TU2.L09.1 - COMPACT POLARIMETRY AT THE MOON: THE MINI-RF RADARS

Compact Polarimetry at the Moon:
The Mini-RF Radars

R. Keith Raney1, Paul Spudis2, Ben Bussey1, J. Robert
Jensen1, Bill Marinelli3, Priscilla McKerracher1, Ron
Schulze1, Herman Sequeira1, and Helene Winters1
1JHU/APL 2LPI/TX 3NASA/Hdqs

IGARSS, Honolulu, HI
25 - 30 July 2010

Outline

Mini-RF Project Overview
Hybrid Polarimetric Architecture
Calibration
Calibration
Results
Results
Conclusions
Conclusions

R. K. Raney IGARSS 2010, Honolulu, HI

Calibration
Calibration
Results
Results
Conclusions
Conclusions


Top-Level Parameters of the Mini-RF radars
Chandrayaan-1
Chandrayaan-1 LRO
LRO
(2008 – 2009)
(2008 – 2009) (2009 -- ))
(2009

Polarizations
Polarizations Tx C; Rx L (H&V)
Tx C; Rx L (H&V) Tx C; Rx L (H&V)
Tx C; Rx L (H&V)

Resolution (m) //Looks
Resolution (m) Looks 150 //16
150 16 Baseline
Baseline 150 //16
150 16
Zoom
Zoom 15 x 30 //8
15 x 30 8
Wavelengths (cm)
Wavelengths (cm) 12.6
12.6 12.6, 4.2
12.6, 4.2

Modes
Modes Strip
Strip Strip, InSAR
Strip, InSAR

Altitude (km)
Altitude (km) 100
100 50
50

Inclination
Inclination ~ Polar
~ Polar ~ Polar
~ Polar

Mass (kg)
Mass (kg) 12
12 15
15

Mini-RF Radar on LRO
H H H
Antenna Interconnect Analog Receiver Digital Receiver
• Tx and Rx S/C Module • Digitize IF signals
• Down-convert
band signals • Perform BAQ
• Generate 90 deg. from RF to IF
• Transmit CP V V V • Generate digital I/Q
Phase shift on • Provide gain
• Receive V&H • CCSDS packetize
V&H Tx channels control
• Isolate transmit &
receive paths QDWS
Analog Exciter
• Filter RF
• Provide LOs & clocks • Timing & control
• Up-convert: S to C • Generate radar
waveforms
Bus
Electronics
Transmitter LO & Clock Timing Signals
(HK/IO)
• Amplify S/C band
signals Controls Telemetry

Control Processor (RAD 750)
• Digitize antenna temperatures
• Collect & report telemetry to bus electronics
• Accept commands from bus electronics
• Control & configure payload electronics
• Provide router interface from digital receiver to
bus electronics for radar data


Technology Demo (LRO): Microwave Power Module

Conventional
TWTA (40 W)

MPM (100 W)

MPM TWT


Mini-RF Radar on LRO During Integration and Test

Solar panel
array (folded)

Mini-RF antenna
(~ 1 m2 area)


Water-Ice – Relatively large CPR*

Mercury’s poles:
Mercury’s poles:
Arecibo S-band,
Arecibo S-band,
delay-Doppler
delay-Doppler
processing--
processing--
enhanced “same-
enhanced “same-
sense” (SC) circular
sense” (SC) circular
polarization, which
polarization, which
is usually the
is usually the
weaker return for
weaker return for
85 circular-polarization
circular-polarization
on transmission
on transmission
80
*COBE: Coherent
Opposition
Harmon et al., 2000
Backscatter Effect
From Ostro, 2000


Dominant Requirements on the Mini-RF Radars

Measure circular polarization ratio (CPR)
Measure circular polarization ratio (CPR)
•• Consequence: radar must transmit Circular Polarization
Consequence: radar must transmit Circular Polarization

Maximal science with minimal flight hardware
Maximal science with minimal flight hardware


Mini_RF Project Overview
Mini_RF Project Overview
Calibration
Calibration
Results
Results
Conclusions
Conclusions


Hierarchy of Polarimetric Imaging Radars

Radar Processing Result Nomenclature
No assumptions 4x4 scattering
matrix Full polarization
Orthogonal Tx pols
Coherent Dual Rx Reciprocity &
3x3 scattering Quadrature
symmetry
matrix polarization

Symmetry 3x3 pseudo-
One Tx Pol, assumptions scattering matrix
Compact
Coherent Dual Rx
No symmetry 2x2 covariance polarization
assumptions matrix

2 magnitudes 2 orthogonal Like-
& co-pol phase pol images & CPD
Two Tx pols
2 orthogonal
2 magnitudes Dual
Like-pol images
polarization
Like- and Cross-
Two Rx pols 2 magnitudes
pol images

One Magnitude Mono-
Real image
polarization polarization

Mini-RF: Compact Polarimetric Radars

Radar Processing Result Nomenclature
No assumptions 4x4 scattering
matrix Full polarization
Orthogonal Tx pols
Coherent Dual Rx Reciprocity &
3x3 scattering Quadrature
symmetry
matrix polarization

Symmetry 3x3 pseudo-
One Tx Pol, assumptions scattering matrix
Compact
Coherent Dual Rx
No symmetry 2x2 covariance polarization
assumptions matrix

2 magnitudes 2 orthogonal Like-
& co-pol phase pol images & CPD
Two Tx pols
2 orthogonal
2 magnitudes Dual
Like-pol images
polarization
Like- and Cross-
Two Rx pols 2 magnitudes
pol images

One Magnitude Mono-
Real image
polarization polarization

Hybrid-Polarity Radar Architecture*
Transmit circular; Receive orthogonal linears and relative phase
Covariance matrix => 4 Stokes
Covariance matrix => 4 Stokes
Transmitter &
90o
waveform parameters => independent of
parameters => independent of
polarization basis => optimize
polarization basis => optimize
radar hardware => Linear pol
radar hardware => Linear pol
Timing & control
V H
receiver => Hybrid Polarity
receiver => Hybrid Polarity
|H|2
S1
H H Rx channel
LNA L-0 L-1 S2
X
H HV*
S3
V V* S4
LNA V Rx channel L-0 L-1 |V|2
V H

Antenna
Part of the Radar Processing
Transmits Facility in the ground-based
circular operations center
polarization
V H

* U. S. Patent # 7,746,267

Stokes Parameters

Linear basis Circular basis Poincaré basis
S1 = < |EH|2 + |EV |2 > + N0 = < |ER|2 + |EL|2 > + N0 = S1
S2 = < |EH|2 – |EV|2 > = 2 Re < EREL* > = m S1 cos 2ψ cos 2χ
S3 = 2 Re < EHEV*> = 2 Im < EREL* > = m S1 sin 2ψ cos 2χ
S4 = – 2 Im < EHEV*> = – < |ER|2 – |EL|2 > = – m S1 sin 2χ
Comments
> Assumes that LCP is transmitted (or a close approximation there to)
> Note that the radar’s additive noise N0 is included in S1 (correctly), but not
in the other Stokes parameters (also correctly)
SNR = < |EH|2 + |EV |2 > / N0
> The child parameters may be found by taking advantage of the equality of the Stokes
parameters across all bases of observation of the received EM field

> The sign of S4 is negative, consistent with the back-scattering alignment (BSA) convention


Stokes Parameters are Independent
of Receive Polarization Basis

Stokes 1 Stokes 2
Stokes parameters
Stokes parameters
derived from
Log CC
derived from

Log CC
airborne SAR data
airborne SAR data
for circularly
for circularly
polarized
polarized
transmissions and
transmissions and Log CL Log CL

dual linear or dual
dual linear or dual
circular received
circular received Stokes 3 Stokes 4

polarizations are
polarizations are

Log CC
Log CC

essentially identical
essentially identical

Log CL Log CL


Stokes Child Parameters

Degree of polarization Comments
m = (S22 + S32 + S42)½ / S1
> Assumes that LCP is
Degree of depolarization mD = 1 – m transmitted (or a close
approximation there to)
Degree of circular polarization
mC = – S4 / mS1 = sin 2χ > Note that the degree of linear
polarization and degree of
Degree of linear polarization
circular polarization include
mL = (S22 + S32)½ / mS1 = cos 2χ
the degree of polarization m
Degree of ellipticity
> The sign of S4 depends on the
mE = tan χ
handedness of the transmitted
Circular polarization ratio circular polarization (and the
µC = (S1 – S4) / (S1 + S4) coordinate convention, BSA vs
FSA)
Linear polarization ratio
µL = (S1 – S2) / (S1 + S2) > Notice the minus sign on
the S4 terms (mC , CPR, & δ)
Relative phase δ = arctan (– S4 / S3 )

Relative Self Calibration

h
H | |2 |H|2
Tx Rx v P X HV*
V | |2 |V|2
Raw signal Image domain
(

domain (before
calibration)
Nadir-viewing

Method*: <[Nadir returns]> => opposite sense of CP;
Method*: <[Nadir returns]> => opposite sense of CP;
V/H magnitude imbalance; V-H phase difference =>
V/H magnitude imbalance; V-H phase difference =>
calibration coefficients Cδδand Cφ
calibration coefficients C and Cφ
If transmitted
1/Cδ
field is not near-
perfect circular h | |2 X |HC|2
polarization, H
P X Cφ HVC*
then external v V | |2 X |VC|2
resources are
Raw signal Image domain
needed domain (after
Cδ
calibration)
(GBT, ART)

CPR is Robust with Non-unity Transmit Axial Ratio

CPR = f(axial ratio, degree of polarization) Notes
> CPR evaluated under the
1.50
assumption of SC backscatter in
1.45
response to LC transmission, hence
1.40 - 45o ≤ χ ≤ 0
m’ = 0.8
1.35
m’ = 0.7
CPR

1.30 1fffffffff2χf
@ m. αsin ff
ffffffffffff
fffffffffff
m’ = 0.6 µC =
1.25 1 + m. αsin 2χ
m’ = 0.5
1.20
> Smaller signal-to-noise ratio
1.15
(larger NES0) has the same effect
1.10 as smaller degree of polarization
1 1.2 1.4 1.6 1.8 2 m:
Transm it Axial Ratio ~2.4
dB m’ = m/(1 + 1/SNR)
> α accounts for imperfect
dielectric and geometric properties
of the source backscatter, which
when evaluated from Mini-RF data
has a nominal value of about 0.19


Linne Crater seen in Total Power
(S1) and Circular Polarization
Ratio (CPR)
Radar
look
aspect


Crater Floor-Wall Image Characteristic

Direct path
(rim image)
Image
location of
floor-wall
backscatter
nge Rim
Floor-far-wall a ra
E xtr Far-side exterior
double bounce ~

Floor


CL-Pol Decomposition: m-δ color code

The decomposition colorization scheme is:
S1 = R2 + G2 + B2
R = [S1m (1 + sin δ)/2]1/2
G = [S1 (1 – m)]1/2
B = [S1m (1 - sin δ)/2]1/2

S1 first Stokes parameter (total power)
m degree of polarization
δ relative H/V phase (e.g., ellipticity)
R (Red) double bounce backscatter (e.g., dihedral, volume ice)
G (Green) randomly polarized (e.g., volume scattering)
B (Blue) odd bounce backscatter (e.g., Bragg scattering)


Radar
look
aspect

Example of m-delta Decomposition
Anomalous odd-bounce and even-bounce (or
COBE?) floor-wall signatures from the same crater


SC CPR

North polar mosaic
Rozhdestvensky
(177 kilometers in diameter) (S-band Zoom
mode) CPR
rendition
(Late June 2010)

Processing, Courtesy of
Catherine Neish, APL

SC
Interesting crater in
the floor of
Rozhdestvensky…


SC

Permanent
sun shadow

Calculate the CPR Not
histograms of permanent
shadowed vs non- sun shadow
shadowed
backscatter
SC background for reference


CPR Signature is Consistent
CPR Signature is Consistent
with Water-Ice Deposition
with Water-Ice Deposition
Inside the Crater
Inside the Crater Permanent
sun shadow

Not
permanent
sun shadow


Conclusions

The Mini-RF radars are the first polarimetric imagers
The Mini-RF radars are the first polarimetric imagers
outside of Earth orbit
outside of Earth orbit
Hybrid-Polarity (Tx Circular, Rx dual coherent linear
Hybrid-Polarity (Tx Circular, Rx dual coherent linear
polarizations) is an ideal compact polarimeter for lunar or
polarizations) is an ideal compact polarimeter for lunar or
planetary exploration: maximum science and minimal hdw
planetary exploration: maximum science and minimal hdw
In the lunar application, CPR interpretations are robust
In the lunar application, CPR interpretations are robust
in response to imperfect circular transmit polarization
in response to imperfect circular transmit polarization
Calibration techniques unique to and pioneered by the
Calibration techniques unique to and pioneered by the
Mini-RF radars have proven to be effective
Mini-RF radars have proven to be effective
Lunar imagery and interpreted products are as expected
Lunar imagery and interpreted products are as expected


TU2.L09.1 - COMPACT POLARIMETRY AT THE MOON: THE MINI-RF RADARS

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