Tethered Balloon-Based Experiment of Surface Water Height Using Satellite Signals of Opportunity

Signals of Opportunity (SoOp) is an area of radio science that leverages existing ambient signals from spacecraft, aircraft, and ground-based radio systems to perform radio science without spending time or resources constructing new transmission infrastructure. It has been conceptualized that SmallSats or CubeSats can perform similar SoOp missions by augmenting pre-existing spacecraft missions - specifically radio/radar missions. During the summer of 2019, student-interns at the National Aeronautics and Space Administration's (NASA) Jet Propulsion Laboratory (JPL) under the Innovation to Flight (i2F) program tested the first airborne SoOp demo via a tethered aerostat - a valuable step towards getting a SoOp demo in orbit. The airborne SoOp demo received direct and bounced signals from multiple geosynchronous equatorial orbit (GEO) satellites by using two on-board wide-band grid antennas. One antenna was pointed at the sky at appropriate azimuth and elevation angles to receive a direct GEO signal. The other antenna was pointed at an identical azimuth angle with a mirrored elevation angle so as to receive the same GEO signal reflected from a body of water below. Both antennas were secured on adjustable mounts to allow for pointing changes and permit data collection from multiple satellites. This initial test proves the scientific and technological feasibility of doing further airborne SoOp tests, potentially on aircraft, unmanned aerial vehicles (UAV), high altitude balloons (HAB), and SmallSats or CubeSats.