Download - Maria's Poster Presentation
Radar Properties and Block Abundance of Impact Craters on the Moon
Maria Arias de Saavedra BenitezDuke University
LPI Visiting Summer Undergraduate Student
Advisors: P.D. Spudis and S.M. Baloga
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
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
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
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)
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
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
CPR Values:Results for Gardner crater
All Floor
Wall Exterior
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
Gardner Crater Rock Counting
Block abundance in Gardner
Pixel Height: 0.88m; Pixel Width: 0.81m
Data Processing (ongoing)
• Cumulative rock count plotted as a function of diameter• Data trimmed where rollover due to resolution occurs
So far, identified 3 classes of rock distributions (post-impact processes?)
Departure from power law
Ongoing Research
• Modeling fits for extrapolation to smaller rock sizes (wavelength-scale)
• Correlation of decimeter-scale surface roughness with CPR values
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