demonstrating scientific applications of gnss reflected ... · demonstrating scientific...

Space Reflecto 2011, Calais, France, 27-28 Oct 2011 1/40

Demonstrating Scientific ApplicationsDemonstrating Scientific Applications

of GNSS Reflected Signalsof GNSS Reflected Signals

from Spacefrom Space

M. M. MartMartíínn--NeiraNeira

European Space AgencyEuropean Space Agency ESTEC ESTEC

(The Netherlands)(The Netherlands)


• 1990 – Consultative Meeting on Imaging Altimeter Requirements and Techniques, Mullard Space Science Laboratory, UK

Mesoscale Ocean Problem Formulated:

8 RA’s

L-BAND ACTIVE REFLECTOMETRY: HISTORICAL REVIEW 1/9

7 days - 50 km

Radar Altimeter

7 days - 400 km

56 days - 50 km


• 1991 – First ESA’s Radar Altimeter launched (ERS-1)

• 1992 – TOPEX-POSEIDON launch

• 1993 – GPS and GLONASS declared operational

8 RA’s


7 days - 50 km

(mesoscale ocean)

GPSGLONASS

RA

7 days - 400 km

56 days - 50 km


• 1993 – PARIS solution proposed (ESA Patent 321)

- Published in ESA Journal Vol.17

1 PARIS

GPS GLONASS

8 RA’s


7 days, 50 km 7 days, 50 km


• Ocean altimetry issues with PARIS:

Poor altimetry resolution (due to limited bandwidth)

dh=64 cm @ 5.8 km

(ERS-1, TOPEX-Poseidon: 5 cm )

Ionospheric delay (C/A at L1; P at L1 and L2)

No bi-static model for ocean available

Strength of reflected signals



• 1994:

A french Alpha-Jet fighter aircraft locks onto a GPS reflected signal over the Atlantic Ocean


GPS



• 1994: First GPS Reflected Signal Measured from Space

Shuttle SIR-C/X-SAR

S.T. Lowe (JPL)



• Serendipitous recording of a GPS reflected signal using the SIR-C/X-SAR instrument on-board the Shuttle

(published in 1997)

L-band antenna: 12 x 2.7 m2

S.T. Lowe (JPL)



• UK-DMC: First Pioneering GNSS-R Experiment

from Space

ocea

n

ice

land

• 2003



[Nature, January 2005]

• 26-Dec-2004: Indian Ocean Tsunami


PARIS Concept

1. PARIS: Passive Reflectometry and Interferometry System

2. Wide Swath, ~1000Km3. Very high spatial-temporal sampling,

~12-16 tracks4. Suited to mesoscale altimetry


Constellations:

• GPS (US)

• GLONASS (Russia)

• GALILEO (EU)

• QZSS (Japan)

• COMPASS (China)

• INSS (India)

GNSS SYSTEMS

Modulation:

• CDMA

• FDMA

Frequency:

• Multi L-band

• e.g. L1/L2/L5 GPS

• 20-90 MHz Power:

• 3-6 dB higher than initial GPS

Satellites / Constellation: 33

• 30 in Medium Earth Orbit + 3 overlay in Geostationary Orbit

Total Satellites > 150 satellites in 2020

Coverage: global


Iso-delay Lines

L-BAND ACTIVE REFLECTOMETRY: PRINCIPLES 1/8

Tx at zenith

Tx at arbitrary elevation


Iso-Doppler Lines




N.J. Willis Bi-static Radar

Iso-power Lines (ovals of Cassini)

Tx Rx

TxRx

Tx Rx

Tx Rx


Glistening Zone


S.T. Lowe (JPL)



Height Error

• Fairly constant over the swath

• Example: for incidence below 35

only 22% variation



Height Error

Interferometer case:

dh = D

d

D across track distance

d

roll angle error

Surface Water OceanTopography Mission (SWOT)



Height Error

100 300 700200 500400 600D(km)Across Track Distance

Height Error

30

20

10

40

50dh (cm)

Interf

eromete

r –7.5

m –

B=10m

PARIS



Height Precision

• PARIS altimetry resolution estimated in 1993:

dh=64 cm @ dx=5.8 km

• Resolution over 100 km:

dh15 cm @ dx=100 km

• Reduction factor due to higher power and new codes: 2

dh7.5 cm @ dx=100 km


PARIS IoD OBJECTIVE

ToTo exploreexplore the the useuse of GNSS of GNSS reflectedreflected signalssignals forfor scientificscientific applicationsapplications::

-- NumberNumber of GNSS of GNSS satellitessatellites willwill bebe aboveabove 150150 and and willwill stay stay forfor decadesdecades::

GPS (US), GLONASS (Russia), GALILEO (EU), COMPASS (China), GPS (US), GLONASS (Russia), GALILEO (EU), COMPASS (China),

QZSS (QZSS (JapanJapan), INSS (India)), INSS (India)

-- Focus of PARIS Focus of PARIS IoDIoD is is mesoscalemesoscale ocean altimetryocean altimetry (most stringent application foreseen)(most stringent application foreseen)

-- The demonstration of The demonstration of mesoscalemesoscale ocean altimetry could lead into a ocean altimetry could lead into a followfollow--on missionon mission


Mission Summary


PARIS IoD Key Features

Based on long ESA experience on GNSS reflectometry

High gain beams for direct signals (D)

High gain beams for reflected signals (R)

Observables obtained by cross-correlation (DxR)

Implicit use of full GNSS bandwidth (3x40 MHz)

Precise estimation of ionospheric delay

Precise on-board amplitude calibration

Precise on-board delay calibration

L1L5 L2

40 MHz 40 MHz 40 MHz


PARIS IoD Capabilities

-- 4 4 simultaneoussimultaneous specular specular pointspoints

-- GPS and/or GALILEOGPS and/or GALILEO

-- Dual frequency (L1/E1 + L5/E5)Dual frequency (L1/E1 + L5/E5)

-- RHCP UP RHCP UP BeamsteeringBeamsteering

-- LHCP DOWN LHCP DOWN BeamsteeringBeamsteering

-- Single and MultiSingle and Multi--Doppler MappingDoppler Mapping

-- Flexible steering:Flexible steering:

-- 00--Doppler lineDoppler line

-- backscatteringbackscattering

-- point target detection steeringpoint target detection steering


GNSS Signals Portfolio

GPS L1 Components Modulation

C/A code (civil) BPSK(1)

P(Y) code (encrypted) BPSK(10)

M code (encrypted) BOC(10,5)

L1C code (civil) BOC(1,1)*, planned to TMBOC


L2C code (civil) BPSK(1)*

P(Y) code (encrypted) BPSK(10)

M code (encrypted) BOC(10,5)


L5C code (civil) BPSK(10)

Galileo E1 Comp Modulation

E1-a (PRS) BOCcos(15,2.5)

E1-b/c (OS/CS/SOL) BOC(1,1)* (recently changed to CBOC)


E5 (OS) AltBOC(15,10)


E6-a (PRS) BOCcos(10,5)

E6-b/c (CS) BPSK(5)

* TBC


cT

dt

cT

dt

Conventional Processing

Interferometric Processing




-5 -4 -3 -2 -1 0 1 2 3 4 50

1

2

3

4

5

6x 10-16 Normalized Cross-Correlation Power Waveform

Am

plitu

de [A

.U.]

Delay [Chips]

C/A codeGPS L1

L1 interferometricC/A


Galileo E1 Composite example

Reflected waveform example for Galileo E1 composite signal

-5 -4 -3 -2 -1 0 1 2 3 4 50.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8x 10-16 Normalized Cross-Correlation Power Waveform

Am

plitu

de [A

.U.]

Delay [Chips]

Galileo E1


Interferometric Processing Proof of Concept: Bridge Experiment

Blue:

Using a clean

replica of C/A code

Green:

Interferometric

Processing

10-fold improvement demonstratedfrom a bridge in quasi-specular

conditions


Interferometric Processing Proof of Concept: Aircraft Experiment

- Interferometric waveform to 6 GPS satellites shown below obtained using low gain antennas from

an aircraft flying at 500 m over the Baltic Sea with rough surface conditions

- Next step: higher altitude flight (3000 m) with directive antennas to estimate range precision


DELAY SELF-CALIBRATION TECHNIQUE:SLOW ANTENNA-RECEIVER SWAPPING


INSTRUMENT ARCHITECTURE

General block diagram of the PARIS altimeter

Up-looking beam

Down-looking beam

Double phased array

BPF

BPF

LO

LO

Master Clock

NCO

A/D

A/D

A/D

A/D

ts /2

ts /2

GNSS receiver

Computer

fs ts

fs /2ts /2

NCOfs /2

ts /2

ts /2

ts /2

I

Q

I

Q

Tc

Tc

T/2

T/2

T/2

T/2

Tc

Tc

T/2

T/2

T/2

T/2


IONOSPHERIC CORRECTION (1/2)

-- One of the One of the mainmain goalsgoals of of thisthis demonstratordemonstrator isis toto show show thatthat the the largelarge ionosphericionospheric delaydelay at at LL--bandband can can bebe correctedcorrected accuratelyaccurately fromfrom orbitorbit toto keepkeep the the requiredrequired altimetricaltimetric performanceperformance

P

G2

O

s2

Ionosphere

i i

G1

s1


IONOSPHERIC CORRECTION (2/2)

0.000

2.000

4.000

6.000

8.000

10.000

12.000

-8000.0 -6000.0 -4000.0 -2000.0 0.0 2000.0 4000.0 6000.0

-10

-8

-6

-4

-2

0

2

4

6

-8000.0 -6000.0 -4000.0 -2000.0 0.0 2000.0 4000.0 6000.0

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

-8000.0 -6000.0 -4000.0 -2000.0 0.0 2000.0 4000.0 6000.0

Vertical Delay (m)

Mesoscale Delay (m)

Residual Delay (m)

200 km averaging of mesoscale delay applied 0.15 m

+0.15 m

+6 m

10 m

+12 m

0 m

Derived from RA-2 real data


PARIS IoD Error Budget

ParameterIOD Height Accuracy on 100Km, G=20dBi, H=800Km

Instrument Noise and Speckle 12.5 cm

Ionosphere Averaging Noise 9.5 cm (2 frequencies, N=3)

Ionosphere Residual 5 cm

Troposphere (Wet and Dry) 5 cm

EM Bias 2 cm

Skewness Bias 1 cm

Orbit / Geometry 5 cm

Instrument error residuals 2 cm

Total RMS Height Accuracy 18 cm at Edge of Swath


POSSIBLE STOWED CONFIGURATION (using the TET platform)

Antenna hold-down and release mechanism

Payload: 50 Kg, 100 W


POSSIBLE DEPLOYED CONFIGURATION (using the TET platform)

Payload Electronics

PARIS Double-phased Array

Deployment mechanisms and signal harness

TET Platform


POSSIBLE LAUNCH ARRANGEMENT

Main passenger

PARIS IoD


PARIS IoD CALENDAR


CONCLUSIONS

Brief historical review of L-band Active Reflectometry

Unique capability to capture tsunami waves

A few basic principles

Strengths of GNSS-R

Potential applications

ESA’s PARIS In-Orbit Demonstration Mission

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