Pluto's Surface Properties from the New Horizons Uplink Bistatic Radar Experiment
Abstract
Exploration of planetary surface properties by scattering radio signals has been carried out via Solar System spacecraft for nearly six decades. During the New Horizons flyby of Pluto on July 14, 2015, an innovative approach reversed the radio path using a high-power uplink transmitted from the Deep Space Network. The uplink illuminated the surface of Pluto, and the scattered signals were recorded onboard the spacecraft by REX the Radioscience instrument, setting a record at 7.6 Bkm for bistatic radar. The high SNR advantage, needed to characterize such a distant object, was nearly three orders of magnitude greater than traditional downlink experiments could have provided.
The bistatic experiment was performed using a radar transmission at 7.18 GHz, from the NASA's Deep Space Network 34-m diameter antenna (designated DSS-26) at Goldstone, California. The transmission was CW at 80 kilowatts in right-hand circular polarization (RCP) and was adjusted in frequency to compensate for predicted Doppler shifts to ensure it would fall within REX's 1.25 kHz bandpass. The received signal's SNR was 30x, (15 dB), and digitized by REX in both polarizations, and in-phase and quadrature, revealing a polarization ratio of ~1/2, and a surface reflectivity of ~0.3. The radar illumination at Pluto's specular point subtended an angle of incidence between 40 degrees and 60 degrees, a near-optimal geometry for modelling surface properties. Characterization of Pluto's surface in the vicinity of the specular point has incorporated Fresnel reflection, as well as electromagnetic scattering models for randomly oriented surface facets as well as subsurface propagation and multidimensional optimization over the distribution of surface slopes and roughness, to obtain both the composition and structure of Pluto's surface and subsurface. These results demonstrate the efficacy of bistatic scattering for planetary surface characterization and suggest that bistatic experiments, if incorporated in future missions to the solar system's planets, moons, dwarf planets and bodies, will substantially increase and enrich their science return.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P34A..01L
- Keywords:
-
- 6297 Instruments and techniques;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6964 Radio wave propagation;
- RADIO SCIENCE;
- 6979 Space and satellite communication;
- RADIO SCIENCE;
- 6994 Instruments and techniques;
- RADIO SCIENCE