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.
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 the development effort of a nanosecond-pulsed optical parametric amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output has ∼500 MHz linewidth and is widely tunable at both near-infrared and mid-infrared wavelengths, with an optical-optical conversion efficiency of up to ∼39% . Using this laser source, we demonstrated open-path measurements of CH 4 (3291 and 1652 nm), CO 2 (1573 nm), H 2 O (1652 nm), and CO (4764 nm) on the ground. The simplicity, tunability, and power scalability of the OPA make it a strong candidate for general planetary lidar instruments, which will offer important information on the origins of the planet's geology, atmosphere, and potential for biology.
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.
Trace gases in planetary atmospheres offer important clues as to the origins of the planet's hydrology, geology,
atmosphere, and potential for biology. We report on the development effort of a nanosecond-pulsed optical parametric
amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output light is single frequency with
high spectral purity and is widely tunable both at 1600 nm and 3300 nm with an optical-optical conversion efficiency of
~40%. We demonstrated open-path atmospheric measurements of CH4 (3291 nm and 1651 nm), CO2 (1573 nm), H2O
(1652 nm) with this laser source.
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.
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.
The experimental data on CO2 and O2 detection in atmosphere using Fabry-Perot technique are presented. The atmosphere's irradiance measurements are an important tool for the remote sensing study. We show results from lab, ground and flight testing of a new instrument called FPICC (Fabry-Perot Interferometer for Column CO2) which is intended for a very precise measurements of atmospheric carbon dioxide and oxygen. The optical setup consists of three channels. The first channel is built to measure the carbon dioxide. This channel operates using the reflected sunlight off the ground and solid Fabry-Perot etalon to restrict the measurement to light in CO2 absorption bands. The free spectral range of the etalon is calculated to be equal to the almost regular spacing between the CO2 spectral bands located near 1,571 μm, R band, where CO2 absorption is significant. The precise alignment of the transmission peaks of the Fabry-Perot etalon to the CO2 absorption lines is achieved through altering the refractive index of the material (fused silica) using its temperature dependence. The second and third channels foucs on the O2 A band (759 - 771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and two different pre-filters. The first pre-filter selects a spectral range around 762 nm which is between the P and R branches, where the absorption coefficient is insensitive to temperature, but is sensitive to pressure changes and therefore to the variations in the O2 column. The second pre-filter is selecting several absorption bands between 765 and 770 nm, which are more sensitive to temperature changes. The experimental data presented show excellent agreement with our theoretical expectations. They are recorded at different gas pressures, temperatures and different weather conditions. Some of the major advantages of the optical setup are its compactness, high sensitivity, high signal-to-noise ratio, and stability.
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.
Global measurements of atmospheric carbon dioxide (CO2) are needed to resolve significant discrepancies that exist in our understanding of the global carbon budget and, therefore, man's role in global climate change. The science measurement requirements for CO2 are extremely demanding (precision <0.3%) No atmospheric chemical species has ever been measured from space with this precision. We are developing a novel application of a Fabry-Perot interferometer to detect spectral absorption of reflected sunlight by CO2 and O2 in the atmosphere. Preliminary design studies indicate that the method will be able to achieve the sensitivity and signal-to-noise required to measure column CO2 at the target specification. We are presently engaged in the construction of a prototype instrument for deployment on an aircraft to test the instrument performance and our ability to retrieve the data in the real atmosphere. In the first 6 months we have assembled a laboratory bench system to begin testing the optical and electronic components. We are also undertaking some measurements of signal and noise levels for actual sunlight reflecting from the ground. We shall present results from some of these ground based studies and discuss their implications for a space based system.