Global maps of Forel–Ule index, hue angle and Secchi disk depth derived from 21 years of monthly ESA Ocean Colour Climate Change Initiative data

• Published in: Earth system science data Vol. 13; no. 2; pp. 481 - 490
• Main Authors: Pitarch, Jaime, Bellacicco, Marco, Marullo, Salvatore, van der Woerd, Hendrik J
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 16-02-2021; Copernicus Publications
• Subjects: Algorithms; Climate change; Color; Data; Datasets; Depth; Ecological studies; Equator; Global temperature changes; Mathematical analysis; Ocean colour; Oceans; Optical properties; Pangea; Reflectance; Remote sensing; Resolution; Satellites; Sensors; Spatial discrimination; Spatial resolution; Time series; Variables
• ISSN: 1866-3516; 1866-3508; 1866-3516
• DOI: 10.5194/essd-13-481-2021

We document the development and public release of a new dataset (1997–2018), consisting of global
maps of the Forel–Ule index, hue angle and Secchi disk depth. Source data come from the European
Space Agency (ESA) Ocean Colour (OC) Climate Change Initiative (CCI), which is providing merged
multi-sensor data from the mid-resolution sensors in operation at a specific time from 1997 to the
present day. Multi-sensor satellite datasets are advantageous tools for ecological studies because
they increase the probabilities of cloud-free data over a given region as data from multiple
satellites whose overpass times differ by a few hours are combined. Moreover, data-merging from
heritage and present satellites can expand the duration of the time series indefinitely, which
allows the calculation of significant trends. Additionally, data are remapped consistently and
analysis-ready for scientists. Also, the products described in this article have the exclusive
advantage of being linkable to in situ historic observations and thus enabling the construction of
very long time series. Monthly data are presented at a spatial resolution of ∼4 km
at the Equator and are available at PANGAEA (https://doi.org/10.1594/PANGAEA.904266; Pitarch et al.,
2019a). Two smaller and easier-to-handle test datasets have been produced from the former: a
global dataset at 1∘ spatial resolution and another one for the North Atlantic at 0.25∘ resolution. The computer code for the generation of the Forel–Ule index, hue angle and Secchi
disk depth from a given remote-sensing reflectance is also shared at https://doi.org/10.5281/zenodo.4439646
(Pitarch et al., 2021) and can be easily set in loop mode for batch calculations.