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

Precision of Ku-Band Reflected Signals of Opportunity Altimetry

This letter provides a proof-of-concept experiment and validation of an error model for bistatic altimetry using signals of opportunity (SoOps). Coastal sea surface height plays a prominent role in measuring the total water-level envelope directly and is one of the key quantities required by storm surge applications and services. Nadir satellite altimeters have a long history of mapping the variability of the earth's open ocean. However, they exhibit problems operating in coastal areas due to the effects, such as land contamination, rapid variations due to tides, and atmospheric effects. One technique for filling this gap is bistatic altimetry using SoOp (e.g., digital communication signal reflections). In this letter, we investigate capabilities of this technique. Twenty three days of data were collected at platform harvest from a single channel of the Ku-Band direct broadcast satellite. The wind speed observed during the experiment was between 4 and 14 m/s and significant wave height was between 0.7 and 4 m as measured by buoy 46, 218 located 8 km away. The standard deviation in the estimation of height was found to be 7.2 cm (the same as predicted from theory). Using a least-squares approach improved the precision reducing the standard deviation to 6.8 cm. It is shown that the error in the estimation of height can be reduced to 3.5 cm by utilizing the full bandwidth (all the channels) of the SoOp. Extrapolating these results, we predict a precision of 5.3 cm from a typical (e.g., Jason) orbit of 1380 km

Precision of Ku-Band Reflected Signals of Opportunity Altimetry

This letter provides a proof-of-concept experiment and validation of an error model for bistatic altimetry using signals of opportunity (SoOps). Coastal sea surface height plays a prominent role in measuring the total water-level envelope directly and is one of the key quantities required by storm surge applications and services. Nadir satellite altimeters have a long history of mapping the variability of the earth's open ocean. However, they exhibit problems operating in coastal areas due to the effects, such as land contamination, rapid variations due to tides, and atmospheric effects. One technique for filling this gap is bistatic altimetry using SoOp (e.g., digital communication signal reflections). In this letter, we investigate capabilities of this technique. Twenty three days of data were collected at platform harvest from a single channel of the Ku-Band direct broadcast satellite. The wind speed observed during the experiment was between 4 and 14 m/s and significant wave height was between 0.7 and 4 m as measured by buoy 46, 218 located 8 km away. The standard deviation in the estimation of height was found to be 7.2 cm (the same as predicted from theory). Using a least-squares approach improved the precision reducing the standard deviation to 6.8 cm. It is shown that the error in the estimation of height can be reduced to 3.5 cm by utilizing the full bandwidth (all the channels) of the SoOp. Extrapolating these results, we predict a precision of 5.3 cm from a typical (e.g., Jason) orbit of 1380 km