A new modulation technique for Continuous Wave (CW) Lidar is presented based on Binary Phase Shift Keying (BPSK) using orthogonal carriers closely spaced in frequency, modulated by Maximum Length ...(ML) sequences, which have a theoretical autocorrelation function with no sidelobes. This makes it possible to conduct multi-channel atmospheric differential absorption measurements in the presence of thin clouds without the need for further processing to remove errors caused by sidelobe interference while sharing the same modulation bandwidth. Flight tests were performed and data were collected using both BPSK and linear swept frequency modulation. This research shows there is minimal or no sidelobe interference in the presence of thin clouds for BPSK compared to linear swept frequency with significant sidelobe levels. Comparisons between of CO(2) optical depth Signal to Noise (SNR) between the BPSK and linear swept frequency cases indicate a 21% drop in SNR for BPSK experimentally using the instrument under consideration.
A deeper understanding of how clouds will respond to a warming climate is one of the outstanding challenges in climate science. Uncertainties in the response of clouds, and particularly shallow ...clouds, have been identified as the dominant source of the discrepancy in model estimates of equilibrium climate sensitivity. As the community gains a deeper understanding of the many processes involved, there is a growing appreciation of the critical role played by fluctuations in water vapor and the coupling of water vapor and atmospheric circulations. Reduction of uncertainties in cloud-climate feedbacks and convection initiation as well as improved understanding of processes governing these effects will result from profiling of water vapor in the lower troposphere with improved accuracy and vertical resolution compared to existing airborne and space-based measurements. This paper highlights new technologies and improved measurement approaches for measuring lower tropospheric water vapor and their expected added value to current observations. Those include differential absorption lidar and radar, microwave occultation between low-Earth orbiters, and hyperspectral microwave remote sensing. Each methodology is briefly explained, and measurement capabilities as well as the current technological readiness for aircraft and satellite implementation are specified. Potential synergies between the technologies are discussed, actual examples hereof are given, and future perspectives are explored. Based on technical maturity and the foreseen near-mid-term development path of the various discussed measurement approaches, we find that improved measurements of water vapor throughout the troposphere would greatly benefit from the combination of differential absorption lidar focusing on the lower troposphere with passive remote sensors constraining the upper-tropospheric humidity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A controlled field pilot has been developed in Bozeman, Montana, USA, to study near surface CO
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transport and detection technologies. A slotted horizontal well divided into six zones was installed ...in the shallow subsurface. The scale and CO
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release rates were chosen to be relevant to developing monitoring strategies for geological carbon storage. The field site was characterized before injection, and CO
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transport and concentrations in saturated soil and the vadose zone were modeled. Controlled releases of CO
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from the horizontal well were performed in the summers of 2007 and 2008, and collaborators from six national labs, three universities, and the U.S. Geological Survey investigated movement of CO
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through the soil, water, plants, and air with a wide range of near surface detection techniques. An overview of these results will be presented.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Measurements of water vapor are important for understanding the hydrological cycle, the thermodynamic structure of the lower troposphere, and broader atmospheric circulation. Subsequently, many ...scientific communities have emphasized a need for high-accuracy and spatial resolution profiles of water vapor within and above the planetary boundary layer (PBL). Advancements in lidar technologies at the NASA Langley Research Center are ongoing to enable the first space-based water vapor differential absorption lidar (DIAL) that can provide high-accuracy and vertical resolution retrievals of moisture in the PBL and through the mid-troposphere. The performance of this space-based DIAL is assessed here for sensitivity throughout the troposphere and globally with representative canonical cases of water vapor and aerosol loading. The specific humidity retrieval sensitivity to systematic and random errors is assessed, and measurement resolutions and capabilities are provided. We show that tunable operation along the side of the 823-nm absorption line allows for the optimization of the lower-tropospheric water vapor retrievals across different meteorological regimes and latitudes and provides the operational flexibility needed to dynamically optimize random errors for different scientific applications. The analysis presented here suggests that baseline and threshold systematic error requirements of <1.5% and <2.5%, respectively, are achievable. Random error is shown to dominate the retrieval, with errors on the order of 5% within the PBL being achievable with 300-m vertical 50-km horizontal resolutions over open ocean and on the order of 10%–15% over high-albedo surfaces. The flexibility of the DIAL method to trade retrieval precision for spatial resolution is shown, highlighting its strengths over passive techniques to tailor retrievals to different scientific applications. Combined, the total error budget demonstrated here indicates a high impact for space-based DIAL, with technologies being advanced for space missions within the next 5–10 years.
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.
Atmospheric aerosol optical properties were observed from 21 to 27 September 2009 over Bozeman, Montana, during a transitional period in which background polluted rural continental aerosols and ...well‐aged biomass‐burning aerosols were the dominant aerosol types of extremely fresh biomass‐burning aerosols resulting from forest fires burning in the northwestern United States and Canada. Aerosol optical properties and relative humidity profiles were retrieved using an eye‐safe micropulse water vapor differential absorption lidar (DIAL) (MP‐DIAL), a single‐channel backscatter lidar, a CIMEL solar radiometer as part of the Aerosol Robotic Network (AERONET), a ground‐based integrating nephelometer, and aerosol products from Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua. Aerosol optical depths (AODs) measured during the case study ranged between 0.03 and 0.17 (0.015 and 0.075) at 532 nm (830 nm) as episodic combinations of fresh and aged biomass‐burning aerosols dominated the optical depth of the pristinely clean background air. Here, a pristinely clean background refers to very low AOD conditions, not that the aerosol scattering and absorption properties are necessarily representative of a clean aerosol type. Diurnal variability in the aerosol extinction to backscatter ratio (Sa) of the background atmosphere derived from the two lidars, which ranged between 55 and 95 sr (50 and 90 sr) at 532 nm (830 nm), showed good agreement with retrievals from AERONET sun and sky measurements over the same time period but were consistently higher than some aerosol models had predicted. Sa measured during the episodic smoke events ranged on average from 60 to 80 sr (50 to 70 sr) at 532 nm (830 nm) while the very fresh biomass‐burning aerosols were shown to exhibit significantly lower Sa ranging between 20 and 40 sr. The shortwave direct radiative forcing that was due to the intrusion of biomass‐burning aerosols was calculated to be on average −10 W/m2 and was shown to compare favorably with regional‐scale forcing calculations using MODIS‐Terra and AERONET data in an effort to assess the accuracy of estimating the regional‐scale aerosol direct radiative forcing effect using aerosol optical properties measured from a single rural site such as Bozeman, Montana.
Key Points
Polluted continental/well‐aged biomass‐burning aerosols have weak accumulation modes
Polluted continental and well‐aged smokes are absorptive and have high Sa's
Extremely fresh smoke is less absorptive and exhibits very low Sa's
This work describes advances in critical lidar technologies and techniques developed as part of the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons CarbonHawk Experiment Simulator ...system for measuring atmospheric column carbon dioxide (CO2) mixing ratios. This work provides an overview of these technologies and results from recent test flights during the NASA Atmospheric Carbon and Transport – America (ACT-America) Earth Venture Suborbital summer 2016 flight campaign.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
A differential absorption lidar (DIAL) instrument for automated profiling of water vapor in the lower troposphere has been designed, tested, and is in routine operation at Montana State ...University. The laser transmitter for the DIAL instrument uses a widely tunable external cavity diode laser (ECDL) to injection seed two cascaded semiconductor optical amplifiers (SOAs) to produce a laser transmitter that accesses the 824–841-nm spectral range. The DIAL receiver utilizes a 28-cm-diameter Schmidt–Cassegrain telescope; an avalanche photodiode (APD) detector; and a narrowband optical filter to collect, discriminate, and measure the scattered light. A technique of correcting for the wavelength-dependent incident angle upon the narrowband optical filter as a function of range has been developed to allow accurate water vapor profiles to be measured down to 225 m above the surface. Data comparisons using the DIAL instrument and collocated radiosonde measurements are presented demonstrating the capabilities of the DIAL instrument.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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