Burst overlapping of ALOS-2 PALSAR-2 ScanSAR-ScanSAR interferometry

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1 Burst overlapping of ALOS-2 PALSAR-2 ScanSAR-ScanSAR interferometry Japan Aerospace Exploration Agency Earth Observation Research Center Ryo Natsuaki, Takeshi Motohka, Shinichi Suzuki and Masanobu Shimada

2 Outline 1. Introduction 2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, Burst misalignment after Feb. 8, Conclusion

3 Outline 1. Introduction 2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, Burst misalignment after Feb. 8, Conclusion

4 1.1 ScanSAR mode of PALSAR-2 High ScanSAR ScanSAR Spotlight Ultra Fine Fine sensitive nominal wide Bandwidth 84MHz 84MHz 42MHz 28MHz 14MHz 28MHz 14MHz Rg Az: Resolution 3m 6m 10m 100m 60m 3 1m Rg Az: 350km 490km Swath 50km 50km 70km 25 25km (5-scan) (7-scan) Polarization SP SP/DP SP/DP/QP/CP SP/DP SP : HH or VV or HV, DP : HH+HV or VV+VH, QP : HH+HV+VH+VV, CP : Compact pol (Experimental) ALOS-2 supports operational ScanSAR ScanSAR interferometry Burst overlap ratio is planned to be 90% in 1 sigma => misalignment within 15.77ms with prob. 68%

5 Burst repetition Burst duration 1.2 Burst overlap of ScanSAR F1 F1 F2 F2 F3 F3 F1 F1 F1 F1 F2 F2 F2 F2 F3 F3 F3 F3 t master t slave ScanSAR mode switches observation direction cyclically For ScanSAR ScanSAR InSAR, master and slave images must transmit the burst at the same orbit position Allowable burst misalignment depends on burst duration ALOS- 2 requires misalignment should be smaller than 15.8 ms TOPSAR mode requires more accurate overlap ratio (e.g., Sentinel-1 req. < 6 ms)

2.1 Example of ALOS-2 ScanSAR InSAR in 2014 20% burst overlap Some pairs have good coherence Some

6 2.1 Example of ALOS-2 ScanSAR InSAR in % burst overlap Some pairs have good coherence Some have poor coherence Others have no coherence Bosnia ALOS / ALOS

2.2 ScanSAR burst overlap Master and slave burst should be alligned in azimuth direction, though it wasn t by Feb. 8, 2015.

7 2.2 ScanSAR burst overlap Master and slave burst should be alligned in azimuth direction, though it wasn t by Feb. 8, This is because of wrong setting in software for estimating azimuth position. JAXA announced the amount of misalignment estimated from orbit data (*) Burst = a 4 t 4 + a 3 t 3 + a 2 t 2 + a 1 t + a 0 (1) t: date difference between8/4, 2014 (in date) a 4 = , a 3 = , a 2 = , a 1 = , a 0 = Misalignment of burst in azimuth (latitude ) direction can be estimated from burst repetition ratio. E.g., in W2 ScanSAR, deg. actual position false position estimated by wrongly set burst alignment algorithm wrong position (ScanSAR software calculated) * ALOS-2 Project Team (2015) Effective data for interferometric analysis with PALSAR-2 ScanSAR mode. rlap_ _e.pdf

2.3 ScanSAR burst overlap Misalignment in azimuth direction appears as azimuth offset. Burst duration is known. overlap ratio can be calculated as 1-offset/duration Burst repetition Azimuth offset E.

8 2.3 ScanSAR burst overlap Misalignment in azimuth direction appears as azimuth offset. Burst duration is known. overlap ratio can be calculated as 1-offset/duration Burst repetition Azimuth offset E.g., :in W2 mode F1, repetition 2100 pixel, Duration 420 pixel If offset is 70 pixel, overlap ratio= 83.3% Burst = mod A sin 2π T P, 2P P For F1, A=3635, P=1050, T is time difference between 2014/12/20 in date ** Lindsey, E.O., Natsuaki, R. et al., Line of sight displacement from ALOS-2 interferometry: M7.8 Gorkha earthquake and mw 7.3 aftershock, Geophysical Research Letters, doi: /2015gl

9 2.4 Sample points 8 identical Orbits, Frames Incl. 2 neighboring Orbit pairs 1 Ascending observation

10 2.5 Burst overlap ratio pre- and post- Feb. 8 pairs Burst overlap ratio >20% pix. = 0.4 ms Predicted from pixel Predicted from orbit Actual offset Two identical estimations have close results * ** Lindsey, E.O., Natsuaki, R. et al., Line of sight displacement from ALOS-2 interferometry: M7.8 Gorkha earthquake and mw 7.3 aftershock, Geophysical Research Letters, doi: /2015gl

11 2.5 Burst overlap ratio pre- and post- Feb. 8 pairs Burst misalignment < 15.8 ms pix. = 0.4 ms Predicted from pixel Predicted from orbit Actual offset Two identical estimations have close results * ** Lindsey, E.O., Natsuaki, R. et al., Line of sight displacement from ALOS-2 interferometry: M7.8 Gorkha earthquake and mw 7.3 aftershock, Geophysical Research Letters, doi: /2015gl

12 Outline 1. Introduction 2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, Burst misalignment after Feb. 8, Conclusion

13 3.1 Nepal Earthquake 2015 Epicenter of main shock Epicenter of after shock Software modification worked! -> How accurate? Apr.5 May 3

14 Software modification worked! -> How accurate? May 3 May Nepal Earthquake 2015 Epicenter of main shock Epicenter of after shock

15 < >30 Sample 3.2 Histogram of misalignment 12 Req ms Misalignment [ms] STD: 12.5 ms for 70 scenes < req ms

16 Post- Feb. 8, 2015 misalignment y 1.5*10 Misalignment of ALOS-2 ScanSAR [ms] 8 x 4 1.8*10 5 x 3 6.7*10 3 x x 26.5 R2=

17 Distribution for orbit Croatia_P92 20 Philip_P24 Philip_P25 10 Napa_P168 Napa_P169 0 Gabon_P88 Hokkaido_P Antarctica_P

18 4. Conclusion Validated PALSAR-2 ScanSAR burst misalignment Limited number of Pre- Feb. 8, 2015 archive have burst overlap with Post- Feb. 8, 2015 data. -> Users must check overlap ratio before ordering. Post- Feb. data have good overlap ratio each other. Misalignment is better than its planned score. However, remaining misalignment seems not random Time dependency / orbit dependency -> can it be better?

20 Name Path Frame Flight direction Number of archives Croatia_P Descending 12 Philippine_P Descending 8 Philippine_P Descending 6 Napa_P Descending 11 Napa_P Descending 8 Gabon_P Descending 13 Hokkaido_P Ascending 5 Antarctica_P Descending 7

21 Comparison between Lindsey et al. and official offset Diff from Official Diff. from actual

1.1 ALOS-2 Technical Specifications Launched: 24 May 2014 Orbit type : Sun-synchronous Altitude : 628 km +/- 500 m (for reference orbit) Revisit time : 14 days LSDN : 12:00 +/- 15 min Solar panels

22 1.1 ALOS-2 Technical Specifications Launched: 24 May 2014 Orbit type : Sun-synchronous Altitude : 628 km +/- 500 m (for reference orbit) Revisit time : 14 days LSDN : 12:00 +/- 15 min Solar panels PALSAR-2 Z Y X PALSAR-2 L-band 24 cm w. length / 1.2 GHz freq. Synthetic Aperture Radar (SAR) Active Phased Array Antenna with two dimensional scans (range and azimuth) Antenna size : 3m(El) x 10m(Az) Bandwidth : 14 84MHz Peak transmit Power : 5100W Observation swath : km Resolution : Range: 3 m to 100 m Azimuth: 1 m to 100 m

27, 2006 10m resolution High resolution with low noise

23 1.2 First image of ALOS-2 PALSAR-2 JERS-1 SAR Apr. 21, m resolution ALOS PALSAR Apr. 27, m resolution High resolution with low noise level Observe in any weather ALOS-2 PALSAR-2 Jun. 19, m resolution

1.3 PALSAR-2 Technical Specifications Calibration Results: bracketed values are requirements and have not been calibrated High ScanSAR ScanSAR Spotlight Ultra Fine Fine sensitive nominal wide

24 1.3 PALSAR-2 Technical Specifications Calibration Results: bracketed values are requirements and have not been calibrated High ScanSAR ScanSAR Spotlight Ultra Fine Fine sensitive nominal wide Bandwidth 84MHz 84MHz 42MHz 28MHz 14MHz 28MHz 14MHz Rg Az: Resolution 3m 6m 10m 100m 60m 3 1m Rg Az: 350km 490km Swath 50km 50km 70km 25 25km (5-scan) (7-scan) Polarization SP SP/DP SP/DP/QP/CP SP/DP NESZ -36.6dB -36.6dB -36.0dB -41.1dB -41.1dB [-23dB] [-23dB] Rg Invisible Invisible Invisible Invisible Invisible Invisible S/A Az 20dB 20dB 20dB 20dB 20dB 20dB SP : HH or VV or HV, DP : HH+HV or VV+VH, QP : HH+HV+VH+VV, CP : Compact pol (Experimental) Main applications: Fine beam (DP): Forest and land cover monitoring / InSAR (Global) ScanSAR (DP): Rapid deforestation / wetlands / InSAR (large area) Spotlight (SP): Height resolution observations Ultra Fine (SP) : Global map, InSAR High sensitive (QP): Global map ScanSAR wide (SP) : Polar ice

Current Status of the ALOS-2 Operation and PALSAR-2 Calibration Activities

Current Status of the ALOS-2 Operation and PALSAR-2 Calibration Activities Takeshi Motohka, Ryo Natsuaki, Yukihiro Kankaku, Shinichi Suzuki, Masanobu Shimada (JAXA) Osamu Isoguchi (RESTEC) CEOS SAR CALVAL