Wave Interaction and Propagation
Why is it important?
At the core of the Wave Interaction and Propagation domain is the understanding of the behaviour of electromagnetic waves in a variety of media and environmental conditions, and the application of this understanding to the definition and exploitation of space missions.
The environment can be a source of perturbations in the use of electromagnetic waves from space. Radio signals from telecom satellites are disrupted by tropical rainstorms, satellite to mobile radio links in urban areas are disturbed by spurious reflections on buildings walls, navigation solutions are degraded by plasma layers in the upper atmosphere and optical images of the Earth surface acquired from space are modified by the atmosphere layer that lies in between. In order to circumvent these effects, they need to be understood, assessed and mitigated.
On the other hand, space provides a unique vantage point from which to probe the Earth or the other planets of the solar system. Remote sensing relies on the ability of electromagnetic waves to carry back to a spaceborne instrument relevant information about a physical or biological property of the natural environment in its field of view. This information is then used for science or applications (e.g. climate studies, meteorology, land use, pollution monitoring, planetology). The quantity of vegetation on a surface drives the response of near infrared channels of optical imagers, the centimetric radar backscatter from the ocean scales with the surface roughness, giving information on the local wind conditions, the radiometric emission of soils in decimetric waves depends on their moisture content, the presence of liquid water underneath Europa ice mantle would change the echo measured from a radar sounder. A thorough understanding of these relations is paramount to make a proper use of remote sensing techniques.
What is it in practice?
Activities in the field of wave interaction and propagation revolve around several main topics:
- Modelling and experimental validation: models are built that provide a quantitative understanding of the relationship between one or several characteristics of the environment (e.g. rain rate, vegetation biomass, trace gases in the atmosphere, electron density in the ionosphere, building characteristics) and their impact - positive or negative - on the electromagnetic signal of interest. These models can be physically based or be constructed from experimental observations, and they are validated through experimental campaigns;
- Mitigation, retrieval and vicarious calibration algorithms: the understanding of the interaction enables the development of processing steps that allow to either extract the information of interest from the signal or to mitigate its disturbing impact. In addition, this knowledge can also be used to support the monitoring of the performance of a spaceborne instrument and the improvement of its products;
- Related end-to-end performance assessment and product quality control: natural and man-made environment are highly heterogeneous and cannot be controlled by careful engineering! Being able to relate the electromagnetic signal to the environment supports the quantification of the end-to-end performance of a mission, the selection of adequate characteristics for the instrument in space and the development of optimal processing steps for the ground segment.
Where can I find out more?
Contact:
Head of the Wave Interaction and Propagation Section, Nicolas Floury, Nicolas.Floury@esa.int