Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NIST 'combs' the atmosphere to measure greenhouse gases

30.10.2014

By remotely "combing" the atmosphere with a custom laser-based instrument, researchers from the National Institute of Standards and Technology (NIST), in collaboration with researchers from the National Oceanic and Atmospheric Administration (NOAA), have developed a new technique that can accurately measure—over a sizeable distance—amounts of several of the major "greenhouse" gases implicated in climate change.

The technique potentially could be used in several ways to support research on atmospheric greenhouse gases. It can provide accurate data to support ongoing and future satellite monitoring of the composition of the atmosphere. With development, more portable systems based on the technology could provide very accurate, continuous regional monitoring of these gases over kilometer scales—a capability lacking with current monitoring techniques.


Photo illustration of NIST experiment using a pair of laser frequency combs (depicted as rainbow-colored cartoons) to detect the simultaneous signatures of several 'greenhouse' gases along a 2-kilometer path between a NIST laboratory roof and a nearby mesa. Each comb 'tooth' represents a different frequency of light. To identify gases in the atmosphere, researchers measured the amount of comb light absorbed at different frequencies along the path.

Credit: Burrus and Irvine/NIST

In the recent demonstration,* NIST's pair of laser frequency combs measured the simultaneous signatures of several greenhouse gases—including carbon dioxide, methane and water vapor—along a 2-kilometer path between a NIST laboratory roof in Boulder, Colo., and a nearby mesa.

Frequency combs are laser-generated tools made up of a large number of very precisely defined frequencies that are evenly spaced, like the teeth on a pocket comb. Each comb "tooth" represents an individual color, or frequency, enabling very accurate measurements of the characteristic absorption signatures of different gas molecules of interest.

Researchers identified gases in the atmosphere by measuring the amount of comb light absorbed at different frequencies during its trip from the NIST lab roof to a mirror on the mesa and back to a detector in a lab. Because the optical frequencies are too high to be measured directly, the researchers borrowed a trick from early radio. They created two combs with slightly different spacing between the teeth. Mixing light from these dual frequency combs together creates a "beat" frequency shifted down to the radio band, low enough to be measured. This was the first demonstration of the technique over long distances outdoors.

Remote sensing of atmospheric gases—from a satellite, for instance—can be performed with conventional instruments called spectrometers, but while satellite instruments have global coverage, they sample specific regions on Earth infrequently. Therefore, regional measurements are made with ground-based point sensors, which have a range that can be measured in meters and varies with wind conditions. There are no portable sensors that can measure multiple gases at long range with consistent results.

The NIST comb system was built to detect gases, including carbon dioxide, methane, and water over 2 kilometers. In principle, the dual-comb technique could detect an even wider range of gases over many kilometers. Accuracy in the measured atmospheric transmission is assured by the well-defined position of each frequency comb tooth.

Because the technique makes repeated measurements rapidly over the same path, it is immune to signal distortions caused by atmospheric turbulence. And because the comb measurements can be averaged over the entire path length rather than relying on a few spot measurements, the comb method is better matched to the scale of atmospheric transport models.

In the demonstration, the research team collected data continuously for three days under varied weather conditions. The results were comparable to data collected by a nearby point sensor under well-mixed atmospheric conditions. The comb measurements were also very precise—with uncertainty of less than 1 part per million for carbon dioxide, for example, obtained in five minutes. That's precise enough to ensure detection of small increases in trace gases due to large, distributed sources such as cities. Future systems should be able to achieve even better sensitivities over shorter timescales.

Overall, the study results suggest that the dual comb technique is ideally suited to precise, reproducible sensing of trace gases in the atmosphere and can support the development of accurate models for use in global, satellite-based greenhouse gas monitoring.

NIST researchers now plan to optimize the comb system by boosting power to improve sensitivity and expanding spectral coverage to identify additional gases. Portable frequency comb systems** could eventually support regional gas monitoring at costs comparable to point sensors, the researchers say, but over the kilometer scales relevant to many transport models and to monitoring of distributed sources such as large cities.

* G.B. Rieker, F.R. Giorgetta, W.C. Swann, J. Kofler, A.M. Zolot, L.C. Sinclair, E. Baumann, C. Cromer, G. Petron, C. Sweeney, P.P. Tans, I. Coddington and N.R. Newbury. Frequency comb-based remote sensing of greenhouse gases over kilometer air paths. Optica. Vol. 1, Issue 5. Posted online Oct. 29, 2014. DOI: 10.1364/OPTICA.1.000290.

** See "Portable Frequency Comb Rolls Out of the Lab" at http://www.nist.gov/pml/div686/sources_detectors/portable_frequency_comb.cfm 

Laura Ost | EurekAlert!

More articles from Earth Sciences:

nachricht AWI researchers measure a record concentration of microplastic in arctic sea ice
24.04.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

nachricht Climate change in a warmer-than-modern world: New findings of Kiel Researchers
24.04.2018 | Christian-Albrechts-Universität zu Kiel

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: BAM@Hannover Messe: innovative 3D printing method for space flight

At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.

Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Getting electrons to move in a semiconductor

25.04.2018 | Physics and Astronomy

Reconstructing what makes us tick

25.04.2018 | Physics and Astronomy

Cheap 3-D printer can produce self-folding materials

25.04.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>