Signals-of-Opportunity SmallSat Constellations for Earth System Science

The signals-of-opportunity (SoOp) concept is reutilization of powerful satellite transmissions in microwave frequencies allocated for space-to-Earth communications and navigation for the purpose of remotely sensing Earth parameters. The geometry used by SoOp is bistatic in forward direction, which views Earth differently from traditional radars and radiometers. Additionally, SoOp enables use of microwave remote sensing frequencies outside the limited number of narrow, protected bands. A powerful example of the science returns achievable using SoOp is currently being demonstrated on orbit by the NASA’s CvGNSS mission, which measures wind strengths at the sea surface using reflected Global Positioning System (GPS) signals. Over the past decade we have seen a growing number of communication and navigation signals coming into existence spanning the range of frequencies from VHF to K Band, which could be used to measure different parameters since different wavelengths are better suited to each of earth science measurements. A list of such earth science parameters would include: Soil Moisture; Sea Surface Salinity; Sea Surface Height; Ocean Vector Winds; Ocean Surface Currents; Snow Water Equivalent; Vegetation Water Content; Surface Deformation; Atmospheric Pressure, Temperature and Water Vapor Profiles; and even 3-D Winds. The use of SoOp for earth remote sensing requires putting small passive receivers in Earth Orbit in SmallSat/CubeSats. This also enables constellations to improve the temporal frequency of Earth science measurement observations. This paper will describe different architecture of SmallSat/CubeSats constellations that could be used to measure different science measurements as well as the achievable performances for operational Earth observations .