The Application of CHRIS Data to the Multi-temporal & Multi-angular Study of Near-shore Marine Bathymetry

Transcription

1 The Application of CHRIS Data to the Multi-temporal & Multi-angular Study of Near-shore Marine Bathymetry PhD/Postgrad students: Libby Boak Stacy Mitchell AJ Lau Indrie Miller School of Biological, Earth, and Environmental Sciences (BEES), The University of New South Wales, Sydney, AUSTRALIA

2 Theory of Bathymetric Estimation Beer s Law I z = I 0 *exp kz I z : The intensity of light at depth z I 0 : The intensity of light at depth zero z: Depth k: Light attenuation coefficient! Red (8m), Green (23m), Blue (30-112m) Case I or II/III waters? The increase of suspended sediment, phytoplankton, detritus and dissolved substances would increase the light attenuation coefficient

3 Two Interrelated Research Paths Part 1:Examination of Wave Zone spectral properties. Includes the determination of land-water boundary. Suspended sediments and aeration influences. Argus coastal monitoring. Part 2:Examination of Near-Shore Zone Bathymetry. Water optics. mapping of sediment and rock-types. multi-temporal topographic survey.

4 Australian Study Sites (CHRIS imagery request) Lady Elliot Island Gt. Barrier Reef Tweed Heads NSW-QLD border Manly Beach, Sydney

5 Surf Zone How does this relate to this

6 Sediment Manly Tweed Heads Narrabeen Duranbah Muriwai Muriwai, NZ

7 Merged Images Oblique View Plan View

8 Halogen lamps θ s = 10 Sensor θ s = 30 θ v = 45 θ s = 60 ψ = 90 ψ = 0 ψ = 180

9 Construction of a Spectral Library from laboratory experiment Boak, E., Turner, I. and Merton, R. (2004), conducted an experiment utilising an ASD Hyperspectral Fieldspec UV/VNIR Hand Held Spectroradiometer to quantify the swash and groundwater features that occur co-incident to the shoreline Experiment attempted to reproduce turbulence and foam and sediments that are seen in the swash zone Results from the experiment that utilised Narrabeen sand were imported from text files to.sli files for use in the ENVI spectral library

10 Shoreline Detection Source: Plant et al., (submitted)

11 Data, Study Area and Methods Description Data Description Hyperspectral Imaging " 128 wavelength bands " nm spectral region with bandwidth ranged between 10 and 20nm and a spatial resolution of 5m " Advantage: acquire at anytime and orbital independence Manly Scene (DeeWhy Scene) " HyMap data " Captured 27th November " Case 2 coastal water

12 Research Area & Tidal Graph

13 Study Area Description Manly Flyby! A very diverse range of coastal environments, including moderate energy surf zone, low angle offshore sand gradient, rip channels, longshore banks and troughs, bomboras, boulder bed forms, fringing rocky reef, seaweed, seagrass, and intertidal rock platforms

14 Methods Description Data preprocessing

15 Minimum Noise Fraction (MNF) data analysis 1 st 21 bands 126 bands # 1st 21 bands ( nm) # 126 bands ( nm) # Determine the reliability of using only 1st 21 bands for bathymetric estimation in the future # Examine the capability of classification of the swash zone from two different spectral ranged data, only water column above 0.3m depth has spectral reflection response at 800nm (Lafon et al. 2002). MNF Transformed Hymap Data Pixel Purity Index PPI (Spatial Data Reduction) n-dimensional Visualization & Identification 1 st Endmembers spectra Spectral Angle Mapper 2 nd Endmembers spectra 1st Spectral Angle Mapper $ Develop an specialised method for selecting the most representative pure endmember from endmember or edgemember groups 2 nd Classification 1Spectral Angle Mapper 2Matched Filtering 3Mixture Tuned Matched Filtering Results 1Geological Feature 2Bathymetry 3Beach Profile

16 Band Ratio analysis Band ratio method enhances the spectral differences between bands and to reduce the effects of topography by dividing one spectral band by another! Reflectance band 3, 10, 25 & 28! 480nm band (i.e. band 3 of HyMap data) can provide the bathymetric information (Jensen 2000).! Around 800nm (i.e. band 25 and 28) can be used to identify the water column above the 0.3m (Lafon et al., 2002), where can be categorized as swash zone of the beach profile.

17 Swash zone identification using band ratio (805/851) on Manly s Beach (right) and DeeWhy (left)

18 Bathymetric Mapping (Band Ratio approach) Result of band ratio (470/577) of Manly s shoreline Result of band ratio (470/577) of DeeWhy Beach

19 Results 2D MNF scatterplot (left), distribution of different features in n-dimensional (right)

20 126 reflectance bands MNF (A) image (RGB: bands 2, 4 and 5) 1st 21 reflectance bands MNF (B) image (RGB: bands 2, 4 and 5)

21 Classification of Geological Features SAM classification of geological features from MNF (A) data

22 Bathymetric Mapping (MNF approach) 1st SAM classification of out-spiral edge members 1st SAM classification of in-spiral edge members

23 Bathymetric estimation using 2nd SAM classification on MNF data

24 Beach Profile Mapping Vector image of bathymetric groups with the indication of sand bar and its descending slope

25 Figure 21. Beach profile mapping using 2 nd SAM classification on MNF (A) data. Beach profile mapping using 2nd SAM classification on MNF (A) data

26 Surf Zone Waves Sea surface topography identification using band ratio (577/805) on Manly s Beach

27