Development of a Seamless, High-Resolution Bathymetric Model to Compare Reef Morphology around the Subtropical Island Shelves of Lord Howe Island and Balls Pyramid, Southwest Pacific Ocean
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Depth Estimation for the Lord Howe Island Shelf
2.2.1. Correction for Atmospheric Interference and Sun Glint Effects
2.2.2. Estimating Bathymetry from Satellite Image Bands
2.2.3. Filter Comparison
2.2.4. Image Partitioning and Error Assessment
2.3. Depth Estimation for the Balls Pyramid Shelf
2.4. Integrated Bathymetry Model
2.5. Geomorphomic Feature Interpretation
3. Results
3.1. Depth Estimation for the Lord Howe Island Shelf
3.2. Depth Estimation for the Balls Pyramid Shelf
3.3. Integrated Bathymetry Model
3.4. Geomorphic Interpretation and Shelf Comparison
3.4.1. Inner Shelf
3.4.2. Middle Shelf
3.4.3. Outer Shelf
4. Discussion
4.1. Comparison of Shelf Morphology
4.2. Applications for Management
5. Conclusions
- Filtering of the band ratio grid with standard deviation and median filters improved the surface for integration with multibeam echosounder data.
- Image partitioning further improved the surface, accounting for east-to-west variation across the image.
- The integration of depth derived from satellite imagery together with multibeam echosounder data produced a seamless 5 m cell size bathymetry model of the shelf from the shoreline to shelf break.
- Geomorphic interpretations of the shelves defined diverse accretionary and erosional features, with mid-shelf fossil reefs shown to dominate both shelves in 25–50 m.
- The mid-shelf fossil reef around Balls Pyramid is approximately half the area of the Lord Howe Island mid-shelf reef, although it represents a similar proportion of shelf area (approximately one third).
- The morphology, size, configuration and depth distribution of outer shelf features are most similar between the two shelves, and are most dissimilar for inner shelf features.
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
Appendix B
References
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Geomorphic Feature | Definition |
---|---|
Coral reef | A tract of corals growing on a massive, wave resistant structure and associated sediments, substantially built by skeletons of successive generations of corals and other calcareous biota [49] |
Channel | A linear or sinuous depression on an otherwise flat surface [48] |
Basin | A depression, in the seafloor, more or less equidimensional in plan and of variable extent [48] |
Depression | A low lying area surrounded by higher ground and with no outlet or opening (i.e., closed) [48] |
Pavement | Flat (or gently sloping), low-relief, solid, carbonate rock with little or no fine-scale rugosity. These areas can be covered with algae, hard coral, gorgonians, zooanthids, or other sessile vertebrates; the coverage may be dense enough to partially obscure the underlying surface. On less colonized pavement features, rock may be covered by a thin sand veneer [47] |
Ridge | A long, narrow elevation, usually sharp crested with steep sides. Larger ridges can form an extended upland between valleys [48] |
Step | A narrow area on the continental (or island) shelf that has a distinctive steep gradient [50] |
Terrace | A relatively level or gently inclined surface defined along one edge by a steeper descending slope and along the other by a steeper ascending slope. Terraces may border a valley floor or shoreline, and they can represent the former position of a flood plain or shoreline [48] |
Shelf break | The line along which there is a marked increase of slope at the seaward margin of a continental (or island) shelf [46] |
Slope | The sloping region that deepens from a shelf to a point where there is a general decrease in gradient [46] |
Filter Type | R2 | Polynomial Type | RMSE for Each Depth Range (m) | ||||||
---|---|---|---|---|---|---|---|---|---|
0–10 | 0–15 | 0–20 | 0–25 | 0–30 | 0–35 | 0–40 | |||
No filter | 0.807 | Order 2 | 1.98 | 2.12 | 2.67 | 3.73 | 3.55 | 3.9 | 4.61 |
Low Pass (3 × 3) | 0.894 | Order 2 | 0.89 | 1.15 | 1.82 | 2.4 | 2.41 | 3.22 | 4.14 |
Median 10 | 0.93 | Order 3 | 0.75 | 1.03 | 1.45 | 2.42 | 2.2 | 3.18 | 4.23 |
Low pass + Median 10 | 0.931 | Order 3 | 0.74 | 1.05 | 1.55 | 2.46 | 2.21 | 3.14 | 4.2 |
Standard deviation (Std) | 0.84 | Order 2 | 1.24 | 1.33 | 1.8 | 3.1 | 3.23 | 3.85 | 5.72 |
Std + Median 10 | 0.935 | Order 3 | 0.72 | 0.97 | 1.12 | 2.4 | 2.19 | 3.15 | 5.36 |
West | 0.72 | 0.97 | 1.12 | 1.48 | 1.37 | 1.98 | 3.1 | ||
East | - | - | 1.11 | 4.03 | 4.12 | 5.25 | 6.23 | ||
Image partition | |||||||||
Std + Median 10 | 0.72 | 0.97 | 1.17 | 2.1 | 1.74 | 2.39 | 3.3 | ||
West | 0.935 | Order 3 | 0.72 | 0.97 | 1.12 | 1.48 | 1.37 | 1.98 | 3.1 |
East | 0.875 | Order 3 | - | - | 1.68 | 3.75 | 3.13 | 3.5 | 3.88 |
Shelf Region | Geomorphic Feature | Lord Howe Island Shelf | Balls Pyramid Shelf | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Area (km2) | % of Shelf | Depth (R) | Depth (Av ± Std) | Slope (Av ± Std) | Area (km2) | % of Shelf | Depth (R) | Depth (Av ± Std) | Slope (Av ± Std) | ||
Inner shelf | Modern fringing reef | 6.5 | 1.3 | 2 to 35 | 10 ± 7.4 | 2.9 ± 3.4 | - | - | - | - | - |
Shallow lagoon | 3.9 | 0.8 | 2 to 9 | 3 ± 0.3 | 0.3 ± 0.3 | - | - | - | - | - | |
Fossil reefs and bedrock outcrops | 22.8 | 4.5 | 1 to 48 | 25 ± 8.9 | 4.5 ± 4.4 | 5.6 | 2.2 | 21 to 41 | 32 ± 2.3 | 1.6 ± 1.2 | |
Basins and intra-reef depressions | 18.4 | 3.7 | 2 to 40 | 26 ± 8.3 | 1.9 ± 1.9 | 0.8 | 0.3 | 32 to 40 | 35 ± 0.7 | 0.9 ± 1.4 | |
Channels | 0.3 | 0.1 | 3 to 31 | 10 ± 5.1 | 3.7 ± 4.3 | 0.6 | 0.2 | 31 to 38 | 35 ± 1.2 | 1.3 ± 1.1 | |
Mid shelf | Patch reefs | 13.6 | 2.7 | 19 to 63 | 38 ± 5.1 | 4.3 ± 5.3 | 1.1 | 0.4 | 36 to 57 | 46 ± 2.8 | 4.5 ± 4.0 |
Fossil reefs: -Upper | 56.0 | 11.1 | 14 to 35 | 31 ± 2.4 | 3.2 ± 2.9 | 13.9 | 5.3 | 18 to35 | 33 ± 1.4 | 2.7 ± 2.5 | |
-Lower | 70.9 | 14.1 | 35 to 76 | 40 ± 4.3 | 2.3 ± 2.5 | 56.1 | 21.5 | 35 to 55 | 42 ± 4.0 | 2.3 ± 2.2 | |
-Intra-reef depressions | 28.5 | 5.7 | 25 to 55 | 37 ± 4.6 | 1.7 ± 1.5 | 16.9 | 6.5 | 28 to 50 | 41 ± 4.1 | 1.6 ± 1.6 | |
Channels | 13.9 | 2.8 | 22 to 67 | 48 ± 9.1 | 1.8 ± 2.3 | - | - | - | - | ||
Basins | 60.0 | 11.9 | 23 to 61 | 44 ± 6.7 | 1.3 ± 1.5 | 24.0 | 9.2 | 30 to 57 | 46 ± 4.3 | 1.0 ± 1.3 | |
Outer shelf | Ridges and patch reefs | 11.5 | 2.3 | 43 to 80 | 57 ± 6.5 | 3.4 ± 3.1 | 10.8 | 4.1 | 41 to 74 | 53 ± 5.5 | 2.1 ± 2.0 |
Pavement | 99.7 | 19.8 | 30 to 80 | 54 ± 5.0 | 1.9 ± 2.0 | 72.7 | 27.9 | 36 to 104 | 54 ± 6.4 | 1.5 ± 2.4 | |
Basins | 8.1 | 1.6 | 42 to 63 | 55 ± 3.9 | 1.7 ± 1.9 | 7.1 | 2.7 | 41 to 67 | 52 ± 3.6 | 1.2 ± 1.2 | |
Channels | 9.9 | 2.0 | 47 to 67 | 59 ± 3.5 | 2.0 ± 2.2 | 0.6 | 0.2 | 50 to 58 | 55 ± 1.2 | 1.4 ± 1.5 | |
Terraces | 79.6 | 15.8 | 45 to 215 | 88 ± 18.4 | 5.5 ± 6.0 | 50.4 | 19.3 | 47 to 217 | 94 ± 23.6 | 4.9 ± 5.8 | |
Terrace steps (line) | - | - | 45 to 213 | 79 ± 19.9 | 8.8 ± 7.4 | - | - | 47 to 136 | 80 ± 17.5 | 7.7 ± 6.7 | |
Shelf break | Shelf break (line) | - | - | 86 to 206 | 130 ± 20.6 | 26.8 ± 8.3 | - | - | 83 to 217 | 130 ± 19.9 | 26.9 ± 1 2.2 |
Total | Entire shelf | 503.8 | 100 | 0 to 215 | 49 ± 21.6 | 2.8 ± 3.6 | 260.7 | 100 | 18 to 217 | 56 ± 22.8 | 2.4 ± 3.5 |
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Linklater, M.; Hamylton, S.M.; Brooke, B.P.; Nichol, S.L.; Jordan, A.R.; Woodroffe, C.D. Development of a Seamless, High-Resolution Bathymetric Model to Compare Reef Morphology around the Subtropical Island Shelves of Lord Howe Island and Balls Pyramid, Southwest Pacific Ocean. Geosciences 2018, 8, 11. https://doi.org/10.3390/geosciences8010011
Linklater M, Hamylton SM, Brooke BP, Nichol SL, Jordan AR, Woodroffe CD. Development of a Seamless, High-Resolution Bathymetric Model to Compare Reef Morphology around the Subtropical Island Shelves of Lord Howe Island and Balls Pyramid, Southwest Pacific Ocean. Geosciences. 2018; 8(1):11. https://doi.org/10.3390/geosciences8010011
Chicago/Turabian StyleLinklater, Michelle, Sarah M. Hamylton, Brendan P. Brooke, Scott L. Nichol, Alan R. Jordan, and Colin D. Woodroffe. 2018. "Development of a Seamless, High-Resolution Bathymetric Model to Compare Reef Morphology around the Subtropical Island Shelves of Lord Howe Island and Balls Pyramid, Southwest Pacific Ocean" Geosciences 8, no. 1: 11. https://doi.org/10.3390/geosciences8010011