SteamR
The Stratosphere-Troposphere Exchange And climate Monitor radiometer, STEAMR, is a Swedish national contribution to the PREMIER mission to be provided to ESA. The instrument is specifically designed to provide accurate measurements of the global distributions of key target species in the UTLS. To achieve good vertical and horizontal resolution, it will utilize a small linear array of receivers, which will image different altitudes simultaneously backward along the satellite track, thereby providing unique information about the 2-D structure of the atmosphere in the orbital plane.
Omnisys is the prime contractor for the instrument and responsible for optics, control software and system tests and is currently performing a breadboard study, demonstrating the key features of the instrument. Omnisys scope of the instrument is the front-end including LO-, IF- and phase-lock system, the digital autocorrelator back-end, the power distribution and control hardware.
The system basically consists of an array of 14 heterodyne receivers based on broad band (8 GHz) sub-harmonically pumped planar Schottky diode mixers operating in the 320-360 GHz spectral range. The signal originating from both sidebands is down-converted to an intermediate frequency (IF) in the range 9-21 GHz. The IF signal is filtered, amplified and spectrally resolved using autocorrelation spectrometers that provide a maximum instantaneous bandwidth of 8 GHz with a baseline spectral resolution of 10 MHz.
The STEAMR design is optimized for limb-sounding of the upper troposphere, which was not visible in the frequency bands near 500 GHz used by Odin SMR. Advances on Aura MLS for this height range are:
Vertical resolution increased by factor 1.5, through use of 320-360 GHz instead of 200-230 GHz
Along-track resolution increased by use of receiver arrays and focusing observations on UTLS range
Accuracy increased, through measuring continously over broad bandwidths and potentially by sideband separation to minimize spectral interference and to characterise continuum.
Upper tropospheric CO distribution much better resolved: increased sensitivity from 346GHz is three times stronger than the 231GHz line used by Aura MLS, which allows more frequent sampling.
These technical advances will yield the higher vertical resolution and denser sampling of the mid- and upper troposphere and lower stratosphere which are mandatory for the PREMIER mission.