La Tecnica di RO, I dati e la loro Elaborazione. Agenzia Spaziale Italiana Centro di Geodesia Spaziale

Transcription

1 La Tecnica di RO, I dati e la loro Elaborazione Agenzia Spaziale Italiana Centro di Geodesia Spaziale

2 The GNSS Radio Occultation Technique In view GNSS Satellite In view GNSS Satellite In occultation GNSS Satellite

3 Ionosphere only One-way: Earth > Mars 50 & 400 MHz Ray-tracing inversion & Abel integral inversion Doppler counts only Neutral atmosphere not detectable Neutral atmosphere only Two-way: Earth > Earth GHz nav link Model-fitting inversion Doppler counts only Atmosphere-ionosphere separable by altitude!

4 "#$ "!% &!'!! () #!( "-!( "- &,! '! * +)

5 "#$ "!% ''!! &, & 1((2 -./ +)0

6 "$ $!% (3 &(! One-way: Earth > Venus One-way: Venus > Earth 50 & 423 MHz uplinks 50 MHz data were not usable; the 423 MHz receiver lost lock at about 37 km altitude 2.3 GHz downlink Obtained data from 90 to ~34 km altitude, then encountered critical refraction ( (!/!!

7 "$ $!% 4( (! 5678! ' 95"78( ' '!: -./ +;

8 66!#! &<&<=( 1+00< ! 0! - :,$ 40 Random Error Limited 30 POD Water Vapor Limited Geodesy 0.2 Ionosphere Mapping Atmospheric Occultation Predicted Temperature Accuracy (K) EOS Goal EOS Requirement 5 10

9 46<"&4&( 1 "/<# ++< > Northern Summer, 1995 Temperature profiles near England At about :00:00 UTC Pressure, mbar Winter Jet Stream 300 Occultation millibarat surface 52.6N. 355 E. Radiosonde at 54.5 N E. Radiosonde at 53.5 N. 357 E. Zonal winds from meridional geopotential gradient Temperature, K S. S. Leroy

10 7"! < 6'&?!

11 "!D "#A'!51)2 &B4C "&4

12 Processing Chain Phase Measurement Cleaning (Double Differencing, Clock Estimation, Iono free combination) Precise Orbital Determination (Pre-processing) Shift Doppler Excess Bending angle α ( a ) f ray-tracing equations a) b) Users: Meteorology? Climatology Space Weather Ionosphere Tomography (?) Space Geodesy Geophysics Refractivity n(r) P(r), T(r), P w Abel Inversion c) Term odinam ic Relationships d)

13 GPS 2 # $! % & " # '! " GPS 1 Link (B) Link (D) Link (A) Ground Receiver Link (C) Earth LEO

14

15 DOP Analysis IGS Network CSK

16 Shift Doppler Excess Bending angle α ( a ) f ray-tracing equations Abel Inversion Innovation: CT/FSI -Holography BPV Refractivity n(r) P(r), T(r), P w Termodinamic Relationships BPV n Integration with Ground GNSS Observations

17 C) from N(α) P,T,W To solve for P d, T and P w it is used : THE HYDROSTATIC EQUILIBRIUM LAW THE IDEAL GAS LAW P Solving (1) for T and combining (2) and (3) dp dh dp dh PV = RT ρ = ρ = ρ + ρ d w md P = + TR = g ρ gmd a2gmd Pw = N a R a R T 1 1 N = a 1 mp TR ( m m ) g w P T + a TR d P w ( m m ) d R 2 P T w w 2 P T w (1) (2) (3) (4) So, we have the two equations: (1) and (4) in three unknowns: P d, T and P w We consider two different cases:

18 D) PROFILES Cold and Dry Areas Wet and Hot Areas

19 Presentation Outline The Origin Description of the Radio Occultation Technique Challenging Tasks NRT x LEO-POD Mission Analysis ROSA on OCEANSAT_2 GPS & GALILEO Conclusions

20 Extinction eight H eight H Recife Recife Our Old Our Old Old Refr Old Refr CHAMP Refr. CHAMP Refr. Our Refr Our Refr. RAOB Refr RAOB Refr Dry Refr Dry Refr Refr 160.@N Refr.@N unitsd ROSA Seldom RO is unable to retrieve profiles down to the ground Solutions: High gain antenna 12 dbm Open Loop Approach

21 The CT and FIO as solution of the multipath 2 2 ( D D + 1) u= 0 x y D x u = H ( ) ( 2 y, D 1 D )u y y Asymptotic short wavelength solution Helmholtz Equation (valid for backpropagation approach) Initial spatial coordinates of ray path ( ) y,η Canonical Transform Integral Fourier Operator indeed distinguishes one and one only ray path New coordinates: a spatial one and the impulse ( z,ξ ) Φ ˆ v x x ( k p) = 2 ( 1 η ) 2π e A x ( y) exp( ik Ψ ( y) ) Geometric optical solution (GO) 2 undistinguished signals (multipath) can now be separated in phase space (have different impulse!) 1/4 1k parcsinη x 2 1 η + a ( arcsinη ) η v~ x x ( η) dη

22 Why Near Real Time? Numerical Weather Prediction Requirements: RO & LEO-POD data within 45 (2 download/orbit at least) must be available Within 1h.30 the Precise Ephemeris of the LEO Satellite (σ<50 cm) must be available Within 1h 45 the RO products to assimilate (level 2-3) must be available; Within 3h must be issued the NWP

23 A different strategy of ASI We have developed a GPS receiver devoted to Radio Occultation: Radio Occultation Sounder for Atmosphere studies We don t have a space mission devoted to RO We try to embark ROSA on available national and/or international Earth space missions: OCEANSAT_2 ( Spring 2009) SAC-D (2010) We have developped a plan with the goal to cover all the processing chain from data acquisition to the delivery of user products and applications

24 ROSA Receiver ROSA Instrument for OCEANSAT-2 major building blocks: the Lagrange GPS Receiver for Radio Occultation the Velocity Antenna assembly, sounding rising occultations the POD Antenna the RF Cables connecting the antennas to the Receiver

25 ROSA Antennas Gain and FOV SATELLITE COORDINATE SYSTEM ELEVATION ANGLE = θ Z NAVIGATION ANTENNA θ = 0 5 db (max) 0 φ θ 90-4 db (min) 0 φ 360 SAT Tangent Earth Circle X Y AZIMUTH ANGLE = φ TANGENT TO THE EARTH RADIO OCCULTATION ANTENNA θ db (min) -45 φ θ 90-3 db (min) -45 φ 45 EARTH

26 ORBIT PARAMETERS Type - Near polar sun-synchronous Altitude Kms Inclination Deg. Period mts. Local time of pass - 12 noon + 10 mts. Repetevity cycle - 2 days Distance between adjacent kms traces Distance between successive Kms ground tracks Average ground trace velocity Kms/sec

27 OCEANSAT-2 PAYLOADS OCM!"#$$ Scatterometer!%&'(()*+, -. * % / ROSA (developed by ASI, Italy) / )0" / #

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29 Velocity Direction 10 Antenna Tilt Nadir Direction

30 OCEANSAT_2 RO Events H=720 Km and I=98.27 ; nr. RO/DAY=272

31 250/day Occultations

32 ROSA: system preliminary architecture OceanSat-2 ROSA Aquarius/SAC-D ROSA 24 GPS and GLONASS MATERA GS Other RO Missions GPS Fiducial Network Data Analysis and Archiving Center USER Comunity

33 ROSA Radio Occultation DATA quantity Closed Loop C/A Code phase L 1, P Code diff phase L 1 -L 2, L1 and L2 Carrier phases, L1 and L2 Hz for 120 sec data x 40 bit 180 Kb/event Open Loop I, Q components of L Hz for 20 sec 4000 data x 40 bit 20 Kb/event 250 events/day 50 Mbytes/day Navigation OCEANSAT-2 POD x, y, z, v x, v y, v Hz 5 x 10 5 data x 40 bit 2.5 Mb/day ORDER OF MAGNITUDE!

34 ROSA PROCESSORS U S E R S ROSA Standard Operations Level 1a data Level 1b data Level 2 data Level 3 data ROSA OCEANSAT GROUND SEGMENT U S E R S ROSA Improved Operations Level 1a data Level 1b data Level 2 data Level 3 data Added Value Products ROSA WEB SCIENCE GRID MIRRORED in INDIA

35 ROSA DATA LEVELS LEVEL 0 DATA - The Radio Occultation RAW DATA extracted from the OCEANSAT-2 data flow telemetry (BEFORE any data organization in well defined files) - The data as they are produced by the GPS Ground Fiducial Network or IGS SATELLITE DATA CLOSED LOOP (L 1 and L 2 carrier phases, pseudoranges and SNRs at 1, 10, 50 Hz) ROSA Radio Occultation raw data OPEN LOOP (I and Q L 1 signal components at 100 Hz) ROSA Radio Occultation raw data ROSA Navigation data Time Tag (referred to GPS Time) OTHER DATA ASI Ground Fiducial Network IGS data (Orbits, Clocks etc.)

36 ROSA DATA LEVELS LEVEL 1a DATA - The Radio Occultation DATA observed from the ROSA on-board OCEANSAT-2, systematically organized in files for further developments - The data from the GPS Ground Fiducial Network or IGS, systematically organized in files for further developments SATELLITE DATA CLOSED LOOP ROSA Radio Occultation daily and Rinex formatted data (L 1 and L 2 carrier phases, pseudoranges and SNRs at 1, 10, 50 Hz) OPEN LOOP ROSA Radio Occultation daily data (I and Q L 1 signal components at 100 Hz) Daily, Rinex formatted ROSA Navigation data (L 1 and L 2 carrier phases, pseudoranges and SNRs at 1Hz) Doppler models predicted by the on-board SW OTHER DATA Hourly, Rinex formatted Ground Fiducial Network data (L 1 and L 2 carrier phases, pseudoranges and SNRs at 0.1 and 1 Hz) 15 min recordings, Rinex formatted IGS data (L 1 and L 2 carrier phases, pseudoranges and SNRs at 0.1 and 1 Hz)

37 The Orbits: (SWORD) Using the previously defined data, from this point it will start the work of the Scientific Team LEVEL 1b DATA (GPS/LEO Orbit Determination and Prediction) for Standard Operations Precise and Ultra Rapid GPS Satellites Orbits provided by IGS Estimated Precise and Rapid OCEANSAT-2 Satellite Orbits computed using dynamical methods (SWORD SW) for Improved Operations Estimated and predicted Precise and Rapid GPS Satellites Orbits Estimated and predicted Precise and Ultra Rapid OCEANSAT-2 Satellite Orbits (<1 h) computed using reduced-dynamical or kinematical methods

38 ROSA DATA LEVELS LEVEL 2 DATA Observed L 1 and L 2 Excess phases (at 50 Hz for CLOSED LOOP data and 100 Hz for OPEN LOOP data) for each occultation event Table of observed Radio Occultation events Table of predicted Radio Occultation events (computed using predicted orbital data) L 1 and L 2 SNRs or signal intensities (at 50 Hz for CLOSED LOOP data and 100 Hz for OPEN LOOP data) for each occultation event Predicted Doppler model using meteorological predictions and predicted orbital data for each occultation event

39 ROSA DATA LEVELS LEVEL 3 - Final Output a. L 1 and L 2 Bendings vs Impact Parameters profiles b. Iono-free Bendings vs Impact Parameters profile c. Stratospheric initialization of Iono-free Bendings vs Impact Parameters profile d. Dry air vertical atmospheric parameters e. Water Vapour and vertical atmospheric parameters f. Electron Density vertical profiles Basic Final Geom. Opt. methods Std techn. needed both L 1 and L 2 Through Global Climatol. Abel, hydrostatic Through Climatol. models Onion Peeling CT, FSI (Physical Opt.) Tomography and use of OL data Through Local Climatol. BPV α NWPs or SA (BPV n ), IDVAR Tomography

40 GALILEO 30 satellites, The Orbits have a period of hours 3 MEO orbits, h= km and I=56 inclinazione rispetto al piano equatoriale di 56 gradi The lifetime of the satellites will be 12 ys at least, Power 1.6 kw, mass di 680 kg and dimensions: 2.7m-1.2m-1.1m 3 orbite Medium Earth Orbit (MEO) altitudine km 2,7 m 1,2 m inclinazione 56 gradi 1,1 m

41 Height: 800 km Inclination ( ) Table of Radio Occultion Events without and with GALILEO Tot. Nr Occultation/Day GPS GAL GPS + GAL Nr. Occ./Day far <100 km from PFS Measurement GPS GAL GPS + GAL GPS Nr. Occ./Day <100 km and t < Torb GAL GPS + GAL

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43 Benefits from GNSS RO Space Geodesy Meteorology Climatology Space Weather TEC

44 Climatology Global All Weather Relevant (refractivity, tropopause etc.) Self Calibrating (could be used for in flight calibration of other sensors but )

45 Point where the RO occurs D Nadir point on the ground We deem RO and Nadir pointing observation overlapped if: D<100 Km; T ro -T np < Orbital Period

46 GPS+GALILEO Radio Occultation Table Height: 800 km Tot. Nr Occultation/Day Nr. Occ./Day far <100 km from PFS Measurement Nr. Occ./Day <100 km and t < Torb Inclination ( ) GPS GAL GPS + GAL GPS GAL GPS + GAL GPS GAL GPS + GAL

47 The number of points suitable for in flight calibration of Nadir pointing instruments with GNSS RO doubles

48 CLIMATE Refractivity can be estimated with RO with a relative accuracy better than Suitable for Climate investigations Refractivity as a fingerprint to investigate the Climate Fingerprint could be formed by combining projections for about 20 different levels below 25 Km, for some 30 different locations over the globe, and for four seasons (Goody et al. (1998).

49 Distribuzione dei Dati ROSA alla comunità scientifica