The proposal of an "ocean Surface TRansport, mechanical Energy, Air-sea fluxes and Mixing" satellite mission will be one of the 16 proposals for ESA's Earth Explorer. It combines a Ka-band radar and a high resolution optical camera to measure surface current and near-surface shear. This proposal is a direct answer to the OceanObs'19 conference, where the ocean sciences community called for more measurements of near-surface current.

STREAM is a mission proposal designed to observe the oceans at high resolution in space and time and with a near-global coverage (up to 85°N). The measurements will fill long standing gaps in our knowledge of the Earth energy cycle. In particular, the joint measurement of the wind stress and the surface current vectors is the first opportunity to estimate globally the work of the wind on the ocean, thus quantifying a major source of mechanical energy with direct impact on the ocean heat budget through mixing and enabling more accurate coupled ocean-atmosphere models from Numerical Weather Prediction to decadal variability and climate change. STREAM carries two main instruments, STREAM-R is  a conically scanning Ka-band radar, with an on-ground incidence angle of 35°, using a 3 m diameter rotating reflector. It will measure total surface currents and wind stress. STREAM-O is a high-resolution (10 m) optical system designed to look at small ocean scenes selected based on cloud absence, and measuring the phase speed of the surface waves, from which surface current, depth and the vertical profile of the ocean current in the top 40 m may be estimated.