Sang Hoon Hong (1)(2)(3) and Shimon Wdowinski (2)

Transcription

1 Revising vegetation scattering theories: Adding a rotated dihedral double bounce scattering to Explain cross polarimetric SAR observations over wetlands Sang Hoon Hong (1)()(3) and Shimon Wdowinski () (1) Korea Aerospace Research Institute, Korea () University of Miami, U.S.A. (3) Florida International University, U.S.A.

2 Outline Wetland InSAR errasar X dual pol observations Radarsat quad pol observations Vegetation scattering theory Decompositions Conclusion

3 Wetland InSAR 1 st acquisition nd acquisition Δt = 4 day (RADARSA) R1 R Dominant scattering mechanism: Double (Even) bounce scattering ΔR Water level level change measurement between the (mm cm) 1st and the nd acquisition

4 L, C, and X band Interferograms ALOS Radarsat 1 errasar X High spatial resolution maps of water level changes. Vertical change (fringes): L band 15 cm; C band 4 cm; X band cm

5 SAR & Vegetation SAR vegetation scattering theory I Current assumption: Short wavelength radar signal interacts mainly with upper levels of the vegetation hus, X- and C-band should not produce coherent interferograms over wetlands. (When we submitted data proposals for X- and C-band data, reviewers were skeptic that the method would work.)

6 X-band Interferograms

7 SAR & Vegetation SAR vegetation scattering theory II Current assumption: Double bounce = - Single bounce = + Volume scattering = HV Gondwe (010) Observations: Cross-polarization (HV) interferograms show water level changes => HV has a double bounce component

8 errasar X dual polarimetric data

9 Water Conservation Area (WCA) Managed wetland 0630/0711 Bp: /080 Bp: 50 HV VH Water level changes can be detected at all polarimetric data. he coherence are the best in pol, and is the next. he cross pol has the lowest coherence.

10 Freshwater wetland v.s. Saltwater mangrove HV VH 096/1007 Bp: /110 Bp: 147 Cross pol acts like double bounce scattering as well as volume scattering

11 Radarsat quad polarimetric data he northeastern part of the area: freshwater herbaceous vegetation he southwestern part of the area: saltwater woody vegetation (mangroves) he transition zone: inhabited by short scrub (a) Radarsat 1 ScanSAR, (b) Jers 1, (c) Radarsat (qual pol), and (d) Landsat 7 image.

12 InSAR processing Radarsat interferograms of study area in south Florida. Each fringe cycle shows about.8 cm water level change in the line of sight. (1) Water level changes due to the north south stream in freshwater herbaceous area () ide induced water level changes in the transition section (3) he decorrelated area in saltwater area covered by tall mangrove in the southwest corner

13 Interferograms (a c) + (single), (double), and HV (volume) polarization interferograms, and (d f) Coherence map of interferogram in each scattering mechanism

14 Scattering behavior in cross pol Double bounce Scattering : rotated dihedral phase Volume scattering : double bounce like phase history H +HV

15 Dihedral and rotated dihedral Dihedral Rotated Dihedral

16 Dihedral and rotated dihedral Cypress Mangroves

17 Modified model based on coherency matrix Pauli matrix: k 1 S S S S S HV 1 N N i1 k k * HV plate * S S S S S S * S S S S S S S S S HV 1 S S 11 Ps S * S S S S S 1 S P v diplane 1 S S Pd cos P v 1 cos 1 0 HV sin 4 * 0 sin 4 sin S HV S S volume * HV * HV 33 SHV Pd sin 3 Re S S S * HV 1 4 P s P v sin 4 plate P diplane P volume d Rotated dihedral from cross pol v Ps surface, Pd double bounce, Pv volume Double bounce component can be derived from cross pol

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19 Double bounce component in cross pol in our decomposition

20 Application with modified decomposition SanFransisco with Radarsat Ps from 11 Pd from Pd from 33 Pv from 33 Color composite image red (Pd from ) green (Pv from 33 ) blue (Ps from 11 )

21 Application with modified decomposition SanFransisco with Radarsat Double bounce component in cross pol in our decomposition

22 Application with modified decomposition SanFransisco with Radarsat Volume component in our decomposition Volume component in previous decomposition

23 Application with modified decomposition Everglade wetland with Radarsat (a) Pauli decomposition color composite image: (red), + (blue), and HV (green) (b) he decomposition image: Ps (blue), Pd (red), and Pv (green) (c) he color composite image with double bounce scattering (red) and volume scattering (green) from cross pol. he relatively high single bounce component was masked out (in white) Because the phase of water level change cannot be detected in region which is represented with very dominant single bounce component (e.g. dense vegetated area).

24 Conclusions We suggest that the cross pol, which is commonly regarded as the volume scattering induced by the upper section of the vegetation, also include a double bounce component reflecting surface water level changes. We suggest that the cross pol signal can be decomposed into double bounce and volume component. A modified scattering model based on the coherency matrix is proposed for extraction of the double bounce component from the cross pol. he model decomposes quad pol data into four components; single, double bounce from both of the co pol and the cross pol and volume scattering.

25 Acknowledgement We thank to CSA and DLR to access Rsat and SX images. his study is a part of WaterSCAPES funded by NASA.