estec 7 dec 2007 1 radio properties of the moon: a brief review of some important bits graham woan...
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ESTEC 7 Dec 20071
Radio Properties of the Moon:
a brief review of some important bits
Graham WoanUniversity of Glasgow
ESTEC 7 Dec 20072
lunar regolith
• Regolith electrical properties from Apollo missions:
• electrical conductivity ~10-14 /Ohm/m at d.c.
• loss tangent ~0.001 to 0.1 at ~10 MHz
• relative permittivity ~6
• Conductivity low enough to allow dipoles to be placed on the regolith without degrading beam pattern too severely (see later).
• dipole antenna pattern has largest lobe on the lunar side
• skin depth of between 1 and 100 (30 km at 1 MHz)
• possible trouble for subsurface reflections (from mascons etc)
ESTEC 7 Dec 20073
lunar exosphere
• Dual-frequency Luna spacecraft measurements give reasonably good evidence that an ionised layer, several kilometres thick, builds up on the illuminated side of the Moon (Vyshlov 1976)
• Max illuminated plasma frequency of ~0.5 MHz
• No layer seen during the lunar night
Luna 22
ESTEC 7 Dec 20074
Dust
• Photo-ionisation may levitate dust electrostatically to give a “dust fountain”:
ESTEC 7 Dec 20075
Lunar opacity
RAE-2 occultation of Earth
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Lunar opacity
RAE-2 occultation of Sun
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Takahashi and Woan
Radio propagation around the Moon, with subsurface penetration and a lunar density model
Lunar opacity
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Takahashi and Woan
Radio propagation at the Mapert Mountain (lunar south pole), with subsurface penetration and a lunar density model
Lunar opacity
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Surface dipole field response
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unresolved lunar radio questions
• What is the electron ‘weather’ really like on the Moon?– Diurnal variations– Solar wind induced variations– Over the terminator
• What are the electrical properties of the regolith at likely sites?
• What is the true attenuation factor of the occulting Moon at the surface?
• What is the noise floor like on the dark, far-side surface?
• Can we achieve the dynamic range needed for HI surveying out to z~100-1000?
ESTEC 7 Dec 200711
What are the other current/planned investigations?
• Kaguya (Japan) and Chang’e 1(China) both have exosphere monitoring experiments, and plans for future lunar low-frequency experiments (see, e.g., Maohai Huang’s talk, IAU 26). More details needed!