1. Track 1

2. Track 2 TRACK LIST 1.An introduction to synthetic aperture radar 2.Mini-RF on LRO 3.The moon as seen by radar 4.The search for ice 5.Conclusions 6.Acknowledgements

3. Track 3 radar Radio describes the long-wavelength end of the electromagnetic spectrum ~1 cm – 1 km ~300 kHz – 30 GHz RADAR stands for RAdio Detection And Ranging. Radar systems emit radio waves that are reflected by a target and detected by a receiver

4. Track 4 radar It is possible to image planetary surfaces using synthetic aperture radar (SAR), even on planets with opaque atmospheres SAR Look Angle Incidence Angle [i 0 ] Suborbital Track Radar Swath

5. Track 5 radar When a SAR system transmits a radio pulse, some energy is reflected back towards the SAR. This energy is what SAR measures. It is known as radar backscatter. SAR cannot measure energy reflected in other directions. SAR

6. Track 6 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 1.Topography: Affects local incidence angle –Does the radio wave bounce towards the receiver or away? Radar bounces towards receiver HIGH BACKSCATTER Radar bounces away from receiver LOW BACKSCATTER SAR

7. Track 7 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 1.Topography: Affects local incidence angle –Does the radio wave bounce towards the receiver or away? The volcano Kilauea, as observed by SIR-C SAR SAR look direction tilted towards tilted away

8. Track 8 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 2.Roughness: Affects direction of backscatter –Is the radio wave scattered in many directions, or is it specularly reflected? Some signal directed towards receiver HIGH BACKSCATTER No signal directed towards receiver LOW BACKSCATTER SAR roughsmooth

9. Track 9 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 2.Roughness: Affects direction of backscatter –Is the radio wave scattered in many directions, or is it specularly reflected? smooth rough Titan’s north polar lakes, as observed by Cassini SAR

10. Track 10 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 3.Composition: Affects dielectric constant (ε) –How well does the surface reflect radio waves? High dielectric constant, more energy reflected HIGH BACKSCATTER Low dielectric constant, little energy reflected LOW BACKSCATTER SAR saturated soildry soil

11. Track 11 radar SAR images provide a wealth of information about the surface being imaged, because radar backscatter depends on three different properties: 3.Composition: Affects dielectric constant (ε) –How well does the surface reflect radio waves? Fields near Melfort, Saskatchewan, as observed by CCRS Airborne SAR Wet Field (high ε) Dry Field (low ε)

12. Track 12 Mini-RF On June 18, 2009 the Lunar Reconnaissance Orbiter launched, carrying with it a miniature radar dubbed Mini-RF

13. Track 13 To date, we have acquired radar data over ~50% of the non-polar regions of the Moon, and nearly full coverage over the two poles First radar views of the lunar far side! Mini-RF

14. Track 14 north pole 70°N

15. Track 15 Part I: Mini-RF Observes the Moon

16. Track 16 gerasimovich d Mini-RF discovered an impact melt in the crater Gerasimovich D that is not observable in optical LROC WAC Mini-RF

17. Track 17 linne crater Linne is a classic, bowl-shaped, “simple” crater Low radar return suggests a halo of block-poor ejecta Disappears over time due to meteoroid bombardment Indicates a young crater High radar return indicates rough, blocky ejecta

18. Track 18 apollo landing sites Apollo sites provide “ground truth” for radar data Apollo 16Apollo 17

19. Track 19 apollo landing sites South Massif

20. Track 20 Centaur SSC Pre-Impact (October 9, 2009) LCROSS impact site Equipped with its own active source, Mini-RF can “see in the dark”! ex. LCROSS impact site

21. Track 21 Post-Impact (March 22, 2010) LCROSS impact site

22. Track 22 Part II: The Search for Ice

23. Track 23 The Moon’s axis of rotation is nearly perpendicular to the Sun, so there are regions near the poles where the Sun never shines These “permanently shadowed regions” are very cold. When comets hit the moon, ice can migrate to these cold craters, possibly collecting there Image of South Pole from Kaguya spacecraft ice on the moon?

24. Track 24 Ice has unique radar properties In weakly absorbing media with scattering centers (like water ice) there will be constructive interference between radar signals that follow the same path in opposite directions. These signals are forward scattered, which preserves the original sense of polarization, leading to large “same-sense” (SC) returns, and high circular polarization ratios (CPR). “rock” “void” Adapted from Campbell (2002) plane wavefront High SC signal CPR = SC/OC > 1 search for ice

25. Track 25 Ice has unique radar properties In weakly absorbing media with scattering centers (like water ice), there will be constructive interference between radar signals that follow the same path in opposite directions. These signals are forward scattered, which preserves the original sense of polarization, leading to large “same-sense” (SC) returns, and high circular polarization ratios (CPR). “rock” “void” plane wavefront High SC signal CPR = SC/OC > 1 Example: High radar return from the north pole of Mercury (Harmon et al. 2001) search for ice

26. Track 26 On October 9, 2009, the LCROSS spacecraft impacted Cabeus crater, located near the south pole of the Moon Early reports from LCROSS indicate the presence of water in Cabeus crater Cabeus LCROSS

27. Track 27 Chandrayaan-1LRO = approximate location of LCROSS impactor LCROSS Low radar return indicates that there is no near- surface, thick deposits of ice in Cabeus crater

28. Track 28 ice in north pole? BUT there are many “anomalous” craters near the north pole which are good candidates for ice ex. “Normal” craters like Main L have high CPR inside and outside the crater, indicative of a rough, blocky ejecta blanket

29. Track 29 ice in north pole? BUT there are many “anomalous” craters near the north pole which are good candidates for ice ex. “Anomalous” craters like this one in Rozhdestvensky have high CPR (>1) inside the crater, and low CPR outside the crater

30. Track 30 north pole 78°N

31. Track 31 conclusions Radar data compliments data obtained at optical wavelengths, yielding information about surface roughness, topography, and composition In particular, ice has unusual properties that can be observed with radar The Mini-RF instrument on LRO has found no evidence for large ice deposits at the LCROSS impact site, but has identified some promising candidates in the north polar regions

32. Track 32 PI Ben Bussey Mini-RF Science Team LRO Project NASA