The STEAM Satellite Project

The proposed satellite project Stratosphere-Troposphere Exchange And climate Monitor (STEAM) is dedicated to the study of the Earth's upper troposphere and lower stratosphere (UT/LS). STEAM will provide comprehensive investigations of chemical, dynamical, and radiative processes in the UT/LS and their links with the Earth climate and stratosphere evolution.

The main objectives are to provide vertically and horizontally resolved information on the global distributions of UT/LS key species such as H₂O, O₃, and CO. In addition, STEAM will provide global informations on compounds involved in stratospheric ozone chemistry.

The UT/LS region plays an important role in the Earth’s climate system. Despite its importance there is still a lack of accurate, height-resolved data from the UT/LS. Confronting 3-D climate and chemical-transport models with STEAM observations will improve our knowledge of this atmospheric region. Furthermore, it will be important to continue monitoring the evolution of the stratosphere regarding the expected decline of halogen compounds and recovery of the ozone layer.

STEAM consists of a limb-sounding microwave instrument, operating in the 320-360 GHz ran­ge to sound the UT/LS and in the 485-505 GHz range to sound the stratosphere, and an optical instrument. By sounding the Earth atmosphere’s limb from 5 to 28 km employing a new technique with 8 simultaneous mea­surements, STEAM will produce a global dataset of UT/LS key species with high vertical (1.5-2.5 km) and horizontal (30-50 km) resolution. The sub-mm band will cover 15 to 40 km. An optical instrument, co-aligned with the mm-wave band, will support micro-wave measurements with cloud indications. In addition the optical instrument will provide measurements of aerosol and cloud properties, ozone and water vapour.

STEAM is planned as a collaboration between laboratories, industry and agencies in several countries. The project's strong heritage from the Odin satellite (e.g., microwave and optical instruments) provides technical maturity and will help to keep instrument development efforts down. This heritage also help the development of the ground-segment with forward models, retrieval models and data assimilation tools.

The current work on STEAM is strongly supported by Swedish Space Corporation. The STEAM mission definition review was held in February 2004, concluding the first part of a phase-A study.