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

Outline

1. Introduction

2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, 2015

3. Burst misalignment after Feb. 8, 2015

4. Conclusion

Outline

1. Introduction

2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, 2015

3. Burst misalignment after Feb. 8, 2015

4. Conclusion

Spotlight Ultra FineHigh

sensitiveFine

ScanSAR

nominal

ScanSAR

wide

Bandwidth 84MHz 84MHz 42MHz 28MHz 14MHz 28MHz 14MHz

ResolutionRg×Az：3×1m

3m 6m 10m 100m 60m

SwathRg×Az：

25×25km50km 50km 70km

350km

(5-scan)

490km

(7-scan)

Polarization SP SP/DP SP/DP/QP/CP SP/DP

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%

SP : HH or VV or HV , DP : HH+HV or VV+VH , QP : HH+HV+VH+VV , CP : Compact pol (Experimental)

1.1 ScanSAR mode of PALSAR-2

1.2 Burst overlap of ScanSAR

• 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)

F1

F2

F3

F1

F2

F3

F1

F2

F3

F1

F2

F3

master

F1

F2

F3

F1

F2

F3

F1

F2

F3

F1

F2

F3

slavett

Bu

rst

du

rati

on

Bu

rst

rep

etit

ion

2.1 Example of ALOS-2 ScanSAR InSAR in 2014

Bosnia ALOS2015722700-140907 / ALOS2021932700-141019

Some pairs have good coherenceSome have poor coherenceOthers have no coherence

20% burst overlap

• Master and slave burst should be alligned in azimuth direction, though it wasn’t by Feb. 8, 2015. This is because of wrong setting in software for estimating azimuth position.

• JAXA announced the amount of misalignment estimated from orbit data (*)

∆𝐵𝑢𝑟𝑠𝑡 = 𝑎4𝑡4 + 𝑎3𝑡

3 + 𝑎2𝑡2 + 𝑎1𝑡 + 𝑎0 (1)

𝑡: date difference between8/4, 2014 (in date) 𝑎4 = −0.000000000194, 𝑎3 =0.000000029289, 𝑎2 = 0.000010685720, 𝑎1 = −0.001106963087, 𝑎0 = −0.057085827546

• Misalignment of burst in azimuth (latitude ) direction can be estimated from burst repetition ratio.E.g., in W2 ScanSAR, 0.048348 deg.

2.2 ScanSAR burst overlap

* ALOS-2 Project Team (2015) Effective data for interferometric analysis with PALSAR-2 ScanSAR mode. https://auig2.jaxa.jp/information_home/ScanSAR_Burst_Overlap_20151127_e.pdf

actual position

false position estimated by wrongly set burst alignment algorithm

wrong position(ScanSAR software calculated)

** 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:10.1002/2015GL065385.

2.3 ScanSAR burst overlap

• Misalignment in azimuth direction appears as azimuth offset.

• Burst duration is known.

• overlap ratio can be calculated as1-offset/duration

• E.g., ：in W2 mode F1,repetition 2100 pixel, Duration 420 pixelIf offset is 70 pixel, overlap ratio= 83.3%

• For F1, A=3635, P=1050, T is time difference between 2014/12/20 in date

Azimuth offset

Burst repetition

∆𝐵𝑢𝑟𝑠𝑡 = 𝑚𝑜𝑑 𝐴 sin 2𝜋 𝑇 365 + 𝑃, 2𝑃 − 𝑃

2.4 Sample points

8 identical Orbits, FramesIncl. 2 neighboring Orbit pairs

1 Ascending observation

2.5 Burst overlap ratio pre- and post- Feb. 8 pairs

-1100

-900

-700

-500

-300

-100

100

300

500

700

900

1100

10.07.2014 29.08.2014 18.10.2014 07.12.2014 26.01.2015

Predicted from pixel Predicted from orbit Actual offset

Burst overlap ratio >20%

Two identical estimations have close results* https://auig2.jaxa.jp/information_home/ScanSAR_Burst_Overlap_20151127_e.pdf** 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:10.1002/2015GL065385.

1pix. = 0.4 ms

2.5 Burst overlap ratio pre- and post- Feb. 8 pairs

-1100

-900

-700

-500

-300

-100

100

300

500

700

900

1100

10.07.2014 29.08.2014 18.10.2014 07.12.2014 26.01.2015

Predicted from pixel Predicted from orbit Actual offset

Burst misalignment < 15.8 ms

Two identical estimations have close results* https://auig2.jaxa.jp/information_home/ScanSAR_Burst_Overlap_20151127_e.pdf** 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:10.1002/2015GL065385.

1pix. = 0.4 ms

Outline

1. Introduction

2. ALOS-2 ScanSAR burst misalignment befor Feb. 8, 2015

3. Burst misalignment after Feb. 8, 2015

4. Conclusion

3.1 Nepal Earthquake 2015

Epicenter of main shock

Epicenter of after shock

Apr.5 – May 3Software modification worked! -> How accurate?

3.1 Nepal Earthquake 2015

Epicenter of main shock

Epicenter of after shock

May 3 – May 17

Software modification worked! -> How accurate?

3.2 Histogram of misalignment

0

2

4

6

8

10

12

<-3

0

-30

-26

-22

-18

-14

-10 -6 -2 2 6

10

14

18

22

26

30

>30

Sam

ple

Misalignment [ms]STD: 12.5 ms for 70 scenes < req. 15.8 ms

Req. 15.8 ms

3.3 Post- Feb. 8, 2015 misalignment

-30

-20

-10

0

10

20

30

40

50

08

.02

.20

15

19

.05

.20

15

27

.08

.20

15

05

.12

.20

15

14

.03

.20

16

22

.06

.20

16

Misalignment of ALOS-2 ScanSAR [ms]

5.2686.010*7.610*8.110*5.1 233548 xxxxy

R2= 0.54

3.4 Distribution for orbit

-30

-20

-10

0

10

20

30

40

500

8.0

2.2

01

5

19

.05

.20

15

27

.08

.20

15

05

.12

.20

15

14

.03

.20

16

22

.06

.20

16

Croatia_P92

Philip_P24

Philip_P25

Napa_P168

Napa_P169

Gabon_P88

Hokkaido_P123

Antarctica_P53

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?

Name Path Frame Flight direction Number of archives

Croatia_P92 92 2700 Descending 12Philippine_P24 24 3350 Descending 8Philippine_P25 25 3350 Descending 6Napa_P168 168 2850 Descending 11Napa_P169 169 2850 Descending 8Gabon_P88 88 3650 Descending 13Hokkaido_P123 123 850 Ascending 5Antarctica_P53 53 5050 Descending 7

Comparison between Lindsey et al. and official offset

-150

-100

-50

0

50

100

150

10.06.2014 30.07.2014 18.09.2014 07.11.2014 27.12.2014 15.02.2015 06.04.2015

Diff from Official Diff. from actual

1.1 ALOS-2 Technical Specifications

Launched: 24 May 2014Orbit type : Sun-synchronousAltitude : 628 km +/- 500 m (for reference orbit)Revisit time : 14 daysLSDN : 12:00 +/- 15 min

PALSAR-2

X

Y

Z

Solar panels

PALSAR-2 L-band

24 cm w. length / 1.2 GHz freq. Synthetic Aperture Radar (SAR)

Active Phased Array Antennawith two dimensional scans (range and azimuth)Antenna size : 3m(El) x 10m(Az)Bandwidth : 14 – 84MHzPeak transmit Power : 5100WObservation swath : 25 – 490 kmResolution : Range: 3 m to 100 m

Azimuth: 1 m to 100 m

1.2 First image of ALOS-2 PALSAR-2

JERS-1 SAR

Apr. 21, 1992

18m resolution

ALOS PALSAR

Apr. 27, 2006

10m resolution

ALOS-2 PALSAR-2

Jun. 19, 2014

3m resolution

High resolution with low noise levelObserve in any weather

Spotlight Ultra FineHigh

sensitiveFine

ScanSAR

nominal

ScanSAR

wide

Bandwidth 84MHz 84MHz 42MHz 28MHz 14MHz 28MHz 14MHz

ResolutionRg×Az：3×1m

3m 6m 10m 100m 60m

SwathRg×Az：

25×25km50km 50km 70km

350km

(5-scan)

490km

(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]

S/ARg Invisible Invisible Invisible Invisible Invisible Invisible

Az 20dB 20dB 20dB 20dB 20dB 20dB

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

SP : HH or VV or HV , DP : HH+HV or VV+VH , QP : HH+HV+VH+VV , CP : Compact pol (Experimental)

1.3 PALSAR-2 Technical Specifications

Calibration Results: bracketed values are requirements and have not been calibrated

http://www.eorc.jaxa.jp/ALOS-2/en/obs/pal2_obs_guide.htm