The Possibility of Internal Waves Causing the Sinking of Indonesian “KRI Nanggala-402” Submarine Analyzed With SAR Imagery

At about 21:00 on April 20, 2021 (UTC), the Indonesian Navy submarine “KRI Nanggala-402” lost contact in the north of Bali Island and eventually sank. To explore the impact of internal waves (IWs) on the sinking of the “Nanggala” submarine, an IW parameter inversion method from the synthetic aperture radar (SAR) image based on an Euler numerical model is proposed. The IW amplitude and propagation speed, 25.2 m and 2.36 m/s, respectively, at the wreck site are retrieved from a Sentinel-1A/SAR image acquired two days before the losing contact using the Euler numerical model with the assistance of geostationary satellite Himawari-8 data. Further considering the barotropic tide current variation trends in the Lombok Strait (LS), the amplitude there was no more than 25 m when the submarine sank. The IWs with such small amplitude could contribute little to the submarine sinking. Therefore, we do not consider IWs as the primary cause of this submarine sinking accident.