Recent Advances in Electronically-Scanning Microwave Sounding and Imaging from Small Satellite Platforms: Design, Development, Testing, and Analysis

Current critical needs of NASA, NOAA, and other agencies carrying out Earth environmental monitoring require higher-performance observing systems that offer lower noise, finer resolution, broader coverage, etc., but that are also lower-cost, can be accommodated on a wide range of launch vehicles and hosted payload platforms, as well as provide flexibility in how they are deployed and used. To achieve these ambitions, it is necessary to consider the observing system as comprising not only the sensor but also the concept of operations, processing, and potential for collaborative and synergistic observations. Here we present a new approach that enables dynamic, data-driven sensing and provides a way to test and evaluate the overall end-to-end system performance in the laboratory prior to launch with realistic Earth scenes. Recent technology advances now enable the utilization of new sensing concepts that reconfigure the sensor in real time to adjust where they are looking, their dwell time, their spatial resolution, and depending on the platform, their geometrical vantage point. For example, at frequencies spanning approximately 10-100 GHz, phased array and reflectarray observations of sea surface wind (speed and direction), wide-swath polarimetric imagery, soil moisture and sea surface temperature, and atmospheric thermodynamic state that are deemed critical by NASA’s Earth Science strategic goals are now possible. These measurements would all be improved by this work, since the sensor would be configured for maximum resolution, coverage, and dwell time for regions in the scene that exhibit the highest variability and would therefore benefit the most from high-fidelity sensing. This approach also efficiently optimizes the use of a fixed set of resources.

Here we describe two new systems recently funded by the NASA Earth Science Technology Office (ESTO) to improve present capabilities for high-resolution atmospheric sensing from small satellite platforms. First, the Configurable Reflectarray Wideband Scanning Radiometer (CREWSR) is a high-resolution, lightweight, low-power multiband (23, 31, and 50-58 GHz) radiometer with a deployable scanning reflectarray. CREWSR is envisioned to be fielded on an ESPA-class small satellite platform, with a stowed volume that fits within a 0.61 m x 0.71 m x 0.97 m envelope. Once in orbit, the platform will deploy a large Reconfigurable Reflective Surface (RRS), as well as a multi-feed antenna connected to a multiband radiometer. These components can provide an electronically-scanned beam for radiometric Earth observation. CREWSR would operate with a single, linear polarization, but fully polarimetric operation is also possible in principle. The reflectarray is also compatible with radar use, thereby enabling wide-swath radar from a small satellite. A prototype, small-scale version of CREWSR is now in the third year of a three-year ESTO Instrument Incubator Program (IIP) to demonstrate the core concept and raise the technology readiness level to an appropriate level for a future flight demonstration. The custom radio frequency integrated circuits (RFICs), three-band antenna patch antennas, panel stack-up, and control electronics have been verified in anticipation of upcoming system-level testing.

Second, there is a critical need to enable development, test, and evaluation of Versatile, Intelligent, and Dynamic Earth Observation (VIDEO), and one key enabler is the recent emergence of metamaterials for use in high-performance blackbody radiometric targets. These materials are very thin (~200 microns) and lightweight (tens of grams), allowing them to be easily scaled up to realize very large targets (> 1 m^2) to subtend an entire sensor field of regard for laboratory measurements. Furthermore, the thin planar structure of the metamaterials provides a relatively small thermal mass, thereby permitting the projection of thermal features with very high spatial frequency content into the sensor field of view at the subpixel level. We will produce a 50 cm x 75 cm (20” x 30”) Radiometric Scene Generator (RSG) operating near 54 GHz with very large thermal contrast at the subpixel level for a typical spaceborne microwave radiometer full-width-at-half-maximum (FWHM) beamwidth in the range of 1-3 degrees. The RSG will use a scanning laser system illuminating a metamaterial surface with high microwave emissivity to project spatial features into the radiometer field of regard that can be detected and acted upon by intelligent processing algorithms. The intelligent processing algorithms will utilize feature detection and machine learning techniques to recognize regions of interest in the atmospheric scene and cause the sensor to react to the scene characteristics by changing the sensor response function. VIDEO is in the second year of a two-year ESTO Advanced Information Systems Technology (AIST) program.

In this presentation, we will provide an overview of these new technologies and discuss how they address current unmet needs for high-resolution sensing from small satellites in the critical frequency bands spanning 20-60 GHz.