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
Polarization
S-band
S-band and X-band
Tx RCP
Rx H & V
•
Scatterometry
S-band
•
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
(none)
4
Mini-RF on Chandrayaan-1
Operational Strategy
5
C-1 SAR Mapping
~ 305 km
~ 5.3 km / orbit
••
Mosaic
Mosaic assembled
assembled from
from aa
sequence
sequence of
of ~338
~338 orbit
orbit strips
strips
••
Alternating
Alternating long
long and
and short
short
strips
strips
••
Swath
Swath width
width 88 km
km
••
Regional
Regional mapping
mapping poleward
poleward
of
of 80°
80°
••
Near-range
Near-range minimum
minimum is
is set
set
by
by 33°
33° incidence
incidence &
& altitude
altitude
=>
=> near-polar
near-polar image
image gap
gap
6
C-1 Optimal Orbits
Twice a month
Chandrayaan-1 has a
91° orbit
Orbit track at
1o offset
inclination
(
50% of these will be in
the correct look
geometry
Can collect data over
key areas in the nominal
SAR gap
7
C-1 Scatterometry
• Fill in polar gap: 85°-90°-85°
• Swath Width: 10 km
• Instrument operated in nadir
direction
• Full polar mosaic acquired
over 14 days
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
LRO
LROMini-RF
Mini-RF
Coverage
Coverage
•• Several
Severalindividual
individualstrips
strips
rather
ratherthan
thanlarge
largearea
area
mapping
mapping
•• Targeted
TargetedObservations
Observations
•• Demonstrate
Demonstratemodes
modes
•• Overlapping
Overlappingcoverage
coveragefor
for
interferometry
interferometryand
andstereo
stereo
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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.
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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
16