|Projektname:||AEXPWIND – Trace Gas Retrieval and Performance of Wind and Greenhouse Gas Profiling in the IRDAS-EXP/ACCURATE Context|
Stig Syndergaard, Danish Meteorological Institute (DMI), Copenhagen, DEN
ESA (European Space Agency)
|Laufzeit:||Jul. 2012 - Mär. 2014|
The objective of the AEXPWIND study was twofold, 1) to perform a detailed Greenhouse Gas (GHG) analysis and validation of the infrared-laser ground link experiment on the Ca-nary Islands, and 2) to develop a new Abel transform to derive line-of-sight (l.o.s.) wind velocities from Low Earth Orbit (LEO-LEO) infrared-laser occultation (LIO) data and to apply it for l.o.s. wind profile retrieval as well as for improving GHG retrievals in windy air by including a correction for the wind-induced Doppler shift.
The first part of AEXPWIND resulted in a robust algorithm and detailed GHG retrieval re-sults for the first infrared-laser ground link experiment carried out in 2011 in the Canary Is-lands, which enabled GHG measurements along a 144 km ray-path. Besides the algorithm development and thorough preparation of validation data sets, comprising weather station data and high-resolution ECMWF analysis fields as well as cavity ring-down spectrometer and sampling flask measurements, a thorough analysis of the recorded infrared-laser link spectra and the GHG retrieval process was performed. This included an uncertainty analysis accounting for uncertainties from spectroscopy, validation data, and spectral correction. Re-trieval results were obtained for CO2 isotopes (12CO2, 13CO2, C18OO), water vapor (H2O) and methane (CH4). The demonstration was successful and showed that the LIO method has a sound basis for GHG monitoring in the free atmosphere.
The second part of AEXPWIND complemented with its advances the ACCURATE mission concept with a l.o.s. wind retrieval capability and an improvement of the GHG retrieval due to wind-induced Doppler shift correction. As a core basis of this work, a new Abel trans-form was developed which converts observed differential transmissions between two chan-nels sitting on the inflexion points of the highly symmetric C18OO absorption line to re-trieved l.o.s. wind profiles. The transform enables l.o.s. wind profile retrieval accuracies of better than about 2 m/s over the stratosphere (15 km to 35 km), which are essentially unbi-ased (e.g., averages accurate to better than 0.5 m/s). The corresponding wind-induced Dop-pler shift in windy air, of the infrared-laser signals for GHG retrieval, can thus also be ro-bustly corrected; a performance analysis of joint l.o.s. wind and CO2, CH4, H2O and O3 re-trieval demonstrated this robustness.