Using SAR data to rapidly assess damage caused by Typhoon Yagi in aquaculture areas in Quang Ninh and Hai Phong
SAR data has been processed by scientists at the Vietnam Space Center to get an initial look at the damage in coastal aquaculture areas. The collected data includes 2 Sentinel-1 images (C-band SAR satellite, 10m spatial resolution) taken on August 29, 2022 (before the storm) and on September 10, 2024 (when the storm just passed).
Using fast image processing tools on VV polarization, image enhancement and sensory assessment, scientists observed 5 areas (see Figure 1).
Area 1: Ha Long Bay, north of Cat Ba Island and south of Hoang Tan Island. In this area, all the aquaculture areas above sea level were destroyed (see Figure 2). After the storm, aquaculture areas were no longer visible.
Area 2: South of Cam Pha city. In this area, it is estimated that about 80% of the cages were destroyed, leaving only the cages that were built quite solidly. This area suffered less damage, perhaps because the cages were built more solidly, and there was a cement export wharf that partially blocked the waves and wind.
Area 3: Bai Tu Long Bay, between Van Canh Island and Ngoc Vung Island. In this area, all aquaculture cages were also completely destroyed.
Area 4. West of Tra Ban Island. In this area, it is also possible to observe that all the cages and rafts were completely destroyed.
Area 5. Coastal area of Cua Luc Bay. The aquaculture areas here are located on land, not completely on water like the areas above. The ponds still exist after the storm. Although not destroyed like the areas on the sea, the damage in this area will probably be to the animals in the ponds.
From the above observations and quick assessments, it can be seen that in all observed areas, small cages were completely destroyed. More solid structures also suffered significant damage. At inland facilities, no damage to infrastructure was observed, however there was certainly damage to livestock (some areas were observed to be flooded).
These results are only initial results based on rapid processing of SAR images by scientists at the Vietnam Space Center. Here, once again, we see the superiority of SAR images in providing information related to natural disasters thanks to the ability to capture through clouds (during this time, optical satellite images cannot observe the ground). For more accurate assessments, higher resolution satellite images are needed (for example, LOTUSat-1 with the highest resolution of 1m) and coordinated with field verification information. However, in the urgent situation of responding to storms, all information obtained is extremely valuable. In the future, the Vietnam Space Center will continue to coordinate with foreign partners to exploit SAR satellite images and quickly process them to provide useful information.
Figure 1: Observation areas for rapid assessment of damage caused by Typhoon Yagi with aquaculture areas
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| Aquaculture cages (Google Map image) | Pre-storm photo of white aquaculture areas due to corner reflection on SAR image | Photo after the storm, aquaculture areas are no longer visible in the photo |
Figure 2: Aquaculture areas in the northern area of Cat Ba Island devastated by Typhoon Yagi
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| Aquaculture cages and rafts (Google Map image) | Pre-storm photo of the west of the | Photo after the storm of the west of the cement wharf, aquaculture rafts were destroyed, significantly reduced |
Figure 3: Aquaculture areas devastated by Typhoon Yagi in the southern region of Cam Pha city
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| Aquaculture cages (Google Map image) | Pre-storm photo, although there is small size but aquaculture raft cages has strong angular reflexes, so it is still observable on SAR images
| Photo after the storm, no longer observed cultivated by raft cages aquatic products, colored sea surface quite bright showing the water surface not flat |
Figure 4: Aquaculture areas devastated by storm Yagi in Bai Tu Long Bay, between Van Canh Island and Ngoc Vung Island
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| Aquaculture cages (Google Map photo) | Pre-storm photos, easy to see | Photo after the storm, no longer observed by aquaculture areas |
Figure 5. Aquaculture areas destroyed by storm Yagi in the western part of Tra Ban Island
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| Ponds (Google Map photo) | Pre-storm photo | Photo after the storm, observed some small areas were flooded across the pond bank or destroyed pond bank |
Figure 6: Aquaculture areas destroyed by Typhoon Yagi in the coastal area of Cua Luc Bay
Translated by Quoc Khanh
Link to Vietnamese version
