Comparison of SeaWiFS and MODIS time series of inherent optical properties for the Adriatic Sea

F Mélin

doi:10.5194/os-7-351-2011

Abstract

Abstract. Time series of inherent optical properties (IOPs) derived from SeaWiFS and MODIS are compared for the Adriatic Sea. The IOPs are outputs of the Quasi-Analytical Algorithm and include total absorption a, phytoplankton absorption aph, absorption associated with colored detrital material (CDM) acdm, and particle backscattering coefficient bbp. The average root-mean square difference Δ computed for log-transformed distributions decreases for $a$ from 0.084 at 412 nm to 0.052 at 490 nm, is higher for aph(443) (0.149) than for acdm(443) (0.071), and is approximately 0.165 for bbp at various wavelengths. The SeaWiFS a at 443 and 490 nm, aph at 443 nm and bbp are on average higher than the MODIS counterparts. Statistics show significant variations in space and time. There is an overall increasing gradient for Δ associated with the absorption terms from the open southern and central Adriatic to the northwest part of the basin, and a reversed gradient for the particulate backscattering coefficient. For time series analysis, only a(412) and acdm(443) currently present an unbiased continuity bridging the SeaWiFS and MODIS periods for the Adriatic Sea.

Highlights

The Adriatic Sea, a sub-basin of the Mediterranean Sea, has been selected as a basin of interest for development and assessment of ocean colour products in the framework of the European COastal-shelf sea OPerational observing and forecasting system (ECOOP) project, in view of improving the use of remote sensing data in regional and coastal seas
This study focuses on the aspect of continuity of time series of inherent optical properties (IOPs) derived from successive satellite missions, namely the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, Hooker et al 1992), and the Moderate Resolution Imaging Spectroradiometer (MODIS, Esaias et al 1998) on board Aqua, with the objective of assessing the differences existing between the IOP records associated with these two missions
A framework of log-normality is preferred, consistently with previous results and analyses associated with Chl a or IOP distributions (Campbell, 1995; Djavidnia et al, 2010; Melin, 2010), and most statistics presented subsequently are those related to log-transformed distributions, even though the general values of |ψ| and ψ are given for completeness

Summary

Introduction

The Adriatic Sea, a sub-basin of the Mediterranean Sea, has been selected as a basin of interest for development and assessment of ocean colour products in the framework of the European COastal-shelf sea OPerational observing and forecasting system (ECOOP) project, in view of improving the use of remote sensing data in regional and coastal seas. In spite of a relatively small size, the Adriatic Sea offers a diversity of bio-optical properties, with a general gradient from oligotrophic to eutrophic conditions from south to north (Zavatarelli et al, 1998) with the exception of eutrophic conditions near the southeastern corner (Marini et al,, 2010), the seasonal occurrence of a phytoplankton bloom in the southern gyre (e.g., Santoleri et al, 2003) and the local influence of river inputs or bottom re-suspension It is an interesting test basin for assessing and developing ocean colour satellite products. Using ocean colour data, Vantrepotte and Melin (2010) documented an increasing trend in the blue-to-green ratio of water-leaving radiance in the northern Adriatic, and a corresponding decrease in the average level of chlorophyll a concentration (Chl a) has been documented (Melin et al, 2011; Mozeticet al., 2010)

Methods

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Conclusion