loading page

Remote Sensing of the water cycle using Signals of Opportunity: challenges and opportunities
  • +4
  • James Garrison,
  • Manuel Vega,
  • Rashmi Shah,
  • Rajat Bindlish,
  • Mehmet Kurum,
  • Benjamin Nold,
  • Seho Kim
James Garrison
Purdue University

Corresponding Author:[email protected]

Author Profile
Manuel Vega
NASA Goddard Space Flight Center
Author Profile
Rashmi Shah
Jet Propulsion Laboratory
Author Profile
Rajat Bindlish
Goddard Earth Sciences Technology and Research
Author Profile
Mehmet Kurum
Mississippi State University
Author Profile
Benjamin Nold
Purdue University
Author Profile
Seho Kim
Purdue University
Author Profile


Recent proof-of-concept experiments have demonstrated the potential utility of Signals of Opportunity (SoOp) in remote sensing. SoOp methods involve the re-use of existing satellite transmissions as sources in bistatic radar, applying fundamental physical principles to estimate surface and scattered medium properties from reflectivity and phase observables in the reflected signal. Through utilizing signals intended for communications, SoOp methods can make these observables using frequencies that are not allocated or protected for scientific use. Two promising applications in hydrology have been studied: Sub-canopy root-zone soil moisture (RZSM) using satellite communications signals below 500 MHz and snow water equivalent (SWE) retrieval from the observed phase different through propagation through the snow layer. Signals of Opportunity P-band Investigation (SNOOPI) is a NASA Cubesat technology demonstration mission to test forward scattering models and validate a prototype instrument for SoOp reflectometry in 250-380 MHz range. Contribution to the panel discussion will focus on the expected contributions of the SoOp techniques validated in the SNOOPI mission and the existing challenges in the full utilization of SoOp methods for both RZSM and SWE remote sensing. Multiple frequencies are required in order to solve the inverse problem and estimating a sub-surface profile. In the case of SoOp, this may require combining observations with diverse geometry due to the different orbits of the potential sources. This presents new challenges in the development of retrieval algorithms and may possibly require the integration of additional data sources. Another important challenge for SWE retrieval is the need for repetitive coverage to extract phase differences between subsequent passes, coupled with orbit determination for the non-cooperative sources. In contrast to GNSS reflectometry (in which high-precision orbits are publicly available for use in positioning), communication satellite orbits are not known to the required meter-level accuracy. Even geostationary sources frequently have a small inclination which results in motion relative to the surface of the Earth. Finally, antenna calibration is a substantial contribution to the error budget.