Considerations towards Future SAR Developments

Transcription

1 Considerations towards Future SAR Developments Vorlesung: Hochauflösende Radarsysteme WS 2007/08, Friedrich-Alexander-Universität Erlangen Nürnberg Lehrstuhl für Hochfrequenztechnik Wolfgang Keydel DLR Oberpfaffenhofen, Institut für Hochfrequenztechnik und Radarsysteme Web: 1

2 Future SAR Systems? Credible? 2

3 Goal Present the Expected Development of Features for future Air- borne & Space-borne SAR based on State of the Art reached on the past Development Line & gained with Extrapolations Point out under that Aspect Perspectives & Visions for Future & Space-borne SAR Systems 3

4 Moore s Law gives a Makro Trend Market Demand & respective Semiconductor Industry Response# Functionality per Chip Double Every 1.5 to 2 Years Observed also for Micro Processing Units (MPU) Performance Corrollary to Moore s Law Manufacturing Productivity Improvements enable the Cost-per-function (Microcents per bit etc.) to decrease by about 29% per year. These Figures Observed & Sufficiently Proved over the Last 30 Years 4

5 State of the Art Operational Space Borne SAR Antennas Active Phased Arrays: (T/R Modules) P-, L-, C-, X-Band; Patches in P-, L-, C-Band, Slot-Arrays in X-Band Example: TerraSAR!! Reflector Antennas are not out!! Main Advantages Multi-Polarization high Bandwidth less complex, Low technological Risk at low Costs, lower Mass, Power Main Drawbacks Limited instantaneous Swath Width Lack of electronic Beam Steering Capability (ScanSAR) Examples: SAR-Lupe, MAPSAR: 5

6 Example for Mass Distribution (ASAR) Antenna: C-Band, Patch Array T/R Modules 60 kg Panels/Elements 322 kg (61%) Distribution Network 48 kg Thermal Isolation 50 kg Total 480 kg Main Support Units Mounting / Housing 21 kg Low Power f. Transmitter / Receiver 26 kg Data Handling/Signal Processing 11 kg Total 48 kg 6

7 Antenna Dimensions m x m x 0,15 m Mass incl. Structure 303 kg Payload 394kg, Bus 549kg, Propellant 78kg TerraSAR-X Δϕ Beamwidth (Az x El): 0.33 x 2.3 Scan (Az; El): ± 0.75 ; ± 19.2 Peak Power: Total 2,3 kw, T/R-M 6W Velocity Measurement Capability Orbit: 500m ~ V satellite 7600msec -! d V 2π t arg et V = t arg et Vsatellite λ V satellite λ Δϕ d 2π = for Δφ = 5 V target =1,3 msec -1 3 Antenna leafs with 4 Panels with 32 active Sub-Arrays in Elevation each comprising an HP & VP slottet Waveguide Radiator 384 Sub-Arrays equipped with T/R Modules The dual-polarized Waveguide Radiator allows Polarization Selection via a Polarization Switch in each T/R Module. Personal Communication:J. Mittermayer, DLR Radar & Microwaves Institute, +49/8153/ , josef.mittermayer@dlr.de 7

8 SAR-Lupe (X-Band), Launch 2006 Volume (3m x 4m x 2m) ca. 24 m 3 Strip Map Ground Velocity 7km/s High Resolution within 8 km x 60 km WEIGHT Power Consumption Images/day Av Power Consumption Orbit Height Spatial Resolution 770kg 250 W > years ca. 500 km < 1m Spot-Light Velocity Reduction Highest Resolution within 5,5km x 5,5 km Antenna Size 3,3 m x 2,7 m 8

9 Major challenging technology elements Active Control of Structure, Surface Profile, and Roughness Under Consideration Dual Polarized SAR Membrane Antenna 3-Layer, Size 12m x 3m Storage Volume < 1 m 3 Total Mass 175 kg Membrane Material & Spacers 45 kg; Sunshield & Insulation 27 kg, Deployment Mechanism 100 kg (57%) Stowage Container 3 kg. Shaubert D., et al.: Lightweight. Deployable Antennas, Earth Science Enterprise Technology Planning Wokshop, JPL, Jan

10 MAPSAR Antenna Elliptical Cassegrain 7,5 m x 5 m Reflecting Surface triaxially woven Fabric Carbon Fibre Reinforced Silicone (CFRS) Reflector Structure main & auxiliary Membrane Ribs, radially deployed & stiffened with Pantograph Mechanism Distance between Reflectors 2,70 m Sub-Reflector Dimension 1,0 m x 0,67 m Horn dimension.1,40 m x 0,45 m x 0, 56 m Main radial ribs Triax CFRS Auxiliary membrane ribs Reflecting surface Mass Budget Central unit: 11 kg, Pantographs & Deployment. 30 kg, Membrane Ribs: 10 kg, Reflecting Surface: 7 kg, Subreflector Support:,.10 kg Totally..68 kg Personal Communication: Leri Datashvili, Institute of LightweightStructures, Technische Universitaet Muenchen, Tel.: +49/ , Datashvili@llb.mw.tum.de: T. Neff, DLR Microwaves & Radar Institute, , 10 Thomas Neff@dlr.de

11 Main Mechanical Antenna Problems Stiffness & Surface Accuracy Deployment & Rigidizing Reliability Antenna Deployment Control & synchronization to achieve high Stiffness Feed Subreflector Possible Stowage Geometry Available stowed Volume 2100 mm * 1500 mm Reflector Mass : 0.5 kg/m kg/m Additional available space, to be considered for package 1900 Reflector Payload Reflector Possibilities: Flexible knitted Mesh, Tensed metalized Membrane parabolic quasi-membrane (flexible shell-membrane) Example MapSAR TAURUS Shroud Configuration 11

12 From SAR Antenna to Antenna SAR ENVISAT Sensors 2145kg SAR-Lupe 2006 SAR only 770 kg TerraSAR 2007 SAR only 480kg MapSAR 2014? SAR only 450kg? Antenna SAR 2025? SAR only 200kg? Antenna 1m x kg Array C-Band Antenna 2,7m x 3,3 m ca. 100 kg Mirror X-Band Antenna 0,7m x 4,8m 303kg Phased Array X-Band Antenna 5m x 7,5m Goal: <70kg (0,7 kg m -2 ) Cassegrain L-Band Antenna 1m x 12m 10kg (0,5 kg m -2 ) Phased Array Multi-Band 12

13 Formation Flying System Deployment of large Number of Low Cost small Satellites acting collaboratively as a Single Collective Unit (Large Antenna) New Members to the Formation can be Introduced over Time. Requirements Guidance & Control System on Board with autonomous Navigation, Formation Positioning & Estimation, Path Planning Functions & extreme Pointing & Attitude Stability. Significant Challenges: Control of Spacecrafts in low Orbits non-uniform Perturbations, potentially, destabilize the Formation Geometry & decrease the Systems Measurement Accuracy. First Step: Tandem 13

14 Digital Beam Forming Simultaneous Multiple Beam Forming on Receive Receiver & AD Converter at Each Element or Subgroup Continuous Beam Dwelling on All Objects within the Illuminated Sector Transmitter Central MPU ADC Rec Processor MPU ADC Rec Unit MPU ADC Rec MPU ADC Zooming Small Part of Large Image with Low Resolution to a Small Image With Higher Resolution (Corresponding to the Fraction of Elements ore Sub-Arrays resp.) Optimum Solution Equip Each Antenna Element or Subarray with an Own Computer Rec 14

15 Multistatic Digital Beam Forming System Schemes Master Satellite Transmitter Satellite Array Formation Flight Comunication Space-borne Array Air-borne UAV Array Fleet Note: In GEO Case the Master Satellite is above Equator! 15

16 Digital Beam Forming Image Processor Central Processor Array Antenna MPU ADC T/R MPU ADC T/R MPU ADC T/R MPU ADC T/R Strip Map Whole Area Whole Arrray Zoom by Squint DBF Single Array Module Whole Array 16

17 Frequency Range: 500 MHz...18 GHz Air - Air +IFF Navigation (GPS) Fire Control Weather Communication + IFF Terrain Following Missile Warning Altimeter Flight Guidance + IFF Kommunikation Air - Ground SAR Reconnaissance Communication + IFF 17

18 ENVISAT Combination of 10 remote sensing instruments MIPAS AATSR ASAR-Antenna (ca. 10 m x 1.33 m and 320 T/R-Modules) MERIS GOMOS RA-2 LRR SCIAMACHY DORIS MWR ASAR 18

19 Candidates for Integrated Antenna Systems CONFORMAL PATCH ARRAYS Spiral ore Cone Patches Covering a Wide Bandwidth. State of the Art Cover the whole RF Spectrum from 500 MHz up to 18 Ghz by 3 Multifunction Apertures 500 MHz to 2 GHz, 2 GHz to 6 GHz, 6 GHz to 18 GHz 19

20 Physical Limits of Transistor Development will be reached within the Near Future Very new Invention of Crossbar Latch Principle promises further Validation of Moore s Law for the next Decades Kuekes, Philip J., Duncan R. Stewart and R. Stanley Williams, Hewlett-Packard Laboratories, Quantum Science Research group: The crossbar latch: Logic value storage, restoration, and inversion in crossbar circuits. Journal of Applied Physics 97, (2005) 20

21 Technical & Technological Development Expectations within the next 2 Decades Power Efficiency of Solid-State devices > 60 %. Higher Miniaturization will reduce Mass & Volume of RF-systems drastically (including the Antenna down to about 10 %). High Degree of Automation of the Radar and Operation Functions will reduce Effort for Post Launch Mission Operation. High Temperature Super Conductors will be applicable for Extremely Small Filtering as well as for T/R Modules with high S/N, Progress in Time Synchronization to nsec-accuracies, Future SAR, mainly, will consist of the Antenna with a small Number of more ore less Peripheral Elements only (Solar cells, GPS, Power Supply etc.). The SAR Antenna will mutate to a complete Antenna SAR 21

22 Future SAR Systems: Software Based & Multi Static with Multi-Polarization, Multi-Frequency Capability, Multiple Operation Modes One ore more Central Illuminators together with a Synchronized Fleet of Airborne, Space Borne, or Ground Based Receivers resp. enable continuous Availability with nearly Global Coverage Extremely High Resolution down to cm Dedicated Information Transfer to specific Users in Real Time, based on Onboard Data Processing Necessary Extremely Accurate Time Synchronisation Very Effective Data & Communication Links 22

23 Future SAR Systems: Technique and Technology Antenna &Transmitter Highly Efficient Reflector Antennas, Wide Angle Beam Illumination, High Power Microwave Vacuum Sources with High Efficiency Receiver Fleet of Receiver Satellites organized as an Intercommunicative Web as a Macro Instrument Concept Coordinated Efforts between Multiple Numbers & Types of Sensing Platforms, including both Orbital & Terrestrial both Fixed & Mobile. Information Gathered by one Sensor Shared & Used by other Web Sensors Each Sensor Communicates with its Local Neighbours & thus Distributes Information to the Instrument as a Whole. 23

24 Develop integrated Antenna Systems with extremely large Bandwith Develop X-Band Patch Antennas Mass Reduction Develop lightweight Material for Mirrorors, Deployment Support etc. Develop Zoom Capability for Digital Beam Forming Develop Formation Flying Concepts based on Tandem Develop Volume Antenna Principles for a Sensor Web Establish Concerted Action regarding Frequency Management between Remote Sensing & other Microwave Services (Com-Nav etc.)! Investigate Dual Use Possibilities of Frequencies for Radar & other Services & Dual System Use for Civil & Military Purposes! Use Experience gained with other Microwave Services (ComNav etc.)! Investigate Fusion with other Sensor Systems & - Techniques! SAR is not a Stand Alone Technique 24

25 Principal Interconnection Scheme for a Sensor Web COM GEO TV RS GEO/2 LEO UAV 25

26 What to do? An exemplary Task Selection Develop new appropriate Waveform Generation & Modulation Schemes! Carry out Experiments for Bistatic SAR Systems (ground based, airborne, space borne using existing Instruments & Satellites)! Study Bistatic Scattering Behavior of Electromagnetic Waves (Polarization, Forward Scattering conflicts with high resolution requirements etc)! Implement all Activities on the Platform as an End-to-End System! Use Experience gained with other Microwave Services (ComNav etc.)! Establish Concerted Action regarding Frequency Management between Remote Sensing & other Microwave Services (Com-Nav etc.)! Investigate Dual Use Possibilities of Frequencies for Radar & other Services & Dual System Use for Civil & Military Purposes! Investigate Fusion with other Sensor Systems & - Techniques! SAR is not a Stand Alone Technique 26

27 Consequence:Vision Autonomous, Global, Integrated "Reconnaissance and Remote Sensing Multisensor System" with Communication and Positioning Capability. Polarimetric Interferometry SAR (10MHz to 10GHz) Central Illuminators for a Synchronised Fleet of Small Airborne and Spaceborne Receivers for Continuos Availability & Global Coverage. Extremely High Resolution down to the dm Range Real Time Feature Processing & Value Adding on Board Dedicated Information Transfer to Specific Users Extremely Accurate Signal and Time Synchronisation Very Effective Data and Communication Links 27

28 'The future cannot be predicted. It has to be invented.' (Dennis Gabor, ) Future Developments, Investigation & Activities necessary 28

29 First Next Step:From TerraSAR-X) to Tandem-X (2009) TerraSAR-X (2007 Tandem-X (2009) 29

30 center frequency 9.65 GHz (X-band) Tx bandwidth up to 150 MHz (300 exp.) PRF 3 KHz to 6,5 KHz transmit duty cycle 13-20% radiated peak power 2260 W system noise figure 5 db 30

31 antenna dimension in azimuth m antenna dimension in elevation m azimuth beamwidth 0.33 elevation beamwidth 2.3 scan angle azimuth ± 0.75 scan angle elevation ±

32 TerraSAR-X Orbit sunlight side night side dusk/down orbit altitude at equator km inclination sun-synchronous repeat orbit: repeat period 11 days revisit time: 4.5 days (100%) 2.5 days (95%) orbits per day 15 2/11 32

33 Antennas Determine Spaceborne Microwave Remote Sensing TerraSAR-X Mission Profile X-Band Downlink 300 Mbit/sec S-Band TM & TC Raw Data Acquisition DLR GS Neustrelitz DLR GS Weilheim Mission Operations DLR Oberpfaffenhofen 33

34 Θ 1 =20 o Flight direction 20 Nadir Track Swath Width 100 km Θ 2 =55 o 45 TerraSAR-X Imaging Modes Stripmap Mode ScanSAR Mode Spotlight Mode (Sliding) HighRes Spotlight Mode (Sliding) Centre of rotation Stripmap ScanSAR Spotlight HighRes Spotlight full perf. inc, angle range scene size along track acqu. length acqu. length 10 km 5 km scene size ground range 30 km 100 km 10 km 10 km single look az. resolution 3 m 16 m 2 m 1 m single look range resolution 3 m (ground) 16 m 5 looks 1.2 m (slant) 1.2 m (slant) 34

35 TerraSAR-X TD-X TanDEM-X TerraSAR add-on for Digital Elevation Measurements 35