Schwenk, Tilmann; Römer-Stange, Nikolas; Feddersen, Greta; Bernhard, Renée; Athanassiadis, Emilia; Spieß, Volkhard: Sediment echosounder processed data (Atlas Parasound P70 echosounder working area dataset, ASD format converted to SEG-Y format) of RV SONNE during cruise SO304, Bengal Fan, Indian Ocean [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.995404 (dataset in review)

During the SO304 cruise (22 February – 07 April 2024), sub‑bottom profiles were collected on the Bengal Fan (Bay of Bengal) with the hull‑mounted Teledyne Reson PARASOUND P70 echosounder on RV SONNE. The archived profiles target a lobe complex on the Bengal Fan. The PARASOUND system generates a secondary low‑frequency signal (SLF; 0.5–6 kHz) by non‑linear interaction of two primary high‑frequency signals (PHF; adjustable between 18.5 and 33 kHz), producing a transmission beam of 4.5° along‑track × 5° across‑track. Consequently, the lateral resolution corresponds to approximately 7.9 % of water depth along‑track and 8.7 % across‑track. Throughout the cruise a 4 kHz SLF with a ≈ 0.25 ms non‑rectangular pulse was used as the standard setting, yielding decimetre‑scale vertical resolution. The profiler operated in quasi‑equidistant mode, transmitting pulses at regular intervals regardless of whether the previously transmitted signal had already been received, thereby maximising horizontal coverage. For the working‑area dataset the ping rate was about 1 s, giving 3–4 m shot‑point spacing for profiles GeoB24‑013, 031, 032 and 045 (≈ 5 kn ship speed) and 6–7 m spacing for profiles P089, P110, P111, and P185 (8–10 kn speed). System depth and ping rates were adjusted using depth information from the EM122 echo‑sounder or from the PHF signal. The carrier signal including the signal phase information has been stored. Raw PHF and SLF data were stored in the native PARASOUND ASD format and also converted to PS3 and SEG‑Y formats. Because occasional gaps appeared in the PS3/SEG‑Y files, the SLF data were replayed on a second acquisition computer with the ATLAS PARASTORE software and re‑exported as gap‑free SEG‑Y files. The dataset provides continuous sub‑bottom profiles of the upper ~100 m of sedimentary layers, enabling structural imaging, identification of suitable coring locations, and imaging of acoustic backscatter from organisms or suspended material in the water column. Coordinates in the SEG-Y files are given in WGS84/UTM45N.