Evaluation of Satellite Retrievals of Chlorophyll-a in the Arabian Gulf

Noora Al-Naimi,Radhouan Ben-Hamadou,Dionysios Raitsos,Yousria Soliman

doi:10.3390/rs9030301

Noora Al-Naimi, Radhouan Ben-Hamadou + Show 2 more

Open Access

https://doi.org/10.3390/rs9030301

Copy DOI

Abstract

The Arabian Gulf is a highly turbid, shallow sedimentary basin whose coastal areas have been classified as optically complex Case II waters (where ocean colour sensors have been proved to be unreliable). Yet, there is no such study assessing the performance and quality of satellite ocean-colour datasets in relation to ground truth data in the Gulf. Here, using a unique set of in situ Chlorophyll-a measurements (Chl-a; an index of phytoplankton biomass), collected from 24 locations in four transects in the central Gulf over six recent research cruises (2015–2016), we evaluated the performance of VIIRS and other merged satellite datasets, for the first time in the region. A highly significant relationship was found (r = 0.795, p < 0.001), though a clear overestimation in satellite-derived Chl-a concentrations is evident. Regardless of this constant overestimation, the remotely sensed Chl-a observations illustrated adequately the seasonal cycles. Due to the optically complex environment, the first optical depth was calculated to be on average 6–10 m depth, and thus the satellite signal is not capturing the deep chlorophyll maximum (DCM at ~25 m). Overall, the ocean colour sensors’ performance was comparable to other Case II waters in other regions, supporting the use of satellite ocean colour in the Gulf. Yet, the development of a regional-tuned algorithm is needed to account for the unique environmental conditions of the Gulf, and ultimately provide a better estimation of surface Chl-a in the region.

Highlights

The Arabian Gulf is a marginal semi-enclosed basin that is located in a subtropical, hyper-arid region
Using a unique set of in situ fluorometric chlorophyll measurements—collected in six cruises from 24 locations down four transects over 18 months (2015–2016)—in the central Arabian Gulf, we aim to evaluate the performance of satellite sensors in their ability to retrieve reliable Chlorophyll-a measurements (Chl-a) concentrations that enable understanding regional temporal and spatial trends and variabilities
Our results are coherent with other studies [16,40], they performed their analysis on the spatio-temporal variations of phytoplankton biomass in the Arabian Gulf using a single-sensor Chl-a dataset

Summary

Introduction

The Arabian Gulf (alternatively referred to as the Persian Gulf in the literature and hereafter referred as the Gulf) is a marginal semi-enclosed basin that is located in a subtropical, hyper-arid region. The extreme temperature and salinity in the Arabian Gulf is probably pushing many species near their physiological limits [3,4] Despite such harsh environmental conditions, the Gulf hosts a wide range of marine ecosystems such as mangrove swamps, seagrass beds, and coral reefs, providing valuable ecosystem services to neighboring countries. These ecosystems host an assorted marine biodiversity as they form shelter, feeding, and nursery grounds for a variety of marine organisms [5,6]. They experience constant, growing pressure from multiple anthropogenic sources in the Arabian Gulf region [1]

Objectives

Methods

Results

Discussion

Conclusion