GAS@IGARSS2011.ppt
- 1. Demonstrator Test Results for the GEO Atmospheric Sounder (GAS) Jacob Christensen 1 , Anders Carlström 1 , Johan Embretsén 2 , Andreas Colliander 3,4 , and Peter de Maagt 4 1 RUAG Space AB, Göteborg, Sweden 2 Omnisys Instruments AB, Göteborg, Sweden 3 Jet Propulsion Laboratory, Pasadena, California, USA 4 European Space Agency, Noordwijk, The Netherlands IGARSS 2011 Vancouver 28 July 2011
- 2. Project Overview The overall study objective (Phase 1&2) has been to develop an imaging microwave sounder concept for Geostationary Earth Orbit (GEO) Phase 1 was a feasibility study where the concept was developed and analysed Phase 2 has demonstrated the concept by developing and testing a fully operational interferometer system Study Team: European Space Agency (ESA) Specifications and coordination of the project RUAG Space (Göteborg, Sweden) Focusing on: System design Image retrieval processing and calibration Antenna design Mechanical/thermal design Omnisys Instruments (Göteborg, Sweden) Focusing on: System design Front-End Electronics design Back-End Electronics design The ESA GEO Atmospheric Sounder Technology Project
- 3. Background and objectives Meteorological needs for nowcasting & short range forecasting in the 2015 – 2020 time frame 15-30 minute revisit time 30 km resolution 380 GHz Four frequency bands of interest centred around: 53, 118, 183, 380 GHz Temperature (AMSU-A) Most important for NWP ! High altitude temperature High altitude humidity Humidity (AMSU-B) 166 346
- 4. Driving requirements Requirements 2015 – 2020 15 - 30min Revisit Time => Geostationary Orbit All Weather Capability => Requires the 53 GHz band 30 km Resolution => 8 m Aperture Solution: Foldable Interferometer Can be Launched Can Operate on GEO S/C Rotating Interferometer Provides images with finer resolution as compared to a stationary interferometer ( for a given number of mm-wave receivers)
- 5. Interferometer element layout Minimum spacing of 3.5 to avoid aliasing Redundant baselines improves the instrument calibration Good signal strength for 6, 9 ,12, 16, 19, 22 due to size of Earth disc Large spacing near the centre to enable interlacing several frequency bands u-v sampling after rotation instantaneous u-v sampling u v x y
- 6. Instrument electronics The polarisation vector rotates during measurement All four Stokes parameters are measured Improved sensitivity
- 7. Mechanical design Deployment hinge Attachment structure Rotational drive Boom structure Radiator Mounting support 53 GHz 380 GHz 118 GHz 183 GHz
- 8. Instrument budgets Four frequency bands with polarimetric capability Power: 406 W Mass: 375 kg The concept is scalable !
- 9. Includes the central part of the instrument: 21 dual-pol interferometer elements (53 GHz band) Objective: to demonstrate the imaging concept with rotation, calibration, and post-processing 53 GHz demonstrator Demonstrator characteristics Parameter Value Remark Frequency band 49-53 GHz Single 90 MHz channel Number of elements 21 Dual polarisation Longest baseline 75 cm ~140 Image Resolution <10 mrad ~300 km on earth Relative accuracy < 2K
- 10. Antenna design Coupling between neighbouring elements: < -67 dB
- 11. Front-end design LO input Antenna RF inputs (2 pol) IF outputs MMIC designed in collaboration with Chalmers
- 12. Demonstrator integration 21 front-ends with antennas Cross-correlator core (42 inputs) Assembled on rotational drive
- 13. Demonstrator test campaign Parameters to verify Image angular resolution Image beam efficiency Image polarisation isolation Image relative accuracy Sources Calibration sources: Hot & Cold Loads Imaging sources: Noise point source CW point sources Distributed source Distributed source Noise CW CW
- 14. Demonstrator test results Relative calibration of all elements using point source in boresight: Gain stability over 2 hours: 0.03 dB RMS @ 51 GHz Phase stability over 2 hours: 0.2 deg RMS @ 51 GHz
- 15. Demonstrator test results Point source imaging: Demonstrator configuration 1 deg/s Polarization XX-pol YY-pol Measured pol. isolation is dominated by co-polar sidelobes ! PS1 PS2
- 16. Demonstrator test results Solar imaging – complete transition (boresight elevation is 47.4 deg): 11:30 12:30 12:00
- 17. Outdoor imaging of distributed source (about 15 minutes of integration): Demonstrator Test Results The resulting image is free from ambiguities!
- 18. Demonstrator Test Results Distributed source imaging: Linearity: 1.1 K RMS Variation over image: 0.7 K Note that both linearity error and variation across image are systematic effects that can be calibrated!
- 19. Distributed source imaging – difference between images -> noise error: Demonstrator Test Results Noise error (Ne T) : 0.8 K RMS at 30 minutes of integration The theoretical model assumes a Gaussian density distribution of the baselines ! Theory:
- 20. Compliance status: Demonstrator requirements are met The concept is demonstrated Test Results Summary Image brightness temp. rel. accuracy:
- 21. Related activities Deployment test Parallel study: Ultra-stable structure for interferometric instrument Parallel study: MMIC for 118 and 183 GHz Results show that the design is viable 90 & 118 GHz 166 & 183 GHz NF = 3.1 dB NF = 6.0 dB Packaging Expected with 50 nm mHEMT (flight design): NF = 2.5 dB NF = 4.8 dB Receivers produced using 100 nm mHEMT:
- 22. Conclusion The rotating sparse array interferometer concept allows optimization of sensitivity for a reduced number of elements We have developed a demonstrator consisting of 21 dual-polarised receivers in a rotating sparse array • We have achieved the performance success criteria defined at the start of the activity: Image resolution: <10 mrad Image beam efficiency: >95% Relative accuracy of brightness temperature: <2K Image polarisation isolation: >10 dB (goal: 20 dB) • The obtained performance parameters agree well with model predictions The breadboarding and demonstration activities have increased the know-how on all levels: from components to systems