Identification of Internal Waves on Lombok Strait using Sentinel-1 Imagery

Abstract Internal waves (IWs) are wave-forming phenomena that occur in the water column due to water stratification. This phenomenon can disrupt naval operations, such as depth control and detection capability, resulting in submarine sub sunk. The Lombok Strait itself is well known as one of Indonesia’s main throughflow pathways, where water is exchanged between the Indian Ocean and the Pacific Ocean. The wide and deep characteristics of the Lombok Strait make it suitable for submarines to maneuver there. Therefore, detecting the Lombok Strait for IWs is critical to prevent undesirable occurrences when submarines pass through. This study uses 10 meters resolution Sentinel-1 satellite imagery to identify IWs in the Lombok Strait and north of Bali Sea. Sampling was done by processing 20 image scenes on 10 different dates, comprising 5 dates before and 5 dates after the disappearance of the KRI Nanggala 402 submarine. The results showed that internal waves were observed on April 18 and April 30, 2021, with solitons in the Lombok Strait and north of Bali Sea, showing increasing length and spacing as they propagated. On April 30, a large internal wave packet near Kangean Island was detected, with solitons ranging from 32 to 111 km. These waves exhibited varied directions, moving both north (N) and west-northwest (WNW). This study suggests that internal waves, which were active during mid to late April, may have influenced the KRI Nanggala 402 submarine incident.