Native and Extracted Underway AC-S Hyperspectral Absorption and Attenuation Measurements from the RV Polarstern PS113 Expedition (Atlantic Ocean, 2018)

This dataset contains hyperspectral absorption and beam attenuation measurements collected during the Atlantic Ocean transect of the RV Polarstern cruise PS113, conducted between May 10 and June 9, 2018. Surface seawater from the ship’s underway intake system was continuously supplied to a flow-through setup equipped with a Sea-Bird Scientific AC-S spectrophotometer. The measurement system followed the underway spectrophotometric configuration described by Slade et al. (2010), enabling continuous observations of the inherent optical properties of surface seawater at an acquisition frequency of approximately 4 Hz. These unprocessed observations constitute the primary source data used to derive particulate absorption spectra and subsequently estimate total and phytoplankton functional type chlorophyll a concentrations presented in Mehdipour et al. (2026). The AC-S measured spectral absorption coefficients, a($\lambda$), and spectral beam-attenuation coefficients, c($\lambda$), over approximately 400–740 nm. Optical coefficients are expressed in $m^{-1}$. The archive contains two corresponding data levels: 1. Native Compass files (*.dat) These are the native data files produced by the Sea-Bird Scientific Compass software. Each file contains approximately 10 minutes of measurements together with the original instrument metadata. The native files are provided without correction, quality control, or temporal aggregation. 2. Extracted text files (*_extracted.txt) These files contain the measurements and metadata extracted from the native Compass files and converted to a CSV-like text format. They include DATE/TIME, Latitude, and Longitude columns together with the hyperspectral measurements. Absorption spectra are stored in columns labeled a* and beam-attenuation spectra in columns labeled c*, where * denotes the wavelength in nanometers (nm). The DATE/TIME column was reconstructed from the Time(ms) channel together with the timestamp encoded in each filename. The reconstructed timestamps were checked for consistency and converted to UTC where required. The *_extracted.txt files represent only the extraction and time-reconstruction stage. They have not undergone the subsequent processing steps required to generate quality-controlled particulate optical products. Both the native and extracted files should therefore be considered uncorrected measurements. The dataset is provided to preserve the original instrument observations, support reproducible AC-S data processing, and enable the development and evaluation of alternative quality-control and optical-processing methods. The associated processing methodology and scientific application are described in: Mehdipour, E., Xi, H., Barth, A., Wilhelm, A., and Bracher, A. (2026). Fusion of Multi-Source Data for Comprehensive Assessment of Phytoplankton Composition. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. https://doi.org/10.1109/JSTARS.2026.3696195