Free Newsletters - Space News - Defense Alert - Environment Report - Energy Monitor
. Earth Science News .




CLIMATE SCIENCE
Accurate water vapour measurements for improved weather and climate models
by Staff Writers
Bundesallee, Germany (SPX) Mar 06, 2013


PTB's laser hygrometer successfully completed 7 flights on a Learjet 35A and in doing so confirmed that it can be used as a comparison standard for other humidity-measuring instruments. Such a metrological standard is necessary to enhance the weight of evidence of measurement data. (Photo: Rolf Maser, enviscope GmbH)

An humidity sensor developed by the Physikalisch-Technische Bundesanstalt (PTB), the SEALDH laser hygrometer, has proven its worth when used aboard an aircraft; it fulfils all pre-conditions to be used as a transfer standard for conventional humidity-measuring instruments. This would allow the quality of air humidity measurements in the Earth's atmosphere - and, thus, also climate model computations - to be improved.

Humidity measurements in the atmosphere are of essential importance, since water vapour, as the most important natural greenhouse gas, has a strong influence on the Earth's atmospheric radiation balance and, thus, decisively influences our climate. In addition, water is responsible for meteorological phenomena such as the formation of clouds and precipitation.

Hence, the atmospheric water content is an essential measurand in all climate models, but also when it comes to forecasting the weather; this measurand has to be determined with great accuracy if reliable predictions are to be made with regard to the weather and to the development of the climate.

However, measuring water vapour as far as into the upper atmosphere is not an easy task, which leads to air humidity measurements differing sometimes by more than 10 % when measured in different research projects, using alternative methods, even within the scope of demanding laboratory comparisons [1].

Cloud-, precipitation- and also complex climate model computations should, however, be based on measurement data which is as accurate as possible to have sufficient significance.

In order to improve the quality of atmospheric water vapour measurements and to provide better comparability, PTB scientists have developed the traceable laser hygrometer SEALDH. SEALDH stands for "Selective Extractive Airborne Laser Diode Hygrometer" and works according to the principle of tunable diode laser absorption spectroscopy (TDLAS).

Its use aboard an aircraft requires the system to be small, light and insensitive to vibrations; in addition, it must be able to perform rapid measurements and to work autonomously [2], e.g. to constantly monitor itself or to be able to resume operation itself after a fault after an unplanned shutdown. But SEALDH is even more than this: it is self-calibrating. This is a clear advantage compared to conventional hygrometers which have to be calibrated frequently - and often under adverse conditions (e.g. in an airplane hangar).

SEALDH has now been tested under field conditions within the scope of a scientific mission on a Learjet 35A, a former passenger plane that was adapted for research purposes; it was able to give proof of its performance during seven flights after having passed a blind comparison with several established aircraft hygrometers at the environmental simulation chamber of Forschungszentrum Julich [3].

During its in-flight operation, the laser hygrometer proved a detection limit in the ppm range, a very large measuring range between 25 ppm and 25,000 ppm of water volume fraction, as well as an excellent temporal resolution of clearly below 1 s.

Furthermore, PTB scientists have compared SEALDH with PTB's national humidity standard and attained a mean deviation of less than 2 % - without prior calibration. Based on these features, it will, in the medium term, be possible to use SEALDH as a transfer standard for the quality assurance of air humidity measurements in atmospheric research.

What does "traceable measurement" mean?
Numerous research groups all around the world are investigating climate-relevant processes in the atmosphere; they use different measurement procedures under different conditions.

To make their measurement results comparable, traceable measurements would make sense, i.e. the measurement uncertainty of a measuring device compared to the best possible standard must be known. In the medium term, SEALDH could be such a standard, since its capacity as a transfer standard has been demonstrated also under real in-flight conditions and compared to PTB's primary humidity standard.

[1] H. Saathoff, C. Schiller, V. Ebert, D. W. Fahey, R.-S. Gao, O. Mohler, and the AQUAVIT Team, The AQUAVIT formal intercomparison of atmospheric water measurement methods, Geophysical Research Abstracts, Vol. 10, EGU2008-A-10485, 2008,SRef-ID: 1607-7962/gra/EGU2008-A-10485, and D. Fahey, R. Gao: Summary of the AquaVIT water vapor inter-comparison: static experiments (2009).

[2] B. Buchholz, N. Bose, S. Wagner, V. Ebert: Entwicklung eines ruckfuhrbaren, selbstkalibrierenden, absoluten TDLAS-Hygrometers in kompakter 19" Bauweise. AMA-Science, ISBN: 978-3-9813484-0-8, 16. GMA/ITG-Fachtagung Sensoren und Messsysteme 201, 22. 5. 2012, Nurnberg, Germany, DOI: 10.5162/sensoren2012/3.2.3

[3] B. Buchholz, B. Kuhnreich, H.G.J. Smit, V. Ebert: Validation of an extractive, airborne, compact TDL spectrometer for atmospheric humidity sensing by blind intercomparison. Applied Physics B: Volume 110, Issue 2 (2013), pp. 249-262

.


Related Links
Physikalisch-Technische Bundesanstalt (PTB)
Climate Science News - Modeling, Mitigation Adaptation






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





CLIMATE SCIENCE
Earth on track to be hottest in 11.3 millennia: study
Washington (AFP) March 7, 2013
The Earth is on track to becoming the hottest it has been at any time in the past 11.3 millennia, a period spanning the history of human civilization, a study published Thursday has found. Based on fossil samples and other data collected from 73 sites around the world, scientists have been able to reconstruct the history of the planet's temperature from the end of the last Ice Age around 11, ... read more


CLIMATE SCIENCE
Fukushima lags in Japan tsunami recovery: official

Living through a tornado does not shake optimism

Japan riled by WHO's Fukushima cancer warning

Chernobyl plant building to be covered

CLIMATE SCIENCE
Atoms with Quantum-Memory

Big data: Searching in large amounts of data quickly and efficiently

Neutron scattering provides data on adsorption of ions in microporous materials

MEXSAT Bicentenario Satellite Completes On-orbit Testing

CLIMATE SCIENCE
Herbal defluoridation of drinking water

80% of Indian sewage flows untreated into rivers: study

New marine species discovered in Pacific Ocean

Shark fin-hungry China drives 'chaotic' fishing in Indonesia

CLIMATE SCIENCE
Canada's glaciers could shrink by a fifth by 2100

Remains of extinct giant camel discovered in High Arctic by Canadian Museum of Nature

LSU researchers find new information about 'Snowball Earth' period

What Lies Beneath: NASA Antarctic Sub Goes Subglacial

CLIMATE SCIENCE
Wild pollinators increase crop fruit set regardless of honey bees

When Good Food Goes Bad: Strengthening the US Response to Foodborne Disease Outbreak

Illinois town provides a historical foundation for today's bee research

Loss of wild insects hurts crops around the world

CLIMATE SCIENCE
Hope and despair as Japan marks tsunami anniversary

Q and A on Japan's disaster two years on

Volcanic aerosols, not pollutants, tamped down recent Earth warming

Netherlands shares flood control expertise

CLIMATE SCIENCE
China's Xi to visit S.Africa this month

UN eases oldest arms embargo to help Somali government

Independence won, freedom yet to come for South Sudan

Outside View: Kenyan democracy

CLIMATE SCIENCE
After the human genome project: The human microbiome project

Walker's World: The time for women

Human cognition depends upon slow-firing neurons

Blueprint for an artificial brain




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement