Retrieval of Stratospheric Trace Gases from FIR/Microwave Limb Sounding Observations

Abstract

The TELIS (TErahertz and submillimeter LImb Sounder) instrument is a new stratospheric balloon-borne cryogenic heterodyne spectrometer developed by the German Aerospace Center (DLR) in cooperation with the Netherlands Institute for Space (SRON), and the Rutherford Appleton Laboratory (RAL) in the United Kingdom. It allows limb sounding of the Earth's atmosphere within the far infrared (FIR) and microwave spectral range. The ambitious spectral coverage of the TELIS instrument is accomplished by use of three frequency channels: 500 GHz, 480-650 GHz, 1.8 THz for RAL, SRON and DLR, respectively. TELIS utilizes state-of-the-art superconducting heterodyne technology and is capable of providing broad spectral coverage, high spectral resolution and extensive flight duration. These features enable us to monitor the diurnal variation of key stratospheric constituents associated with ozone depletion and climate change. The instrument was mounted on a balloon gondola together with the MIPAS-B (Michelson Interferometer for Passive Atmospheric Sounding - Balloon) instrument, developed by the Karlsruhe Institute of Technology (KIT), Germany. The combination of TELIS and MIPAS-B covers a wide range of the electromagnetic spectrum that is used for atmospheric research and offers great synergies for cross-validating of measured vertical distributions of trace gas species. In addition, TELIS acts as a technology demonstrator to future spaceborne FIR/microwave limb sounding instruments planned by the European Space Agency (ESA). The development of FIR/microwave limb sounding techniques contributes to an increased demand in high resolution radiative transfer modelling and efficient inversion strategy for better understanding of atmospheric environment. The Remote Sensing Technology Institute at DLR has developed a retrieval code PILS (Profile Inversion for Limb Sounding), whose forward model is built on GARLIC (General Atmospheric Radiation Line-by-line Infrared Code). The goal of PILS is to solve the nonlinear inverse problems arising in the analysis of limb sounding measurements obtained by TELIS, SMILES (Superconducting subMIllimeter-wave Limb-Emission Sounder), or Odin/SMR (Sub-Millimetre Radiometer) instruments. In this work we present the results of various trace gas retrievals from the TELIS measurements of the DLR/SRON channels by employing PILS. The error analysis is also conducted to investigate the retrieval feasibility of key profiles of the data processing. The intercomparison between TELIS and SMILES is currently ongoing in order to consolidate the performance of the instrument and the reliability of the retrieval results.