Development of the Next Generation GRAS Instrument

Transcription

1 Development of the Next Generation GRAS Instrument Jacob Christensen Magnus Bonnedal, Anders Carlström, Thomas Lindgren Sean Healy (ECMWF), Hans-Henrik Benzon (DMI) RUAG Space Gothenburg Sweden D-I-HO RSE, issue 22

2 MetOp GRAS (Launch: 2006, 2012, 2017) Availability > 99% Dependability: 700 Occs/day & Instr. Performance: 0,5 urad 2 RUAG Space COSMIC WS, Boulder Oct 2012 Plots Credit to EUMETSAT

3 MetOp-GRAS Follow-on. GNSS POD Receiver POD and Precise On-board NAV Miniaturized technology European EO: 20 Receivers US & Asian missions Single, Dual & Triple Band LNAs Institutional & Commercial: ~100 LNAs PEC & Helix GNSS antennas (LEO & GEO) Institutional & Commercial: ~40 Ant:s On-S/C antenna optimization 3 RUAG Space COSMIC WS, Boulder Oct 2012

4 GRAS-2: Next Generation RO Instrument More occultations: 2800 per day All GNSS constellations AGGA-4 based Ionosphere coverage Low altitude DF tracking Enhanced open loop tracking Model based code & carrier sampling Doppler & Range models Equivalent rise & set performance Improved bending angle noise Enhanced Reliability & Redundancy Redund. pwr, S/C I/F & Nav function 4 RUAG Space COSMIC WS, Boulder Oct 2012

5 ROPE: High Altitude Performance GRAS-2: ~40% reduction of residuals Predicted from Parametric Model Predicts MetOp-GRAS performance Spectral Error Characteristics 5 RUAG Space COSMIC WS, Boulder Oct 2012 High antenna gain Ultra-Stable Oscillator Low phase-noise Optimized accommodation for low local multi-path;

6 Optimization for Local multipath Electro-magnetic modelling of antennas and neighbouring structures Antenna pattern disturbance due to local multipath Improved antenna accommodation with 6-element antenna 6 RUAG Space COSMIC WS, Boulder Oct 2012

7 ROSIM: Full Altitude Performance EUMETSAT study with ECMWF, DMI & RUAG noise and co-channel Ref. Atmospheres 55 ECMWF cases PRN & Chip Modulation Wave Optics Forward Model DMI 7 RUAG Space COSMIC WS, Boulder Oct 2012 Retrieval Model Instrument Model, Design Reference for GRAS-2

8 GRAS-2 Tracking simulation Setting Rising GRAS-2 captures all signal energy propagating through the atmosphere, using open-loop sampling. 8 RUAG Space COSMIC WS, Boulder Oct 2012

9 Atmosphere Conditions 55 Cases with global representation defined by ECMWF Dotted: Northern Solid: Tropics Dashed: Southern dn/dh Limits Category No of Cases , ,157 low Using Bending Angle derived from Abel transform as reference: Cat. 1 & 2 Performs well Cat. 3 often under estimate peaks Cat. 4 always under estimate peaks Prob. (Global) Cum Prob. 45% 17% 45% 62% 0,157 25% 87% - 13% 100% high 0,0785 0,0785 0,1 9 RUAG Space COSMIC WS, Boulder Oct 2012

10 Bending Angle for Cat. 4 with ideal instrument C/A C/No for Case 15 from WOP file: ALLModFreqFile1kHzDataLinCase Cat-4: 13 Atmospheres dn/dh > % of Occs Abel vs WO: ~0% 45 C/No [dbhz] RUAG Space COSMIC WS, Boulder Oct Time since start of occultation [s]

11 Bending Angle for Cat. 3 with ideal instrument C/A C/No for Case 11 from WOP file: ALLModFreqFile1kHzDataLinCase Cat-3: 13 Atmospheres 0.1 < dn/dh < % of Occs 87% Cat-3 Abel vs. WO ~25% (5%) ~50% (10%) 45 C/No [dbhz] Time since start of occultation [s] 11 RUAG Space COSMIC WS, Boulder Oct

12 Bending Angle for Cat. 2 with ideal instrument C/A C/No for Case 7 from WOP file: ALLModFreqFile1kHzDataLinCase Cat-2: 10 Atmospheres < dn/dh < % of Occs 62% Cat-2 Abel vs WO: ~90% (5%) 45 C/No [dbhz] RUAG Space COSMIC WS, Boulder Oct Time since start of occultation [s]

13 Bending Angle for Cat. 1 with ideal instrument C/A C/No for Case 32 from WOP file: ALLModFreqFile1kHzDataLinCase Cat-1: 45% of Occs Abel vs WO OK C/No [dbhz] 19 Atmospheres 0 < dn/dh < RUAG Space COSMIC WS, Boulder Oct Time since start of occultation [s]

14 Abel vs, WOP + FSI The Able transform provides a good representation of the physics for low refractivity gradients. About ~30% (cat 4 & part of cat 3) deviate in excess of 5% between Abel & (WOP+FSI) at low altitude About ~15% (cat 4) experience super critical refractivity where Abel predicts non physical measurements, as the rays never reach the receiver. WOP + FSI provides an alternative forward model, which is more representative at high gradients. Agreement between Abel & (WOP+FSI) for the 55 cases: - Cat 1: 100% agree to 5% - Cat 2: 9 of 10 agree to 5%: - Cat 3: 3 of 13 agree to 5%: - Cat 3: 6 of 13 agree to 10%: - Cat 4: All deviate > 20% dn/dh Prob Cum Prob. Cum Abel Abel vs vs WO OK WO OK (5%) 0, % 45% 100% 45% 0,0785 0,1 17% 62% 90% 61% 13 0,1 0,157 25% 87% 25% 67% 13 0,157-13% 100% 0% 67% Category No of Cases low high RUAG Space COSMIC WS, Boulder Oct 2012

15 RO assimilation today and its relation to End-to-End Instrument Performance Threshold for assimilation of RO in NWP: dn/dh < (ECMWF today, empirical) dn/dh limit determined from forward model Only cat 1, ~50% of occs, are used all the way down. Cat 2 most likely also OK to assimilate all the way down. For Cat 4 and at least some of Cat 3, measurements can not be used all the way down. 15 RUAG Space COSMIC WS, Boulder Oct 2012

16 Future RO assimilation? and its relation to End-to-End Instrument Performance? Using real physical & Instrument models would enable all instrument data to be assimilated (i.e. full altitude) Wave optics & 2D forward model Overloads the NWP processing Is there something better than Abel but less computational demanding than full wave optics? Ultimate End-to-End performance can be evaluated using an ideal forward model But how do we find and agree on such an ideal model?? 16 RUAG Space COSMIC WS, Boulder Oct 2012

17 Thank you! 17 RUAG Space COSMIC WS, Boulder Oct 2012