Concept of the future SAR mission for wide swath SAR observation A.Karasawa 1, Y.Okada 1, Y.Yokota 1, S.Nakamura 1 1) Mitsubishi Electric Corporation 1
Outline 1:Development of SAR systems in MELCO 2:Development of SAR Mission 3:The Latest SAR Mission : PALSAR-2 onboard ALOS-2 4:Expected Concept of Future SAR Mission 5:Case Study 6:Technical Essence 7:Conclusion 2
１ Development of SAR systems in MELCO MELCO*1 has been promoting development of airborne and space-borne SAR systems. Space-borne SAR 1992 1998 18 m class 2006-2011 10 m class ASNARO-2 ALOS-2 X-band 1 m class ALOS*2 JERS Airborne SAR 20141 m class SAR mission : MELCO Satellite Bus : NEC *2 Contract as supplier of SAR component (TRM etc ) Transmit & 送受信部 Receive unit Signal Processing 信号処理部 Unit アンテナ部 ANT Ku-band, 0.3 m class Ku-band, 0.1 m class Multi Receiving Channel Export Model to Taiwan This presentation focuses on SAR missions, and its feature and future concept. *1 Mitsubishi Electric Corporation 3
１ Development of SAR systems in MELCO MELCO*1 has been promoting development of airborne and space-borne SAR systems. Space-borne SAR 1992 1998 18 m class 2006-2011 10 m class ASNARO-2 ALOS-2 X-band 1 m class ALOS*2 JERS 20141 m class SAR mission : MELCO Satellite Bus : NEC *2 Contract as supplier of SAR component (TRM etc ) Airborne SAR Ku-band, 0.3 m class Ku-band, 0.1 m class Multi Receiving Channel Export Model to Taiwan This presentation focuses on SAR missions, and its feature and future concept. *1 Mitsubishi Electric Corporation 4
2. Development of SAR mission Japanese SAR mission has been developed continuously by JAXA and future SAR mission will follow.? JERS ALOS ALOS-2 Future 1992-1998 New generation SAR 2006-2011 system will be expected. 2014-2020 - Azimuth Resolution Swath 18 m 10 m 1-3m 1-3m* * Objective 75 km 70 km 50 km > 200 km* By successful results of ALOS-2 SAR missions, SAR sensor is expected as an important tool for the earth surface monitoring. Future SAR mission is expected as JAXA : Japan Aerospace exploration Agency a follow on and improved SAR mission of ALOS-2. 5
３.The Latest SAR Mission : PALSAR-2 onboard ALOS-2 PALSAR-2/ALOS-2 is the Latest SAR mission with High Resolution and Wide Swath Overview and Features of ALOS-2 PALSAR-2 is the SAR sensor on ALOS-2, as the Japanese 3 rd L-bad SAR satellite launched in 2014. Main Mission : Disaster Monitoring PALSAR-2 applies DRC to achieve both of High Resolution and Wide Swath. DRC is the technique to enhance PRF by using one Tx-ANT and divided Rx-ANT. Direction of Flight ALOS -2 : 2014(JFY)- Xsar Specifications Front Receive Receiver 1 A/D 1 Front-H Transmit Transmitter Rear Receiver 2 A/D 2 Rear-H Receive Receiver 3 PALSAR-2 Front-V ANT Receiver 4 Mode Stripmap A/D 3 A/D 4 Rear-V PALSAR-2 has full polarimetric mode. PALSAR: Phased Array type Synthetic Aperture Radar DRC : Dual Receive Channels PALSAR-2 achieves high resolution with wide swath by DRC technique. Spotlight ScanSAR Resolution 3m 10m 1m x 3m (RgxAz) 100m 50 m Swath 50 km 70 km 25 km 350 km 490 km [1] Y.Okada et.al, SYSTEM DESIGN OF WIDE SWATH, HIGH RESOLUTION, FULL POLARIMIETORIC L-BAND SAR ONBOARD ALOS-2, Geoscience and Remote Sensing Symposium(IGARSS), pp.894897, 2013 IEEE International. 6
4. Expected Concept of Future SAR Mission Motivation and Concept The Concept: Observe wider area with fine resolution To follow and improve the missions of ALOS-2, more frequent observations are expected to be required. Missions of ALOS-2 Global Monitoring Disaster Monitoring Wide Swath and Fine Resolution are crucial Ex : 50 km swath and 3m resolution? Expected improvement for Future mission More Frequent Observation - Respond to increase observation chances. - Increase accuracy of disaster/global monitoring. - Quick response to disaster Wider Observation Area is essential Ex : At least 100 km to several hundreds km. Requirement : Expand swath with fine resolution. Expected concept of future SAR mission; Resolution: 3m Good for serious disasters, such as landslide and flooding Swath : more than 4 times wider than ALOS-2. (ex. 200 km<) Performances Resolution (Stripmap) Swath ALOS-2 3m 50 km Expected Future SAR Mission 3m (maintain) at least 4 times wider than ALOS-2(200 km<) 7
4. Expected Concept of Future SAR Mission Comparison to other missions Compare the performance of future SAR with other SAR missions. S/R (Swath to Resolution ratio) is introduced as a parameter for comparison. The higher S/R, the better 2 Sw S / R R rg R az 6 Table. Comparison of our case study to other SAR missions Performances ALOS ALOS-2 TerraSAR-X RADARSAT-2 Sentinel-1 Future SAR Resolution Az 10 m 3 m 3 m 3 m 5 m 3 m Rg 10 m 3 m 3 m 3 m 5 m 3 m Swath 70 km 55 km 100 km 20 km 80 km >200 km S/R 49 336 100 44 80 >4400 The S/R can be drastically improved! 1 10 R rg : Range resolution, R az : Azimuth resolution, Sw : Range swath Our case study 8
5. Case Study There are 2 options ; Case study Step1 : To expand the swath Method(1) : Divide wide swath into small pieces(sub-swath). ScanSAR / TOPS Method(2) : Expand timing-window (Receive reflected signals for longer period) Expand Timing-window in single PRI Dual Receive Channel Use timing-window over multiple PRIs DBF Reduce PRF and obtain longer PRI Combine swath over multi PRIs PRI PRI#1 PRI#2 Orbit Orbit Tx Pulse Sub-Swath Range Swath Sub-Swath Range Swath AD Gate Expand PRI Time Time Swath#1 Swath#2 Combine Swats ScanSAR TOPS AD Gate = Swath Time Swath Applied to scansar mode of ALOS/ALOS-2 TOPS: Terrain Observation by Progressive Scan DBF: Digital Beam Forming Achieved in ALOS-2 Expected for Future 9
Comparison 5. Case Study Method (1) vs Method (2)- For the (1), wide swath can be achieved (ex. 490 km in ALOS-2), but Az resolution must be affected because synthetic aperture time is divided into short period. To keep better Az resolution, ANT must be small so that NESZ and range S/A should be degraded. For the (2), wide swath can be achieved without affecting synthetic aperture time. Method (1) Method (2) Technique ScanSAR / TOPS Dual Receive Channel DBF Azimuth Resolution Swath H/W Score Expand a swath with a fine resolution by enlarging a timing-window Low (10m ) Wide (several hundreds km) Relatively small Resolution is not high enough to the objective Possibly fine (3m ) Wide Large (multi Rx channels are required) Possibly fine (3m ) Wide ( 200 km ) Large (multi Rx channels are required) Can achieve both of fine resolution and wide swath Method (2) should be adopted to achieve wide swath and fine resolution. 10
5. Case Study Evaluation of a performance with H/W scale- Baselines for the case study. System performance objectives ANT : APAA (same as ALOS-2) Method of observation : Stripmap Resolution : 3m x 3 m (Az x Rg ) Swath : wider than 200 km Band width : 84 MHz 3 cases below are evaluated. 1 Dual/multi receive channel is applied 2 DBF technique is applied 3 Both of 1 and 2 are applied 11
Resolution Swath NESZ Azimuth S/A Range S/A 5. Case Study Result of the evaluation. Rx Channel Number ANT shape image 1 Apply multi Rx channels 2 Apply DBF 3 Apply 1 and 2 3m x 3m (Az x Rg) 200 km around -20 db around 20 db around 20 db Az 4 1 2 Rg 1 16 6 Size : 24 m 1.8m Az:24 m Size : 6.0 m 7.0m El :7.0m Size : 12.0 m 3.5 m Az:12m El :3.5 m El :1.8 m Az :6.0 m A 3m Az resolution and 200 km swath can be achieved for any case. However, huge H/W (ANT size and number of Rx channels) is unavoidable. From point of view of mountability, the case 3 should be realistic. - case 1 need to be folded in Az direction for more than 10 times. - case 2 need to be folded in both of Az and El directions. - case 3 can be folded in Az direction for 4 or 5 times (same as ALOS-2). 12
6. Technical Essence In order to achieve both of wide swath and high resolution, following technological improvements of SAR system are required. Improvement of NESZ is required to expand the swath. By considering an increment of data rate, high downlink rate will be required. Requirement Method for improvement Key Technologies Improve NESZ Transmit High Power GaN HPA GaN HPA with actual achievement on ALOS-2 can be continuously applied to future missions. 45W class high power GaN HPA onboard ALOS-2 Consider drastically increase of SAR data-rate High Speed Downlink Achieved high speed down-link system of 800 Mbps on ALOS-2 should be improved to Gbps class by such as inter-satellite communication. TRM : Transmit Receive Module HPA : High Power Amplifier GaN : Gallium Nitride 13
7. Conclusion About SAR missions SAR has been continuously developed as an important tool of Earth observation. Future SAR will follow on mission of ALOS-2. Mission concept of future SAR mission A wider swath is essential to improve ALOS-2 mission. The future SAR mission is expected to have swath several times wider than that of ALOS-2. Case study The expansion of timing-window is better than the sub-swath approach. Large H/W is required to expand swath. The technology based on both of the DBF and multi-rx channels should be for the reliable mountability. Technical Essences Improvement of NESZ is essential with a wide swath. High power TRMs with GaN HPA could be the solution. The down link data-rate will be also improved from Mbps to Gbps by such as intersatellite communication. 14
Thank you for your attention. Transmit & 送受信部 Receive unit Signal Processing 信号処理部 Unit アンテナ部 ANT 15