Mars Radar Sounders
LA RIPRESA DELLE MISSIONI
VERSO MARTE
Mars Global Surveyor
Mars Odissey
USA
USA
Mars
Pathfinder
USA
Deep Space 1
Nozomi
JPN
USA
Mars Observer
USA
Mars 96
Russia
Phobos 1 & 2
Mars Climate Mars Polar
Orbiter USA Lander, USA
URSS
1988
1992
1996
1998
1999
2001
Strategia di ricerca scientifica
Ricerca dell’ acqua
A
Vita
C
Q
Clima
U
A
Quando
Dove
Forma
Quantità
Geologia
Preparazione per l’
esplorazione umana
Mars Radar Sounders
Mars Radar Sounders
What is SHARAD?
SHARAD is a radar sounder provided by ASI to NASA as a facility
instrument, payload of the MRO mission
Science Objectives
The primary objective of the SHARAD experiment is to map, in
selected locales, dielectric interfaces to a kilometer in depth in
the martian subsurface and to interpret these results in terms of
the occurrence and distribution of expected materials, including
competent rock, regolith, water and ice.
 Map the thickness, extent and continuity of the layers within the
polar deposits.
 Map the thickness, extent and continuity of sedimentary layers.
 Map the distribution of shallow buried channels.
 Identify regions on Mars for follow-up surface-based water/ice
exploration.
Mars Radar Sounders
U.S. Programma di esplorazione di Marte
Mars Radar Sounders
MRO Strumenti della missione
Strumenti scientifici
HiRISE
CRISM
MCS
(High Resolution Imaging Science Experiment) (20m/pixel)
(Compact Reconnaissance Imaging Spectrometer for Mars) (0.4-4)
(Mars Climate Sounder) (analisi atmosfera, profilo acqua, sabbia, CO2,
temperatura)
MARCI
(MArs Color Imager) (analisi atmosfera, nubi, ozono, albedo etc. 0.28-0.8)
CTX
(ConTeXt imager) (6m/pixel)
SHARAD (SHAllow (subsurface) RADar). L’ italia è responsabile sia dello
studio che della implementazione.
Engineering Payload
Electra UHF communication and navigation package
Optical navigation camera experiment
Ka band telecommunication experiment
Mars Radar Sounders
Caratteristiche dello S/C
Launch mass: 2180 kg
Size: 14 m solar array tip to tip and 7
m high
Array power: 2 kW in Mars orbit
Maximum data rate: 5.6 Mb/s
3 m HGA and 100W TWTA
Rolls to +/-30 deg.
160 Gbit solid state recorder
Mars Radar Sounders
MRO orbiter
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MRO Orbiter
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Antenna di MARSIS e SHARAD
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MRO Orbiter prima del lancio
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MRO Lanciatore
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MRO Sequenza lancio
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Apertura dei pannelli solari dopo l’ uscita dall’
atmosfera terrestre
Mars Radar Sounders
MRO Traiettoria di crociera interplanetaria
Mars Radar Sounders
MOLA Mappa di Marte
Campo magnetico di Marte
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Temperatura media annuale superficiale
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IONOSPERA: frequenza di plasma
Mars Radar Sounders
Immagini da Spirit e Opportunity
Opportunity 2005
Spirit 2005
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Mars Radar Sounders
Mars Radar Sounders
MARSIS
Antenna
Beam
r
2H/c

h
Mars Crust
Surface Subsurface
Echo
Echo
A
B&C
2z/c
A
C
z
B
Water Reservoir
time
Mars Radar Sounders
I parametri di sistema
Bande di frequenza
1,3-2,3 MHz: 2,5-3,5 MHz; 3,5-4,5 MHz; 4,5-5,5 MHz
Risoluzione verticale (εr=5)
~ 70 m (Banda=1 MHz) [150 m nello spazio libero]
Profondità di penetrazione
Da ~ 0,5 Km a ~5 Km
Risoluzione verticale
5-9 Km(along track) x 15-30 Km (across tack)
Mars Radar Sounders
Le tecniche di riduzione del clutter di superficie
Doppler Beam Sharpening: Consiste nel ridurre l’ampiezza del fascio d’antenna
sfruttando il moto del satellite per sintetizzare un’antenna di dimensione maggiore di
quella reale. In tal modo si riduce l’ampiezza del footprint nella direzione del moto del
satellite (along track) con diminuzione degli effetti di riflessione off-nadir.
Dual Antenna: Aggiunta di una seconda antenna con un nullo nel diagramma di
radiazione in direzione nadir. Ciò consente di valutare le eco off-nadir, che possono
essere sottratte da quelle dell’antenna primaria.
Dual Frequency Processing: La riflessione superficiale non dipende dalla frequenza,
cosa che invece avviene per le riflessioni subsuperficiali. L’utilizzazione di due
frequenze e l’elaborazione delle eco relative consente la discriminazione desiderata.
Mars Radar Sounders
System Parameters (from the SHARAD SFRD)
 Centre Frequency:
20 MHz
 Pulse Bandwidth:
10 MHz
 Radiated Peak Power:
10 W
 Pulse Length:
85 us
 Antenna Efficiency:
> 10%
 Pulse Repetition Frequency: 700 Hz, 670Hz, 775 Hz
(350, 335, 387.6 Hz)
alternate PRF added to cope with orbital extremes during extended phase
(including topography margin)
 Receive window:
 Receiver gain
 A/D Resolution:
 Downloaded sample bits
 A/D frequency:
 Maximum Data Rate:
135 us
80 dB
8 bits
8 (default), 6, 4
26.67 MHz
20.16Mbit/s (@ 700 Hz, no pre-
summing)
 On-board pre-summing range
1 to 32 samples
Mars Radar Sounders
DESCRIPTION OF OPERATING GEOMETRY
SHARAD is a nadir looking radar sounder with synthetic aperture capabilities
Mars Radar Sounders
Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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Radar sounder
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PRINCIPLES OF OPERATION OF A RADAR SOUNDER 2/3
 In the presence of a dielectric discontinuity in the subsurface, the radar
sounder will receive a second echo that is much weaker than the first surface
echo. How much weaker this second echo will be depends upon the crust
attenuation and the characteristics of the dielectric discontinuity.
 If D is the system detection dynamic range, the detection of this second echo
will be possible only if its power is no more than D dB less than the first
surface signal.
 If z is the depth of the interface and f is the frequency of the radar sounder,
the instrument will be able to detect this second echo if and only if
ss z, f  |dB s |dB  D
Necessary dynamic
Available dynamic
 The available detection dynamic could be affected by:
 Surface Clutter Echoes (coming from off nadir)
 Noise
 Sidelobes and other artifacts due to the compression of the strong surface echo in
presence of phase and amplitude errors
Mars Radar Sounders
2.3 Planning Tool General Criteria 1/2
SHARAD
Sun elevation
Ionosphere  fpm
Magnetic Field
Mars Surface
SurfaceClutter
Visible Zone  S/N>0
Not Visible Zone  S/N<0
Sub Surface Material
Mars Radar Sounders
HORIZONTAL RESOLUTION (ALONG-TRACK AND CROSS-TRACK)
ROUGH SURFACE
Limiting the synthetic length at the dimension of DPL in order to avoid
RCM problems and more complicated processing, the along-track
resolution will be bounded by the DPL dimension as a function of
frequency and S/C height.
CROSS TRACK RESOLUTION  DPLdiameter  2  2 R ;
ALONG TRACK RESOLUTION  RAZ 

4

 c 

  
2

B
c 

R
2
SPECULAR SURFACE
the synthetic length is limited by the first Fresnel circle diameter the Raz is a
function of S/C height and frequency,
Raz    R
8
The cross-track res. matches the Fresnel diameter
Fr  2 
R
2
Mars Radar Sounders
HORIZONTAL RESOLUTION
(ALONG-TRACK AND CROSS-TRACK) BOUNDARY CONDITIONS
Mars Radar Sounders
Radar sounder
Mars Radar Sounders
RANGE (DEPTH) RESOLUTION
weighed compressed chirp sidelobes
for four different weighting function
vs. time and depth of the possible synchronous interface echo
depth resolution
Vs. the real part of the crust dielectric constant
for different weighting function
Mars Radar Sounders
SHARAD ON BOARD PROCESSING
Mars Radar Sounders
OBSERVATION GEOMETRY
•MRO Orbit Characteristic
•periapsis altitude near 255 km;
•apoapsis altitude near 320 km;
•near-polar inclination of 92.6 degrees;
•approximate ground-track repeat cycle of 17 days
Mars Radar Sounders
Doppler phase evolution
VR
It is possible to denote the following
quantities with the following symbols:
R0:Slant range of the observed point
 H: Orbital altitude
 VR: Radial Velocity of the S/C
 VT: Tangential Velocity of the S/C
VT


The evolution of the distance in the
synthetic aperture time as a function
of the orbit position, including also
the surface slope θs, is given is given
by:
H
R0
P
1 Vt 2  t az
R (t az )  H  Vr  t az  VT  s  t az  
;
2
H
2

Ta
T
 t AZ  a
2
2
Ta 
LAZ
H

;
VT
2 RazVT
x0
Mars Radar Sounders
Doppler phase evolution
If monochromatic wave of frequency f and wavelength  is transmitted the
phase difference between transmitted and received waveform due to the two
way travel over range R is given by:
 (t A )  4
R(t A )

 (t Az )  0  2f At Az  2
 2V  2VT  s 
f A     R




2
2V
k d ( )  T
H
kd 2
t Az
2
Doppler Centroid
due to the radial velocity and the tangential velocity component due
to surface slope
Doppler Rate
describes the linear frequency modulation induced by the S/C
tangential motion
Variable with λ:
high fractional bandwidth should
be considered
Mars Radar Sounders
AZIMUTH PROCESSING FOR A LOW FREQUENCY WIDE BAND
RADAR: FOCUSED PROCESSING
Doppler rate compensation has to be done adaptively in the frequency
If it is done only on the carrier the resulting azimuth compressed pulse is the
following

k d ( f p ) 2 

1
Y ( f , )  exp  j 2  f A ( f p )   
    exp  j 2    a 2 
 C  2   C 1   j  S  2   S 1 
2
2





 TA

 a     TA  2  a  
 2

2  2   
 TA

 a      TA  2  a   ;
 2

1  2    
2a  2
f A ( f p  f )  k d ( f p ) 
kd ( f p  f )
  0.5  k d  f p  f 
Mars Radar Sounders
AZIMUTH PROCESSING FOR A LOW FREQUENCY WIDE BAND
RADAR: FOCUSED PROCESSING
The same result could have been obtained considering again the maximum
mismatching in the Doppler rate (as for Cook and Bernfeld chap 6)
fp  f
dk d
cH
BDTA 
2
2
kd
f
2 fR AZ
The doppler rate correction has to
be performed adaptively in the
frequency with a step of at least
1Mhz.
Mars Radar Sounders
What is the doppler spectrum received?
 PRF is very high→ high over-sampling of the received doppler spectrum
•
Datarate has to be optimized maintaining the SNR
 SHARAD antenna is a have a width beam-width
•
Doppler spectrum is not determined by the antenna!!
 For very “rough surfaces” there will be not negligible return at off nadir
 As more the surface is smooth as more rapidly the returns from the surface at
off-nadir angles will drop off

R
H
h
x
z
cTRX
2 R
cTRX
2
Mars Radar Sounders
SHARAD on Board and on Ground Processing:
The on board processing of SHARAD foresee the following steps
 Possible compensation of the linear phase term due to the radial velocity
and to the surface slope and tangential velocity; this compensation is
carried on only on the carrier frequency
 Doppler presumming of a certain number of echoes to optimize data
production rate and data volume
The on ground processing include the compensation of the quadratic
phase term.
 The latter compensation should take into account the high fractional band
of the signal therefore it should be executed in the frequency domain and
adaptively for each frequency in the band
 The more accurate reconstructed orbital parameter will allow to overcome
the uncertainties on the radial and doppler velocity
 Techniques to overcome the surface/subsurface slope uncertainties is
under study (doppler filter bank)
Mars Radar Sounders
PRESUMMING LIMITATION
•
Number of adjacent pulses that is possible to pre-sum will be
strongly limited by the operative environment and by the desired
performance of the radar.
Pre-summing setting will be a trade off among desired
performance and data production rate
•
•
Two possible causes for limitation in the pre-summing :
1.
Maximum residual phase shift tolerable at the edge of the synthetic
aperture if the compensation of the radial velocity and surface slope is
not performed (or if it is not correct)
→ Influenced by the surface slope
2.
Limit in the aliasing of the Doppler spectrum (due to off nadir clutter
power) imposed by the desired detection dynamic range
→ Influenced by the surface roughness
Mars Radar Sounders
SHARAD PRESUMMING:PHASE ERRORS LIMITATIONS 1/4
 what is the maximum number of pulses that is possible to pre-sum given by
the useful doppler band?
 Limiting the maximum phase shift in a pre-summing interval (k/PRF) to π/4
and considering that the maximum phase shift occurs at the edges of the
synthetic aperture:
<Ls>
maximun phase drift
is at the edge
<minimum phase drift>
zero phase drift curve
max (k )   ( N A / 2 PRF )   ( N A / 2 PRF  k / PRF )
kd
fA
2
k  2
(
kN

k
)
A
2
PRF
2 PRF
2
4 VR
4 VT  s
2 VT
2

k
k
(
kN

k
)
A
2
PRF 
PRF 
HPRF 
 2
point scatterer
Mars Radar Sounders
SHARAD PRESUMMING:PHASE ERRORS LIMITATIONS 2/4
•Max pre-sum as a function of the surface slope correction accuracy
obtainable in the on board processing
•0.175 rad≈ 10 deg 0.0175rad=1deg
•Vt=3410m/s, Vr=30m/sec,H=290km
•This limit is related to the accuracy in the knoledge of the MARS surface
slope and in the polinomial approximation
Mars Radar Sounders
SHARAD PRESUMMING:PHASE ERRORS LIMITATIONS 3/4
 what is the maximum number of pulses that is possible to pre-sum given the
high fractional bandwidth?
 As the on board compensation of the linear term is performed only on the
carrier frequency (due to the difficulties to realize an on board FFT ) The
residual phase shift in the signal bandwidth could be very high and could
strongly influence the maximum number of presummable pulses.
 The error as a function of the presuming rate and of the frequency error (ff0= 5Mhz) becomes:
4 VR
4 VT  s
2 VT
 f (k ) 
f  k 
f  k 
f  k ( N A  k )
2
PRF c
PRF c
HPRF c
2
Mars Radar Sounders
SHARAD PRESUMMING:PHASE ERRORS LIMITATIONS 4/4
•Max pre-sum as a function of the surface slope due to the wide fractional
bandwidth
•0.175 rad≈ 10 deg 0.0175rad=1deg Vt=3410m/s, Vr=30m/sec,H=290km
•This is an absolute limit resulting from the wide fractional band and the limitation
in the on board processing
Mars Radar Sounders
SHARAD PRESUMMING:CLUTTER LIMITATIONS
 Synthetic aperture processing requires additionally that aliasing in
the observed Doppler spectrum must be avoided (SAR makes an
intrinsic spatial sampling).
 Supposing an isotropic antenna pattern in the along track direction,
and considering the clutter formulation it is possible to determine
the off nadir observation angle  beyond which the off nadir surface
clutter returns are 30 dB or more lower than the nadir surface echo:
()/ (0)<-30 dB
 The Doppler bandwidth to be observed and thus sampled by the
system will then be the one enveloped by twice the calculated and
therefore to satisfy the Nyquist condition:
2V
PRF
 2 T sin 
k

 And thence
k
PRF 
4VT sin 
Mars Radar Sounders
SHARAD PRESUMMING:PHASE ERRORS LIMITATIONS 4/4
Max number of presumable as a function of the surface roughness (to be
evaluated on a scale of the order of the DPL) in the hypothesis on stationary
surface of the region interested by the receiving window
Mars Radar Sounders
SHARAD PRESUMMING:CONCLUSIONS
There are 3 factors that have to be considered in the maximum
pre-summing rate evaluation
1. A high tilt in the surface will increase the errors due to the wide
fractional band
2. If the surface tilt is low but the accuracy in the
knoledge/rapresentation of the slope is coarse the driving
factor in the limitation will be the residual phase errors
3. If the small scale roughness of the surface is high the return
doppler band will increase, consequently the equivalent PRF to
be utilized will increase and the usable pre-summing rate will
decrease
Mars Radar Sounders
Marsis primi dati scientifici
Dati Simulati
Mars Radar Sounders
SHARAD OPERATIONS
Mars Radar Sounders
Operations & Science Data Processing System
SHARAD operation center will be sited in Rome, Italy, under the
Team Leader Institution (INFOCOM responsibility).
 Facility off-campus will be rented for this purpose (as for MARSIS
operation center) Still TBD the availability of a university
structure
 SHARAD operation center will accomplish the following tasks and
will maintain all the related HW, SW and procedures
• SHARAD Planning
• SHARAD Commanding
• SHARAD Data Processing
– Instrument Monitoring
– Quick Look
– Science Processing
SHARAD SOPC reside at JPL and is be accessible remotely (SSH
Login)
 Although slowly
ASI provides the archiving facilities at its ASDC (under ASI
responsibility), Frascati, Italy, site.
 ASDC will accomplish the data archiving, and distribution (to the
PDS node and to the science team)
Mars Radar Sounders
Operations & Science Data Processing System
Sci Product Telemetry
Engineering Data (TBC)
Commanding
RAW Sci Data
Server
(RSDS)
Telemetry
Delivery
System (TDS)
S/C
Engineering
Data
Operation planning
SOPC (JPL)
Planning and
commanding Files
Data processing
DOM
Planning Files
JPL
SHARAD OPERATION CENTER: INFOCOM
Processed data
NAIF
Server
Science data distribution
and archive
SPK CK files
ASDC
PDS
Science data
products
SHARAD Team Members
Mars Radar Sounders
SHARAD OBSERVATION CONSTRAINTS
•SSR (solid state recorder) allocation
 34 GBit reserved to SHARAD
 It is managed cyclically (FIFO)
 In case of overflow data is truncated
•Downlink allocation
 Data down-linked for SHARAD is equivalent to 15% of the mission
downlink →Roughly from 7 to 15 Gbit per day
•Possible Electromagnetic incompatibility with the S/C
transmission in X-band
•SHARAD can operate when the S/C is pointed nadir (+-10
degree)
Mars Radar Sounders
Basic Assumption in SHARAD operation (1)
According to its system characteristics SHARAD is in principle able to
operate at any time in the orbit, independently of the sun illumination
conditions. Constraints may then be those arising from the overall
mission design
Polar Observations
 SHARAD Team wants some continuous observations over poles, and other
specific targets of particular scientific interest, in daylight
 SHARAD would get an allocation of ~200 (TBD) dedicate polar passes per
pole, ~400 (TBD) total during PSP
Remembering :
 that SHARAD is a nadir instrument
 that SHARAD does not require any pointing (in routine operation)
 that SHARAD can operate with other instrument off-nadir pointing (up to
10deg TBC)
=> SHARAD observation will be mostly in the nighttime therefore
NIO
=> Dayside Observation for SHARAD will be managed as IO.
Mars Radar Sounders
Basic Assumption in SHARAD operation (2)
The SHARAD team will develop and maintain a database of desired
targets of observation.
The SHARAD team will develop and maintain a Coverage Database
The operation of SHARAD will be mainly dedicated to use all the
available information about the MARS operative environment to set
properly the on board pre-processing parameters and optimize the data
production rate:
 MARSIS measurements, MOLA topography, other existing science datasets
and already-processed SHARAD data can be used to estimate dynamic
range, the off-nadir clutter power and the predicted performance of the
radar
 those information can be used to set properly on board processing
parameters
 The on board parameters setting will determine the SHARAD Data rate
 SHARAD data volume allocation and SSR partition will determine the
operative time of the instrument
Mars Radar Sounders
How the instrument data rate changes with the
presumming?
PRF NOMINAL
FM Measured Data Rate Mbps
Pre-summing
4 bit
6bits
8 bits
1
10.75
15.56
20.36
2
5.37
7.78
10.18
4
2.68
3.89
5.09
8
1.34
1.94
2.54
16
0.67
0.97
1.27
28
0.38
0.55
0.72
32
0.34
0.48
0.63
Mars Radar Sounders
SHARAD OBSERVATION PLANNING
During the mission SHARAD team will submit planning files in
the form of PTF (payload target files):
•SHARAD PTF Shall contain in particular
 Latitude –Areodetic center latitude for the observation
 Orbit Number and Orbit Alternatives (optional).
 Observation Duration
 Setup Duration –number of seconds by which loading of the
sequence precedes the start of actual data acquisition
 Orbital Data Table filename; Parameters Table filename ;
Sequence Filename (OST) filename.
•MRO JPL team will:
• Integrate all instrument PTF
• Ensure there are no conflicts
•MRO JPL team will delivered IPTF and convert IPTF into
binary ITL file and uplinks to MRO
Mars Radar Sounders
Uplink Process: OST PT ODT Files
•
ITL initiates SHARAD block and instrument file load SHARAD
nominally does not uplink commands
• During the regular instrument programming three files for
each active orbital pass are uploaded:
 the OST (Operational Sequence Table) file
•
The OST, shall contain SHARAD measurement modes programming for the active
portion of an orbit.
 the PT (Parameter Table) file
•
Parameters contained in the PT
– Configuration parameters & Calibration parameters
– Operating parameters among which:
– Topography polynomial coefficients
– Surface Slope polynomial coefficients
– Starting Latitude for each of the above coefficients.
 The ODT (Orbital Data Table) file.
•
The Orbital Data Table shall contain the following 32 bit floating point values:
– Latitude (or True Anomaly),Radius (Kilometres),Radius Rate (meter/sec),Tangential
Velocity (meters/sec)