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Assessment of TerraSAR-X for mapping salt marsh Yoon-Kyung Lee 1), Wook Park 1), Jong-kuk Choi 2), Joo-Hyung Ryu 2), Joong-Sun Won 1) 1) Remote Sensing.

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Presentation on theme: "Assessment of TerraSAR-X for mapping salt marsh Yoon-Kyung Lee 1), Wook Park 1), Jong-kuk Choi 2), Joo-Hyung Ryu 2), Joong-Sun Won 1) 1) Remote Sensing."— Presentation transcript:

1 Assessment of TerraSAR-X for mapping salt marsh Yoon-Kyung Lee 1), Wook Park 1), Jong-kuk Choi 2), Joo-Hyung Ryu 2), Joong-Sun Won 1) 1) Remote Sensing Lab., Yonsei University 2) Korea Ocean Satellite Center, KORDI

2 1 1 Study area & Data 2 2 4 4 3 3 5 5 Introduction Processing Results Summary Contents

3 Introduction

4 Importance of salt marsh Buffer zone from storms and contaminations (Kirwan and Murray, 2007; Li and Yang 2009) Exchanging materials between tidal flats and open water (Mitch and Gosselink, 2000) Removing large amount of carbon from the atmosphere (Belyea and Warner, 1996; Choi and Wang, 2004) 1 1 2 2 3 3 Average global value of salt marsh is 8,535 $/ha/yr (Costanza et al., 1997) 4 4 Accurate mapping of salt marsh is useful for understanding salt marsh functions and monitoring their response to natural and anthropogenic actions (Barker et al., 2006)

5 Importance of halophyte Salt marsh vegetation communities (halophyte) play a fundamental role in the topography and stability of coastal wetlands by mean of a soil accretion, resulting from incoming flux of organic matter and sediment trapping. Physical factor Biological factor Elevation of marsh platform in response to rising sea level cause a landward migration of the marsh (Gardner and Porter, 2001). Equilibrium between mean sea level and interactions of physical factors adjust production of halophytes and location of communities (Morris et al., 2002). Type of salt marsh (high marsh/low marsh) is altered in response to the environmental change (Bertness et al., 2002)

6 Limitation of optical data Aerial photo ; High spatial resolution Low spectral resolution Landsat ETM+ ; Low spatial resolution Medium spectral resolution It is difficult to acquire data over tidal flats at the optimum water condition with cloud free. X-band SAR is suited for the detection and monitoring of herbaceous wetlands because of its short penetration paths to the ground

7 Objects To differentiate halophyte species based upon radar backscattering characteristics 1. To differentiate halophyte species based upon radar backscattering characteristics To generate salt marsh map 3. To generate salt marsh map 2. To determine the optimum season of the year and tidal condition for salt marsh mapping

8 Study area & Data

9 Study area Located in the mid-west of the Korean Peninsula Habitat for migratory birds (especially for the endangered species such as spoonbill, crane etc.) Planned to be nominated as the 1 st national tidal flats preservation area. Halophyte densely development: the western of the Donggum-do bridge, northern part of the Yeongjong-do tidal flat TerraSAR-X image acquire on 03, July 2009 (HH pol.) Ganghwa-do Inchon internatinal airport Yeongjong-do Donggum-do

10 Main halophyte species Phragmites australisSuaeda japonica perennial annual shoots emerge from perennial underground of rhizomes grows in or near fresh water, brackish water grows up to 3-4m in height annual stems grows up to 50cm in height rapid growth at the beginning of the growth stage grows in saline soil, but cannot grows in the shadow the color of short succulent leaves change green to red with an accumulation of red pigment (betacyanin)

11 Sudden dieback of S. japonica 18, May 2006 4, May 2009 : vertical accretion rate, low dissolved oxygen levels, high sulfides, high concentration of nutrients, fungus and sea level rise etc. Possible reasons of sudden dieback

12 Data TerraSAR-X Field survey Landsat ETM+ 2008: 6/13 (ebb, 225), 7/27 (flood, 272), 10/12 (ebb, 425), 11/25 (ebb, 362), 12/06 (flood, 378) 2009: 4/17 (flood, 466), 7/3 (ebb, 273), 12/15 (ebb, 618) 2010: 3/24 (flood, 347), 7/1 (flood, 464), 9/5 (flood, 421) 2008: 1/30 (ebb, 611), 4/19 (ebb, 108), 5/5 (ebb, 839), 8/9 (ebb, 608), 8/25 (ebb, 630), 9/10 (flood, 540), 10/12 (flood, 291), 12/15 (flood, 106) 2009: 2/1 (ebb, 501), 3/21 (flood, 510), 4/6 (flood, 392), 5/8 (ebb, 134), 5/24 (flood, 210), 8/28 (ebb, 574), 9/13 (ebb, 603), 10/15 (flood, 493), 12/18 (ebb, 78) 2010: 1/3 (ebb, 114), 2/4 (ebb, 513), 4/9 (flood, 507), 9/16 (ebb, 504), 10/18 (flood, 460) 2010.05.12 2010.07.12 2010.08.20 2010.09.16 HH 2008: 7/11 (flood, 315), 9/24 (flood, 431), 10/5 (flood, 685) VV/VH

13 Processing Statistical analysis TerraSAR-X GPS Decision tree

14 Results

15 SAVI (Soil adjusted vegetation index) Phragmites australisSuaeda japonicaTidal flats The seasonal variation pattern of SAVI matched well with phenelogical cycle of halophyte P. australis and S. japonica is hard to be distinguished from SAVI P. australis, S. japonica and tidal flats have similar SAVI values during winter

16 Characteristics of sigma naught (HH) - 1 Almost 350 pixels for each classes The quality of sigma naught were identified using average of industrial area P. austalis: - slightly stable and higher than S. japonica S. japonica: - lower value in winter and increased from spring to peak in summer Tidal flats: - significant variation according to surface condition - remnant water within the ripple control the backscattering Industrial area Tidal flats P. austalis S. japonica Water

17 Sigma Naught (dB) P. australisS. japonica Characteristics of sigma naught of halophyte Temporal variation of sigma naught during 3 years - P. australis: not agree with its plant cycle - S. japonica : peak in summer to autumn, presence of S.japonica structure roles as scatter although it is dead in Nov. Difference between S. japonica and P. austalis - Increased in winter, decreased from summer to autumn on-season

18 Characteristics of sigma naught (VV/VH) The average VV/VH difference of S. japonica: 6.2 dB (from image), 10.2 dB (from field survey) P. australisS. japonica Similar value in VV also between halophytes during Nov. (Park et al., 2010)

19 Consideration tidal condition Sigma naught (dB) P. australis S. japonica Tidal flats Water Ebb condition during the off-season is the best condition to distinguish between P. australis and S. japonica Ebb condition is good to distinguish halophyte

20 Decision rule based on statistical analysis ClassPolarization Tidal conditio n SeasonsS. japonicaTidal flatOcean water P.australis HH ebb On 0.10 ( p = 0.301) 7.3219.26 Off6.6119.2918.88 flood On1.015.7718.08 Off4.3311.2518.47 VV On-2.923.3617.39 VH On-2.738.5711.06 S. japonica HH ebb On7.2219.16 Off12.6712.27 flood On4.7517.06 Off6.9214.14 VV On6.2820.31 VH On11.3112.80 Tidal flat HH ebb On11.94 Off0.40 flood On12.31 Off7.22 VV On14.02 VH On2.49 Mean difference of sigma naught (T-test) HH > -19.28 dB in ebb (on-season) HH <-23.57 dB In flood (on-season) HH > -9.43 dB in ebb (off-season) HH > -16.16 dB in flood (rains)

21 Salt marsh map Reference Data Tidal flatsRunnelsWaterS. japonicaP. austalisLandRow total Tidal206262235607503115 Runnels1744653531742902653 Water0000000 S. japonica16140136300196 P. austalis0000000 Land000003329 Colum total3822128940931013433299293 Total accuracy: 66.5 %

22 Summary Optimum data acquisition plan by high resolution spaceborne X- band SAR should focus on on-season on the ebb tide when the halophyte return the strongest signal and off-season on the ebb tide to distinguish annual and perennial. Generated salt marsh map has 66.5 % total accuracy. For long-term monitoring the distribution of S. japonica in association with sea level fluctuation, it is important to set up date for annual data acquisition. 1 1 2 2 3 3

23 Thank you for your attention.

24 Seasonal change of S. japonica March July SeptemberDecember 3 Feb., 2010


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