The global and regional quantification of methane fluxes and identification of its sources and sinks has been highlighted as one of the goals of the NASA 2017 Earth Science Decadal Survey. Detecting methane from space and airborne platforms with an active (laser) remote sensing instrument presents several unique technology and measurement challenges. The instrument must have a single frequency, narrow-linewidth light source, and photon-sensitive detector at the right spectral region to make continuous measurements from orbit, day and night, all seasons and at all latitudes. It must have a high signal to noise ratio and must be relatively immune to biases from aerosol/cloud scattering, spectroscopic and meteorological data uncertainties, and instrument systematic errors.
At Goddard Space Flight Center (GSFC), in collaboration with industry, we have developed an airborne instrument to measure methane. Our instrument is a nadir-viewing lidar that uses Integrated Path Differential Absorption (IPDA), to measure methane near 1.65 μm. We sample the absorption line using multiple wavelengths from a narrow linewidth laser source and a sensitive photodetector. This measurement approach provides maximum information content about the CH4 column, and minimizes biases in the XCH4 retrieval.
In this paper, we will review our progress to date and discuss the technology challenges, options and tradeoffs to measure methane from space and airborne platforms.
NASA Goddard’s CO2 Sounder is a pulsed, multiple-wavelength, IPDA-lidar. It was flown onboard the NASA DC-8 to measure atmospheric CO2 column concentrations (XCO2) in the lower stratosphere and troposphere of the Arctic region of North America as part of the 2017 ASCENDS airborne campaign. Eight flights covering 40,000 km were flown in late July and August over Alaska and Canada’s Northwest Territories, including a northern transit east of the Rockies and a return transit partly over the ocean between Alaska and California. The Arctic flights were coordinated with the 2017 Arctic-Boreal Vulnerability Experiment (ABoVE) campaign. The metrological conditions were challenging: a non-uniform CO2 distribution, a dynamic atmosphere and varied surface-reflectivity. To assess the accuracy of our lidar the aircraft’s scientific payload included the AVOCET and Picarro instruments. These two instruments measured in-situ XCO2 during the flights and column XCO2 from 47 separate descent spirals from ~12 km altitude to near ground at local airfields distributed throughout the measurement region. Each spiral maneuver allows a direct comparison between the retrievals of XCO2 from the lidar against those computed from insitu instruments. The CO2 Sounder worked very well during all phases of the campaign. Analysis to date shows the lidar measured column concentrations are in close agreement with in-situ column measurements with a precision of better than 0.8 ppm with 1 second averaging. In addition, preliminary analyses of measurements to the ubiquitous cloud tops also produced column concentrations and information on the vertical XCO2 structure.
Trace gases and their isotopic ratios in planetary atmospheres offer important but subtle clues as to the origins of a planet's atmosphere, hydrology, geology, and potential for biology. An orbiting laser remote sensing instrument is capable of measuring trace gases on a global scale with unprecedented accuracy, and higher spatial resolution that can be obtained by passive instruments.
For Earth we have developed laser technique for the remote measurement of the tropospheric CO2, O2, and CH4 concentrations from space. Our goal is to develop a space instrument and mission approach for active CO2 measurements. Our technique uses several on and off-line wavelengths tuned to the CO2 and O2 absorption lines. This exploits the atmospheric pressure broadening of the gas lines to weigh the measurement sensitivity to the atmospheric column below 5 km and maximizes sensitivity to CO2 changes in the boundary layer where variations caused by surface sources and sinks are largest. Simultaneous measurements of O2 column use a selected region in the Oxygen A-band. Laser altimetry and atmospheric backscatter can also be measured simultaneously, which permits determining the surface height and measurements made to thick cloud tops and through aerosol layers.
We use the same technique but with a different transmitter at 1.65 um to measure methane concentrations. Methane is also a very important trace gas on earth, and a stronger greenhouse gas than CO2 on a per molecule basis. Accurate, global observations are needed in order to better understand climate change and reduce the uncertainty in the carbon budget. Although carbon dioxide is currently the primary greenhouse gas of interest, methane can have a much larger impact on climate change. Methane levels have remained relatively constant over the last decade but recent observations in the Arctic have indicated that levels may be on the rise due to permafrost thawing. NASA’s Decadal Survey underscored the importance of Methane as a greenhouse gas and called for a mission to measure CO2, CO and CH4. Methane has absorptions in the mid-infrared (3.3 um) and the near infrared (1.65 um). The 3.3 um spectral region is ideal for planetary (Mars) Methane monitoring, but unfortunately is not suitable for earth monitoring since the Methane absorption lines are severely interfered with by water. The near infra-red overtones of Methane at 1.65 um are relatively free of interference from other atmospheric species and are suitable for Earth observations. The methane instrument uses Optical Parametric Generation (OPG) along with sensitive detectors to achieve the necessary sensitivity. Our instrument generates and detects tunable laser signals in the 3.3 or 1.65 um spectral regions with different detectors in order to measure methane on Earth or Mars. For Mars, the main interest in methane is its importance as a biogenic marker.
We report on an airborne demonstration of atmospheric methane (CH4) measurements with an integrated path differential absorption lidar using an optical parametric amplifier and optical parametric oscillator laser transmitter and sensitive avalanche photodiode detector. The lidar measures the atmospheric CH4 absorption at multiple, discrete wavelengths near 1650.96 nm. The instrument was deployed in the fall of 2015, aboard NASA’s DC-8 airborne laboratory along with an in situ spectrometer and measured CH4 over a wide range of surfaces and atmospheric conditions from altitudes of 2 to 13 km. We will show the results from our flights, compare the performance of the two laser transmitters, and identify areas of improvement for the lidar.
We report on an airborne demonstration of atmospheric methane (CH4) measurements with an Integrated Path Differential Absorption (IPDA) lidar using an optical parametric oscillator (OPO) and optical parametric amplifier (OPA) laser transmitter and a sensitive avalanche photo detector. The lidar measures the CH4 absorption at multiple, discrete wavelengths around 1650.9 nm. In September 2015, the instrument was deployed on NASA’s DC-8 airborne laboratory and measured atmospheric methane over a wide range of topography and weather conditions from altitudes of 3 km to 13 km. In this paper, we will review the results from our flights, and identify areas of improvement.
We demonstrate the airborne measurement of atmospheric methane using a pulsed lidar at 1650 nm using an integrated path differential absorption scheme. Our seeded nanosecond-pulsed optical parametric amplifier (OPA)-based instrument works up to the highest altitudes flown (<10 km). The obtained absorption profile is in good agreement with theoretical predictions based on the HITRAN database.
We report on ground and airborne atmospheric methane measurements with a differential absorption lidar using an
optical parametric amplifier (OPA). Methane is a strong greenhouse gas on Earth and its accurate global mapping is
urgently needed to understand climate change. We are developing a nanosecond-pulsed OPA for remote measurements
of methane from an Earth-orbiting satellite. We have successfully demonstrated the detection of methane on the ground
and from an airplane at ~11-km altitude.
Many fundamental questions about planetary evolution require monitoring of the
planet's atmosphere with unprecedented accuracy at both high and low latitudes, over both
day and night and all seasons. Each planetary atmosphere presents its own unique challenges.
For the planets/moons that have relatively low surface pressure and low trace gas
concentrations, such as Mars or Europa, the challenge is to have enough sensitivity to
measure the trace gas of interest. For Earth, the challenge is to measure trace gases with very
high precision and accuracy in the presence of other interfering species.
An orbiting laser remote sensing instrument is capable of measuring trace gases on a global
scale with unprecedented accuracy, and higher spatial resolution that can be obtained by
passive instruments. For Mars, our proposed measurement uses Optical Parametric
Amplifiers (OPA) and Integrated Path Differential Absorption (IDPA) in the 3-4 um spectral
range to map various trace gas concentrations from orbit on a global scale. For earth, we
propose to use Erbium Doped Fiber Amplifier technology (EDFA) and IDPA at 1.57 and
OPA at 1.65 μm to measure carbon dioxide and methane concentrations respectively.
We report on a lidar approach to measure atmospheric CO2 column concentration being developed as a candidate for
NASA's ASCENDS mission. It uses a pulsed dual-wavelength lidar measurement based on the integrated path
differential absorption (IPDA) technique. We demonstrated the approach using the CO2 measurement from aircraft
in July and August 2009 over various locations. The results show clear CO2 line shape and absorption signals, which
follow the expected changes with aircraft altitude from 3 to 13 km. The column absorption measurements show
altitude dependence in good agreement with column number density estimates calculated from airborne in-situ
measurements. The approaches for O2 measurements and for scaling the technique to space are discussed.
Mounting concern regarding global warming and the increasing carbon dioxide (CO2) concentration has stimulated
interest in the feasibility of measuring CO2 mixing ratios from space. Precise satellite observations with adequate spatial
and temporal resolution would substantially increase our knowledge of the atmospheric CO2distribution and allow
improved modeling of the CO2 cycle. Current estimates indicate that a measurement precision of better than 1 part per
million (1 ppm) will be needed in order to improve estimates of carbon uptake by land and ocean reservoirs. A 1-ppm
CO2 measurement corresponds to approximately 1 in 380 or 0.26% long-term measurement precision. This requirement
imposes stringent long-term precision (stability) requirements on the instrument In this paper we discuss methods and
techniques to achieve the 1-ppm precision for a space-borne lidar.
A series of sensitivity studies is carried out to explore the feasibility of space-based global carbon dioxide (CO2) measurements for global and regional carbon cycle studies. The detection method uses absorption of reflected sunlight in the CO2 vibration-rotation band at 1.58 μm. The sensitivities of the detected radiances are calculated using a line-by-line model implemented with the DISORT model to include atmospheric scattering. The results indicate that (a) the small (~1%) changes in CO2 near the Earth’s surface are detectable in this CO2 band provided adequate sensor signal-to-noise ratio and spectral resolution are achievable; (b) the modification of sunlight path length by scattering of aerosols and cirrus clouds could lead to large systematic errors in the retrieval; therefore, ancillary aerosol/cirrus cloud data are important to reduce retrieval errors; (c) the atmospheric path length, over which the CO2 absorption occurs, must be known in order to correctly interpret horizontal gradients of total column CO2; thus an additional sensor for surface pressure measurement needs to be attached for a complete measurement package; (d) CO2 retrieval requires good knowledge of the atmospheric temperature profile, e.g. approximately 1-K RMS error in layer temperature. Several candidate technologies are available to potentially meet these requirements.
We present a brief review of results on the surface impedance of cuprate superconductors, focusing mainly on YBa2Cu3O7-(delta ) (YBCO) and evidence of d-wave superconductivity in that material. We then discuss our recent results on Ba-K-Bi-O thin films, and the effects of DC electric fields on the surface impedance of YBCO films. A summary of our data on high quality thin films and single crystals of the electron-doped Nd1.85Ce0.15CuO4-(delta ) (NCCO) cuprate superconductor follows. Surprisingly, the measurements on NCCO are consistent with the behavior of an s-wave BCS superconductor, in striking contrast to recent results on YBCO. Finally we discuss some of the interesting potential implications of d-wave superconductivity for microwave applications of the cuprates.