TITLE:
Evaluation of MODIS Products in the Great Australian Bight and Adjacent Coastal Waters
AUTHORS:
Ana Redondo Rodriguez, Edward King, Mark Doubell, Paul van Ruth
KEYWORDS:
Great Australian Bight, MODIS, Remote Sensing, Ocean Color, Chlorophyll, Euphotic Depth
JOURNAL NAME:
Open Journal of Marine Science,
Vol.8 No.4,
October
26,
2018
ABSTRACT: Satellite remote sensing data can produce global environmental data and is
easily accessible and widely used by the scientific and non-scientific community.
However, to use satellite data, it is important to know its limitations and
how it validates against in situ measurements for the different regions. Here,
field measurements of chlorophyll-a concentration and euphotic depth within
the Great Australian Bight, Gulf St Vincent and Spencer Gulf were used to
validate ocean colour products derived from the Moderate Resolution Imaging
Spectroradiometer (MODIS) onboard the Aqua satellite. The field data
include in situ and in vivo chlorophyll-a concentration, which were compared
against MODIS chlorophyll-a products derived from three algorithms
(OC3M, Carder, and Garver-Siegel-Maritorena (GSM)), as well as euphotic
depth measurements derived from photosynthetically active radiation (PAR)
profiles, which were compared against two MODIS euphotic depth products
(derived semi-analytically and from surface chlorophyll-a). The OC3M
product performed well in open waters, with errors below the 35% NASA accepted
limit, but it overestimated chlorophyll-a values in shallow (in situ euphotic depth were robust, with errors lower
than 20%. MODIS products showed weaker or no significant relationships to in situ measurements in the Eastern Great Australian Bight. This is thought
to be due to the summertime subsurface upwelling pool that is characteristic
of the area. Based on these results, the OC3M product provides the most reliable
estimates of chlorophyll-a, and is recommended for further applications
of MODIS imagery, if the limitations in shallow waters are taken into account.
Alternatively, the GSM product could be a better option if the algorithm
were locally adjusted. Changes in the sampling methodology to improve the algorithms are discussed. Derived euphotic depth products can be
used with confidence in applying MODIS products for monitoring water
clarity, ecosystem health or primary productivity in the region.