UK Support for the ALISS Bilateral Mission Study

STFC Rutherford Appleton Laboratory

Project Funded in the CEOI-ST 7th Call for EO Technologies.

Pathfinder Project (typically 6 months duration)

ALiSS, the Atmospheric Limb Sounding Satellite, is a Canadian-Swedish concept for a Space Mission to provide a limb-sounding satellite to measure the chemistry and composition of the Upper Troposphere – Lower Stratosphere (UTLS). The UK has a long-standing technology stake in the submillimetre-wave radiometer STEAM-R which is one of two prime instruments of the ALiSS mission payload. A new generation of sideband-separating heterodyne receivers for submillimetre-wave remote sensing has been developed at RAL and Airbus Defence and Space with previous CEOI funding. These receivers have been designed specifically for a UTLS instrument like STEAMR, where the benefits of the spectral separation of wide pressure-broadened molecular emission lines are most apparent.

The CEOI-ST funded project was initially conceived to address further technology development for STEAM-R. However, during the course of the activity a second, potentially attractive, opportunity was identified for the UK to provide a small infrared instrument, providing synergy with the millimetre wave instrument. Therefore, the remaining part of the study was re-directed to assess the feasibility of developing a micro-Fourier Transform Spectrometer (µFTS) within the timeframe of the ALiSS mission and to quantify the expected scientific impact.

Project Outcome and Achievements

The CEOI-ST Pathfinder project has concluded with the following outcomes:

  • The technical characteristics of the μFTS, its mass and power requirements, as well as an estimate of its measurement performance has been derived from lab measurements.
  • The retrieval performance of the µFTS in atmospheric limb-sounding mode has been estimated based upon lab measurement performance. The retrieval simulations show, that for a choice selection of scientific observables the low resolution of the μFTS is no obstacle to good scientific performance.

In addition, the option of deploying the μFTS within the MARSCHALS instrument frame from the stratospheric research aircraft M55 Geophysica has been assessed both in terms of the engineering feasibility and the measurement performance from an airborne platform.

The overall conclusion is that a space-borne limb-sounding infrared μFTS is technically feasible and scientifically relevant. It would provide an important contribution to the ALiSS mission, complementing the mm-wave STEAM-R limb sounder.