202509/26
The Aerial Survey and Remote Sensing Branch (ASRS) of the Forestry and Nature Conservation Agency (FANCA), Ministry of Agriculture, has successfully obtained comprehensive imagery of the Matai’an Creek landslide dam disaster, covering the upstream landslide dam to the downstream disaster areas, including the creek channel.
The ASRS stated that since the Matai’an Creek landslide dam was first detected by satellite in July this year, it has intensively dispatched aerial survey and remote sensing aircraft for imaging to the area. Prior to the installation of monitoring instruments by the FANCA, aerial survey photogrammetric technology was employed to measure the size of the dam and water level changes. A total of 17 missions were carried out, making a significant contribution to the early monitoring of the landslide dam. Before Typhoon Ragasa hit, the ASRS had completed preparations and made multiple attempts to capture images on the day after the disaster struck. Unfortunately, thick cloud cover and intense convective cloud systems hindered operations. After the weather cleared up yesterday morning (9/25), personnel immediately flew over the area before afternoon clouds developed in the mountainous area, successfully capturing comprehensive imagery covering more than 30,000 hectares in both upstream and downstream areas (Figure 1).
The ASRS further pointed out that in addition to the LEICA DMCIII digital camera, the RIEGL VQ-1560II-S LiDAR scanner, which was installed last year, was also used in this survey mission. Not only can it provide images with a ground resolution of up to 15 cm, it can also simultaneously obtain LiDAR data with a point cloud density of approximately two points per square meter. This enabled more precise monitoring of terrain changes before and after the disaster, which has attracted public attention, including the elevation of the landslide dam and its embankment, as well as variations in soil and sediment within the disaster area, the creek channel and the riverbed.
ASRS Branch Director Huang Chyun-Shiou explained that due to the massive volume of data, three dedicated workstation-level computers at the ASRS finally completed the processing of 145 images at 16:00 yesterday (9/25). Image comparisons clearly revealed differences in the dam’s size compared to pre-disaster conditions on August 18 (Figure 2). At the same time, the data was immediately shared with relevant agencies for use through the groups and platforms of the National Science and Technology Center for Disaster Reduction. As for the LiDAR point cloud data, the area surrounding the landslide dam was prioritized for analysis. With the assistance of a team from National Yang-Ming Chiao Tung University and the collaborative efforts of personnel from the ASRS, post-disaster topographic data (Figure 3) was produced overnight. The map clearly depicts the current terrain and overflow locations.
Branch Director Huang also stated that the ASRS will continue to closely monitor the disaster area. He particularly emphasized that the aerial survey aircraft and related sensing instruments deployed this time were only established in 2019 with the support of the Executive Yuan. This capability proved vital during the disaster, validating the importance of establishing autonomous aerial surveying and disaster data collection capabilities for disaster-prone Taiwan, a point emphasized when securing the initial budget.