Analysis of Urban Areas Scattering with Simulated SAR Imagery

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Emery Patterson
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1 Analysis of Urban Areas Scattering with Simulated SAR Imagery G. Margarit, J. J. Mallorquí, I. Corney, L. Pipia, C. López-Martínez, X. Fàbregas, A. Aguasca Remote Sensing Laboratory (RSLab) D3-211 Campus Nord, C\ Jordi Girona 1-3, E-08034, Barcelona, Spain 1/20 Dept. Signal Theory & Communications

2 Outline! High resolution new sensors are increasing the sensitivity to targets geometry changes, specially in urban areas.! Realistic models are required for better data interpretation. The lack of ground-truth or controlled scenarios can be compensated with simulated data.! This work uses the SAR simulator GRECOSAR to perform a scattering study of urban areas. Support to UPC s GB-SAR experimental campaigns. Determine which geometries presents more stable polarimetric responses with respect observation conditions. Support the development of new analysis methods based on PolInSAR: Classification. Urban Subsidence monitoring with DInSAR. The influence of time dimension is preliminary studied. 2/20 Dept. Signal Theory & Communications

3 GRECOSAR: SAR Simulator of real targets! SAR simulator based on high-frequency EM calculations: Any SAR sensor (orbital, airborne and ground-based) at any band and resolution Stripmap, Scansar, Spotlight or ISAR (future sliding-spot, tops, ) Polarimetry and Interferometry Realistic 3D models based on dielectric facets considering material information.! Previous usage of GRECOSAR in ship scattering studies. This experience is extended now to urban environments. Sensor Parameters Trajectory Calculations Target Pos./Head./Speed View Calculations Target Model Radar Parameters Radar Signal Simulation f i, Pol. GRECO SAR Image f i, A i,! i GRECO Postproc. Raw Data Inverse/Strip/Scan SAR Processor 3/20 Dept. Signal Theory & Communications

$! High-frequency methods for solving the EM problem (Physical Optics, Physical Theory of Diffraction, Multiple reflection analysis by a Geometrical Optics (GO) + PO ray-tracing algorithm, etc.$ ) Visible Surfaces + Multiple Ray Hits Visible Edges They avoid the unrealistic computational requirements imposed by the discretization of Maxwell s equations when applied to very large electrical

) Visible Surfaces + Multiple Ray Hits Visible Edges They avoid the unrealistic computational requirements imposed by the discretization of Maxwell s equations when applied to very large electrical

4 GRECO": : Electromagnetic Solver! Polarimetric RCS estimation of complex targets in the frequency domain.! High-frequency methods for solving the EM problem (Physical Optics, Physical Theory of Diffraction, Multiple reflection analysis by a Geometrical Optics (GO) + PO ray-tracing algorithm, etc.) Visible Surfaces + Multiple Ray Hits Visible Edges They avoid the unrealistic computational requirements imposed by the discretization of Maxwell s equations when applied to very large electrical models. Back-facing Surfaces Hidden Edges! A novel approach that takes profit of PC graphic s processor for intensive geometric calculations.! High computational efficiency and multiprocessor capability.! Post-processing tools # Ray-tracing inspector for a fixed view. 4/20 Dept. Signal Theory & Communications

5 Simulation of realistic models of buildings! Two real buildings with material information (approx.). 1 2 TARGET CONSIDERATIONS TARGET 2 1 à Coarse surface roughness. àhigh degree of detail with small scale targets. 5/20 Dept. Signal Theory & Communications

Simulation of realistic models of buildings (II)!

distorted angles EFFECTS TARGET 1 TARGET 2 à Perfect

in real data: stealth buildings and strong scatters hiding

$à With coarse roughness and distorted angles, diffraction and$

6 Simulation of realistic models of buildings (II)! Perfect surfaces and angles vs Coarse surface roughness and distorted angles EFFECTS TARGET 1 TARGET 2 à Perfect surfaces/angles cause undesirable effects that do not appear in real data: stealth buildings and strong scatters hiding weaker ones. à With coarse roughness and distorted angles, diffraction and multi-reflection phenomena are increased while the presence of strong canonical targets reduced. 6/20 Dept. Signal Theory & Communications

7 UPC s Ground-Based SAR Sensor! Design constraints: Simplicity, portability (size & weight), power consumption, cost Based on off-the-shelf components Flexible in the sense of adaptable to different frequency bands (C, X and Ka) FM-CW modulation (permits low power solid state transmitter) Frequency and power stability for millimeter accuracy Interferometric and Polarimetric capabilities Fast acquisition speed, not based in Vector Network Analyzer (VNA) CW-FM Modulated Chirp (Direct Digital Synthesizer (DDS) chipset ) Latest Results - Time (min) Single Polarization (Continuous) 1:00 Single Polarization (S&G) 2:00 PolSAR (S&G) 2:20 PolInSAR (S&G) 4:10 7/20 Dept. Signal Theory & Communications

UPC s Ground-Based SAR Sensor POL-InSAR Antennas (Bistatic Configuration) POL-SAR Antennas 80 cm 24 cm Rail = 2 5 m RX Antennas TX Antennas UPC GB-SAR Sensor Parameters f 0 (X-Band) PRF Chirp

8 UPC s Ground-Based SAR Sensor POL-InSAR Antennas (Bistatic Configuration) POL-SAR Antennas 80 cm 24 cm Rail = 2 5 m RX Antennas TX Antennas UPC GB-SAR Sensor Parameters f 0 (X-Band) PRF Chirp Bandwidth Base-Band Bw. A/D Sampling Rate Transmitted Power Pyramidal Horns Gain 3dB Beamwidth Polarization Rail Min. Disp GHz 20 KHz MHz 20 MHz 82 Ms/sec 27dBm 15 db 30º HH/HV/VH/VV 100!m 8/20 Dept. Signal Theory & Communications

9 GB-SAR Urban Monitoring! Since June 2006 the RSLab, in collaboration with ICC, is carrying a subsidence monitoring campaign in Sallent, a village in the central Catalonia, were potash salt mines were traditionally exploited.! The Enrique mine was under exploitation until It had a maximum depth of 260 m and in 1954 a cavity of approx. 120 m high and 40 m wide was found while mining.! This cavity, caused by water circulation of the nearby river, is located under the South-East part of Sallent, in the neighbourhood of La Estació.! Water floods in 1957 and 1962 forced to abandon this part that was filled with saturated salty water.! The melting of the salt caused subsidence and during the 90s caused damages in the structures of most of the buildings. Some of them had to be demolished. 9/20 Dept. Signal Theory & Communications

sensitivity to vertical displacement. Incidence angles ranging from 40º to 75º and max.

10 GB-SAR measurement campaign: diurnal and nocturnal! Sensor has to be placed as high as possible to reduce shadowing effects and have the best sensitivity to vertical displacement. Incidence angles ranging from 40º to 75º and max. unambiguous range 1,5 km. Geo-coded reflectivity image RGB Pauli image Trihedral Dihedral Anti-symmetric 10/20 Dept. Signal Theory & Communications

11 GB-SAR measurement campaign: DInSAR results! PolDInSAR subsidence maps. cm / year! Amplitude- and phase-based criteria for reference pixels.! CPT technique for reliable pixels selection. 11/20 Dept. Signal Theory & Communications

GB-SAR measurement campaign: Polarimetric analysis! Stability of urban targets.

Strange polarimetric patterns along time series that may affect the selection of reference pixels in subsidence monitoring.

$Maybe, effects of refraction index for grazing incidence angles or direct impact of human activity.$

12 GB-SAR measurement campaign: Polarimetric analysis! Stability of urban targets. DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7 DAY 8 DAY 9 DAY 10 DAY TARGET 2! Strange polarimetric patterns along time series that may affect the selection of reference pixels in subsidence monitoring.! Up to now, there is not a robust explanation for all cases. Maybe, effects of refraction index for grazing incidence angles or direct impact of human activity.! The SAR simulator of complex targets GRECOSAR is used for: Studying urban scattering for different real-like building models. Studying the impact of time dimension. NIGHT Trying to reproduce the strange phenomena observed in real data. Assessing usefulness of PolInSAR building identification. TARGET 1 TARGET 2 TARGET 1 12/20 Dept. Signal Theory & Communications

13 ISAR Scattering Study: Human Activity (I)! Building model 1 v1.0. Cross- Range &' % $ Slant-Range frame points joint point %=60º, $=20º Real GB-SAR data /20 Dept. Signal Theory & Communications

14 ISAR Scattering Study: Human Activity (II)! Building model 1 v2.0. Garage door opened Opening the door induces a strange dihedral strip frame points joint point %=60º, $=20º Real GB- SAR data /20 Dept. Signal Theory & Communications

15 ISAR Scattering Study: Changing Incidence! Building model 1 v1.0. Changing incidence modifies the presence of some mechanisms frame points joint point %=75º, $=20º Real GB- SAR data /20 Dept. Signal Theory & Communications

16 ISAR Scattering Study: Realistic Structures (Building 1 v3.0) joint point banister point # Realistic signatures matching real data. frame points %=60º, $=10º Real GB-SAR data /20 Dept. Signal Theory & Communications

17 ISAR Scattering Study! Building model 2 v1.0. # Realistic signatures matching real data. # Structural changes does not seem to affect in excess the polarimetric response. %=60, $=10 Real GB- SAR data /20 Dept. Signal Theory & Communications

18 Scattering Study: New Elements! Building model 2 v1.0. # The addition of a marquee does not modify in excess the global signature. %=60, $=10 Real GB- SAR data /20 Dept. Signal Theory & Communications

19 ISAR Scattering Study Summary! The simulated response of buildings seems to match real data measurements. Similar scattering centers can be identified taking sense according to the geometry of the imaged building Trihedral mechanisms associated with corners (flat roof or joint sections) are reasonably stable with incidence angles. Dihedral mechanisms associated with banisters present lower phase stability with incidence angles. For dihedral wall interactions, certain stability is expected.! Each building can be associated with a particular scattering response that identifies the different geometries.! The response of buildings seems quite stable along the relative orientation.! Human activity may have an important impact on the polarimetric signature of buildings. Time dimension is crucial as the scene is alive.! PolInSAR data can be used to isolate the different scattering centers of the imaged building. 19/20 Dept. Signal Theory & Communications

20 Future Activities! Generate GB-SAR images from the developed models and compare with real data.! Increase the database of buildings and extent the study to other sensors (airborne, orbital), frequencies and resolutions.! Apply PolInSAR techniques to isolate the different scattering centers of the buildings and study its applicability to DInSAR.! Time dimension should be considered a crucial factor for high resolution SAR.! Currently, GRECO TM is being adapted to bistatic configurations. Bistatic polarimetry is a whole new world. This work has been supported by the Spanish Ministerio de Educación y Ciencia and the Institut Cartogràfic de Catalunya 20/20 Dept. Signal Theory & Communications

21 Simulated PolInSAR images! 3D scattering map retrieved with single-pass PolInSAR with a baseline of 30 m (X band). 7.09, 7.2 Similar response to that found with ISAR with notable height accuracy 5.11, 5.5 TARGET 1 TARGET 2 3.7, 4 2.3, , /20 Dept. Signal Theory & Communications

22 Simulated PolInSAR images! 3D scattering map retrieved with single-pass PolInSAR with a baseline of 30 m (X band) , , 9.5 Similar response to that found with ISAR with notable height accuracy 9.66, , , , 3.1 TARGET 1 TARGET 2 0, 0 22/20 Dept. Signal Theory & Communications

23 GB-SAR measurement campaign! Polarimetric Interferometric GB-SAR sensor based on DDR chipset. Signal Generation Unit +PC with Sampling Card RF-Block+ Deramping PolSAR hornbased antennas with 80 cm of baseline 2.5m 23/20 Dept. Signal Theory & Communications

24 Sensor Parameters Trajectory Calculations Target Pos./Head./Speed View Calculations Target Model Radar Parameters Radar Signal Simulation f i, Pol. GRECO SAR Image f i, A i,! i GRECO Postproc. Raw Data Inverse/Strip/Scan SAR Processor 24/20 Dept. Signal Theory & Communications

25 Satellite Parameters Orbit Calculations Latitude Swath Pos. Visible Surfaces + Multiple Rays Hits Geographical Target Position Target Heading Visible Edges Target Speed Doppler Yaw-steering View Calculations Sea State Radar Parameters Radar Signal Simulation f i, Pol. White points multi-reflection GRECO Back-facing Surfaces f i, A i,! i GRECO Postprocessing Target Model Hidden Edges TARGET 2 TARGET 1 Full Polarimetric Image Inverse/Strip/Scan SAR Processor Raw Data GRECO# EM solver, high-frequency, processing using graphic card. 25/20 Dept. Signal Theory & Communications

of investigate to identify, quantify and

26 Subsidence phenomena and monitoring Deformation Speed (2 cm/year) ICC in charge of investigate to identify, quantify and model this subsidence. Several techniques have been used: topographic leveling, geological mapping, geophysic prospection, extensometric measurements, drilling, orbital DInSAR, etc. 26/20 Dept. Signal Theory & Communications

shadowing effects and have the best sensitivity to vertical displacement.

27 GB-SAR Deployment 41º N 1º E H = 361 m Sensor has to be placed as high as possible to reduce shadowing effects and have the best sensitivity to vertical displacement. Incidence angles ranging from 64º to 74º. Maximum unambiguous range is 1,5 km. 27/20 Dept. Signal Theory & Communications

Mission Status and Data Availability: TanDEM-X

Mission Status and Data Availability: TanDEM-X Irena Hajnsek, Thomas Busche, Alberto Moreira & TanDEM-X Team Microwaves and Radar Institute, German Aerospace Center irena.hajnsek@dlr.de 26-Jan-2009 Outline