Investigation of Spatial and Temporal Trends in Lake Toba Water Level Based on ICESat-2 Data
Widyani Galih Pangersa (a*), Ni Made Rai Ratih Cahya Perbani, Ir., M. Si (b)

a) Undergraduate Program in Geodetic Engineering, Institut Teknologi Nasional Bandung, Indonesia
b) Doctoral Program in Geodesy and Geomatics, Institut Teknologi Bandung, Indonesia
*glhpngrs[at]gmail.com

Abstract

Lake Toba is the largest volcanic lake in Indonesia and one of the 15 lakes prioritized by the Indonesian government. As the largest volcanic lake in Southeast Asia, it serves as a critical freshwater reservoir, supports fisheries and tourism, and influences local hydrological and climatic conditions. It also plays an important role in climate change, so fluctuations in its water level need to be monitored continuously. ICESat-2 is a laser based measurement satellite equipped with the Advanced Topographic Laser Altimeter System (ATLAS), which works by counting photons and enables periodic monitoring of water levels. This study focuses on identifying spatial and temporal trends in water levels in Lake Toba using ICESat-2 ATL13 data from 2018 to 2024. The parameters analyzed were segment latitude (segmen_lat), segment longitude (segmen_long), and water surface height (ht_water_surf) from Tracks 385, 825, and 1269. Spatial analysis was conducted using profiles and 3D models along the satellite tracks across Lake Toba. Meanwhile, temporal analysis was performed using temporal data samples on tracks 285, 825, and 1269, which were bounded by the area along each respective track, by selecting data that had the most observation months. Then least square analysis was conducted for temporal modeling Based on the analysis of ICESat-2 data in Tracks 385, 825, and 1269, it was found that the water level in the eastern part of Lake Toba is higher than in the western and central parts, with differences reaching approximately 2.4 meters. A pattern of water level accumulation toward the mainland was also observed in the three-dimensional profiles. Between 2018 and 2024, the lowest water level occurred in 2021. In general, the variation in water levels was influenced by both annual (Sa) and semi-annual (Ssa) cycles, with Ssa being more dominant. These findings provide new insights into the spatial and temporal dynamics of Lake Toba water levels.

Keywords: ICESat-2 ATL-13, Lake Toba, Spatial trend, Temporal trend, Water level

Topic: Topic B: Applications of Remote Sensing