1,1,- 1University of Colorado Boulder, Department of Aerospace Engineering Sciences, Boulder, United States of America (thorsteinn.kristinsson@colorado.edu)
- 2Department of Earth and Planetary Sciences, University of California Riverside, Riverside, CA 92521, USA
- 32Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
- 4Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- 5Physical Insights, LLC, Kaneohe, HI 96744, USA
Recent work has shown the potential for passive sounding to increase the science return for radar investigations of the icy satellites of Jupiter in a noisy sub-Jovian environment. For example, Schroeder et al. analyzed the active radar link budget during Jovian burst activity (which can exceed the background noise environment by several orders of magnitude) and showed that strong Jovian Decametric radio bursts could severely degrade the detectability of surface and subsurface radar returns [1,2]. Gerekos et al. simulated radargrams for the icy moons of Jupiter and found that active radar sounding was unable to reveal surface features for key target areas in the presence of noise at the expected Jovian burst flux densities, whereas passive radar processing was still able to recover the surface reflections using both modeled and observed Jovian noise signals [3]. Peters et al. further demonstrated the potential for passive synthetic aperture radar (SAR) imaging using radio-astronomical sources to recover surface topography [4]. The Radar for Icy Moon Exploration (RIME) or Radar for Europa Assessment and Sounding: Ocean to Near- surface (REASON) could be potential candidates for the addition of a passive sounding mode that complements active radar techniques in the presence of strong Jovian Decametric radio bursts [1,2]; however, this proposed technique had never been experimentally demonstrated.
Astronomical radio sources have been tested on Earth as sources for sounding and echo detection using the passive radar approach, by using the quiescent solar emissions in VHF (300 MHz) [5] as well as Jovian radio bursts in the HF band (25MHz) [6]. These sources are one of the strongest in the sky in their respective bands. The Sun’s flux increases with frequency following blackbody radiation curve and approaches the magnitude of the diffused galactic background around 300MHz [5]. The Jovian bursts however are mainly due to the interaction of Jupiter’s magnetosphere and Io‘s magnetic field, which creates a strong radio burst centered around 25MHz [7]. While this mechanism indicates that Jovian bursts are not continuous like solar emissions, they are predictable based on 26 years of observations. Recent work has shown that there exists a clear combination pattern of Io’s phase and Jupiter’s system III central meridian longitude (CML) facing observer, which offers a way to forecast opportunity windows of highest burst probability and activity [8].
The Passive Autonomy, Navigation, Topography, and Habitability Exploration Radar (PANTHER) project utilizes both sources by capturing their emissions using the Ettus X310 + TwinRX software defined radio (SDR). The wide instantaneous bandwidth and usable range of receiver center frequencies allows us to rapidly test both passive sounding configurations. In the spring of 2025, the PANTHER team went to the hills of Dante’s view to experimentally demonstrate the predictability of Jovian bursts using the hardware mentioned prior to it being integrated and operated off AC powered power station. The results showed a significant increase across the received power spectrum (15-35MHz) during the predicted Jovian burst activity window, and the autocorrelation of the received signals showed a strong echo peak in the range profile. This result served as the first experimental demonstration of using the Jovian radio burst as a predictable illumination source in HF band [6]
The PANTHER team has now scheduled its first extensive field-testing campaign during the summer 2026 in the Icelandic volcanic and glacier environment, which will focus on the radar sounding of buried ice [9], glacier structures [10], in addition to water lava contacts at the Holuhraun lava flow [11]. At these field sites, passive sounding using radio-astronomical sources will be tested, as well as validated with a commercial GPR, to identify the technique’s limits and potential for future applications. Passive sounding is a promising approach for geological monitoring on Earth and in future planetary exploration missions.
Acknowledgments: The PANTHER project was funded by the National Aeronautics and Space Administration (NASA) through PSTAR grant No. 80NSSC24K1261. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
[1] D. M. Schroeder et al., Planetary and Space Science, 2016
[2] A. Romero-Wolf et al., Icarus, 2015
[3] C. Gerekos et al., IEEE Transactions on Geoscience and Remote Sensing, 2020
[4] S. T. Peters et al., IEEE Transactions on Geoscience and Remote Sensing, 2021
[5] S. T. Peters et al., IEEE Transactions on Geoscience and Remote Sensing, 2018
[6] T. H. Kristinsson et al., EGU General Assembly 2026
[7] P. Zarka et al., Journal of Geophysical Research (Space Physics), 2004
[8] M. S. Marques et al., AA, 2017
[9] E. S. Shoemaker Thackston et al., Journal of Geophysical Research: Planets, 2024
[10] H. Björnsson H, Annals of Glaciology. 2020
[11] C. M. Dundas et al., Journal of Volcanology and Geothermal Research, 2020
How to cite: Kristinsson, T., Peters, S., Voigt, J. R. C., Steinbrugge, G., Hamilton, C. W., Diniega, S., Williams, J., and Romero-Wolf, A.: PANTHER – Utilizing Astronomical Radio Sources for passive echo detection and sounding, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-738, https://doi.org/10.5194/epsc2026-738, 2026.
