Review Jurnal Penginderaan Jauh Sinar Tampak "Evaluation of Standar & Regional Satellite Chlorophyll-a Algorithms for MODIS in the Bohai & Yellow Seas, China" oleh Wang et al. (2019)

1. Evaluation of standar and regional satellite
chlorophyll-a algorithms for MODIS
in the Bohai and Yellow Seas, China
Wang et al,
2019

3. Outline
Conclusions
Introduction
Data and Methods
Results and Discussions
01
02
03
04

4. Introduction
Chlorophyll-a (chl-a) concentration
has long been regarded as a
powerful way of representing
phytoplankton biomass in the oce
an.
In recent decades, remotely sense
d
satellite ocean colour products ha
ve been widely used to detect syn
optic
spatial and temporal patterns and
variability of sea surface chl-a
concentrations.
However, when applied to coastal
waters which are shallow in depth
and/or have high turbidity, satellite
-derived chl-a may produce
significant biases due to inaccurac
ies in atmospheric correction mod
els
and improper inversion algorithms
.
Therefore, careful evaluation of th
e
existing satellite chl-a algorithms a
nd developing new regional algorit
hms are essential for satellite oce
an colour applications over opticall
y complex waters.

5. To evaluate the performance of the standar
d OC3M (ocean chl-a three-band algorithm f
or MODIS (moderate-resolution imaging sp
ectro
radiometer)) chl-a algorithm.
The aim

6. Data & Methods
In situ measurements of
chl-a
Figure 1.
(a) Map of the BYS and (b)–(j) the sites of the in situ chl-a measurem
ents during each cruise;
(b) 20 April–4 May 2010; (c) 2 May– 20 May 2012;
(d) 2 November–19 November 2012; (e) 22 June–9 July 2013;
(f) 6 November–24 November 2013; (g) 28 April–18 May 2014;
(h) 7 November–23 November 2014; (i) 17 August-5 September 2015
;
(j) 15 January–30 January 2016.

7. The daily MODIS/Aqua standard local area
coverage (LAC) remote-sensing reflectance (
Rrs)
images for 10 available visible bands were
downloaded from the NASA
(National Aeronautics and Space
Administration)
Satellite chl-a data
spatial resolution of approximately 1 km ×1 km
and over the time span from
4 July 2010 to 31 December 2016.

8. 1 2
3 4
Method for satellite chl-a data validation
The satellite chl-a values were extract
ed and compared against the coincide
nt in
Situ chl-a measurements.
Visual inspections of spatial difference
s
between in situ, OC3M and GAM
(correlation analyses).
The BYS was subdivided into three
subregions Including:
a coastal region (<20 m isobath);
an offshore region (>50 m isobath);
as well as a transitional region (betwe
en 20 and 50 m isobaths).
The chl-a series for the specific regi
ons were calculated and compared
with
the corresponding in situ chl-a serie
s
over each time span during the year
s 2010–2016.

9. Statistical comparisons
Results
2(a). The MRD value of 1.
13 mg m−3 indicates a dist
inct
overestimation in OC3M c
hl-a estimates.
2(b). In contrast, the GAM
chl-a algorithm was
characterized by much low
er uncertainty (MAPD = 33
.56%, MRD = 0.09 mg m−
3).

10. Spatial comparisons for each cruise
Figure 3. Spatial distribution
s
of:
(a) in situ chl-a measuremen
ts;
(b) OC3M satellite chl-a;
(c) GAM satellite chl-a;
composites for each of the 9
cruises (from left to right in
order: January 2016, April–
May 2010, April–May 2014,
May 2012, June–July 2013,
August–September 2015,
November 2012, November
2014 and November 2013);
(d) the series of chl-a averag
es during the period of each
cruise.

11. Time series comparisons
Figure 4. The time series of monthly chl-a
averages generated from satellite products for
:
(a) the entire BYS region,
(b) coastal region,
(c) transition region, and
(d) deep region.
The solid line is the OC3M chl-a, the dotted lin
e is GAM chl-a, and filled circle is in situ chl-a
averages for each cruise.
Table 1. Results of the Spearman rank correlation
analyses between satellite-derived and in situ
measured chl-a over different regions.

12. Conclusio
n
The extent of overestimati
on of chl-a values by the
standard OC3M algorithm
values was quantified, and
the extent of distortion of c
hl-a seasonality was show
n to be significant.
The result of this study
opposes the use of the
standard OC3M algorithm i
n the BYS.
Compared with the
OC3M algorithm, a
previously reported
regional GAM chl-a
algorithm for the BYS
produced more
accurate derived chl-a
values and a
seasonality consistent
with the in situ
measurements, makin
g it a more suitable ch
l-a algorithm for use in
the BYS.

13. Thank you