Satellite Formation Flying for Surface Topography and Vegetation (STV) Mapping: The Distributed Aperture Radar Tomographic Sensors (DARTS)

The 2017-2027 Decadal Survey recommended the global mapping of surface topography and three-dimensional vegetation structure (STV) as one of the high-priority incubator measurements to undertake in the next decade. Ecosystems, Solid Earth, Cryosphere, Hydrology, and Coastal Processes are the key science disciplines and applications to benefit from global and systematic surface topography and vegetation observations at high resolution. In response to the Decadal Survey, NASA conducted a 1-year study to identify product needs and technology gaps associated with the measurement of STV from space. The study generated a set of desired product characteristics for each science discipline and applications, as well as a list of technologies that require maturation, as detailed in the 2021 STV Study Report. Multiple and simultaneous radar observations taken from different look angles have demonstrated the ability to provide high-resolution, gap-free maps of vegetation structure and underlying topography. Previous experiments have been conducted mainly with repeated airborne acquisitions. A space mission for SAR tomography requires multiple simultaneous observations in order for the measurement to be insensitive to undesired changes in vegetation, soil and atmosphere. A distributed formation poses challenges associated with the optimal geometry and coordination of the formation flying, including its accurate positioning and signal synchronization for coherent radar processing. A recently-funded NASA IIP project, the Distributed Aperture Radar Tomographic Sensors (DARTS), aims to mature a set of technologies that will enable formation of satellites to perform systematic observations of STV from space. In this talk, we provide an overview of DARTS and describe its notional architecture informed by the 2021 STV Study Report. The technology and algorithm development challenges of single-pass tomography are discussed along with proposed and demonstrated solutions for both post-processing and real-time scenarios. A central component of DARTS is the trade study tool that allows exploring the complex trade space to design the optimal satellite radar formations for STV. The talk illustrates performance and sensitivity examples generated with the trade study tool for representative STV targets.