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Optical Techniques (OT) Group
OT Group Members:
Summary of Activities:
TGround-based remote sensing
For the entire month of March 2006, as part of the MIRAGE field campaign, the Optical Techniques group deployed its .06cm -1 resolution Fourier transform spectrometer at a site 30 km north of Mexico City . High resolution spectra of atmospheric infrared absorption was recorded during 28 days under various conditions of flow and pollution. Using techniques developed in its airborne and high-latitude ground-based studies, infrared spectra were fit to retrieve column amounts, and some vertical profiles, of a number of gases of interest in an urban plume environment. Results for 15 tropospheric gases, including CO, H 2 O, NH 3 and C 2 H 4 , have been submitted to the MIRAGE archive. Analysis of the OT data set and its connection with the much more extensive MIRAGE data set is still in progress.
As part of the international Network for the Detection of Atmospheric Composition Change (NDACC) formerly the NDSC, the Optical Techniques group operates an infrared Fourier transform spectrometer (FTS) at Thule , Greenland (76.53°N). The NDACC is a network of high quality ground based observing stations for early measurement of changes in the composition and state of the stratosphere and troposphere and determination of their causes. Operation of the spectrometer at Thule is mostly automatic, with monitoring from Boulder , whenever the weather is suitable and the sun is above the horizon. Observations were made on 95 days of the possible 225 sunlit days of 2005. Missed days usually are due to stormy weather. Those data were analyzed for column amounts and some vertical profiles of gases, including both stratospheric gases important in ozone chemistry and tropospheric gases related to climate change.
In conjunction with other observations from the network, composed mostly of research teams from nations other than the US , the OT Thule measurements are being used in the validation activities of recently launched satellite-borne instruments. Collaborations are ongoing with instruments aboard the ENVISAT (EU) platform, the NASA EOS-Aura satellite ( US , UK , Netherlands , Finland ) and the Atmospheric Chemistry Experiment (ACE) instrument aboard the Canadian SCISAT-1 satellite.
Space-borne remote sensing
As co-investigators on the High Resolution Dynamics Limb Sounder (HIRDLS) instrument for EOS-Aura, OT personnel contribute to the ongoing analysis of instrument performance and data production and lead efforts in the validation of certain HIRDLS products.
NTEX-B was sponsored primarily by NSF, with supplemental funding from NASA.
UTLS Activities
Results from observations by the airborne Fourier transform spectrometer (0.06 cm -1 resolution), that span more than 20 years, have been used to produce a unique archive of observations, from the base of the stratosphere, covering a wide range of latitude and season. This archive of infrared spectra has been used along with recent advances in regression fitting to study the long-term trends in water and its isotopes. Water transfer across the tropopause and redistribution in the lower stratosphere are important factors to the chemistry, radiation and dynamics of that important atmospheric transition region. Variations in the behavior of the water isotopes can provide insight into the sources and distribution of water. A remarkable result from that study was that HDO showed an enhanced depletion with respect to H 2 16 O for low latitude upper tropospheric /lower stratospheric air, as shown in the figure below, ( Coffey , M. T., J. W. Hannigan , and A. Goldman (2006), Observations of upper tropospheric /lower stratospheric water vapor and its isotopes, J. Geophys . Res., 111, D14313, doi :10.1029 /2005JD006093).
Fraction of HDO, H 2 17 O and H 2 18 O with respect to H 2 16 O, using Standard Mean Ocean Water as a reference, for the period from August 1987 to February 1989.
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