ADEN ALOS PALSAR PRODUCT VERIFICATION Patricia Wright 1 , Peter - - PowerPoint PPT Presentation

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ADEN ALOS PALSAR PRODUCT VERIFICATION Patricia Wright 1 , Peter Meadows 1 , Gordon Mack 2 , Nuno Miranda 3 & Marco Lavalle 4 1 BAE SYSTEMS Advanced Technology Centre, Chelmsford, UK 2 VEGA Group PLC, Welwyn Garden City, UK 3 ESA/ESRIN, Frascati,

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SLIDE 1

ALOS PI Symposium, 3rd November 2008

ADEN ALOS PALSAR PRODUCT VERIFICATION

Advanced Technology Centre

Patricia Wright1, Peter Meadows1, Gordon Mack2, Nuno Miranda3 & Marco Lavalle4

1BAE SYSTEMS Advanced Technology Centre, Chelmsford, UK 2VEGA Group PLC, Welwyn Garden City, UK 3ESA/ESRIN, Frascati, Italy 4University of Rome “Tor Vergata”, Italy

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SLIDE 2

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Introduction

  • Within the ALOS Data European Node (ADEN) the verification of

PALSAR products is an important and continuing activity, to ensure data utility for the users.

  • This is performed for ESA-ESRIN by the PALSAR team within

Instrument Data Quality Evaluation and Analysis Service (IDEAS).

  • There are three levels of PALSAR products: L0 (raw data), L1.1

(complex data) and L1.5 (detected data).

  • We examine four product types: fine mode single polarisation (FBS),

fine mode dual polarisation (FBD), fine mode quad polarisation (PLR) and wideswath (WS).

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SLIDE 3

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Routine Analysis

  • Header analysis of all PALSAR

products distributed electronically by ADEN (Level 1.0, 1.1 and 1.5).

  • Parameters examined include:
  • Data Coverage
  • Doppler frequency
  • Spacecraft attitude
  • Pulse repetition frequency
  • Orbit state vectors
  • 1600
  • 1100
  • 600
  • 100

400 1000 2000 3000 4000 5000 6000 7000 8000 Frame Doppler Centroid Frequency (Hz)

Doppler centroid frequency monitoring – note the data points at -1600Hz due to suspension of yaw steering.

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SLIDE 4

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Product Visualisation

  • Visual inspection performed on

a sample set of PALSAR products.

  • Several types of artefacts
  • bserved:
  • Interference
  • Ambiguities
  • Wideswath sub-swath

boundaries

  • Wideswath scalloping
  • Wideswath azimuth

fluctuation

Interference Range Ambiguities

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SLIDE 5

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • The majority of the artefacts are seen in wideswath imagery, some

in single/dual polarisation imagery and very few in quad pol data.

Wideswath sub-swath boundaries and azimuth intensity fluctuations

Product Type P1.1 P1.5W1.5H1.1H1.5 Sub-Swath Boundaries 20 Azimuth Ambiguity 1 7 5 Scalloping 10 1 Incorrect Antenna Pattern Correction 1 1 Range Ambiguity 1 2 6 5 12 Azimuth Focusing 1 1 Sub-Swath Range Intensity Fluctuation 3 Azimuth Intensity Fluctuation 7 Interference 6 1 Total Number Of Products Inspected 19 28 46 34 68

P is quad-pol, W is wideswath and H is single or dual pol

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SLIDE 6

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Impulse Response Function (IRF) Analysis

  • IRF analysis assesses the spatial resolution and sidelobe properties
  • f the data (for comparison with theoretical results).
  • PALSAR products acquired over ground stations at Maspalomas,

Spain, Matera, Italy and Tromsø, Norway and the DLR corner reflectors, Germany have been used.

Maspalomas Ground Station IRF in wideswath imagery (rcs too high for fine mode imagery) Resampled Image Slice through IRF Peak

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SLIDE 7

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • IRF measurements include azimuth and range spatial resolution,

integrated sidelobe, peak sidelobe and spurious sidelobe ratios.

Acq Date Inc Ang Azi Res (m) Range Res (m) ISLR (dB) PSLR (dB) SSLR (dB) 16/04/07 39.2 169.1 120.9

  • 15.1
  • 8.5
  • 11.9

10/07/07 20.2 131.7 135.3 0.5

  • 8.9
  • 9.0

25/08/07 40.7 166.8 187.6

  • 5.0
  • 10.9
  • 12.1

10/10/07 40.7 128.5 129.4

  • 7.7
  • 8.6
  • 11.5

25/11/07 40.8 165.7 123.0

  • 12.4
  • 6.5
  • 11.7

02/12/07 23.0 170.3 121.3

  • 0.9
  • 9.1
  • 9.0

11/04/08 40.8 165.3 147.5

  • 2.6
  • 11.2
  • 9.6

03/09/08 22.7 133.5 125.8 6.3

  • 4.6
  • 6.4
  • Variability in the spatial resolution is due to the data being

undersampled (pixel size is 100m). The ISLR is also quite variable while the PSLR and SSLR are acceptable.

Maspalomas WS HH IRF Measurements

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SLIDE 8

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Matera Level 1.5 FBS and FBD HH IRF Measurements Matera Ground Station IRF in Level 1.1 Single Polarisation Imagery

Acq Date Inc Ang Azi Res (m) Range Res (m) ISLR (dB) PSLR (dB) SSLR (dB) 20/02/07 38.7 8.5 7.7

  • 9.4
  • 7.9
  • 10.7

Acq Date Inc Ang Azi Res (m) Range Res (m) ISLR (dB) PSLR (dB) SSLR (dB) 23/08/07 38.6 21.2 21.2 11.5

  • 0.8

10.9

  • Spatial resolution indicates that the data is undersampled (pixel

size is 6.25m for FBS and 12.5m for FBD). The FBD sidelobes high.

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SLIDE 9

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008 Acq Date Inc Ang Azi Res (m) Range Res (m) ISLR (dB) PSLR (dB) SSLR (dB) 05/01/07 38.9 4.47 4.59

  • 3.47
  • 20/02/07 38.8 4.47

4.47

  • 2.10
  • 08/01/08 38.7 4.59

4.61

  • 3.78
  • 23/02/08 38.6 4.28

4.55

  • 1.34
  • 09/04/08 38.6 4.23

4.44

  • 0.00
  • Acq Date

Inc Ang Azi Res (m) Range Res (m) ISLR (dB) PSLR (dB) SSLR (dB) 08/07/07 38.7 4.75 9.33 0.93

  • 23/08/07 38.7 4.61

9.20 1.15

  • 25/05/08 38.6 5.71

9.56 1.79

  • 10/07/08 38.8 4.37

10.00 2.61

  • 25/08/08 38.9 4.71

9.08 4.79

  • 25/08/08 38.9 5.46

9.91 2.68

  • Matera Level 1.1 FBS and FBD HH IRF Measurements
  • Spatial resolutions comparable with theoretical values (data also

adequately sampled). ISLR high due to ground station rcs being low (~30dbm2) and consequently the background is quite high relative to the IRF. This is the reason why PSLR and SSLR is not calculated.

  • Tromsø ground station results similar to Matera (also FBS and FBD).
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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

DLR Level 1.5 PLR IRF Measurements

  • During the ADEN commissioning phase six corner reflectors

deployed by DLR, Germany as suitable point targets for IRF analysis.

Acq Date Pol Azi Res (m) Range Res (m) ISLR (m) PSLR (m) SSLR (m) 06/09/06 HH 16.7 22.3

  • 1.1
  • 6.0
  • 12.7

06/09/06 VV 16.5 26.4

  • 1.2
  • 8.4
  • 12.7

15/11/06 HH 18.0 27.3

  • 0.1
  • 7.7
  • 10.0

15/11/06 VV 17.1 26.7 0.9

  • 7.5
  • 10.6
  • The Level 1.5 spatial resolution measurements indicate that the

products are undersampled in azimuth (the PLR pixel size is 12.5m) but not in range. The ISLR values are high while the PSLR and SSLR values are reasonable.

  • The Level 1.1 spatial resolution measurements are comparable with

their theoretical values and the sidelobe ratios are lower than the corresponding Level 1.5 measurements.

Acq Date Pol Azi Res (m) Range Res (m) ISLR (m) PSLR (m) SSLR (m) 06/09/06 HH 4.48 9.63

  • 5.2
  • 12.7
  • 17.2

06/09/06 VV 4.44 9.85

  • 5.3
  • 14.0
  • 14.7

15/11/06 HH 4.58 9.77

  • 5.4
  • 11.6
  • 16.7

15/11/06 VV 4.66 9.78

  • 5.7
  • 11.2
  • 17.4

DLR Level 1.1 PLR IRF Measurements

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Radiometric Stability

  • A successful method of assessing the stability the SAR instruments

such as ERS-2 SAR and Envisat ASAR has been to be the Amazon rainforest by calculating and monitoring gamma (σ0/cos(i)).

  • Since Amazon rainforest data is not available for PALSAR data

within the ADEN node, an alternative site within the African rainforest has been selected.

Fine Mode Level 1.5 African Rainforest Image Gamma range profile

  • 6.2
  • 6.0
  • 5.8
  • 5.6
  • 5.4

36 37 38 39 40 41 Incidence Angle (deg) Gamma (dB)

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • There is some variability in the mean gamma (max – min = 0.18dB)

and in the slope of gamma from near to far range. The mean gamma is -5.76±0.07dB.

  • This indicates an excellent PALSAR radiometric stability of 0.07dB.

Acq Date Orbit Mean Gamma Trend 21/02/07 5745

  • 5.75 dB
  • 0.02 dB

09/10/07 9100

  • 5.81 dB
  • 0.10 dB

24/11/07 9771

  • 5.82 dB
  • 0.23 dB

09/01/08 10442

  • 5.84 dB

0.27 dB 24/02/08 11113

  • 5.70 dB

0.37 dB 10/04/08 11784

  • 5.66 dB

0.00 dB

Mean gamma and trend for Fine Mode African Rainforest Imagery (HH polarisation)

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SLIDE 13

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Noise Equivalent Sigma0

  • The upper limit to the noise equivalent radar cross-section

(NESigma0) of an image can be estimated by measuring the radar cross-section of low intensity regions (usually ocean region under low wind speed conditions).

  • Measurements compare favourably with the JAXA specifications of
  • 21dB for HH & VV polarisations and -25dB for HV & VH

polarisations.

NESigma0 Measurements Mean NESigma0

  • 40
  • 35
  • 30
  • 25
  • 20

15 20 25 30 35 40 45 Incidence angle (deg) NESigma0 (dB)

HV VH VV HH

Polarisation NESigma0 HH

  • 24.84±2.89

HV

  • 30.61±1.96

VH

  • 27.44±3.23
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SLIDE 14

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

ENL and Radiometric Resolution

  • The equivalent number of looks and the radiometric resolution can

be measured directly from PALSAR imagery by using large uniform distributed targets.

  • The measured ENL are close to the actual ENL used in the

processing:

ENL and RR Measurements

Product Actual ENL ENL Rad Res (dB)

  • No. Results

P1.1 1 0.87 3.17 9 P1.5 4 4.23 1.72 4 H1.1 (FBS) 1 0.98 3.04 1 H1.5 (FBS) 2 1.28 2.79 5 H1.1 (FBD) 1 0.82 3.24 2 H1.5 (FBD) 4 3.35 1.89 6 W1.5 8 7.21 1.41 7

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Ambiguities

  • Both azimuth and range ambiguities have been found in fine and

wideswath mode PALSAR imagery.

  • The image below shows azimuth ambiguities from towns and the high

rcs from mountains.

FBD acquisition from 20th February 2007

  • Azimuth ambiguity

measurements of between

  • 11.0dB and -15.1dB have been

made c.f. a specification of

  • 16dB.
  • Range ambiguity ratio

difficult to measure as source

  • f ambiguity is outside image.
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SLIDE 16

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Image Localisation

  • Although the ALOS platform operates with yaw steering it does not

acquire data with a non-zero Doppler. This is because the ALOS yaw axis is aligned with the centre of the earth rather than being aligned to maintain local orthogonality.

  • A consequence of this type of yaw steering is that the Doppler

frequency is not set to zero and changes as a function of latitude and beam number.

  • The ADEN PALSAR ground range Level 1.5 products are processed

to zero-Doppler but not the slant range Level 1.1 products.

  • Consequently Level 1.1 products need to have a range dependant

azimuth shift applied.

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • The absolute localisation accuracy (ALE) has been derived from the

average difference between the predicted and measured pixel positions of the six DLR corner reflectors.

  • The Level 1.1 range ALE is small at less than 6m while the azimuth

ALE is still less than 20m in all but one of the products.

Acq Date Product Type Range ALE (m) Azimuth ALE (m) 06/08/06 FBS

  • 4.87
  • 18.37

01/08/06 FBS

  • 4.38

5.90 14/07/06 FBD

  • 5.16

46.25 23/05/06 FBD

  • 1.03
  • 16.90

06/09/06 PLR

  • 4.80

6.55 15/11/06 PLR

  • 1.91

4.84

Level 1.1 Absolute Localisation Accuracy

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • The Level 1.5 range ALE differs between products and is up to 100m

in one case. In azimuth there is less difference in the ALE at less than 20m.

Acq Date Product Type Range ALE (m) Azimuth ALE (m) 06/08/06 FBS 30.08

  • 6.72

01/08/06 FBS

  • 0.87
  • 7.12

14/07/06 FBD

  • 103.79

6.32 23/05/06 FBD 48.57

  • 2.86

06/09/06 PLR

  • 6.38
  • 19.48

15/11/06 PLR

  • 26.78

1.02

Level 1.5 Absolute Localisation Accuracy

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SLIDE 19

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Polarimetric Calibration

  • The quad polarisation (PLR) mean channel registration in range is

0.94±0.80m and 0.83±0.98m in azimuth (i.e. sub-pixel). For dual polarisation (FBD) data, the mean channel registration in range is 1.34±1.04m and in azimuth is 1.06m±0.71m (i.e. sub-pixel).

  • Occasional product has high phase correlation:

Orbit Frame HVVH phase Mean HV/VH amplitude Mean (dB) SNR Mean (dB) VVVH coherence Mean HHHV coherence Mean HHVV phase. Mean 6940 1260 23.1±24.6° 3.2±5.5 6.1±3.8 0.26±0.11 0.23±0.11 19.3±9.7° 7072 1020 2.2±22.6°

  • 0.2±6.6

1.4±5.8 0.14±0.08 0.17±0.11 6.2±27.7° 6321 2640 3.0±33.1° 0.2±6.5 1.1±6.2 0.20±0.10 0.22±0.11 6.1±26.6° 5650 2640 2.1±21.1° 0.2±5.8 5.3±5.7 0.14±0.08 0.15±0.09

  • 4.6±23.7°

7024 800 3.1±15.2°

  • 0.1±6.7

1.8±4.5 0.21±0.11 0.23±0.12 3.9 ±10.7° 6474 1080 26.5±22.8°

  • 1.0±7.4
  • 3.3±2.6

0.19±0.08 0.19±0.07 4.3±7.4° 6575 1380 1.2±2.4° 0.1±4.8 9.8±2.6 0.12±0.06 0.14±0.07 0.0±3.9° 6327 1370 0.9±2.8° 0.1±5.0 8.0±2.7 0.11±0.61 0.14±0.07

  • 2.0±5.2°

7189 100 24.0±2.0° 3.4±4.0 11.7±1.6 0.10±0.05 0.11±0.06 21.0±10.6° 7233 100 0.9±1.2° 0.3±3.5 12.2±1.8 0.09±0.05 0.09±0.05

  • 1.6±14.8°

7261 100 3.3±15.3° 0.2±4.4 11.8±4.6 0.10±0.06 0.11±0.06 0.6±6.7° 7276 100 1.18±1.3° 0.1±3.6 11.7±2.1 0.09±0.05 0.1±0.05 7.1±9.6° 6248 2690 4.8±11.6° 0.0±6.3 3.7±3.7 0.19±0.12 0.22±0.14 3.7±14.7° 4230 7150 0.3±2.7°

  • 0.3±3.5

11.7±1.5 0.09±0.05 0.09±0.05 6.6±13.6°

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SLIDE 20

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • Cross-talk generally within expected range of -25dB to -30dB
  • A is the channel reciprocity
  • W is the transmit H to V cross talk
  • U is the receive H to V cross talk
  • V is the transmit V to H cross talk
  • Z is the receive V to H cross talk

Orbit Latitude (°) Frame Calculated values (mean) A U(dB) Z(dB) W(dB) V(dB) 7072 51.08 1020 0.97

  • 32.7±5.0
  • 31.1±1.0
  • 35.7±2.6
  • 36.1±4.9

6940 62.29 1260 0.92

  • 29.7±0.0
  • 30.2±0.0
  • 30.2±0.1
  • 31.6±2.3

6321 48.14 2640 0.86

  • 21.2±2.4
  • 25.8±1.5
  • 23.7±0.5
  • 31.8±5.1

5650 48.14 2640 0.98

  • 33.0±0.1
  • 33.3±1.8
  • 34.8±2.8
  • 36.9±0.7

7204 40.25 800 0.83

  • 26.2±8.4
  • 31.8±5.7
  • 25.3±5.8
  • 29.3±2.9

7189 5.50 100 1.19

  • 48.6±0.8
  • 34.4±0.5
  • 32.4±8.1
  • 31.3±2.5
  • No significant variations in cross-talk with range
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SLIDE 21

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Faraday Rotation (FR)

  • FR has the effect of rotating the plane of polarisation.
  • It leads to a much lower return than expected in co-pol channels and

a much higher return in the cross-pol channels.

  • FR greatest at mid-latitudes, at around 1-2pm local time and at the

equinoxes.

  • FR least at just before dawn, at polar and equatorial locations and at

the solstices.

  • The accuracies of retrieved geophysical parameters such as soil

moisture can be affected if FR exceeds ~5-8°.

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • Equatorial products give a baseline mean FR values of 0.51°.
  • Non-equatorial day time products around the vernal equinox give FR

values of ~2.5°.

Orbit Latitude (°) Longitude (°) Frame

  • Acq. Date

UT Local time Calculated FR (deg) 7072 51.08 11.02 1020 23/05/07 21:21 21:50 1.20±0.53 6940 62.29 23.9 1260 14/05/07 20:13 21:26 3.02±0.34 6321 48.14 11.28 2640 2/04/07 10:06 11:06 2.54±1.14 5650 48.14 11.29 2640 15/02/07 10:05 11:06 1.13±1.03 7204 40.25

  • 3.48

800 01/06/07 22:29 22:00 1.95±0.32 6474 54.00 8.29 1080 12/04/07 21:28 21:50 0.76±0.24 6575 68.55 27.59 1380 19/04/07 19:43 21:05 0.95±0.17 6327 68.05 28.54 1370 02/04/07 19:41 21:18 0.90±0.18 7189 5.50 14.50 100 31/05/07 21:38 22:26 0.70±0.29 7233 5.50 8.60 100 03/06/07 22:02 22:26 0.59±018 7261 5.50 37.56 100 05/06/07 20:06 22:26 0.35±0.2 7276 5.50 27.37 100 06/06/07 20:47 22:26 0.41±0.16 6248 45.4 11.9 2690 28/3/07 10:00 11:06 2.50±0.34 4230

  • 2.00
  • 61.7

7150 10/11/06 10:02 10:48

  • 0.98±0.21
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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • Additional analysis of 30 PLR products gives a comparison from FR

derived from imagery and TEC data:

  • The measured FR values are clustered around 0 while the TEC based

values are just above zero. Both have FR values within ±10°.

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SLIDE 24

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

  • A comparison of FR derived from data before and after polarimetric

calibration show a good correlation for the majority of products:

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Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

ADEN JAXA Processor Status

  • Prior to v5.02 of the JAXA processor becoming operational by 19th

September 2008 a verification of sample products was performed.

  • An example of an improvement is the wideswath elevation antenna

pattern:

v4.03 v5.02

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SLIDE 26

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Other Issues

  • JAXA conducts PALSAR calibration acquisitions before and after

normal acquisition operations. Scenes containing data from these calibration acquisitions have been found to be present in the ADEN catalogue.

  • Processing of these products to levels 1.1 and 1.5 will fail, however it

is possible to order this data at level 1.0.

  • An operation is currently underway to clean this calibration data

from the catalogue to avoid users ordering such data.

  • JAXA have recommended that only Level 1.1 products should be

used for point target radar cross-section measurements.

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SLIDE 27

Advanced Technology Centre ALOS PI Symposium, 3rd November 2008

Summary

  • A variety of quality and calibration parameters have been measured

by the IDEAS PALSAR team and presented here. Many of these measurements are available to users in the PALSAR cyclic reports (once approved by JAXA).

  • These cyclic reports, a FAQ, product format descriptions and

processor version history are available from the ESA PCS web site (http://earth.esa.int/pcs/alos/palsar/).

  • Additional information can be found on the ESA Earthnet Online

web site (http://earth.esa.int/ALOS/) including a document on PALSAR products and their radiometric calibration (“Information on ALOS PALSAR Products for ADEN Users”, ALOS-GSEG-EOPG-TN- 07-0001).