Riverine plume extent and frequency between 2017-2023 in Sri Lankas Exclusive Economic Zone and southern tip of India

Riverine plume extent and the frequency of plume occurrence between 2017-2023 derived from ocean colour Sentinel-3 Ocean and Land Colour Instrument (OLCI) data in Sri Lanka's Exclusive Economic Zone (EEZ) and southern tip of India. This data was created under Ocean Country Partnership Programme (OCPP) funded Defra (funding: project number GB-GOV-7-BPFOCPP)

Methodology of deriving plume extent and frequency. Sentinel-3 OLCI L1 data was atmospherically corrected using Polymer atmospheric correction to derive water leaving reflectance (Rw). Rw was used to calculate Forel-Ule Index (FUI) in Python based on the GitHub repository here: https://github.com/CefasRepRes/FUME FUI is a 21 colour scale ranging from indigo blue to cola brown, qualitatively describing bio-geo-chemical properties of the water (http://www.citclops.eu/water-colour/measuring-water-colour). Daily FUI values were resampled to a regular grid and aggregated to monthly composites using mean FUI per pixel. Statistics (mean, minimum, maximum per pixel) between 2017-2023 were calculated using the mean monthly FUI composites. Maximum mean FUI between 2017-2023, where FUI>=10, was used as a threshold to map the presence of the plume extent based on Fronkova et al, 2022 https://doi.org/10.3390/rs14102375. The contour of the plume extent was simplified using 5km distance using ArcGIS Pro.

Frequency of FUI>= 10 was calculated in Python and normalised between 0 and 1, where 1 means the plume occurred all of the times between 2017-2023 in the particular pixel, and 0 means no data. The plume frequency was calculated based on four seasons in Sri Lanka:

First inter-monsoon (March-April): SLKplumefreqmeanfirstintermoons2017_2023.tif
Southwest monsoon (May-September): SLKplumefreqmeanswmonsoon2017_2023.tif
Second inter-monsoon (October-November): SLKplumefreqmeansecondintermonsoon2017_2023.tif
Northeast monsoon (December-February): SLKplumefreqmeannemonsoon2017_2023.tif
Spatial resolution of the frequency data is 300m and EPSG 4326 (geotiffs)

Input data sources for the analysis: Copernicus Sentinel data [2017 - 2023] , EUMETSAT products 0409 and 0577 https://data.eumetsat.int/product/EO:EUM:DAT:0409 and https://data.eumetsat.int/product/EO:EUM:DAT:0577