Mars Radar Sounders LA RIPRESA DELLE MISSIONI VERSO MARTE 198820011999199819961992 Phobos 1 & 2 URSS...

Mars Radar Sounders LA RIPRESA DELLE MISSIONI VERSO MARTE

1988 20011999199819961992

Phobos 1 & 2

URSS

Mars Observer

USAMars 96

Russia

Mars Global Surveyor

USA

Mars Pathfinder

USA

Mars Climate Orbiter USA

Nozomi JPN

Mars Polar Lander, USA

Deep Space 1

USA

Mars Odissey

USA

Mars Radar Sounders Strategia di ricerca scientifica

Ricerca dell’ acqua

Geologia

Vita

Clima

Preparazione per l’ esplorazione umana

A

C

Q

U

A

QuandoDove

FormaQuantità

Mars Radar Sounders

Science ObjectivesThe 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.

SHARAD is a radar sounder provided by ASI to NASA as a facility instrument, payload of the MRO mission

What is SHARAD?

Mars Radar Sounders

U.S. Programma di esplorazione di Marte

Mars Radar Sounders

MRO Strumenti della missione

Strumenti scientificiHiRISE (High Resolution Imaging Science Experiment) (20m/pixel)

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) (0.4-4)

MCS (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 PayloadElectra 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 orbitMaximum data rate: 5.6 Mb/s3 m HGA and 100W TWTARolls to +/-30 deg.160 Gbit solid state recorder

Mars Radar Sounders

MRO orbiter

Mars Radar Sounders

MRO Orbiter

Mars Radar Sounders

Antenna di MARSIS e SHARAD

Mars Radar Sounders

MRO Orbiter prima del lancio

Mars Radar Sounders

MRO Lanciatore

Mars Radar Sounders

MRO Sequenza lancio

Mars Radar Sounders 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

Mars Radar Sounders Campo magnetico di Marte

Mars Radar Sounders

Temperatura media annuale superficiale

Mars Radar Sounders IONOSPERA: frequenza di plasma

Mars Radar Sounders

Immagini da Spirit e Opportunity

Opportunity 2005

Spirit 2005

Mars Radar Sounders

Mars Radar Sounders

Bande di frequenza

Risoluzione verticale (εr=5)

Profondità di penetrazione

Risoluzione verticale

1,3-2,3 MHz: 2,5-3,5 MHz; 3,5-4,5 MHz; 4,5-5,5 MHz

~ 70 m (Banda=1 MHz) [150 m nello spazio libero]

Da ~ 0,5 Km a ~5 Km

5-9 Km(along track) x 15-30 Km (across tack)

I parametri di sistema

Mars Radar Sounders

Le tecniche di riduzione del clutter di superficie

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.

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 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 MHzPulse Bandwidth: 10 MHzRadiated Peak Power: 10 WPulse Length: 85 usAntenna 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: 135 usReceiver gain 80 dBA/D Resolution: 8 bitsDownloaded sample bits 8 (default), 6, 4A/D frequency: 26.67 MHzMaximum Data Rate: 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

Zmax

H

Echoes dynamic rangeafter signal compression & SAR Processing

Surface Clutter

Echo from subsurface

PR range presentation time

PD range presentation time

time

time

time

Along Track

Cross Track

v

Height

Isorange Contour

Isodoppler Contour

Mars Radar Sounders

Radar sounder

Mars Radar Sounders

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

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

Dfz dBsdBss ||,

Necessary dynamicAvailable dynamic

Mars Radar Sounders

2.3 Planning Tool General Criteria 1/2

Ionosphere fpm

Sub Surface Material

Magnetic Field

Not Visible Zone S/N<0

Visible Zone S/N>0

Sun elevation SHARAD

Mars Surface

SurfaceClutter

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.

8RRaz

c

diameter B

cRDPLRESOLUTIONTRACKCROSS

2 ;22

24

R

RRESOLUTIONTRACKALONG AZ

SPECULAR SURFACE the synthetic length is limited by the first Fresnel circle diameter the Raz is a function of S/C height and frequency,

The cross-track res. matches the Fresnel diameter 2

R2Fr

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 resolutionVs. 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

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

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:

VR

H

VT

P

x0

R0

;2

1)(

22

H

tVtVtVHtR azt

azsTazraz

;222 TazT

AZa

aAZ

a

VR

H

V

LT

Tt

T

Mars Radar Sounders

Doppler phase evolution

20 2

22)( Azd

AzAAz tk

tft

sTRA

VVf

22

H

Vk T

d

22)(

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:

Doppler Centroiddue to the radial velocity and the tangential velocity component due to surface slope

Doppler Ratedescribes the linear frequency modulation induced by the S/C tangential motion

)(t

4)(t AA

R

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 frequencyIf it is done only on the carrier the resulting azimuth compressed pulse is the following

121222

2

12exp

2

)()(2exp),(

SSjCCj

fkffjfY apd

pA

;22

2

22

2

1

2

aa

aa

AA

AA

TT

TT

)(

)()(22

ffk

fkfff

pd

pdpAa

ffk pd 5.0

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)

22 2

f

ff

fR

cHTB

k

dk p

AZ

ADd

d

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

R

RXcT

2

2RXcT

z

x

h

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:

)(244

)(2

22

)/2/()2/()(

22

2

22

max

kkNV

HPRFk

V

PRFk

V

PRF

kkNPRF

kk

PRF

f

PRFkPRFNPRFNk

ATsTR

AdA

AA

<Ls>

point scatterer

zero phase drift curve

<minimum phase drift>

maximun phase drift

is at the edge

Mars Radar Sounders

•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


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 (f-f0= 5Mhz) becomes:

)(f2

f4

f 4

)(2

2kNk

c

V

HPRFk

c

V

PRFk

c

V

PRFk A

TsTRf

Mars Radar Sounders

•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:

And thence

sin2

2 TV

k

PRF

sin4 TV

PRFk

Mars Radar Sounders


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 SystemSHARAD 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

Science data distribution and archive

ASDC

PDS

Science dataproducts

Operation planning

Data processing

SHARAD OPERATION CENTER: INFOCOM

Processed data

Commanding

Telemetry Delivery

System (TDS)

RAW Sci Data Server(RSDS)

DOM

NAIFServer

S/C EngineeringData

Planning Files

SPK CK files

SOPC (JPL)

Sci Product TelemetryEngineering Data (TBC)

Planning and commanding Files

JPL

SHARAD Team Members

Mars Radar Sounders

SHARAD OBSERVATION CONSTRAINTS

•SSR (solid state recorder) allocation34 GBit reserved to SHARAD It is managed cyclically (FIFO) In case of overflow data is truncated

•Downlink allocationData 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 designPolar 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 DatabaseThe 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 particularLatitude –Areodetic center latitude for the observationOrbit Number and Orbit Alternatives (optional).Observation Duration Setup Duration –number of seconds by which loading of

the sequence precedes the start of actual data acquisitionOrbital 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)

Mars Radar Sounders LA RIPRESA DELLE MISSIONI VERSO MARTE 198820011999199819961992 Phobos 1 & 2 URSS...

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Transcript of Mars Radar Sounders LA RIPRESA DELLE MISSIONI VERSO MARTE 198820011999199819961992 Phobos 1 & 2 URSS...