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Remote Sens. 2016, 8(6), 449; doi:10.3390/rs8060449

MERIS Phytoplankton Time Series Products from the SW Iberian Peninsula (Sagres) Using Seasonal-Trend Decomposition Based on Loess

1
Centre for Marine and Environmental Research (CIMA), FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
2
Faculty of Marine and Environmental Sciences, University of Cadiz, Campus of Puerto Real, Polígono San Pedro s/n, Puerto Real, 11510 Cadiz, Spain
3
Faculty of Sciences and Technology (FCT), University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
4
Center of Statistics and Applications (CEAUL), Faculty of Sciences of the University of Lisbon, Bloco C6—Piso 4, Campo Grande, 1749-016 Lisbon, Portugal
5
Pixalytics Ltd., 1 Davy Road, Plymouth Science Park, Plymouth, Devon PL6 8BX, UK
6
Sagremarisco Lda., Apartado 21, 8650-999 Vila do Bispo, Portugal
7
Norwegian Institute for Air Research (NILU)-IMPEC, Box 100, 2027 Kjeller, Norway
*
Author to whom correspondence should be addressed.
Academic Editors: Xiaofeng Li and Prasad S. Thenkabail
Received: 21 January 2016 / Revised: 15 April 2016 / Accepted: 19 May 2016 / Published: 26 May 2016
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Abstract

The European Space Agency has acquired 10 years of data on the temporal and spatial distribution of phytoplankton biomass from the MEdium Resolution Imaging Spectrometer (MERIS) sensor for ocean color. The phytoplankton biomass was estimated with the MERIS product Algal Pigment Index 1 (API 1). Seasonal-Trend decomposition of time series based on Loess (STL) identified the temporal variability of the dynamical features in the MERIS products for water leaving reflectance (ρw(λ)) and API 1. The advantages of STL is that it can identify seasonal components changing over time, it is responsive to nonlinear trends, and it is robust in the presence of outliers. One of the novelties in this study is the development and the implementation of an automatic procedure, stl.fit(), that searches the best data modeling by varying the values of the smoothing parameters, and by selecting the model with the lowest error measure. This procedure was applied to 10 years of monthly time series from Sagres in the Southwestern Iberian Peninsula at three Stations, 2, 10 and 18 km from the shore. Decomposing the MERIS products into seasonal, trend and irregular components with stl.fit(), the ρw(λ) indicated dominance of the seasonal and irregular components while API 1 was mainly dominated by the seasonal component, with an increasing effect from inshore to offshore. A comparison of the seasonal components between the ρw(λ) and the API 1 product, showed that the variations decrease along this time period due to the changes in phytoplankton functional types. Furthermore, inter-annual seasonal variation for API 1 showed the influence of upwelling events and in which month of the year these occur at each of the three Sagres stations. The stl.fit() is a good tool for any remote sensing study of time series, particularly those addressing inter-annual variations. This procedure will be made available in R software. View Full-Text
Keywords: MERIS; time series; Seasonal-Trend Decomposition; stl.fit(); Algal Pigment Index 1; water leaving reflectance; inter-annual seasonal variability; Iberian Peninsula; Sagres MERIS; time series; Seasonal-Trend Decomposition; stl.fit(); Algal Pigment Index 1; water leaving reflectance; inter-annual seasonal variability; Iberian Peninsula; Sagres
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Cristina, S.; Cordeiro, C.; Lavender, S.; Costa Goela, P.; Icely, J.; Newton, A. MERIS Phytoplankton Time Series Products from the SW Iberian Peninsula (Sagres) Using Seasonal-Trend Decomposition Based on Loess. Remote Sens. 2016, 8, 449.

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