EVALUATION OF PLEIADES-1A TRIPLET ON TRENTO...

EVALUATION OF PLEIADES-1A TRIPLET ON TRENTO TESTFIELD

D. Poli a, F. Remondino b, E. Angiuli c, G. Agugiaro b

a Terra Messflug GmbH, Austria b 3D Optical Metrology Unit, Fondazione Bruno Kessler, Trento, Italy

c Joint Research Center, European Commission, Ispra (VA), Italy

Outline

• Motivation

• Pleiades sensor description

• Data description

• Radiometric analysis

• Geometric processing

• DSM quality assessment

• Conclusion

22/5/2013 EVALUATION OF PLEIADES-1A TRIPLET ON TRENTO TESTFIELD 2

Motivation

• Evaluation of 3D information extraction from VHR spaceborne image sensors on Trento testfield

• Analysis started with WorldView-2 and GeoEye-1 stereopairs (Melbourne, 2012)

• Pleiades triplet available through evaluation program organized by ASTRIUM GEO

• Few publications on Pleiades


Trento testfield


Area: ca. 15x15km Min height: 150m Max height: 2181m Trento Population: 115000 inh. Height: ca. 200m

Trento testfield


Space- and airborne imagery overview • Pleiades triplet • WorldView-2 stereopair • GeoEye-1 stereopair • Quickbird, Quickbird

single scenes • Aerial images (white) • UAV images • SPOT

Trento testfield – other data

• DSM/DTM derived from a LiDAR flight in 2006/7. Cell size 1m (2m on mountainous areas). Reference dataset for the geometric analyses.

• 230 digital orthophotos (2006 and 2009), GSD 50 cm.

• Aerial flight with RMK TOP15 analogic camera (2009) over the city of Trento. GSD 12 cm.

• 180 UAV images (2012), acquired by a Microdrones MD4-200 mounting a Pentax Optio A40 digital camera (overlap: 80% along track, 40% across track). GSD 3 cm

• 70 ground points (2011), acq. by GNSS

• 12 ground points (2012), acq. by total station


Pleiades mission

• Part of the French-Italian ORFEO system

• Military and civil use

• Pleiades system: – Pleiades 1A (launched in December 2011)

– Pleiades 1B (launched in December 2012)

• Orbit:

– height 694km

– near-polar (98.2°)

– sun-synchronous

– 180° satellite phase


Pleiades images

• HiRi CCD cameras (1 camera/satellite) – GSD 0.7m PAN (nadir)

– GSD 2.8m MS (nadir)

• Revisit time: 1 day

• Acquisition modes (one pass): – Target, Strip Mapping, Tri-stereo

– Corridor and Persistent Surveillance

• Stereo acquisition modes: – Stereo

– Tri-stereo


Pleiades images


Pleiade images over Trento

Image 1 Image 2 Image 3

Along-track (°) 12.35 -12.69 17.38

Across-track (°) 1.83 3.00 1.78

GSD (m) 0.72x0.73 0.74x0.73 0.78x0.74

Size (columns) 41427 41149 40436

Size (rows) 36199 36348 34446

Acquisition time 10:22:15 10:23:01 10:22:06

Solar Azimuth (°) 157.85 158.24 157.85

Solar Elevation (°) 51.79 51.85 51.79

Cloud cover 0 0 0



Image 1 Image 2 Image 3

Pleiade images over Trento

Radiometric analysis • Image quality and suitability are strongly affected by

sensor viewing angle, sun acquisition angle and atmospheric conditions.

• Although not possible to compensate the effects induced by each component, through radiometric and DN analysis we can evaluate and distinguish some problems.

• Even if data is available at 12-bit, the main information is distributed between 0 and 10 bit.


Noise estimation

• With the term “noise”, we refer to all the anomalies and non-homogeneity that can be found in the image

• Spilling effects not present in the images

• “Non-homogeneity” noise effects (“filth” analysis of homogeneous areas)

– Image divided into 5 bins (0-255, 256-511, 512-1023, 1024-2047, 2048-4095)

– For each bin i, normalized standard deviation computed for samples j in 5x5 pixel window


Noise estimation Channel Image 0

255

256 511

512 1023

1024 2047

2048 4095

Pan 1 2.26 2.28 2.60 2.61 2.60

Pan 2 2.06 2.06 2.60 2.61 2.63

Pan 3 2.27 2.30 2.60 2.69 2.70

Red 1 2.07 2.26 2.52 N/A N/A

Red 2 1.93 2.03 2.57 N/A N/A

Red 3 2.10 2.33 2.04 N/A N/A

Green 1 2.14 2.40 2.60 2.62 2.62

Green 2 1.97 2.18 2.16 2.79 2.8

Green 3 2.17 2.44 2.60 N/A N/A

Blue 1 2.56 2.49 2.51 2.63 2.65

Blue 2 N/A 2.50 2.40 N/A N/A

Blue 3 2.57 2.50 2.57 N/A N/A

NIR 1 1.60 2.08 2.39 2.43 2.50

NIR 2 1.33 2.05 2.10 2.57 2.63

NIR 3 1.58 2.07 2.39 2.63 2.75


Geometric processing


Data acquisition • Pleaides triplet

• Ground points

Image orientation

• RPC model (RPC provided in metadata file)

• RPC correction with affine model

• Sub-pixel accuracy in check points

Image matching • Least-square matching

• Measurement of few seed points

DSM generation

• Triangulazion and rasterization

• No editing

• Output: three DSMs (1m grid)

• From triplet

• From two pairs (1-2 and 2-3)

Orthorectification

OpticalSCAPE

• ENVI module, recently released

• Developed by sarmap SA (Switzerland) and 4DiXplorer AG (Switzerland)

• Functionalities of SAT-PP software for geometric processing, plus DEM fusion (i.e. optical/SAR)

• Advantage of ENVI environment


DSM quality analysis

• Visual inspection

• Quantitative comparison of DSM from triplet with Lidar

• Comparison between triplet and stereo pairs

• Comparison with WV2 and GE1 DSMs



• DSM successfully generated from triplet and stereo pairs

22/5/2013 EVALUATION OF PLEIADES-1A TRIPLET ON TRENTO TESTFIELD


• Shape of the terrain in flat, hilly and mountain areas is correctly modelled, even in case of rapid height changes

• Urban areas: the road network, building blocks and large single buildings can be clearly recognised in the surface model, as well as the shape of large buildings

• Surface well modelled on homogeneous areas, like rural fields


Comparison with Lidar

• Quantitative analysis in 3 areas

• Computed height differences and statistics within areas (min, max, avg, median, stdev, RMSE)


Trento center Historical city centre. Completely built up area, irregular building shapes, narrow streets, nearly no vegetation

Trento railway station Large regular buildings, larger streets with some trees

Trento Fersina Residential area. Regular geometries, courtyards and streets with trees.

Comparison with Lidar – Trento center


min: -42.39 max: 24.22

mean: 1.38

Median: 0.06 RMSE: 6.12

Lidar Pleiades DSM Height differences Lidar above the DSM Lidar below the DSM

Comparison with Lidar – Trento station


min: -33.10 max: 54.69

mean: 1.05


Lidar Pleiades DSM Height differences Lidar above the DSM Lidar below the DSM

Comparison with Lidar – Trento Fersina


min: -42.91 max: 24.22

mean: 0.47


Lidar

Pleiades DSM Height differences Lidar above the DSM Lidar below the DSM

Comparison with Lidar – height profiles


Profiles: Lidar, Pleiades

Comparison between triplet and pairs

• No significant differences in the statistics of the height differences with respect to the reference Lidar DSM

• Advantage of triplet: reduction of local blunders, mainly in presence of occlusions


Comparison with WV2 and GE1 • Data and processing in (Agugiaro et al., 2012 - ISPRS

Melbourne)


WorldView-2 (WV2) stereopair: Acquisition on: 22 Aug 2010, 10:40 am (GMT) PAN + MS8 (R, G, B, NIR, coastal, yellow, red edge, and

NIR-2), avg GSD 0.5 m (PAN), 2 m (MS) Processing level: Stereo 1B Provided with RPCs FS, in-track view. angle 15.9°, RS, -14.0° Cloud cover <10%

GeoEye-1 (GE1) stereopair:

Acquisition on: 8 Sep 2011, 10:20 am (GMT)

PAN + MS4

avg GSD 0.5 m (PAN), 2 m (MS)

Processing level: GeoStereo

Provided with RPCs

RS, in-track view. angle 15°, RS, -20°

Cloud cover <4%

Comparison with WV2 and GE1 • DSM quality analysis (1m size)


Min Max mean RMSE

Trento centre Pleiades -42.4 24.2 1.4 6.1

WV2 -53.9 26.7 1.9 7.4

GE1 -44.4 26.5 2.3 6.9

Trento train station Pleiades -33.1 54.7 1.0 6.5

WV2 -39.0 58.4 0.7 7.4

GE1 -28.1 53.5 1.7 7.1

Trento Fersina Pleiades -42.9 24.2 0.5 6.7

WV2 -43.7 27.7 0.3 8.5

GE1 -46.3 28.8 0.5 7.9

Mean GSD: WV2 0.51m, GE1 0.51m, Pleiades 0.75m

Conclusions

• Trento testfield is update with last VHR satellite images, mainly for 3D investigations.

• Pleiades triplet analyzed radiometrically and geometrically

• Good radiometric quality

• Triplet and stereo DSMs (no edited) show good quality, both visually and after quantitative comparison to Lidar

• Similar behavior of WV2 and GE1, despite lower GSD

• Problematic areas are occlusions, but triplet acquisition reduces local blunders


Conclusions

• Triplet geometry of current triplet not optical. Better results are expected with nadir scene + two off-nadir


• Future work:

– Radiometric comparison with WV2 and GE1

– Comparison of Pleiades DSM with Elevation1 product

Courtesy: Astrium

Thank you for

your attention

Credits: ASTRIUM GEO-Information Services Provincia Autonoma di Trento, Italy

3M project (co-founded Marie-Curie Actions FP7 – PCOFOUND – GA-2008-226070, acronym “Trentino Project”)

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