PARIS In-Orbit Demonstrator

Transcription

1 1/52 PARIS In-Orbit Demonstrator Manuel Martín-Neira Neira,, Salvatore D Addio,, Christopher Buck (TEC-ETP) ETP) Acknowledgments: F. Coromina (TEC-ETP) ETP) N. Floury (TEC-EEP) EEP) J. Santiago Prowald (TEC-MCS) G. Toso (TEC-EEA) EEA) M. Rapisarda (TEC-ETN) ETN)

2 2/52 Mission Instrument Principle Instrument Design

3 Why PARIS IOD? 3/52 PARIS-IOD IOD will prove that ocean altimetry off the satellite ground track is feasible using reflected GPS/Galileo signals This will be of great value for, in particular, mesoscale ocean altimetry Requirement: 5 cm in 100 km

4 Secondary Objectives 4/52 Ionospheric Total Electron Content Ocean Scatterometry Significant Wave Height, Wind Speed, Currents Sea-Ice Ice freeboard measurements, ice age, ice extent Soil Moisture Biomass

5 What are the Constraints? 5/52 40 M M including launch and operation for 3 years

6 Proba Class Satellite 6/52

7 Launcher 7/52 PARIS-IOD IOD will be a piggyback passenger with another satellite Possible launchers: Rockot Vega Dnjepr PSLV Example: Rockot with SMOS and Proba-2

8 Piggyback on Rockot 8/52 The minimum diameter of the PARIS antenna required is 110 cm Need for a dedicated interface cone Vega similar scenario 110cm

9 System Concept - Rationale 9/52 Requirements Performance: Performance: Mesoscale Mesoscale Altimetry Altimetry Mass Mass Power Power Launcher Launcher Envelope Envelope Issues SNR SNR Height Height Precision Precision Ionospheric Ionospheric Delay Delay Height Height Accuracy Accuracy Instrument Instrument Delay Delay Calibration Calibration Height Height Accuracy Accuracy Instrument Instrument Ampl Ampl Calibration Calibration Height Height Accuracy Accuracy High High Gain Gain Down-Looking Down-Looking Antenna Antenna Multi-Frequency Multi-Frequency High High Gain Gain Up-Looking Up-Looking Antenna Antenna Switch Switch at at Antenna Antenna Elements Elements Radiometric Radiometric Techniques Techniques Solutions Civil Civil GNSS GNSS Signals Signals Interferometric Interferometric Processing Processing

10 System Concept - Summary 10/52 High gain beams for direct signals (D) High gain beams for reflected signals (R) Observables obtained by cross-correlation correlation (DxR( DxR) Implicit use of full GNSS bandwidth (3x40 MHz) Precise estimation of ionospheric delay Low noise ionospheric correction Precise on-board delay calibration Precise on-board amplitude calibration L5 L2 L1 40 MHz 40 MHz 40 MHz

11 Geometry 11/52 Geometry plays an important roll in the definition of critical parameters of the PARIS mission, such as: (a) Accuracy (b) Sampling and Coverage G P Ionosphere i i s O

12 Geometry: altimetric accuracy 12/52 a) Altimetric performance degrades with incidence angle b) Ionospheric delay and antenna losses increase with incidence angle (a) dh = dρ 2cosi (b) P G Antenna gain Ionosphere i i s dh i dρ The incidence angle i should be minimised. O

13 Geometry: sampling and coverage 13/52 c) The number of reflection points increases with incidence angle d) The coverage (swath) increases with incidence angle Number of reflection points swath P h p β ζ R i s i H G α γ R E g O The incidence angle i should be maximised.

14 Geometry: trade-off 14/ Fix incidence angle to guarantee altimetric accuracy 2.- Increase height to reach desired sampling and coverage 3.- Increase antenna size to maintain signal to noise ratio Number of reflection points P 2 h 2 swath P 1 G 1 i i h 1 p i s i G 2 α γ O

15 Ionospheric Correction: Facts 15/52 - At L-band,, the ionosphere is a major contributor to the propagation delay ρ = 2h cos i + I with 40.3 = TEC f I 2 - Multi-frequency observations allow to remove the ionospheric effect ρ1 = 2hcosi + ρ5 = 2hcosi + I f 2 1 I f 2 5 h 15 = ρ5 ρ cosi 2cosi However this is at the expense of a severe error amplification factor σ h 15 = σ ρ

16 Ionospheric Correction: Method 16/52 - Multi-frequency observations are taken y y = 1 f f h x - The ionospheric delays are retrieved with the following uncertainties 1 σ 78σ 2 f 1 x = 1. y σ x = 3. 2σ 2 y f5 1 - A regression is performed over N samples of ionospheric delay 1 σ 2 f x = σ y σ x = σ 2 y N f5 N -The smoothed ionospheric delay is used in the range equations, resulting in an improved error amplification factor σ h N 3.2 4N 2 2 = + + σ y σ h 1. 08σ y = (N=5 regression)

17 Ionospheric Correction: Example 1/2 17/52 - What matters in mesoscale ocean altimetry is the difference between the ionospheric delay at two specular points - Worst case is between nadir (i=0 ) ) and edge of swath (i=30 ) G 1 G 2 P Ionosphere i i s 1 s 2 O

18 Ionospheric Correction: Example 2/2 18/52 Vertical Delay (m) m Derived from RA-2 real data m Mesoscale Delay (m) m m Residual Delay (m) m km averaging of mesoscale delay applied m

19 Mission Summary Table 19/52

20 Payload Mass Budget 20/52 No of array elements Radiators + structure 62 LNAs Harness Mechanisms BFN (phase shifters) Processor + power conditioning X-band transmitter and antenna Total kg 3kg 6kg 3kg 2kg 6kg 3kg 44kg

21 Payload Power Budget 21/52 Item LNAs (62x0.4W) Signal Processor Solid-State State Mass Memory Instrument Control Unit (ASIC) Total Power 25W 12W 5W 4W 46W

22 Mission Budget 22/52 Payload (and pre-development): Platform: 17M 15M Ground Segment, Ops. (3 years): 5M Launch (as secondary passenger) 3M Total = 40M

23 Development Schedule 23/52 Framework preparation 1 year KO Critical breadboarding Phase A Phase B (EM model) Phase C/D Storage Launch Campaign Commissioning Phase Phase E 1-Nov years (from KO till Phase C/D) 6 months 1 year (+3 months) 3 years (+3 months) 6 months 3 months 6 months 2.5 years

24 24/52

25 25/52 Mission Instrument Principle Instrument Design

26 Interferometric Processing 26/52 UP CHAIN DOWN CHAIN BPF BPF DOCON fc up DOCON XC T c () dt 2 W 1 (τ) W 2 (τ) W 3 (τ) W N (τ) ( ) Wi τ N fc down Based on the cross-correlation correlation of the received direct and Earth-reflected reflected signals Pro: : Exploitation of the full TX Bandwidth and Power of GNSS Signals, Hardware Simplification, Flexibility Cons: : Signal-to to-noise Ratio Degradation (minor)

27 Interferometric Processing 27/52 SNR at the output of the correlator SNR = SNRo 1+ SNR SNR D U SNRo 1 SNR U If SNR U >> 1 then SNR=SNR o

28 SNR GPS L1 (C/A+P+M+L1C) 28/52 SNR Interferometric Processing example: GPS L1 Composite (C/A+P+M+L1C) Orbit Height: 800Km, incidence angle: 35deg Down-Looking Antenna Gain: 23 dbi SNR o = 9.6 db SNR D = 15 db Up-Looking Antenna Gain: 23 dbi SNR degradation ~ 1.1dB SNR = 8.5 db

29 Composite GNSS Signals In Space 29/52 Galileo E1 Comp Modulation GPS L1 Components Modulation E1-a a (PRS) BOCcos(15,2.5) C/A code (civil) BPSK(1) E1-b/c (OS/CS/SOL) Galileo E6 Comp BOC(1,1)* (recently changed to CBOC) Modulation P(Y) code (encrypted) M code (encrypted) L1C code (civil) BPSK(10) BOC(10,5) BOC(1,1)*, planned to TMBOC E6-a a (PRS) E6-b/c (CS) BOCcos(10,5) BPSK(5) GPS L2 Components L2C code (civil) Modulation BPSK(1)* Galileo E5 Comp Modulation P(Y) code (encrypted) M code (encrypted) BPSK(10) BOC(10,5) E5 (OS) AltBOC(15,10) GPS L5 Components Modulation * TBC L5C code (civil) BPSK(10)

30 Composite Autocorrelation Function 30/52 GPS L1 Composite Autocorrelation Function (squared) ACF Normalised Squared Amplitude C/A Component 0.7 ACF Ampltiude Composite L Delay [Chips]

31 Composite Power Waveform: Example 31/52 GPS L1 Composite Waveform (antenna gain: 23dBi) Amplitude [A.U.] 6 x Normalized Cross-Correlation Power Waveform C/A code GPS L1 Comparable Power Levels, But L1 Composite Waveform is much steeper than C/A, => Improved Precision Delay [Chips]

32 Altimetric Precision, Noise and Speckle 32/52 The height measurement precision of a PARIS altimeter is mainly driven by bandwidth, signal-to to-noise ratio (SNR) Antenna Gain Dimensioned to guarantee sufficient SNR and signal-to to-speckle ratio (SSR) Incoherent Averaging Upper Limited by the wanted Spatial Resolution The speckle is the dominant source of height precision error

33 Coherent Integration 33/52 UP CHAIN DOWN CHAIN BPF BPF DOCON fc up DOCON XC T c () dt 2 W 1 (τ) W 2 (τ) W 3 (τ) W N (τ) ( ) Wi τ N fc down Coherent integration is performed to restore sufficient SNR In the coherent integration, the coherent time Tc that maximises the height precision has to be adopted

34 PARIS Flight Direction Coherent Integration 34/52 Spatial filtering due to the delay-doppler doppler coherent integration SP, τ=0 RX 1 chip delay

35 Incoherent Integration 35/52 UP CHAIN DOWN CHAIN BPF BPF DOCON fc up DOCON XC T c () dt 2 W 1 (τ) W 2 (τ) W 3 (τ) W N (τ) ( ) Wi τ N fc down Incoherent Integration is performed in order to reduce the amplitude variability due to speckle Incoherent Integration is traded-off with along-track Spatial Resolution on the Ocean Surface

36 Altimetric Precision: Analytical Model 36/52 The height measurement precision can be analytically represented as: σ h elev, SP 2 2 cps = sinθ P Ninc, s SNR Ninc, n SNR s

37 37/52 Mission Instrument Principle Instrument Design

38 Instrument Design: Overall Block Diagram 38/52 Up-looking beam BPF LO NCO f s /2 A/D t s /2 t s /2 I T/2 T/2 A/D t s /2 Q T/2 T/2 f s t s Double phased array GNSS receiver Computer Master Clock Σ Tc Σ Tc Σ Tc Σ Tc Down-looking beam BPF LO NCO f s /2 A/D t s /2 t s /2 I T/2 T/2 A/D t s /2 Q T/2 T/2 General block diagram of the PARIS altimeter

39 39/52 Phased array Nominal directivity 22.9 dbic 31 elements Up-looking is RHCP Down-looking is LHCP L1, L5, E5 Scanning angle (from boresight): - downlooking 30 - up-looking 42 <1.1m Antenna Overview <1.1m space for the electronics height < 8 cm Uplooking antenna Downlooking antenna

40 Antenna and Front-end Electronics 40/52 Up-looking Antenna Elements Pressure connector 10 mm Honeycomb panel Electrical Harness Calibration Switch and LNA Aluminium Beam Pressure connector 10 mm Honeycomb panel < 8 cm Down-looking Antenna Elements

41 Antenna Electrical Block Diagram 41/52 Beamformer B S1 Switch circuit UP 1 Antenna element B1 Beamformer A T1 α 1 B2 α Sn LNA BPF B3 Power Divider Tn Phase Shifter DOWN DOWN 1 UP m Power Combiner UP β 1 β DOWN m

42 Antenna Accommodation 42/52 Stowed Configuration Solar Panel HRM PARIS Antenna 110 cm HRM Spring motor Solar panel Electrical motor PROBA-2 like platform Top View (60 x 70 x 80 cm 3 ) Side View

43 Antenna Deployment 43/52 PARIS Antenna 110 cm PARIS In-Orbit Demonstrator (1) Clearance Open Solar Panel (2) Up-looking Antenna Down-looking Antenna First deployment: spring release Second deployment: electrical motor actuation

44 Delay Calibration: Front-end Switch 44/52 - Allows on-board delay and amplitude calibration UP 1:2 switch 1:3 switch LNA 2 loads LNA 1 1:3 switch 1:2 switch DOWN

45 Delay Calibration: Receiver Swapping 1/2 45/52 Beamformer B UP 1 Antenna element Beamformer A S1 B1 T1 α 1 B2 α Sn LNA BPF B3 Power Divider Tn Phase Shifter DOWN 1 DOWN UP m UP β 1 β DOWN m x( t) = x1( t a α e) xm ( t b β e) y( t) = y1( t a α e ) ym ( t b β e )

46 Delay Calibration: Receiver Swapping 2/2 46/52 Beamformer B T1 Switch circuit UP 1 Antenna element B1 Beamformer A S1 α 2 B2 α Tn LNA BPF B3 Power Divider Sn Phase Shifter UP DOWN 1 UP m Power Combiner DOWN β 2 β DOWN m x( t) = x1( t a α e ) xm ( t b β e ) y( t) = y1( t a α e) ym ( t b β e)

47 Amplitude Calibration: : Background 47/52 - Needed to track the specular reflection point (waveform retracking) 6 x Normalized Cross-Correlation Power Waveform 5 C/A code GPS L1 4 Amplitude [A.U.] Delay [Chips] - Enables secondary applications (scatterometry, biomass ) - Based on microwave radiometry techniques (e.g. in SMOS)

48 Amplitude Calibration: Cold Sky View 48/52 Switch circuit UP 1 Antenna element B1 Beamformer A T1 B2 α LOAD UP m LNA BPF B3 Power Divider Tn Phase Shifter Power Combiner Variable Attenuator 0 or L Detector UP β LOAD

49 Amplitude Calibration: Matched Load 49/52 T ph UP 1 Switch circuit UP 1 Antenna element B1 Beamformer A T1 B2 α T ph UP m T ph LOAD UP m LNA BPF B3 Power Divider Tn Phase Shifter Power Combiner Variable Attenuator 0 or L Detector UP β The loads are equivalent to external absorbers T ph LOAD

50 Amplitude Calibration: Auto-correlation 50/52 - Auto-correlation of GNSS signals measured on-board for accurate retracking on-ground ground; - Expected SNR > 43 db BPF A/D I t s T T Up-looking beam LO NCO f s t s A/D Q t s T T Double phased array GPS receiver f s t s Computer Master Clock Σ Σ Σ Σ t s Down-looking beam On-board Measurement of the Auto-Correlation Function

51 Beam Steering: other Applications 51/52 - Down-looking beams steered to measure: G G P P Backscatter 0 doppler line B S D S (a) Backscatter (b) 0-doppler 0 line

52 Conclusions 52/52 - The objective of the PARIS In-Orbit Demonstrator is to demonstrate accurate mesoscale ocean altimetry using GNSS reflected signals - An instrument concept has been presented to achieve this goal - Based on interferometric processing between direct and reflected signals - Advanced antenna design with high gain in up and down beams - Accurate delay and amplitude calibration techniques devised - Low noise ionospheric delay compensation - We look forward to your participation in this potential project from the scientific, industrial and financial point of view

53 Delay Calibration: Method 53/ Go into delay calibration mode a few times per orbit 2.- Measure range with switch in position 1 1 τ 1 = ( a a + α α b b + β β ) + ( e e ) M 3.- Measure range with switch in position 2 1 τ2 = ( a a + α α b b + β β) ( e e ) M 4.- Find internal delay by the semi-difference of the two ranges above τ τ τ = ( a a b b ) + ( e ) 2 M e o = 5.- Go back into measurement mode and apply correction 1 1 τ = τ τ o 2 2 τ = τ + τ o

54 Delay Calibration: Other Considerations 54/52 - Sign of doppler frequency and delay shifts also flips Up-looking beam BPF LO NCO f s /2 A/D t s /2 t s /2 I T/2 T/2 A/D t s /2 Q T/2 T/2 f s t s Double phased array GNSS receiver Computer Master Clock Σ Tc Σ Tc Σ Tc Σ Tc Down-looking beam BPF LO NCO f s /2 A/D t s /2 t s /2 I T/2 T/2 A/D t s /2 Q T/2 T/2

55 Amplitude Calibration: : 4-point 4 Method 55/ Go into external amplitude calibration mode once a month 2.- Measure cold sky with and without IF attenuation G P 1 = P0 + G( T C + TR ) P 2 = P0 + ( T C + TR ) L 3.- Measure internal load with and without IF attenuation G P 3 = P0 + G( T L + TR ) P 4 = P0 + ( T L + TR ) L 4.- Find offset, receiver gain and noise temperature P P P P P P = o P3 P1 P G P3 P T L T C = 1 T = P3 TL P1 P P 5.- Apply those parameters to de-normalise the cross-correlations correlations T R C 1 3 TC P4 + TLP P + P 2 4 2

56 Amplitude Calibration: Other Issues 56/52 Amplitude Calibration of Beamformer-B: 1.- Go into amplitude calibration mode once a month 2.- Go from Earth pointing to inertial pointing (satellite upside down) 3.- Apply 4-point method to down-looking antenna and beamformer B Amplitude Calibration Tracking: - In-between between external calibration events, use internal load reference

57 System Performance 57/52 - Mesoscale ocean altimetry requirement: 5 cm in 100 km