Poster presentation for Karsh International Scholars Program at Duke University

1. Radar Properties and Block Abundance of
Impact Craters on the Moon
Maria Arias de Saavedra Benitez
Duke University
LPI Visiting Summer Undergraduate Student
Advisors: P.D. Spudis and S.M. Baloga

2. Project Goals
• Studying the features of a number of craters with an anomalous
radar signal identified by previous work, creating a detailed
database
• Contribute to our understanding of how block fields are created in
the Moon and how they evolve
• Determine how these craters differ from polar, permanently
shadowed craters with similar radar signal but which are
candidates for ice

3. Objectives
• Understand the mechanisms of diffuse backscatter in radar
images of lunar craters
• Determine the density of decimeter-scale (~10 cm) rocks in
relation to impact craters
• Determine how such rock densities correlate (or not) with Mini-
RF measurements of circular polarization ratio
• Use these results to distinguish high-CPR ice deposits from
blocky impact ejecta in radar images of the poles

4. Data Used
• LRO-MRF (S band λ=12.6 cm, 30 m/pixel, 48° incidence) for
measuring CPR
• The Lunar Reconnaissance Orbiter Narrow Angle Camera
images(0.5-1.6 m/pixel) for counting blocks

5. Mini-RF
Imaging Radar on Chandrayaan-1 and LRO
Mini-RF is a two frequency (S-
band (12.6 cm) and X-band
(4.5 cm) imaging radar with
hybrid polarity architecture
Map both polar regions at 30
m/pixel, 48° incidence
Transmit LCP, receive H and V
linear, coherently
Use Stokes parameters and
derived “daughter” products to
describe backscattered field
Map locations and extent of
anomalous radar reflectivity
Cross-correlate with other data
sets (topography, thermal,
neutron)

6. Circular Polarization Ratio (CPR)
Ratio of received power in both
right and left senses
Normal rocky planet surfaces =
polarization inversion (receive
opposite sense from that
transmitted)
“Same sense” received indicates
something unusual:
double- or even-multiple-
bounce reflections
Volume scattering from RF-
transparent material
High CPR (enhanced “same
sense” reception) is common
for fresh, rough (at wavelength
scale) targets and water ice

7. Radar Data Collection Procedure
• Identify and collect Mini-RF images from
Planetary Database System (PDS)
• Convert images to raw files via USGS “ISIS”
imaging software
• Analyze images with NIH “ImageJ”
• Record mean and σ for each distribution

8. CPR Values:
Results for Gardner crater
All Floor
Wall Exterior

9. Rock Count Data Collection Procedure
• LROC and NAC images obtained from Quickmap (LROC image
browser)
• Images orthographic map projected with ISIS
• Analyze with feature function of ArcGIS, taking long dimensions
of blocks and counting at least ~200 rocks per crater.
• Areas coincide with CPR areas as closely as possible

10. Gardner Crater Rock Counting

11. Block abundance in Gardner
Pixel Height: 0.88m; Pixel Width: 0.81m

12. Data Processing (ongoing)
• Cumulative rock count plotted as a function of diameter
• Data trimmed where rollover due to resolution occurs

13. So far, identified 3 classes
of rock distributions
(post-impact processes?)
Departure from power law

14. Ongoing Research
• Modeling fits for extrapolation to smaller rock
sizes (wavelength-scale)
• Correlation of decimeter-scale surface
roughness with CPR values

15. Future Results useful for:
• Understanding uneven processes of erosion
(high block abundance inside crater, low in the
exterior)
• Understanding radar properties of possible ice
deposits in permanently shadowed craters in the
poles