The High Resolution Spectrometer for SOFIA-GREAT: Instrumentation, Atmospheric Modeling and Observations
The purpose of the thesis is the development of a high resolution spectrometer, in association with atmospheric modeling and observations. The new spectrometer, the "Chirp-Transform-Spectrometer (CTS)" as part of the "German REceiver for Astronomy at Terahertz frequencies (GREAT)" on the "Stratospheric Observatory For Infrared Astronomy (SOFIA)", will provide unprecedented spectral resolving power and linearity response. The analog Fourier transform performed by the CTS spectrometer was significantly improved through a new design called "Adaptive Digital Chirp Processor (ADCP)". The principle behind the ADCP consists of digitally generating the dispersive signal which adapts to the convolver dispersive properties, achieving higher spectral resolution and higher dynamic range. This development demanded a rational and optimum combination of different technologies, such as quadrature-modulation, high performance spectral filtering, ultra-stable frequency sources and a deep study of the problem through numerical simulations with an ad hoc model. The newly developed CTS is a prevailing instrument for the study of planetary atmospheres, especially as part of the SOFIA mission providing highly resolved altitude profiles of temperature, wind, water vapour and minor species from ground level up to an altitude of 80 km. Consequently, the link between the spectroscopic observations and the physical phenomena in study was addressed via the development of a general circulation model (GCM) for the Martian atmosphere. A running prototype of SOFIA-GREAT-CTS mounted at the Submillimeter Telescope in Arizona was used for remote sensing of Mars through the broadened line of CO at 345 GHz, providing temperature measurements which were then used as data assimilation inputs for the GCM. The new CTS also demonstrated itself to be a powerful tool for the study of narrow line features typical of cometary bodies, through the detection of hydrogen cyanide and outgassing asymmetries on comet Encke.
- Pub Date:
- October 2004
- High-resolution Spectroscopy;
- Planetary Sciences;
- General Circulation Model;