The Ka-Band Interferometric Radar Mission Proposal for Cold Environments - SKADI

Abstract

SKADI[1] is a mission proposal submitted to the Earth Explorer 11 call that aims to address and quantify dynamic processes in cold environments by measuring the static and dynamic topography. This information is essential for understanding, modelling and forecasting the dynamics and interactions within the different elements of the cryosphere and with other Earth system components. SKADI will provide very accurate high-resolution, multi-temporal topographic data that will make it possible to derive mass balances and structural changes in the cryosphere, with a focus on permafrost areas as well as glaciers and ice caps, ice sheets and sea ice. At the same time, SKADI will enable unprecedented measurements of volume change processes in the geosphere, including volcanic, landslide and seismic activities. In addition, SKADI will generate a global digital elevation model (DEM) of about one order of magnitude better, in terms of resolution and height accuracy, than the current reference provided by TanDEM-X. The SKADI instrument consists of a cross-platform Ka-band radar interferometer with two spacecraft that fly in a reconfigurable formation and can dynamically adapt to the needs of scientific observation. Cross-track SAR interferometry is an established remote sensing technique for large-scale measurements of static and dynamic topography and the use of Ka band minimizes systematic biases and errors that would be caused at lower frequencies due to wave penetration into semi-transparent media. SKADI’s unique ability to provide time series of highly accurate surface topography measurements allows the mission’s primary scientific objectives to be optimally fulfilled, namely a) the monitoring of permafrost degradation by means of DEM acquisitions with short repetition intervals and estimates of volume changes in time, b) the measurement of snow topographic changes to observe different snow regimes to feed hydrological models for a more precise prediction of water availability, and c) the measurements of glaciers, ice caps, ice-clad volcanoes and their mass balance and modelling of ice dynamics and ice/climate interactions. At the same time, the SKADI measurements allow to serve a number of secondary science objectives related to floating ice and geosphere applications such as a) the measurement of sea ice and fresh water ice topography to define the surface-air-interface, b) the monitoring of geohazards involving large deformations and volume changes caused by landslides, glacier lake outbursts, rockfalls, mining, landfill, volcanic activities and seismic events, c) the measurement of a global DEM with unprecedented resolution and accuracy. SKADI will moreover complement and fill critical observation gaps of the current Copernicus and Earth Explorer missions (e.g., Sentinel, Cryosat) by providing frequency diversity and enhanced spatial resolution, while at the same time offering the Earth Observation community and future ESA missions (e.g., Aeolus, EarthCARE) a global topographic reference of superior accuracy and resolution, which enables a major step forward in improving the quality and interpretation of a vast amount of past, present, and future Earth observation data. A first order performance of the mission products reveal that very accurate DEM change products can be expected, with accuracies in the order of decimetres to centimetres. In comparison to previous SAR missions, the short wavelength in Ka band allows a reduction of the size and weight of the antennas and spacecraft and enables the joint launch of two radar satellites with a single medium-sized launch vehicle like Vega C. In this regard, the SKADI space segment offers also a unique platform to explore and demonstrate new bi- and multistatic SAR techniques, technologies and applications which are expected to shape the future of radar remote sensing. The SKADI mission concept and the associated space segment have been developed in two Pre-Phase 0 studies in close collaboration with Airbus DS and OHB. Both industry partners proposed innovative Ka-band SAR instrument architectures and showed the feasibility of SKADI within the programmatic constraints and the cost cap provided by ESA in its call for Earth Explorer 11 mission ideas. We believe that the versatility and technological innovation of SKADI are an important complement to its unique scientific objectives, thereby increasing its impact on societal welfare. The consolidated mission objectives, the well-defined mission products, the highly accurate performance and the innovative instrument design will be presented. Following the encouraging recommendations provided in the ACEO (Advisory Committee for Earth Observation) report, the SKADI team is working towards the submission of a revised version of the mission proposal for the next call for ESA Earth Explorer missions. [1] In Norse mythology, Skaði (/ˈskɑːði/, sometimes anglicized as Skadi, Skade, or Skathi) is a jötunn and goddess associated with winter and mountains.