Physicists find a way to measure precise ocean temperature from afar
Russian scientists from the National University of Science and Technology MISiS, MIPT, and Prokhorov General Physics Institute (GPI) of the Russian Academy of Sciences have compared the effectiveness of several techniques of remote water temperature detection based on laser spectroscopy and evaluated various approaches to spectral profile interpretation.
The paper detailing the study was published in Optics Letters. The researchers examined four data processing techniques drawing on the relevant analyses in prior publications. The technique which the authors themselves previously proposed, developed and obtained a patent for proved to be precise up to 0.15 degrees Celsius.
The research findings will support further development of sea surface temperature remote sensing solutions, enabling scientists to keep track of thermal energy flows in hard-to-reach areas such as the Arctic region, where average temperatures are rising approximately twice as fast as they are elsewhere on the planet.
In their study, the scientists focused on Raman spectroscopy, which is based on the phenomenon of Raman scattering discovered in the 1920s. It involves the interaction of a medium with a light wave: The scattered light is modulated by the molecular vibrations of the medium, resulting in the wavelengths of some of the photons being shifted; in other words, some of the scattered light changes its color.
Raman scattering and, by extension, the field of Raman spectroscopy were named after Sir C. V. Raman, an Indian physicist who was awarded a Nobel Prize for the discovery of this effect. Interestingly, Russian scientific literature tends to refer to the same phenomenon as "combination scattering," a term coined to emphasize its independent discovery by Soviet researchers.
"With the climate changing so rapidly, remote sensing of water temperature is a priority, but the radiometry techniques currently in use are only precise up to about a half degree. Raman spectroscopy enables measurements with a much greater precision," claims Mikhail Grishin, one of the authors of the study, a Ph.D. student at MIPT, and a researcher at the Laser Spectroscopy Laboratory of the Wave Research Center at GPI.
The experiment carried out by the scientists involved probing water with a pulsed laser and using a spectrometer to analyze the light that was scattered back. Depending on the temperature of the water, its characteristic OH stretching vibrations spectral band was variably transformed. The scientists needed to find out whether it is possible to establish a clear relationship between water temperature and one of the spectral band parameters.
The scientists examined the temperature dependence of several spectral band parameters (aka metrics), viz., certain parts of the area below the graph (see Fig. 1), differential spectra (the result of subtraction of two spectra), and the location of the peak of the curve fitting the band spectrum. Although it proved possible to establish a relationship between water temperature and each of the abovementioned metrics, the estimated temperature measurement accuracy of the respective techniques varied.
Statistical analysis of experimental data showed that temperature dependence was most pronounced when the wavelength that corresponds to the peak of the curve fitting the band spectrum was used as a metric. The scientists were granted a patent for the corresponding approach to spectral profile interpretation by the Russian patent office.
Seawater temperatures in the Arctic are currently monitored using a range of techniques including direct measurements made by weather buoys and merchant or research vessels. However, to track the temperature dynamics of sea surface water in real time and over vast areas, it is necessary to make aerial observations using sensing equipment installed on aircraft or satellites, which irradiates the water with a laser and collects the scattered light.
A spatial resolution of less than one kilometer enables researchers to create very detailed temperature maps which can be used to monitor the transfer of heat by ocean currents, predict how fast Arctic ice is going to melt, and make a global climate change forecast. As unmanned aerial vehicles (UAVs) become better, remote sensing equipment should also be improved to be more precise, lightweight, compact, and energy-efficient. The scientists are developing both the software and the laser-detector system.
Vasily Lednev, one of the authors of the study, a leading expert at the Department of Certification and Analytical Control of NUST MISiS, told us how he sees the future of this research: "One of the main hurdles faced in remote sensing of the sea surface is the necessity to calibrate equipment and verify satellite measurement results against contact measurements of seawater parameters (temperature, chlorophyll concentration, etc.).
The development and design of compact autonomous lidar (laser radar) systems which can be mounted on UAVs will enable us to obtain detailed sea charts featuring a range of water parameters. These lidar systems are also of immediate interest to the study of hard-to-reach and dangerous objects like icebergs or ice shelves."
The average annual changes in the temperature of the world's oceans tend to be very small. It is currently heating up by a mere tenth of a degree every ten years, whereas seasonal temperature variations can amount to several degrees. This means that an error of just half of a degree will cause a significant drop in precision of the overall picture of temperature dynamics that we get. In the case of seasonal measurements, the uncertainty can reach 20 percent or more, while long-term climate trends may remain unidentified due to the measurement error.
The remote-sensing thermometers currently in use operate in the microwave spectral range. Raman scattering spectrometry has a significant advantage over microwave radiometry in that the probing laser radiation falls into the visible (blue-green) part of the spectrum. Unlike microwave radiation, to which water is almost completely opaque, visible light can penetrate a layer of water that is 1-10 meters thick.
With microwave sensing, the data is only available for the 30-micron-thick surface layer whose temperature is significantly affected by the cold Arctic winds. This gives rise to an error, which is almost entirely avoided in measurements based on Raman scattering. To correct errors of this kind, satellite-based microwave radiometers need to be calibrated against ground-based measurements. By contrast, Raman spectrometry does not face this obstacle and can produce useful data independently from contact observations.
Asya Shepunova | EurekAlert!
Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie
Seeing the quantum future... literally
16.01.2017 | University of Sydney
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction