# Documentation of Collected Data

**Dataset Name:** `ODER~SO | Oder River Disaster 2022 | Data | SP04: Sentinel-2 chlorophyll-a estimates at ODER~SO sampling sites`

**Version:** `v1.0`

**Description:** `Time series of chlorophyll-a concentrations derived from the complete archive of Sentinel-2 imagery available over the ODER~SO sampling sites along Oder River between 2016 and 2025. Chlorophyll-a concentrations were retrieved using an algorithm based on the Case 2 Regional CoastColour (C2RCC) processing. For each valid Sentinel-2 observation, estimates were aggregated across all pixels classified as water within a 3 × 3 pixel window (approximately 3600 m²) centred on each sampling site. The dataset includes the median, mean, standard deviation, and number of contributing water pixels within each spatial window. Two additional daily gap-filled series, based on a moving average and a 17th-order polynomial fit, are included to represent chlorophyll-a dynamics between valid satellite observations.`

**Creators or Authors:** `Jorrit Scholze (Brockmann Consult GmbH), Kerstin Stelzer (Brockmann Consult GmbH), Paula Torre Zaffaroni (Leibniz-IGB, ORCID 0000-0002-1007-843X)`

**Dataset Context:** `This dataset was produced within the ODER~SO project to characterize temporal changes in phytoplankton biomass at locations included in the project's field-sampling programme. It supports comparison of satellite-derived chlorophyll-a dynamics with site-based observations, assessment of long-term and seasonal variability, interpretation of the 2022 Prymnesium parvum bloom, and subsequent monitoring activities.`

**Versioning Information:** `v1.0: initial compilation`

**Limitations and Quality:** `Chlorophyll-a concentrations were estimated from Sentinel-2 imagery using a regionally calibrated retrieval algorithm based on C2RCC processing. The observed chlorophyll-a statistics depend on the availability of valid satellite imagery, the performance of the atmospheric correction and retrieval procedure, and the presence of pixels classified as water within the 3 × 3 pixel window. Consequently, raw spatial statistics may be unavailable on cloudy dates or when no valid water pixel was identified. The chl_count variable reports the number of water pixels contributing to each spatial summary and should be considered when evaluating representativeness. Data gaps were filled using a moving-average interpolation and a 17th-order polynomial fit applied to individual site time series. These gap-filling methods may introduce uncertainty near the temporal boundaries of the record and during extended periods without valid observations. Gap-filled values between November and February should be excluded from analyses. Validation against in situ observations yielded coefficients of determination generally exceeding 0.6, although absolute prediction errors remained substantial (RMSE = 30–50 µg L⁻¹ depending on the reference dataset).`

**Format and Structure:** `The dataset is provided in tabular format. Each row reports chlorophyll-a information for a given date and sampling site, with the associated ODER~SO subproject identifier (TP) included when available. Observed Sentinel-2 statistics are provided in chl_median, chl_mean, chl_std, and chl_count. The moving_average and polyfit columns contain daily gap-filled chlorophyll-a estimates and may therefore contain values on dates for which the observed spatial statistics are missing. Missing values are represented as NA. A chl_count value of 0 indicates that no water pixel contributed to the spatial statistics for that record. Detailed column definitions, formats, and units are provided in the accompanying data-dictionary file.`

**Access Information:** `The dataset is licensed under the Creative Commons Attribution 4.0 International licence (CC BY 4.0). All contents may be reused, adapted, and redistributed provided that the dataset is cited. Please check the permanent DOI and package information at https://fred.igb-berlin.de/data/package/1102.`

**Contact Information:** `For further questions, contact: **paula.torre.zaffaroni@igb-berlin.de**`

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