The successful launch of Sentinel-1A in April 2014 signified the beginning of the dedicated space segment for the Copernicus Programme, the result of the partnership between the European Union (EU) and the European Space Agency (ESA). Sentinel-1A is the first of a long-term operational series of Earth Observation (EO) satellites to be launched by Europe that will complement the already well-established series of meteorological missions. For the first time, these missions will provide a continuous and long-term European capability for systematic observations of the Earth surface, its oceans and atmosphere to unprecedented accuracies, resolutions, and temporal coverage. If additional cost-effective missions could be flown together with these operational missions (including operational meteorological satellite series such as MetOp (Second Generation - SG) then the possibilities for meeting new Earth science and application objectives could be far-reaching e.g. fulfilling observational gaps, synergistic measurements of Earth system processes, etc. With this in mind, the ESA initiated three exploratory paper studies (known as the EO-Convoy studies). The aim of these studies is two fold: Firstly, to identify scientific and operational objectives and needs that would benefit from additional in-orbit support. Secondly, to identify and develop a number of cost-effective mission concepts that would meet these objectives and needs. Each EO Convoy study is dedicated to a specific theme, namely: Study 1- Ocean and Ice Applications, Study 2 - Land Applications and Study 3 - Atmospheric Applications. As a result of the Ocean and Ice study the following concepts have been selected and further investigated:

1. A passive C-band SAR flying with Sentinel-1 convoy concept comprises a single passive SAR satellite flying in a near-pendulum formation with Sentinel-1. The aims of this mission include the generation of high accuracy Digital Elevation Models (DEMs) from the across-track InSAR e.g. to capture glacial and permafrost surface tomography and topographic change measurements, as well as to potentially characterize ocean, sea ice and glacial motion using along-track InSAR. Other aims include the provision of snow accumulation measurements on ice sheets and ice sheet mapping.
2. A laser altimeter instrument flying with Sentinel-3 comprises a laser altimeter flying together with the radar altimeter (SRAL) of Sentinel-3. The aims of this mission include the measurement of surface topography of ice sheets, ice caps, sea-ice and large glaciers and support measurements related to mass balance. Other aims include improved ice thickness measurements, snow cover characterization, ridge and sea-ice deformation measurement (though limited by sampling). For the ocean domain additional support in the area of mean dynamic topography was identified as well as retrievals of absolute surface current and upper layer dynamics.
3. A Ku-band scatterometer flying with MetOp-SG comprises a Ku-band scatterometer flying in a leader-follower formation with MetOp-SG (MWI, SCAT). The aims of this mission are to retrieve snow accumulation on ice sheets and large ice caps, to measure snow mass on land from snow water equivalence (SWE), to examine the freeze / thaw cycle of soil and to examine snow microphysical properties. This mission exploits dual-frequency radar backscatter (Ku-band and C-band) and multi-frequency microwave radiometer measurements.