absorption LIDAR (DIAL) method, to measure spatially resolved rocket plume temperature profiles from solid-aluminized propellants. The core of this effort was a numerical simulation of the dynamics of the laser-plume interaction and the retrieval of average temperatures from the received signals using parameters appropriate to a low-altitude rocket plume. Signal-to-noise ratios were adequate for the assumed experimental conditions and for both a clear and moderately clear atmosphere, to ensure detectability of the returned signals over most of the plume. For the chosen laser frequencies, the simulated experimental results indicate reasonable quantitative agreement with flowfield model predictions.

Concentration estimation from differential absorption lidar using nonstationary Wiener filtering

An approach is presented for smoothing and differentiating path-integrated concentration estimates provided by range-resolved differential absorption lidar that is based on a nonstationary implementation of the Wiener-Kolmogorov filtering theory. The primary advantage of the method lies in its ability to provide filtered estimates that are smoothed relative to the local uncertainty in the input data. The approach is derived and illustrated on both synthetic and actual lidar data.

Range-resolved differential absorption lidar: optimization of range and sensitivity

A practical range-resolved differential absorption and scattering lidar has been optimized for maximum range and sensitivity. Compression of the signal amplitude dynamics, quasi-simultaneous dual-pulse operation, the processing sequence of the primary signals, a method of alignment mismatch compensation, and the effects of temporal and spatial averaging are discussed. Experimental verifications with a four-laser system for NO2 and SO2 are presented. For NO2 a range of up to 6 km at a sensitivity of 10 ppb and for SO2 a range up to 3 km at 15-ppb sensitivity have been accomplished.

Sensitivity of coherent rage-resolved differential absorption lidar

A range-resolved DIAL (differential absorption lidar) system with heterodyne detection has been developed. A hybrid TEA CO2 laser was employed as the transmitter oscillator, which emitted single-frequency pulses of 140 mJ. The heterodyne receiver, which had a minimum detectable power of 2 × 10−11 W, could detect the echo signals backscattered from atmospheric aerosols at a 5-km or greater range. The system sensitivity to the target gas, defined as the product of the minimum detectable concentration and the difference in the absorption coefficients, was experimentally found to be 3.7 × 10−4 m−1 for a range resolution of 300 m after averaging over fifty backscattered signals.

Laser prf considerations in differential absorption lidar applications

Laser pulse repetition frequency (prf) is a major factor in determining the performance of differential absorption lidar (DIAL) systems. The effects of laser prf on concentration measurement accuracy and maximum usable range are quantified. Heterodyne-detection (coherent) and direct-detection (noncoherent) as well as path-averaged and range-resolved DIAL systems are analyzed.