Mini-RF: Imaging Radars for Exploring the Lunar Poles
Ben Bussey, Paul Spudis, Keith Raney, Helene Winters JHU/APL Stu Nozette, Chris Lichtenberg, Bill Marinelli NAWC
1 Mini-RF Organization, Science and Resource Evaluation Objectives
• Mini-RF is a suite of radar instruments funded by NASA (SOMD & ESMD) and DoD.
• Search for areas near the lunar poles that have the anomalous radar reflectivity signatures (high radar albedo and Circular Polarization Ratios) that differentiate volumetric water-ice deposits from more typical lunar surfaces • Map the morphology of permanently dark regions near the poles
2 Search for Ice
• The case for water-ice can be resolved only if robust and repeatable data of the lunar polar regions support that conclusion. This rigorous standard can be met only by a dedicated polar-orbiting radar.
• Mini-RF will use a unique hybrid polarity architecture to look for ice deposits • Transmit circular polarization (e.g. right-circular polarization RCP) • Receive coherent orthogonal polarizations • Derive Stokes parameters of the received signal • Use Stokes parameters to reconstruct and investigate the nature of the backscatter field. Distinguish between surface (roughness) and volume (ice) scattering
3 Top-level Radar Overview
Parameter Chandrayaan-1 LRO • Frequency S-band S-band and X-band • Polarization Tx RCP Rx H & V
• Scatterometry S-band (none) • Imager Regional maps Site-specific selections • Resolution (m/pixel) 75 75, 7.5 azimuth x 15 range • Looks 16 16 or 8 • Swath (km) 8 6 or 4 • Altitude (km) 100 50 • Incidence 33° 45° • Topography No Yes
4 Mini-RF on Chandrayaan-1 Operational Strategy
5 C-1C-1 SARSAR MappingMapping
~ 305 km •• Mosaic Mosaic assembledassembled fromfrom aa sequencesequence ofof ~338~338 orbitorbit stripsstrips
•• Alternating Alternating longlong andand shortshort stripsstrips
•• Swath Swath widthwidth 88 kmkm
•• Regional Regional mappingmapping polewardpoleward ofof 80°80° ~ 5.3 km / orbit •• Near-range Near-range minimumminimum isis setset byby 33°33° incidence incidence && altitudealtitude =>=> near-polarnear-polar imageimage gapgap
6 C-1C-1 OptimalOptimal OrbitsOrbits
TwiceTwice aa monthmonth Chandrayaan-1Chandrayaan-1 hashas aa 91°91° orbit orbit
50% of these will be in Orbit track at 50% of these will be in 1o offset ( thethe correctcorrect looklook inclination geometrygeometry
CanCan collectcollect datadata overover keykey areasareas inin thethe nominalnominal SARSAR gapgap
7 C-1C-1 ScatterometryScatterometry
•• Fill Fill inin polarpolar gap:gap: 85°-90°-85°85°-90°-85°
•• Swath Swath Width:Width: 1010 kmkm
•• Instrument Instrument operatedoperated inin nadirnadir directiondirection
•• Full Full polarpolar mosaicmosaic acquiredacquired overover 1414 daysdays
8 Lunar (Polar) Mapping Chandrayaan-1 data products
• Initial products – Geolocated strips, complex multi-look SAR data (35° incidence, H, V + cross product ) – Along-track scatterometer profiles (0° incidence, >85° latitude) • Intermediate products – SAR image mosaics >80° latitude, both right and left looking – Stokes parameter maps • Derived same-sense, opposite-sense polarization, albedo maps • Left-side and right-side looking – Scatterometry mosaics (four per pole, >85° latitude) • Fill in near-pole mean reflectivity data • Lower-resolution, average reflectivity, vertical incidence • Final products – Maps to indicate size and location of likely water-ice deposits – Maps of areas having anomalous reflectivity – All Mini-RF data archived to the NASA PDS. 9 Mini-RF on LRO
• Communications Experiment – Testing use of Mini-RF hardware for comms • Multiple SAR Modes – S & X bands – Baseline & zoom resolutions • Topography Generation – Interferometry & SAR stereo techniques
10 Data Value
• Resource Characterization – Multiple bands increases robustness of confidence in ice detection – Zoom mode provides details on the extent of deposits • Outpost Site Safety – Map surface roughness at 12 cm and 4 cm scales – Map the floor of permanently-shadowed regions
11 Mini-RF on LRO Operational Strategy
12 LROLRO Mini-RFMini-RF CoverageCoverage
•• Several Several individual individual strips strips ratherrather than than large large area area mappingmapping
•• Targeted Targeted Observations Observations
•• Demonstrate Demonstrate modes modes
•• Overlapping Overlapping coverage coverage for for interferometryinterferometry and and stereo stereo
13 Possible Extended Mission Options
• By the end of the nominal 12-month LRO mission the following data should be available – Regional S band SAR maps from Mini-RF on Chandrayaan-1 – 20 targeted SAR strips from Mini-RF on LRO – Higher-resolution neutron data from LEND on LRO
• Mini-RF on LRO would use observation opportunities from an extended mission to acquire more data – Currently defined by supplemental science goals – Also wish to acquire additional communications experiment data.
14 Supplemental Science
ITEM TASK
SUP_RF_011 GOAL: Verification—RF imagery over “suspected” sites
SUP_RF_012 GOAL: Exploration—RF imagery over any lunar region at Team discretion SUP_RF_013 GOAL: Near-polar imagery—RF imagery as close as possible to N or S pole SUP_RF_014 GOAL: Topography—InSAR mode over likely landing sites
SUP_RF_015 GOAL: Calibration reference site—e.g., same incidence as Arecibo data SUP_RF_016 GOAL: Bistatic (s/c)—Co-orbiting w/ Chandrayaan-1, “receive only”
SUP_RF_017 GOAL: Bistatic (Earth)—Transmit to Moon, Receive on Earth (~Clementine)
15 Bistatic Observations
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