Ocean colo a mosphe ic
co ec ion me hods in iew o
usabili y o di e en op ical
wa e ypes
Ma in Hie onymi
1
*, Shun Bi
1
, Dagma Mülle
2
, Eike M. Schü
1,3
,
Daniel Beh
1
, Ca s en B ockmann
2
, Ca ole Leb e on
2
,
F anc¸ois S einme z
4
, Ke s in S elze
2
and Quin en Vanhellemon
5
1
Depa men o Op ical Oceanog aphy, Ins i u e o Ca bon Cycles, Helmhol z-Zen um He eon,
Gees hach , Ge many,
2
B ockmann Consul GmbH, Hambu g, Ge many,
3
Ea h Obse a ion and
Modelling, Depa men o Geog aphy, Kiel Uni e si y, Kiel, Ge many,
4
HYGEOS, Lille, F ance,
5
Royal
Belgian Ins i u e o Na u al Sciences, Ope a ional Di ec o a e Na u al En i onmen s, B ussels, Belgium
Sa elli e emo e sensing allows la ge-scale global obse a ions o aqua ic
ecosys ems and ma e fluxes om he sou ce h ough i e s and lakes o
coas s, ma ginal seas in o he open ocean. Fuzzy logic classifica ion o op ical
wa e ypes (OWT) is inc easingly used o op imally de e mine wa e p ope ies
and enable seamless ansi ions be ween wa e ypes. Howe e , e ec i e
exploi a ion o his me hod equi es a success ul a mosphe ic co ec ion (AC)
o e he en i e spec al ange, i.e., he ups eam AC is sui able o each wa e ype
and always deli e s classifiable emo e-sensing eflec ances. In his s udy, we
compa e fi e di e en AC me hods o Sen inel-3/OLCI ocean colo image y,
namely IPF, C2RCC, A4O, POLYMER, and ACOLITE-DSF (all in he 2022 cu en
e sion). We e alua e hei esul s, i.e., emo e-sensing eflec ance, in e ms o
spa ial exploi abili y, indi idual flagging, spec al plausibili y compa ed o in si u
da a, and OWT classifiabili y wi h ou di e en classifica ion schemes. Especially
he esul s o A4O show ha i is beneficial i he pe o mance spec um o he
a mosphe ic co ec ion is ailo ed o an OWT sys em and ice e sa. The s udy
gi es hin s on how o imp o e AC pe o mance, e.g., wi h espec o
homogenei y and flagging, bu also how an OWT classifica ion sys em should
be designed o global deploymen .
KEYWORDS
a mosphe ic co ec ion, ocean colo , op ical wa e ypes, sa elli e emo e sensing,
essen ial clima e a iable, Sen inel-3/OLCI
F on ie s in Ma ine Science on ie sin.o g01
OPEN ACCESS
EDITED BY
Ja ie A. Concha,
Eu opean Space Resea ch Ins i u e (ESRIN),
I aly
REVIEWED BY
Jona han J. She man,
Na ional Oceanic and A mosphe ic
Adminis a ion (NOAA), Uni ed S a es
Ila ia Cazzaniga,
Join Resea ch Cen e, I aly
Su ya P akash Tiwa i,
King Fahd Uni e si y o Pe oleum and
Mine als, Saudi A abia
*CORRESPONDENCE
Ma in Hie onymi
[email p o ec ed]
RECEIVED 22 Decembe 2022
ACCEPTED 22 June 2023
PUBLISHED 20 July 2023
CITATION
Hie onymi M, Bi S, Mülle D, Schü EM,
Beh D, B ockmann C, Leb e on C,
S einme z F, S elze K and Vanhellemon Q
(2023) Ocean colo a mosphe ic
co ec ion me hods in iew o usabili y o
di e en op ical wa e ypes.
F on . Ma . Sci. 10:1129876.
doi: 10.3389/ ma s.2023.1129876
COPYRIGHT
© 2023 Hie onymi, Bi, Mülle , Schü , Beh ,
B ockmann, Leb e on, S einme z, S elze and
Vanhellemon . This is an open-access a icle
dis ibu ed unde he e ms o he C ea i e
Commons A ibu ion License (CC BY). The
use, dis ibu ion o ep oduc ion in o he
o ums is pe mi ed, p o ided he o iginal
au ho (s) and he copy igh owne (s) a e
c edi ed and ha he o iginal publica ion in
his jou nal is ci ed, in acco dance wi h
accep ed academic p ac ice. No use,
dis ibu ion o ep oduc ion is pe mi ed
which does no comply wi h hese e ms.
TYPE O iginal Resea ch
PUBLISHED 20 July 2023
DOI 10.3389/ ma s.2023.1129876
1 In oduc ion
Ocean Colo (OC) has been iden ified as an Essen ial Clima e
Va iable (ECV), because o i s capabili y o obse e a ious aspec s
o he ma ine en i onmen synop ically a global scales (GCOS,
2011;Hollmann e al., 2013). The colo o he ocean is de e mined
by abso p ion and sca e ing in e ac ions o sunligh wi h wa e ,
ee-floa ing pa icles and dissol ed subs ances in he uppe wa e
laye (cu en s a e o esea ch on his is summa ized by Bi e al.,
2023). Colo , o mo e specifically he emo e-sensing eflec ance,
R
s
,isdefined as he spec al (back-sca e ed) wa e -lea ing
adiance, L
w
, in p opo ion o he o al down-welling plane
i adiance, E
d
. The e e ence poin lies di ec ly abo e he sea
su ace a he bo om-o -a mosphe e (BOA). The spec al ange
o R
s
includes no only he isible (VIS) ange, which is pe cei ed as
colo o en defined o wa eleng hs om 380 o 760 nm, bu also
pa s o he ul a iole (UV) and nea -in a ed (NIR) spec al ange;
i is p ima ily de e mined by he pu e wa e abso p ion (e.g., Bi
e al., 2023). Space-bo ne ocean colo senso s, howe e , measu e
spec al adiances, L
TOA
, a he op-o -a mosphe e (TOA) om he
gi en iewing di ec ion. This signal is s ongly influenced by ligh
in e ac ions in he a mosphe e, like sca e ing by ai molecules, and
ae osols o abso p ion by a mosphe ic gases, bu also by ligh
eflec ions a he sea su ace (e.g., IOCCG, 2010;F ouin e al.,
2019). Mo eo e , whi ecaps and ai bubbles in wa e , no ela ed o
he ac ual ocean colo , con ibu e o he wa e -lea ing signal (e.g.,
Die ssen, 2019). The p ocess o e ie ing unobs uc ed emo e-
sensing eflec ance a su ace le el om TOA adiance is ypically
e e ed o as a mosphe ic co ec ion (AC).
Spec al emo e-sensing eflec ance is he undamen al pa ame e
om which biogeo-op ical p ope ies and co esponding
concen a ions o op ically ac i e wa e cons i uen s can be de i ed.
The concen a ion o he pigmen chlo ophyll-a in wa e , Chl,iswidely
used as a p oxy o he phy oplank on biomass in he uppe wa e laye ;
Chl is also conside ed as an ECV as i is linked o he ma ine ca bon-
cycle. The Global Clima e Obse ing Sys em (GCOS, 2011)defines a
a ge accu acy equi emen o R
s
(s ic ly speaking o he wa e -
lea ing adiance) o 5% specifically o he blue and g een wa eleng hs
and 30% o Chl. This applies o so-called Case-1 (C1) wa e s whose
inhe en op ical p ope ies (IOPs) p ima ily depend on phy oplank on,
i s abundance and i s deg ada ion p oduc s; his is gene ally he case o
open oceans. In con as , all “op ically complex”wa e s o ma ginal
seas, coas al and inland wa e bodies a e summa ized as Case-2 (C2)
whe e addi ional wa e cons i uen s such as non-algal pa icles (NAP)
and colo ed dissol ed o ganic ma e (CDOM) conside ably influence
he wa e colo (Mo el and P ieu , 1977;Bi e al., 2023). CDOM is
p ima ily leached om decaying de i us and e es ial o ganic ma e ,
bu i can also be yielded om p ecipi a ion wi h ele a ed CDOM le els
in con inen ally influenced ainwa e (Kiebe e al., 2006). The accep ed
unce ain ies o R
s
and subsequen ocean colo p oduc s a e
conside ably highe o Case-2 wa e s and GCOS ecommends he
implemen a ion o specifically ailo ed algo i hms. Based on his
a ionale, EUMETSAT o example o e s wo independen Chl
p oduc s (based on di e en AC me hods) om he ope a ional
Ocean and Land Colo Ins umen (OLCI) on boa d he Sen inel-3
sa elli es, namely CHL_OC4ME o Case-1 and CHL_NN o Case-2
wa e s. Use consul a ions, howe e , e eal a clea p io i y o ocean
colo algo i hms ha wo kac ossC1-C2wa e s,o a leas ha
dema ca e he bounda y be ween he wo; mo eo e , app op ia e
and s eady ocean colo p oduc s a e equi ed o clima e change
s udies (Sa hyend ana h e al., 2017).
The usage o b anching and blending o specialized algo i hms
o seamless ansi ion and case-op imized phy oplank on es ima es
has inc eased o e he cou se o he ecen yea s. Smi h e al. (2018)
and Kajiyama e al. (2018) o example ha e de eloped OLCI-
specific bipa i e swi ching algo i hms o egionally op imized Chl
e ie als. Mo e holis ic app oaches in ol e a p e-classifica ion o
R
s
spec a in o se e al op ical wa e ypes (OWT) in o de o
display he ull spec al di e si y o oceanic, coas al, and inland
wa e s (e.g., Moo e e al., 2001;Ma in T ayko ski and Sosik, 2003;
Van epo e e al., 2012;Shi e al., 2013;Moo e e al., 2014;Melin
and Van epo e, 2015;Minu e al., 2016;Ele eld e al., 2017;
Hie onymi e al., 2017;Jackson e al., 2017;Spy akos e al., 2018;
Soome s e al., 2019;Uudebe g e al., 2020;Jia e al., 2021;Wei e al.,
2022). Howe e , e ec i e exploi a ion o his me hod p esumes a
success ul a mosphe ic co ec ion o e he en i e spec al ange.
Residual e o s om impe ec a mosphe ic co ec ion, which a e
no ep oducible by combina ion o mean OWT eflec ance spec a,
can esul in e y low o al membe ships and he e o e, p o e he
unfi ness o he p ocessing cons ella ion o his case. This leads o
he need ha he ups eam AC me hod is wi hin he scope o each
wa e ype and ha i deli e s always-su ficien o al membe ships.
The e a e a ious senso -specific AC me hods, which supply
emo e-sensing eflec ance mos ly op imized o ei he oceanic,
coas al o inland wa e s, e.g., desc ibed in IOCCG (2010) o
F ouin e al. (2019). The co esponding AC pe o mance can
di e significan ly depending on he selec ed e alua ion da a,
op ical wa e ypes, applied flagging, senso p ope ies like came a
bounda ies, he p esence o anspa en clouds o sun glin (e.g.,
Goyens e al., 2013;Mülle e al., 2015a;Mülle e al., 2015b;Qin
e al., 2017;Tils one e al., 2017;Mog ane e al., 2019). F ouin e al.
(2019) lis ed a numbe o significan issues o a mosphe ic
co ec ion including clouds, adjacency e ec s, whi ecaps, he
Ea h a mosphe e’s cu a u e, mul iple sca e ing, and
pola iza ion. Mo eo e , a mosphe ic co ec ions ha e se ious
di ficul ies in cases wi h high CDOM o NAP concen a ions in
wa e , i.e., e y da k o b igh , so called ex eme Case-2 wa e s
(Hie onymi e al., 2016;Hie onymi e al., 2017). Abso p ion o
dissol ed o ganic ma e causes an exponen ial educ ion o he
eflec ance especially in he blue; his is om a TOA- eflec ance
poin o iew, a compa able spec al e ec as Rayleigh sca e ing by
ai molecules and hence ambiguous. Abso bing o ex emely
abso bing Case-2 wa e s (C2A, C2AX) a e cha ac e ized by low
spec al R
s
wi h maximum in he g een and in cases wi h e y high
CDOM-con en (i.e., a
CDOM
(440) >1 m
-1
) in he yellow, ed, o e en
NIR spec al ange. Pa icles in wa e abso b, bu abo e all also
sca e ligh , which leads o inc eased eflec ance a highe
concen a ions, pa ly also in he NIR. The spec al abso p ion
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g02
and much highe sca e ing o non-algae pa icles also ha e an
app oxima ely exponen ial cou se, as does he Rayleigh influence.
A ela i ely high NAP concen a ions o 1 g m
-3
, one speaks o
sca e ing Case-2 wa e s (C2S); a NAP > 100 g m
-3
o ex emely
sca e ing wa e s (C2SX) espec i ely. Fu he mo e, AC p oblems
a ise in he p esence o e y high concen a ions o phy oplank on
and floa ing scum wi h non-negligible NIR eflec ance (e.g., Reina
and Ku se , 2006). Clea ly, a combina ion o di e en AC
algo i hms can po en ially imp o e an all-wa e - ype-emb acing
R
s
- e ie al; examples a e gi en in Shi and Wang (2009);Au in
e al. (2013);Bi e al. (2018);Liu e al. (2019), and Sch oede e al.
(2022). Howe e , p og amma ic linking o undamen ally di e en
AC algo i hms can be challenging and swi ching may lead o spa ial
inconsis ency o a e ac s in he e ie als.
Se e al AC me hods exis o ocean colo image y o Sen inel-3/
OLCI. Howe e , hei ange o alidi y is no always clea and hey
do no always ulfil all equi emen s o unlimi ed usabili y o
OWT-based wa e algo i hms like he ONNS algo i hm by
Hie onymi e al. (2017). In his s udy, we compa e fi e
concep ually di e en a mosphe ic co ec ion me hods o
Sen inel-3/OLCI (specified in Table 1): 1) he s anda d (baseline)
Le el-2 AC –Ins umen P ocessing Facili y (IPF), 2) he
al e na i e Le el-2 AC C2RCC, 3) a no el a mosphe ic co ec ion
o di e se op ical wa e ypes (A4O) by Hie onymi e al. (in p ep.),
4) POLYMER by S einme z e al. (2011), and 5) he Da k Spec um
Fi ing (DSF) implemen ed in ACOLITE by Vanhellemon and
Ruddick (2021). The e a e also o he me hods a ailable ha can be
applied o OLCI (e.g., Guan e e al., 2010;Gossn e al., 2019;
Sch oede e al., 2022), bu we ocus on hese fi e ACs as
ep esen a i e examples o di e se app oaches. Based on op ically
di e se Sen inel-3/OLCI images, we compa e he capaci y o da a
exploi a ion, he spa ial plausibili y and homogenei y (noise), and
analyze he AC ou pu , namely R
s
, in iew o di e en OWT
classifica ion schemes. Mo eo e , we show compa isons wi h in
si u ma ch-up da a. We a e he eby a emp ing o dema ca e he
scope o applica ion o each AC me hod and iden i y po en ials o
u u e imp o emen s.
2 Applied me hods and
e alua ion da a
2.1 A mosphe ic co ec ion me hods
unde conside a ion
2.1.1 IPF
The Eu opean Space Agency (ESA), oge he wi h he Eu opean
O ganisa ion o he Exploi a ion o Me eo ological Sa elli es
(EUMETSAT), ope a es he Sen inel se ies o sa elli es om he
Eu opean Union Cope nicus P og amme. EUMETSAT p o ides
Le el-2 (L2) s anda d wa e p oduc s o Sen inel-3/OLCI. Ou
wo k e e s o da a o he ocean colo “baseline a mosphe ic
co ec ion” om he Ins umen P ocessing Facili y (IPF), which
has been ope a ional since 2021 (OLCI Collec ion-3). The
eflec ances p o ided a e he basis o he es ima ion o he
chlo ophyll-a concen a ion in Case-1 wa e , CHL_OC4ME. The
AC was de eloped o he open ocean and is based on wo k o
Go don and Wang (1994); u he de elopmen s o his me hod
we e summa ized by Go don (2021).Significan u he
de elopmen s ega ding MERIS and OLCI a e based on An oine
and Mo el (1998), and An oine and Mo el (1999);Moo e e al.
(1999), and Nobileau and An oine (2005). Majo upda es o IPF
ha e been in oduced in he Sen inel-3/OLCI L2 epo o baseline
collec ion (EUMETSAT, 2021); he epo includes se e al
compa isons wi h in si u da a and e e ence missions, and lis s
he ecommended flags. Pa icula ly no ewo hy is he ecen ly
implemen ed e ision o he so-called b igh pixel co ec ion
wi hin he AC, which is applied e e ywhe e, bu b ings
imp o emen s especially in NAP-domina ed coas al wa e s.
2.1.2 C2RCC
The OLCI L2 p ocessing includes a second “al e na i e”AC
whose esul s a e no p o ided, bu hey o m he basis o he L2
Case-2 wa e p oduc s like chlo ophyll-a concen a ion, CHL_NN.
The AC uses neu al ne wo ks (NN) o he e ie al o R
s
and also
TABLE 1 Examined a mosphe ic co ec ion me hods o Sen inel-3/OLCI ocean colo p ocessing wi h AC-specific masking (plus INVALID and LAND
o all).
AC Full name and Ve sion O iginal
scope
Flags o in alid pixel exp ession Addi ional wa ning flags
IPF IPF L2-WFR OLCI Collec ion-3
OL_L2M.003.00
C1 CLOUD, CLOUD_AMBIGUOUS, CLOUD_MARGIN,
COSMETIC, SATURATED, SUSPECT, HISOLZEN,
HIGHGLINT, SNOW_ICE, AC_FAIL, ADJAC,
WHITECAPS, RWNEG_[O2-O8]
TURBID_ATM, TIDAL, MEGLINT,
AC_FAIL, WHITE_SCATT, LOWRW,
HIGHRW, ANNOT, RWNEG_[O1, O9-12,
O16-18, O21]
C2R C2RCC 1.7 including IPF gains C2S, C2A RHOW_OOR, IDEPIX_CLOUD, IDEPIX_CLOUD_BUFFER,
IDEPIX_CLOUD_SHADOW, IDEPIX_SNOW_ICE,
RTOSA_OOR
RTOSA_OOS, CLOUD_RISK
A4O A4O 0.23 (2022-01-19) C1, C2S/X,
C2A/X
CLOUD_RISK, SEA_ICE FLOATING, SUSPECT, GLINT_RISK,
ADJACENCY, RTOA_EXCESS
POL POLYMER 4.14 (2021-12-17) C1, C2S,
C2A
CLOUD_BASE, OUT_OF_BOUNDS, EXCEPTION,
THICK_AEROSOL, HIGH_AIR_MASS
NEGATIVE_BB, EXTERNAL_MASK,
CASE2, INCONSISTENCY
DSF ACOLITE-DSF 2022-10-25.0 C2S/X NIR_SWIR_THRES, CIRRUS, TOA_THRESH, NEGATIVE,
EXTENT
The e a e some imes addi ional flags o subsequen wa e algo i hms ha a e no shown he e.
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g03
goes back o he MERIS he i age wi h wo ks o Doe e and Schille
(2007). The o iginal Case-2 Regional (C2R) algo i hm, which
con ains AC and wa e algo i hms, was op imized o coas al
wa e s o he No h Sea. The algo i hm was u he de eloped in
he Coas Colou p ojec (ESA) and is now known as C2RCC
(B ockmann e al., 2016). C2RCC is a ailable in he Sen inel
Toolbox (SNAP). The neu al ne wo ks used in he OLCI L2
p ocessing and hose o C2RCC a e iden ical. Howe e , he e a e
small di e ences be ween OLCI ope a ional NN p oduc s and
ou pu s om he SNAP C2RCC p ocessing due o some di e en
p e-p ocessing s eps. In his s udy, he IPF-de i ed SVC gains ( om
Collec ion 3) a e used o C2RCC p ocessing di ec ly on OLCI L1B
da a, which is done sligh ly di e en in he OLCI L2 g ound
segmen NN p ocessing (EUMETSAT, 2021). The applica ion o
senso -specific and AC-specific sys em ica ious calib a ion (SVC)
gains may ha e he bigges impac also in compa ison wi h p e ious
s udies; in some s udies, such as Cazzaniga e al. (2023), he same
SVC gains a e applied, in ea lie s udies han 2021, o he SVC gains
we e used in some cases (e.g., Giannini e al., 2021). The pixel
iden ifica ion ool IdePix was used o cloud de ec ion and
co esponding addi ional flagging (B ockmann e al., 2013).
Agains usual ecommenda ions o use equal p ocessing le els o
ma ch-up analysis, he non-no malized R
s
p oduc o C2RCC is
used, which has a b oade spec al ange in he NIR necessa y o
some OWT models.
2.1.3 A4O
In he cou se o he las ew yea s, Hie onymi e al. (in p ep.)
de eloped a no el a mosphe ic co ec ion o di e se op ical wa e
ypes (A4O). The basis was C2RCC, bu wi h undamen al
concep ual e ision o op imize classifiabili y wi h he OWT
amewo k implemen ed in he OLCI Neu al Ne wo k Swa m
(ONNS) wa e algo i hm (Hie onymi e al., 2017). The aim o
A4O is o be applicable o all na u al wa e s, om Case-1 o
ex emely sca e ing o abso bing Case-2 wa e s. Special a en ion
was dedica ed o phy oplank on di e si y. A4O applies an ensemble
o di e en neu al ne wo ks and p o ides ully no malized R
s
.In
addi ion, he e a e o he di e ences o C2RCC; hese include he
specifica ion o wa e empe a u e and salini y using global
clima ological da a, he ea men o ocean whi ecaps, he
expansion o ea u es in he NN aining da a, flagging, and an
op ion o spec al and spa ial smoo hing o he signal. The IPF-
SVC gains a e also aken in o accoun he e p ima ily o compensa e
o senso -specific di e ences, i.e., he ins umen s on Sen inel-3A
and -3B. The in alid pixel exp ession e e s p ima ily o an own
cloud masking, all isible wa e a eas a e alid in p inciple (non-
physical nega i e eflec ance is ne e deli e ed). Howe e , he e a e
a numbe o wa ning flags, e.g., o pixels wi h possible land
influence o s ong sun glin signal, whe e esul s migh be aul y.
I is planned o publish A4O and ONNS in SNAP in he
medium e m.
2.1.4 POLYMER
POLYMER is an AC algo i hm o iginally de eloped o oceanic
and coas al wa e s (S einme z e al., 2011;S einme z and Ramon,
2018). I uses a spec al fi ing scheme ha elies on wo models: a
polynomial-like model o a mosphe ic eflec ance and a model o
wa e eflec ance. I was de eloped p ima ily o co ec ing sun-
glin con amina ion on images o he MERIS senso , and has hen
been applied o se e al mul ispec al and hype spec al senso s
including OLCI. In addi ion o sun glin co ec ion, i is also obus
o ae osol con amina ion and o he a mosphe ic and su ace e ec s
such as hin clouds and adjacency e ec s (S einme z and Ramon,
2018;Zhang e al., 2019). POLYMER is he only me hod in his
s udy ha does no use he IPF-SVC gains because all bands a e
used simul aneously o a mosphe ic co ec ion. Thus, specific
gains a e used, gene a ed by a dedica ed spec ally coupled
SVC scheme.
2.1.5 ACOLITE-DSF
The Da k Spec um Fi ing (DSF) algo i hm as implemen ed in
ACOLITE, was o iginally de eloped o aqua ic applica ions o
sa elli e da a wi h high spa ial esolu ion in he me e o
decame e scale, e.g., he Landsa se ies, Sen inel-2/MSI, Pleiades,
and Plane Scope (Vanhellemon and Ruddick, 2018;Vanhellemon ,
2019a;Vanhellemon , 2019b;Vanhellemon , 2020). Vanhellemon
and Ruddick (2021) adap ed he AC o Sen inel-3/OLCI especially
o mapping o suspended pa icula e ma e and chlo ophyll-a
concen a ion in u bid coas al wa e s. Thus, he main scope o
ACOLITE-DSF is o aqua ic applica ions o inland and coas al
wa e s, bu i can also be used o e clea e wa e s and e en land.
The gains om IPF-SVC a e also being conside ed he e.
2.2 Re e ence sa elli e and ma ch-up da a
2.2.1 Selec ed scenes o spa ial analysis
Ten ull- esolu ion OLCI (Le el-1) scenes we e selec ed o
analysis o he spa ial AC pe o mance (pixel size 300 m a nadi ,
swa h wid h app oxima ely 1270 km). They co e a wide a ie y o
op ical wa e ypes, egions, sun ele a ions, and senso - iewing
angles ela i e o he sun (Table 2;Appendix Figu e A1).
App oxima ely 47% o he obse ed Ea h su ace in he images is
co e ed by wa e . O hese wa e a eas, 36% a e flagged o cloud-
isk and 9% o sun-glin acco ding o he A4O designa ion. Fo a
ep esen a i e analysis o hese scenes, common masks we e used
whe e all 5x5 pixels a ound a cen al pixel mus be alid. This is o
elimina e possible cloud a e ac s, cloud shadows, sun glin , and
land adjacency e ec s as much as possible. The eely isible and in
p inciple un es ic ed wa e a eas we e isually checked. Howe e ,
many o hese wa e pixels a e masked by he indi idual AC
me hods; especially IPF masks la ge a eas because i p oduces
nega i e R
s
alues he e. The selec ed ee wa e a eas co e 31.5
million pixels. Inland wa e s accoun o 4%. Abou 0.6% o he
pixels show a cha ac e is ic ed edge inc ease o TOA eflec ance
caused by floa ing biomass a he sea su ace and a e labelled as
FLOATING in A4O. Hie onymi e al. (2016) sugges ed a defini ion
o ex emely sca e ing wa e s wi h R
s
(865) ≥0.005 s
-1
; hus, he
co e age o b igh pixels depends on he AC me hod and is up
o 4%.
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g04
2.2.2 Ma ch-up da a om in si u measu emen s
and sa elli e obse a ions
2.2.2.1 AERONET-OC
Independen alida ion was ca ied ou o ma ch-ups be ween
OLCI image y and AERONET-OC in si u measu emen da a
(Zibo di e al., 2009) om 2016 o 2020 dis ibu ed h ough he
ESA OC-CCI in si u da abase (Valen e e al., 2022). The da a se was
limi ed o OLCI bands (± 2 nm). All R
s
measu emen s a e
no malized ollowing Pa k and Ruddick (2005). The s a ions a e
widely dis ibu ed geog aphically, bu o en nea coas s o in inland
wa e s (GLO –Glo ia, Black Sea; GDT –Gus a Dalen Towe ,
Bal ic Sea; HLH –Helsinki Ligh house, Bal ic Sea; LIS –LISCO,
Long Island Sound; LUC –Lucinda, Eas Coas o Aus alia; MVC –
MVCO, US Eas Coas ; PAL –Palg unden, Lake in Sweden; VEN –
Venice, Ad ia ic Sea; WAV –Wa ecis_si e_csi_6, Gul o Mexico).
The e o e, he wa e ypes a e e y simila and he da a a e no
ep esen a i e o he ull ange o all na u al wa e s. In he cases
whe e he en i e spec a a e a ailable, he maximum eflec ance lies
a 560 nm in 89% cases o he da a, only 11% ha e he maximum a
490 o 510 nm; he e is no in si u da a included wi h he maximum
in blue bands<490 nm o a bands >560 nm. The as majo i y o
he da a coun s as Case-2 wa e . Fo band-wise compa isons,
howe e , da a om Case-1 wa e s a e also included. Some o he
AERONET-OC da a om he Bal ic Sea and he Black Sea ep esen
dis inc blooms o cyanobac e ia o coccoli hopho es (e.g.,
Cazzaniga e al., 2021;Zibo di e al., 2022;Cazzaniga e al., 2023).
Howe e , o a compa ison o AC esul s a all 16 (ou o 21) OLCI
bands, in si u da a a e o en missing, especially in ed and NIR
bands. In gene al, band-shi ing me hods can be used o de i e
OLCI spec a om di e en band configu a ions, and he mean
pe cen age e ie al e o in he spec al ange be ween 400 and 600
nm is usually less han 5%, bu o ed and NIR bands he
unce ain ies a e much la ge (Hie onymi, 2019). Fo his eason,
addi ional band shi ing was no used in his wo k, since he main
pu pose o he ma ch-up compa ison is o show he spec al
plausibili y o he AC esul s.
2.2.2.2 O he in si u da a
In o de o be able o udimen a y quan i y he spa ial scenes in
he ansi ion om coas al wa e ypes and also o con ex ualize
e y u bid wa e s ha a e no co e ed in AERONET-OC,
exempla y u he in si u measu emen da a a e conside ed.
Fi s ly, eflec ance measu ed by Hie onymi e al. in he No h
Sea/Ge man Bigh (OLCI ma ch-up wi h scene #2) wi h a p o ocol
desc ibed in Tils one e al. (2020) and no malized wi h Pa k and
Ruddick (2005). Secondly, OLCI ma ch-ups wi h he PANTHYR
sys em (Vans eenwegen e al., 2019) ha is loca ed in u bid coas al
wa e s in Belgium. The da a a e p o ided by Vanhellemon and
Ruddick (2021); ACOLITE-DSF was specially designed o hese
wa e s and a compa ison wi h he AC candida es (albei in di e en
e sions o ACOLITE-DSF, IPF, and C2RCC, bu wi hou A4O)
was discussed in hei o iginal pape . App oxima ely hal o he
PANTHYR da a a e conside ed as ex emely sca e ing wa e s using
he abo e-men ioned defini ion, he o he a e C2S.
2.2.2.3 Ma ch-up p ocedu e
The Cal alus sys em (Fom e a e al., 2012) was used o iden i y
OLCI image ma ches wi h in si u da a wi hin h ee hou s o he
sa elli e o e pass. Al oge he , he e a e 2545 ma ch-ups be ween
2016 and 2020 o he nine AERONET-OC s a ions and 62 o
PANTHYR (2019-2020) o OLCI-A & B. Fo some s a ions, he e
a e only a ew spec al bands o he compa ison and he ma ch-up
numbe a ies o each AC acco ding o he fil e ing o alid da a
poin s. Duplica ed-flagged alues a e no used. Mini-scenes o
abou 10x10 pixels in size we e selec ed a IPF, C2RCC, and A4O,
and 5x5 mac o-pixels we e ex ac ed om hem. In he case o
POLYMER and ACOLITE-DSF, he comple e scenes we e
p ocessed fi s and he mac o-pixels ex ac ed om hem.
ACOLITE-DSF can be a he sensi i e o size o he scene o sub-
scene, and i is usually ecommended o use a spa ially limi ed s udy
a ea wi h a single ae osol e ie al. Fo la ge scenes, as used he e,
he ae osol e ie al is iled and in e pola ed o he ull ex en .
Indi idual ile con en s may skew he esul s be ween ile cen e s.
TABLE 2 Selec ed es scenes wi h la ge cloud- ee a eas ha co e high op ical di e si y (shown in Appendix Figu e A1).
Scene Senso -Da e-UTC Region Special ea u es
#1 S3A-20160720-092821 Ba en s Sea High la i udes, bloom o coccoli hopho es
#2 S3A-20160720-093421 No h Sea, Wadden Sea Mode a ely o ex emely sca e ing wa e s, idal a eas, in si u da a
#3 S3A-20170114-130626 Sou h A lan ic Ocean, Rio de la Pla a es ua y Ex emely sca e ing wa e s, clea oceanic wa e s, sun glin , Sou h A lan ic
Anomaly
#4 S3A-20170527-015236 Yellow Sea, Eas China Sea, Yang ze, Lake
Taihu
Ex emely sca e ing wa e s, idal a eas, la ge i e s, abso bing ae osols, sun glin
#5 S3A-20170529-092334 Medi e anean Sea La ge a eas wi h clea wa e s, sun glin
#6 S3A-20170913-080730 Black Sea, Aegean Sea Clea and abso bing wa e s
#7 S3A-20180715-093613 No h Sea, Bal ic Sea In ense bloom o cyanobac e ia pa ly wi h scum
#8, #9 S3A-20200601-092517,
S3B-20200601-084546
No h Sea, Bal ic Sea In e -compa ison o S3A and S3B wi h di e en obse a ion angles, abso bing
wa e s
#10 S3B-20200406-093801 No h Sea, Bal ic Sea High OWT di e si y
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g05

The agg ega ion o he 5x5 mac o-pixel ollows mos ly he p ocedu e
desc ibed in Mülle e al. (2015a). The alid pixel exp essions o each AC
(Table 1) a e applied; all alid pixels a e sc eened o ou lie s pe band
using a h eshold o 2.5 s anda d de ia ions. F om he emaining alid
pixels hei mean alue, m, and s anda d de ia ion, s,iscalcula edand
he numbe o alid obse a ions (excluding he ou lie s) is eco ded.
Based on he pe cen age coe ficien o a ia ion, CV,ama ch-upis
conside ed in u he analysis, i he spa ial homogenei y is high o he
pa icula band and he e o e CV =s/m× 100% < 15%. Second, a leas
hal o he pixels in he mac o-pixel mus be alid. These c i e ia a e
checked o each da a poin and band independen ly, so ha AC
solu ions wi h some noise in a pa o he spec al ange may lose
good ma ch-ups he e bu e ain pa o he spec um in o he spec al
egions. The numbe o ma ch-ups will he e o e a y pe band, which
allows some in e p e a ion in e ms o spa ial noise.
To compa e he pe o mance o he AC me hods, we use he
ma ch-up s a is ics ecommended by EUMETSAT (2022). Besides he
well-known linea eg ession s a is ics wi h he co ela ion coe ficien
( ), we use he oo -mean-squa e-e o (RMSE), median absolu e
de ia ion (mdAD), median absolu e pe cen age de ia ion (mdAPD),
he spec al angle mappe (SAM), and he Chi-squa ed es (c²).
2.3 Op ical wa e ype amewo ks
The classifica ion o na u al wa e s in o op ical wa e ypes
se es he pu pose o compa abili y and, in he case o la ge-scale
sa elli e image p ocessing, he selec ion and blending o esul s o
sui able algo i hms. Basically, cha ac e is ic R
s
-spec a and hei
co a iance a e gi en o define a class. An OWT algo i hm ies o
combine class-specific spec a in such a way ha he inpu R
s
-
spec um can be ep oduced, whe eby weigh s a e assigned o he
con ibu ing classes. The numbe o defined classes, shape and
ampli ude o he mean spec a, as well as he ma hema ical
de e mina ion o he class weigh s can a y g ea ly in he di e en
app oaches (see Figu e 1).
In o de o e alua e esul s o he fi e AC me hods wi h ega d
o OWT, ou OWT classifica ion me hods we e selec ed wi h
di e en emphases, e.g., ocusing on ma ine o inland wa e s. Fo
he selec ion o he OWT me hods, i was necessa y o conside he
deg ee o a filia ion o he clus e cen e s. The e o e, me hods based
on uzzy logic clus e ing and using he Mahalanobis dis ance and
c²-dis ibu ion o calcula e he o al membe ship alues we e
chosen (Moo e e al., 2001;Moo e e al., 2014). Fu he mo e,
only hype spec al o a leas OLCI band-based OWT me hods
we e selec ed, bu no me hods using band a ios o concen a ion
h esholds. Fo he selec ion, i was also impo an o ep esen a
wide a ie y o spec al o ms ha a e conside ed impo an in he
di e en me hods. The e o e, in gene al, o he classifica ion
app oaches could be conside ed ha migh p o ide mo e obus
esul s o he AC me hods unde conside a ion o ha a e no oo
ocusedonei he ma ineo inlandwa e s.TheusedOWT
classifica ion me hods a e:
1. J17 (Jackson e al., 2017) is an OWT me hod ha was
de eloped in he ame o ESA’s Ocean Colou Clima e
A B
D
C
FIGURE 1
Spec al eflec ance o op ical wa e ypes om ou amewo ks by (A) Jackson e al. (2017),(B) Moo e e al. (2014),(C) Hie onymi e al. (2017), and
(D) Bi e al. (2019), and Bi e al. (2021). The line deno es he o iginal spec al cen oid o each wa e ype and he shaded ibbon deno es he
s anda d de ia ion om espec i e aining da ase s.
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g06
Change Ini ia i e (OC-CCI). Millions o pixels om
me ged sa elli e da a we e selec ed o clus e ing. 11
spec al ypes o ma ine wa e s we e iden ified, and h ee
addi ional “highly- u bid”coas al spec a om Moo e e al.
(2014) we e also adop ed. The o iginal publica ion e e ed
o he OC-CCI da ase 2 wi h SeaWIFS bands; in 2020,
new op ical wa e class se we e defined o he da ase 5
o MERIS- e e enced da a wi h POLYMER ( 4.12) as he
a mosphe ic co ec ion (Sa hyend ana h e al., 2021). Thus,
he adap ed OWT me hod uses 14 classes and six OLCI
bands be ween 412 and 665 nm.
2. M14 (Moo e e al., 2014) uses hype spec al R
s
be ween
400 and 800 nm ha a e p ima ily ep esen a i e o coas al
egions and lakes, whe e he cen oids we e ained based
on in si u measu emen s. The app oach dis inguishes se en
classes, bu ac ually no blue (oceanic) wa e s. Thei o iginal
OWT analysis ac ually e e s o he unde wa e emo e-
sensing a io,
s
, which can be ans e ed abo e-wa e o
R
s
.
3. H17 (Hie onymi e al., 2017) is a mo e holis ic app oach o
OWT classifica ion as i aims o co e “mos na u al
wa e s”, om he open ocean o ex emely abso bing o
sca e ing wa e s. The basis o H17 a e adia i e ans e
simula ions wi h Hyd oligh (Mobley, 1994), which is a
common app oach wi h he AC me hods C2RCC and A4O.
The la e was e en op imized in e ms o OWT
classifiabili y wi h H17. The OWT scheme uses 11 OLCI
bands om 400 o 865 nm and dis inguishes 13 classes. In
o de o a oid conflic wi h possible nega i e eflec ances,
he spec a a e ans o med by log
10
(R
s
+1)and
b igh ness-no malized, so ha he classifica ion is based
on he shape o he spec um alone.
4. B21 is an ex ended OWT amewo k based on he wo ks o
Bi e al. (2019), and Bi e al. (2021), de eloped specifically
o inland wa e s. The hype spec al aining da a, which
we e esampled o 15 OLCI bands om 400 o 865 nm,
we e mos ly measu ed a la ge lakes, ese oi s, and i e s
ac oss China. The app oach di e en ia es 17 classes
including eu ophic and hype ophic cases wi h high
biological p oduc i i y and e en su ace scum. The
spec a a e no malized by di iding hem by hei in eg als
because, acco ding o hei easoning, he composi ion o
inland wa e s a ies g ea ly, which changes he shape o he
eflec ance spec um a he han he magni ude.
The selec ed OWT amewo ks ha e di e en app oaches o
classi ying he spec a. In H17 and B21 he spec a a e no malized
(albei in di e en ways) o highligh di e ences in spec al shapes
be ween ypes, while in J17 and M14 di e ences in he magni ude o
he spec a a e aken in o accoun . The e o e, i is expec ed ha he
in e p e a ion o a mosphe ically co ec ed da a will depend in pa
on he egion obse ed by he sa elli e, as he di e en wa e s o
which hese me hods we e ini ially de eloped a e e y di e en . Fo
example, B21 will no be able o ep esen oceanic wa e due o he
lack o “blue ypes”, while J17 will ha e di ficul y dis inguishing
eu ophic inland wa e s, which a e no o eseen in he ma ine
model o POLYMER, on which J17 is based. In addi ion o he
selec ed OWT amewo ks, we also use he (OLCI) wa eleng h o
he R
s
maximum as a di ec and in ui i e indica ion o wa e ypes;
a simila app oach using he spec ally-weigh ed Appa en Visible
Wa eleng h has been shown o be e ec i e o di e en op ical
condi ions (Vande meulen e al., 2020). In gene al, he maximum
eflec ance in clea seawa e is a sho e wa eleng hs (mo e blue o
g een), whe eas in u bid wa e he maximum is shi ed owa ds
longe wa eleng hs (mo e g een, b own, and ed).
2.4 E alua ion o he classifiabili y
In op ical uzzy logic classifica ion, he class membe ship is
calcula ed by he cumula i e c²dis ibu ion wi h ndeg ees o
eedom (band numbe ) and he Mahalanobis dis ance be ween
he spec um and he OWT cen oid, no malized by he OWT
s anda d de ia ion (see calcula ion de ails in Moo e e al., 2001). To
assess he classifiabili y o an AC-de i ed spec um, we calcula e he
o al membe ship o he OWT classifica ion scheme, u
. An ideal
classifica ion esul should gi e u
close o (o e en sligh ly highe
han) one. A lowe u
, he classifica ion is pe o ming poo ly wi h a
h eshold on o ally non-classifiable defined as u
≤10
-8
. Such cases
can occu ei he because o insu ficien ype ep esen a ion in he
amewo k o because o e o s o he spec al shape o in ensi y
i sel , i.e., unde pe o mance o a mosphe ic co ec ion,
unco ec ed influences om adjacency e ec s o bo om
eflec ions, e c. (Moo e e al., 2014). Jackson e al. (2017) also
men ioned ha u
should no be much la ge han one in he ideal
classifica ion esul ei he , which indica es o e lap and edundancy
be ween ypes. Howe e , in his s udy, we allow u
o be g ea e han
one, because using amewo ks ac oss di e en wa e a eas will
ine i ably induce o e lap be ween ypes. We define fi e le els o
classifiabili y as shown in Table 3. A spec um is no classifiable i
no OWT can be assigned, whe eas OWT membe ships a e
dis ibu ed be ween he classes a he o he ou le els. E alua ion
c i e ia ha e been discussed in a ious publica ions, e.g., Melin e al.
(2011);Van epo e e al. (2012),o Hie onymi e al. (2017); he
chosen le els a e a bi a y, bu wo k easonably well o he
e alua ion o he classifica ion. A e all, he pe cen ages o
classifiable alues in he di e en wa e ypes as well as in he
en i e da a se a e calcula ed. The highe he pe cen age o high o
medium alues, he be e he classifiabili y o R
s
.
TABLE 3 Classifica ion le els ela ed o he o al membe ship om all
classes.
Assignable le els u
anges
Non-classifiable u ≤10−8≈0
Below- h eshold 0<u
<10−4
Low 10−4≤u <0:3
Medium 0:3≤u <0:8
High u ≥0:8
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g07
3 Resul s
3.1 Spa ial homogenei y and plausibili y o
sa elli e da a
The a ious a mosphe ic co ec ion me hods p o ide indi idual
masks a di e en le els indica ing pe o mance limi s and
unce ain ies (Table 1). Flagging is usually a ade-o be ween
limi ed alidi y wi h suspec esul s a some spec al bands and
s ill use ul esul s in ano he spec al ange. Many ocean colo
algo i hms u ilize only one o a ew bands o which he AC esul s
can be adequa e. O he in-wa e algo i hms use many bands ac oss
he spec um, e.g., p inciple componen analysis o some neu al
ne wo ks. Fo OWT applica ions, he whole spec um is impo an .
O e co ec ion o an AC mani es s o en in nega i e R
s
, usually
ei he in blue (especially IPF) o NIR bands; in any case, his is no a
physically plausible esul and may be an in alid inpu o he in-
wa e algo i hm. Looking a he whole spec um, IPF and
POLYMER p oduce e y la ge a eas wi h nega i e eflec ances,
bo h abou hal o he ee wa e a ea (albei he alues a e o en e y
close o ze o). The IPF exp ession o alid pixels equi es posi i e
eflec ances a leas in he cen al VIS ange (412-665 nm), which
canno be sa isfied o e la ge pa s and is he main eason o >50%
in alid masking (Table 4). POLYMER does no ha e his es ic i e
flagging, so e e y hing emains alid. Depending on he p ocessing
se ings, ACOLITE-DSF does no ou pu nega i e eflec ances, bu
i s flagging esul s as NaN in he ou pu files, which is he main
con ibu o o he 20% in alid flagging ( hese cases also occu in
C2SX wa e s, o which ACOLITE-DSF was designed, e.g., isible in
Figu es 2-A5,C5). C2RCC and A4O apply neu al ne wo ks o
app oxima e log- ans o med R
s
di ec ly om R
TOA
wi hou
sub ac ing indi idual con ibu ions om Rayleigh sca e ing o
glin . Resul ing nega i e eflec ances a e uled ou , because o he
log- ans o ma ion and he alue ange o he NN aining. This is
an impo an ad an age wi h ega d o con inuous usabili y o he
esul s wi h di e en ypes o wa e and allows R
s
es ima ion e en
o e y small alues close o ze o wi h less noise. The sligh ly mo e
sensi i e cloud de ec ion in C2RCC p ocessing wi h IdePix esul s
in an addi ional 1% masking o he wa e a eas.
Figu e 2 shows ex ac s o sa elli e images (#3, #7, #2, and #1;
Table 2;Appendix Figu e A1) o he AC esul s o R
s
(560) wi h
espec i e in alid flagging. Spa ial noise usually ans e s o he
ocean colo p oduc s and is hus an indica o o AC pe o mance.
In his con ex , he Sou h A lan ic Anomaly (SAA) a ea (Figu e 2A)
is special; clea spec al ou lie s o indi idual bands occu he e in
isola ed pixels and he peaks a e usually no iceably highe a longe
wa eleng hs. Some AC me hods succeed in smoo hing he pixel
spec um, he eby educing spa ial discon inui ies. C2RCC
p oduces he mos isible noise in his a ea (Figu e 2-A2), which
is p obably due o he use o neu al ne wo ks ha a e e y sensi i e
o small spec al changes. A4O also uses NNs, bu has significan ly
lowe spa ial noise due o a ious p ocessing s eps, including a
dedica ed spec al smoo hing o suspec ou lie s and a e aging o
he esul s o di e en NNs (Figu e 2-A3). Mo eo e , an op ion is
ecommended o A4O ha applies a Gaussian fil e o e 3x3
mac o-pixels, which smoo hs esul s o wa e a eas, a enua es
cloud a e ac s, and ea s down came a bounda ies. ACOLITE-DSF,
as applied he e, in e pola es a mosphe ic pa ame e s o e a la ge
spa ial egion, which e ec i ely educes he AC-induced noise le el.
Looking a he spa ial homogenei y c i e ion (CV) a di e en
wa eleng hs o homogeneous a eas o 100x100 pixels (Appendix
Figu e A1), we see a low and compa able noise le els o he AC-
inpu adiance a TOA o Case-1 and -2 wa e s; in he SAA a ea,
CV alues a e abou wice as high (Table 4). In Case-1 wa e in he
SAA (scene #3, Appendix Figu e A1), we see he bigges di e ences
o CV(R
s
)be ween A4O and C2RCC, wi h A4O ha ing he leas
noise o all he me hods. In ano he (p esumably clea e ) Case-1
wa e sea a ea in he Medi e anean Sea (eas o he island Sa dinia,
TABLE 4 E alua ion o selec ed spa ial ea u es o 31.5 million ee wa e pixels in en es scenes o he fi e a mosphe ic co ec ion models.
Fea u e L
TOA
IPF C2R A4O POL DSF
In alid flagged wa e a ea 51.3 1.0 0 0 20.5
R
s
(412)< 0 18.5 0 0 0.5 0
R
s
(865)< 0 40.2 0 0 46.7 0
CV(412) in Case-1 wa e s 0.4 4.3 5.3 0.9 7.8 2.0
CV(560) in Case-1 wa e s 0.8 9.3 4.9 1.0 4.6 3.6
CV(665) in Case-1 wa e s 1.3 55.4 7.0 3.6 27.0 7.3
CV(412) in Case-1 wa e s (SAA) 0.9 9.3 16.0 5.3 17.8 9.7
CV(560) in Case-1 wa e s (SAA) 1.8 14.0 133.6 3.8 8.7 12.4
CV(665) in Case-1 wa e s (SAA) 4.0 129.1 >1000 9.5 63.0 36.1
CV(412) in Case-2 wa e s 0.4 >1000 15.5 2.6 33.0 2.9
CV(560) in Case-2 wa e s 0.6 7.6 18.9 1.5 6.2 3.6
CV(665) in Case-2 wa e s 1.0 24.7 16.5 1.8 11.1 10.2
The coe ficien s o a ia ions o AC-de i ed R
s
e e o homogeneous subse s o 100x100 pixels; co esponding alues o ini ial TOA adiance a e included o compa ison (see Appendix Figu e
A1). All alues ha e he uni [%].
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g08
scene #5, Appendix Figu e A1), he noise o C2RCC is significan ly
lowe and compa able o he o he me hods, IPF and POLYMER
ha e he highes noise in he ed band a 665 nm abo e he alid-
ma ch-up h eshold o 15%. In his e y clea blue wa e , R
s
(665)
becomes e y small and app oaches ze o. In ac , he a iabili y o
R
s
(665) in case o IPF and POLYMER is pu e andom noise, in
A4O wa e mass s uc u es a e s ill clea ly isible and de e mine CV
(665), and in C2RCC one can see weak noisy s uc u es as well.
ACOLITE-DSF,whichisno designed o suchclea wa e ,
p o ides an R
s
(665) image wi h much highe alues compa ed o
he o he ACs ( ac o 10 highe ). Because ACOLITE-DSF does no
pe o m pixel-by-pixel a mosphe ic co ec ion, i shows clea
FIGURE 2
Subse s om OLCI images (see Appendix Figu e A1). The op ow shows RGB images o L1 adiance a op-o -a mosphe e (A–D); poin s o spec al
compa isons a e ma ked he e (see Figu e 3). The fi e ows below show he esul s o R
s
(560) o he compa ed AC me hods: IPF (A1-D1), C2RCC
(A2-D2), A4O (A3-D3), POLYMER (A4-D4), and ACOLITE-DSF (A5-D5). A eas o AC-specific in alid pixel exp essions a e highligh ed anspa en ly o
wi h NaN.
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g09
membe ships a e. Only hal o he POLYMER eflec ances can be
classified as ha ing weigh s abo e he h eshold, bu o al
membe ship emains mos ly low. Insu ficien membe ships a e
usually ound in highly sca e ing o p oduc i e wa e s, o when
POLYMER p o ides nega i e eflec ances in Case-1 wa e s. A4O
ma ches all defined classes, bu has low membe ships o p oduc i e
wa e s OWTs 7-8, ha a e masked wi h BLOOM. The eason o
low membe ships is likely he pa icula ly high a iance o na u al
R
s
a NIR bands, which is no well cap u ed by he H17 c²-
dis ibu ion. Howe e , i is impo an ha he class is iden ified
co ec ly, which enables pos -classifica ion adap a ion o op imal
wa e algo i hm selec ion. All o he ACs do no deli e such spec al
shapes; (w ong) C2RCC can be ela i ely well classified. The
majo i y o spec a p o ided by IPF, POLYMER, o ACOLITE-
DSF wi h he maximum in he sho wa eleng hs (<560 nm) a e no
classifiable wi h H17, b igh pixel spec a o IPF and ACOLITE-
DSF, howe e , a e o en well classifiable. This shows ha low
eflec ance alues play a majo ole in he log- ans o med
classifica ion and ha he associa ed noise-le el o some bands
leads o shape a ia ions no expec ed by H17.
Me hod B21 dis inguishes mos classes bu has a ocus on
inland and coas al wa e s wi h li le ega d o he ocean. In
addi ion, he shape is also gi en mo e conside a ion he e, and he
allowed a ia ions a e ai ly limi ed. None o he AC me hods
succeeds in p o iding comp ehensi e spec a ha can be classified
wi h he me hod o B21. Fo C2RCC, ne e heless, hal o he pixels
a e classifiable wi h u
abo e he h eshold (>10
-4
). Fo all ACs, a
leas 85% o he classifiable cases a e dis ibu ed among he fi s
FIGURE 7
Same OWT classifiabili y o AC esul s as in Figu e 6, bu a X-axis wi h he OLCI wa eleng h o he R
s
maximum and co esponding pe cen age
dis ibu ion no ed a he op ( his dis ibu ion is independen o he OWT me hod and he e o e he same o all).
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g16

h ee OWTs; he o he 14 classes a e spa sely used. C2RCC, A4O,
and ACOLITE-DSF yield >90% usable spec a o BLOOM-labelled
pixels. Again, C2RCC p o ides a highe pe cen age o well-
classifiable esul s, bu hese a e no in he in ended classes
(OWTs 14-17). A4O p o ides such spec a, he majo i y o which
ha e use ul membe ships. Figu e 7T shows sligh ad an ages o he
classifiabili y o ACOLITE-DSF spec a wi h he maximum in
sho e wa eleng hs.
4 Discussions and ou look
4.1 E alua ion o AC me hods
In e -compa ison esul s a e o en a snapsho in ime, as bo h
AC and wa e algo i hms unde go con inuous e olu ion. This pape
e e s o he mos ecen AC e sions (as o Oc obe 2022) and is
au ho ed by some o hei main de elope s. I is clea ha he
me hods a e a di e en ma u i y le els and ha some ha e been
op imized using obse a ional da a, which is also eflec ed in he
e o o unce ain y p oduc s and flagging. A4O by Hie onymi
e al. is a u he de elopmen o C2RCC, bu is no ye publicly
a ailable and he e is no o ficial e e ence o i as well. IPF is used in
ope a ional se ice, bu one mus also app ecia e he con inuous
de elopmen s, whe e wi h he OLCI Collec ion-3 (since 2021)
imp o emen s ha e been achie ed, e.g., o coas al wa e s
(Zibo di e al., 2022). One canno say ha his is a Case-1 ocean
colo specific algo i hm anymo e, because he compa isons wi h
Case-2 domina ed ma ch-up da a documen good ag eemen o e
mos o he spec um (wi h specific p oblems desc ibed he e). Ou
compa isons wi h AERONET-OC and o he da a show be e
ag eemen s o IPF han p e iously epo ed (especially also wi h
ega d o he p e ious IPF e sion Collec ion 2), e.g., Liu e al., 2021;
Tils one e al., 2021;Vanhellemon and Ruddick, 2021;Li e al.,
2022;o Windle e al., 2022. One influencing ac o is ce ainly he
conside a ion o ecommended flags and he use o he same IPF-
SVC gains o all AC me hods (excep o POLYMER). Ideally, AC-
specific SVC gains should be used, bu hese a e no ye a ailable o
C2RCC, A4O, and ACOLITE-DSF; specially fi ed SVC would ha e
he po en ial o significan ly imp o e hei esul s. In he men ioned
s udies, likewise o he e sions o C2RCC, POLYMER, and
ACOLITE-DSF a e used; ne e heless, some simila obse a ions
can be confi med, like he p incipal sui abili y o C2RCC and
POLYMER o Case-2 wa e s especially o he cen al isible
ange. A4O and ACOLITE-DSF ha e pa ly less a o able a ings
compa ed o AERONET-OC da a, bu bo h p ocedu es a e
cu en ly unde going a g ea e dynamic in hei de elopmen
( hey ha e unde gone se e al upda es in 2022). Fo all ACs,
sui able me hods mus be ound in he u u e o be e iden i y
ob ious ou lie s in o de o achie e be e spa ial and s a is ical
e alua ions. This also includes e en be e cloud iden ifica ion.
Conside ing he s ic in alid flagging o IPF, howe e , one
po en ially loses conside able amoun s o obse a ional da a,
which should be econside ed.
Spa ial homogenei y, which has a s ong impac on he numbe
o ma ch-ups, should be gi en mo e a en ion in u u e. Fo his
pu pose, measu es o homogenize a mosphe ic p ope ies a mac o-
pixel le el (A4O & ACOLITE-DSF) as well as he log-
ans o ma ion o he R
s
e ie al o e y small alues (A4O &
C2RCC) ha e p o en o be e ficien . In combina ion wi h spec al
smoo hing (as in A4O), his is also ad an ageous o la ge a eas
a ec ed by he Sou h A lan ic Anomaly. One may a gue ha using a
non-s ic pixel-by-pixel a mosphe ic co ec ion limi s he high
spa ial esolu ion (o up o 300 m), howe e , ele an a mosphe ic
and oceanog aphic ea u es a e usually la ge in a ea and AC-
induced noise is a significan sou ce o unce ain y o ocean
colo p oduc s.
High accu acy o e all magni udes o e ie ed R
s
is expec ed
o e he en i e spec al ange o a ious applica ions. Recen
e iews summa ize he equi emen s o ocean colo emo e
sensing and especially a mosphe ic co ec ion, e.g., in e ms o
de i ing inhe en op ical p ope ies o wa e (We dell e al., 2018),
phy oplank on di e si y (B ache e al., 2017), ca bon con en
(B ewin e al., 2023), and essen ial biodi e si y a iables (Mulle -
Ka ge e al., 2018)–and his goes beyond he OLCI bands, also o
u u e hype spec al applica ions.
The selec ed AC me hod has o en a significan influence on he
de i ed ocean colo p oduc s, e.g., he es ima e o he concen a ion
o ca boninwa e o hephy oplank on biomass wi h
co esponding p ima y p oduc ion. Juhls e al. (2022) o example
compa ed in si u da a wi h OLCI ma ch-up esul s om IPF,
C2RCC, and POLYMER and, mo eo e , di e en models o he
es ima ion o CDOM abso p ion. This was done in o de o
in es iga e fluxes o ela ed dissol ed o ganic ca bon om a la ge
i e ac oss he u bid coas al zone in o he clea A c ic Ocean, hus
in high la i udes (he e, POLYMER is iden ified as he mos
sui able). The s onges op ical e ec o CDOM is isible in he
blue bands, whe e, acco ding o ou s udy, C2RCC and A4O ha e
sligh ad an ages also in e ms o noise and spec al beha io ;
ACOLITE-DSF has no iceable p oblems. In his example, he ac ual
pe o mance may be inconsis en along he op ical g adien ,
especially a sho wa eleng hs; OWT-op imized wa e algo i hms
could po en ially con ibu e o educing he unce ain ies (i he
classifica ion is success ul).
Concen a ions o phy oplank on in he o de o Chl >1mgm
-3
a e usually necessa y o hype -spec ally dis inguish special pigmen
abso p ion ea u es and he eby phy oplank on di e si y; mo eo e , he
cen al isible ange (450 o 650 nm) is pa icula ly impo an o ha
(e.g., Xi e al., 2015;Xi e al., 2017;Bi e al., 2023). The in ensi y and
spec al shape o he eflec ance in he case o “mode a e”algal blooms
a e gene ally well ep oduced by all AC me hods in es iga ed (e.g.,
Figu e 3C). Resul s om he cu en e sion o A4O, howe e , mos ly
show an unde es ima ion (which may also ha e o do wi h influences
o he angle no maliza ion ha s ill need o be cla ified). A highe Chl
(>10 mg m
-3
), he ed edge abso p ion ea u e becomes impo an in
he Chl e ie al (e.g., Gons, 1999;Ruddick e al., 2001). High
concen a ions o cyanobac e ia wi h possible scum a he wa e
su ace, which is a equen phenomenon in inland wa e s and he
Bal ic Sea, a e a pa icula challenge o AC. Spec a om IPF, C2RCC,
and POLYMER a e mos ly un us wo hy he e and he esul s a e
pa ly no su ficien ly accompanied by wa nings (Figu e 3D). A4O,
which has a specific wa ning flag o his, p o ides a plausible spec al
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g17
shape and indica es enhanced R
s
unce ain ies in co esponding
p oduc s (which is also easoned by he usual small-scale
he e ogenei y o such blooms). The spec a om A4O can be
assigned o he designa ed wa e classes in H17 and B21, bu o en
wi h low membe ships. In he shown example (Figu e 3D), he shape o
ACOLITE-DSF is also plausible excep o he fi s wo bands ha a e
likely o e es ima ed and may be impac ed by smile co ec ion a e ac s
( he spec a a e usually no well-classifiable in H17 o B21). Howe e ,
he e is a possible ad an age o he da k-spec um-fi ing app oach in
he ange 500-700 nm, which can be help ul o phycocyanin ea u e
de ec ion (a ma ke o cyanobac e ia).
The o he example wi h a bloom o coccoli hopho es
(Figu e 3G) shows compa able spec al shapes deli e ed by all
ACs, bu also clea di e ences in he b igh ness o he e ie ed
eflec ance (al hough all esul s a e o a ealis ic o de o magni ude,
e.g., Cazzaniga e al., 2021). Me hods o emo ely sense pa icula e
ino ganic ca bon ocus on op ical de ec ion o coccoli hopho es,
e.g., wi h a colo index made om a ios o g een, ed, and NIR
bands (Mi chell e al., 2017;B ewin e al., 2023); he e significan
di e ences would occu depending on he AC used. Rega ding he
exploi a ion o ed and NIR bands in ocean-wa e algo i hms (also
impo an o he es ima ion o he fluo escence line heigh ), he
spa ial homogenei y and nega i e eflec ances a e imp o able o
IPF and POLYMER, and he emo al o a e ac s om small-scale
a mosphe ic a iabili y o ACOLITE-DSF.
4.2 Discussion on OWT amewo ks
The dis inc ion o op ical wa e ypes is impo an o many
aspec s o ma ine biology, physical oceanog aphy, unde wa e
isibili y, e c., and he defini ion o specific p ope ies has a long
adi ion (e.g., Je lo , 1976). Cu en esea ch aims o de e mine
eliable wa e quali y cha ac e is ics om sa elli e da a o he en i e
aqua ic con inuum o land-coas -ocean. Howe e , a balance
be ween e o and benefi mus be ound he e and ca e mus be
aken in sa elli e images o ensu e no unwan ed discon inui ies
a ise. The e may be specific challenges o oceanog aphic o
limnological ques ions, e.g., wi h ega d o wa e cons i uen s, sun
glin , whi ecaps, shallow wa e , o adjacency e ec s, bu om an
op ical emo e sensing poin o iew, i does no make much sense
o educe onesel o one applica ion. This common disconnec ion
ac ually hinde s eliable s udies on ma e ans e om land o he
sea, which is impo an o he ca bon cycle, o example.
The lack o classes wi h cha ac e is ic op ical ea u es is a
p oblem o all OWT me hods ha we e examined, e.g., classes
ep esen a i e o oligo ophic ocean, e y high NAP concen a ions,
o hype -eu ophic wa e s a e o en missing. On he o he hand,
he e may be spec al classes ha a e di ficul o explain om an
IOP pe spec i e. Especially inland wa e OWT amewo ks a e
o en based on clus e ing o la ge in si u da a collec ions, which
include po en ial measu emen e o s such as adjacency e ec s,
bo om eflec ions o inadequa e sky-glin co ec ion.
Consequen ly, classes wi h ques ionable mean eflec ances can
also be defined. Some OWT amewo ks a e p ima ily used o
e alua e he quali y o R
s
spec a (e.g., Wei e al., 2016). An
independen con ol is he Quali y Wa e Index Polynomial
(QWIP) me hod o Die ssen e al. (2022). The QWIP sco e o
hype spec al da a should no exceed 0.2, o mul ispec al da a as
o OLCI he nominal h eshold can be elaxed o 0.3, alues abo e
he h eshold should be subjec o addi ional checks. In ac , he
QWIP me hod does no include “g een ypes”wi h R
s
maximum in
he NIR, such as defined by B21. Howe e , ew classes o B21, e.g.,
hei OWT 2, ecei e a QWIP sco e close o 0.2 (no e ha some
OWT amewo ks like Spy akos e al. (2018) define classes wi h
highe sco es ha possibly ail he QWIP quali y con ol). The B21
OWT 2 class-mean spec um has a local minimum a 440 nm
(Figu e 1D). Ou OWT analysis shows ha B21-classifiable spec a
o IPF, C2RCC, A4O, and POLYMER a e in his OWT 2 wi h less
han 1%, whe eas 80% o ACOLITE-DSF spec a all in o his class.
The compa isons wi h AERONET-OC indica e an unde es ima ion
o he a mosphe ic signal o ACOLITE-DSF in blue bands;
u he mo e, he e is eason o conclude ha adjacency e ec s,
e.g., om b igh clouds, play a ole (Bulga elli and Zibo di, 2018).
Indeed, QWIP can be used di ec ly o quali y con ol o sa elli e-
de i ed R
s
, e.g., Tu ne e al. (2022) compa ed esul s om
ACOLITE-DSF and POLYMER (in o he e sions) as well as he
s anda d NASA SeaDAS algo i hm o OLCI (L2gen) o an es ua y
a he US Eas Coas finding POLYMER o be he p e e ed
app oach. Applying he QWIP sco e o he AC esul s o ou
s udy o alid ee wa e pixels in he scenes and assuming a
h eshold o ≤0.2 gi es 100% eliable R
s
o A4O and C2RCC, 99%
o POLYMER, 81% o IPF, and 45% o ACOLITE-DSF. Wi h a
less s ingen h eshold o ≤0.3, ACOLITE-DSF achie es abou 88%
quali y-assu ed R s. Wi h a e y s ic QWIP sco e o ≤0.1, A4O
s ill eaches 99.4%. This means ha i ually all esul s om A4O,
C2RCC and POLYMER pass he QWIP quali y con ol wi h sligh
ad an ages o A4O. Bu as men ioned, he e ie ed R
s
can ac ually
ha e he “w ong”shape.
The abili y o fill all classes and gene ally good classifiabili y o
eflec ances om POLYMER in he J17 amewo k o om A4O in
H17 shows he g ea ad an ages o ma ching AC and OWT
amewo ks. As desc ibed, howe e , he e is a dange o o e -
aluing alse spec a om he AC o measu emen s/simula ions.
Ne e heless, i has also p o en ine ec i e no o allow la ge
a iances om he expec ed spec um, i.e., po en ial e o s o he
AC. Ob iously good spec a om IPF o POLYMER, bu also om
A4O, canno be classified well wi h H17. This is especially ue o
B21, whe e in p inciple he esul s o all ACs do no ulfil
he expec a ions.
A comp ehensi e e alua ion o he OWT sys ems and o he
pe o mance o di e en a mosphe ic co ec ions is di ficul because
he ac ual a eas o applica ion and alidi y o e lap some imes only
sligh ly, i.e., inland wa e s s. ocean. La ge a eas o inland wa e s a e
in alid flagged o a leas ha e wa ning flags aised, so i is no
su p ising ha almos all da a all in o one o only a ew designa ed
ocean classes o M14 o B21. Howe e , some o he AC me hods
gi e plausible and usable esul s o inland wa e s, which is pa ly
e iden in he compa ison wi h AERONET-OC. Lea ing aside he
ac ha he e a e also e oneous es ima es o he R
s
shape, C2RCC
and A4O p oduce classifiable esul s o a leas 95% o he cases in
he OWT amewo ks J17, M14, and H17, whe e A4O co e s mo e
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g18
in ended classes. POLYMER also achie es his classifiabili y a e o
J17 and M14, bu only 70% o H17. Conside ing he ecommended
flags, he sui abili y o IPF and ACOLITE-DSF in he in es iga ed
classifica ions is insu ficien . The wo k by Liu e al. (2021) also
compa es IPF, C2RCC, POLYMER, and o he OLCI AC me hods in
con ex wi h he op ical wa e ype and quali y con ol amewo k
o Wei e al. (2016), which di e en ia es 22 classes; hey conclude
ha POLYMER has bes pe o mance ollowed by C2RCC and IPF.
Figu e 3A illus a es a emaining p oblem, namely ha
undamen ally di e en spec al shapes o he de i ed R
s
can
o en occu in he ansi ion om coas o sea, when he
eshwa e CDOM concen a ion is dilu ed. In some cases, he e
a e ea u es in he TOA signal ha can be used o flag po en ial
unce ain ies, e.g., a ed-edge enhancemen (Figu e 3D). The
ambigui ies o he op ical e ec s o di e en componen s in he
wa e , a he ai -sea in e ace, and in he a mosphe e a e ela i ely
la ge o spec ally smoo h TOA eflec ance wi h colo nuances o
blue. Wi hou sys ema ic compa isons wi h sui able in si u da a, we
ha e no means o de e mining which spec al shape is co ec , i.e.,
which OWT is p esen . Fo his pu pose, mo e hype spec al
fiducial e e ence measu emen s especially wi h maximum R
s
a
wa eleng hs ≤510 nm a e needed.
5 Conclusions
Fi e a mosphe ic co ec ion me hods o Sen inel-3/OLCI
ocean colo image y we e compa ed in e ms o spa ial and
spec al esul s and indi idual flagging. The models unde
in es iga ion a e he mos ecen e sions o OLCI L2 baseline
a mosphe ic co ec ion (IPF), C2RCC, a new me hod A4O,
POLYMER, and ACOLITE-DSF. The ex en o which AC
me hods p o ide use ul and con inuous esul s o a wide a ie y
o na u al wa e s was in es iga ed. Fo his pu pose, he sa elli e-
de i ed emo e-sensing eflec ances we e e alua ed in ou op ical
wa e ype schemes.
Flagging leads in some cases o majo limi a ions in da a
exploi a ion e en o clea ly isible wa e a eas; IPF ecommends
e y s ic c i e ia, esul ing in 50% less co e age in ou sa elli e
image y. Ou pu o R
s
wi h nega i e alues is a majo issue he e.
Howe e , we ha e also shown ha many cases a e inadequa ely
flagged by he AC me hods; an example a e high concen a ions o
cyanobac e ia a he sea su ace. Only A4O has a dedica ed wa ning
flag o floa ing algae, bu A4O is alid he e and deli e s as he only
one easonable R
s
o e he en i e spec um. Ne e heless, a e ision
o he indi idual flags wi h espec o spa ial and spec al
inconsis encies is ecommended o all AC me hods. Cloud and
cloud shadow de ec ion also need o be imp o ed o all me hods, as
co esponding deficiencies a e eflec ed in he de i ed wa e
quali y p oduc s.
Pixel-based app oxima ion o a mosphe ic p ope ies and
eflec ance leads o AC-induced spa ial noise. High spa ial
he e ogenei y, especially a low eflec ance (and o e co ec ed
nega i e alues), leads o conside able losses o possible ma ch-
ups wi h in si u measu emen da a. The noise le el can be e ec i ely
educed by means o log- ans o ma ion in he R
s
e ie al p ocess
and app op ia e smoo hing, which is bo h applied in A4O. Mainly
because o i s high spa ial homogenei y, A4O achie es significan ly
mo e ma ch-ups wi h AERONET-OC da a han all o he me hods,
namely a leas wice as many poin s in he blue and NIR bands. The
numbe o ma ch-ups achie ed also a ec s he s a is ical e alua ion
o R
s
e ie al pe o mance. Compa ison wi h in si u da a, which
a e mo e ep esen a i e o coas al and inland wa e s, shows ha he
spec al shape and magni ude o R
s
is essen ially well ep oduced
by IPF, C2RCC, and POLYMER, a leas in he cen al isible ange.
The cu en e sion o A4O mos ly gi es a easonable shape o R
s
,
bu o en sligh ly lowe alues han obse ed. ACOLITE-DSF
p o ides good ma ches o b igh pixel, i.e., highly sca e ing
wa e s, bu has significan defici s o low wa e eflec ance in
pa icula in he sho wa eleng hs. Hype spec al in si u da a in
he 400 o 865 nm ange a e un o una ely no a ailable o all wa e
ypes, especially clea oceanic and hype -eu ophic cases a e
missing; howe e , his would be impo an o ha e o u u e
OWT- ela ed alida ion o AC me hods.
Op ical wa e ype classifica ion is used o he selec ion o
app op ia e wa e quali y algo i hms and seamless blending o hei
esul s. This equi es good classifiabili y o he AC-de i ed R
s
and i
is ad an ageous i all spec al o ms o R
s
can be ep oduced.
Compa ison o he fi e AC me hods shows ha A4O p o ides he
g ea es op ical flexibili y. A4O p o ides mo e han 95% usable
esul s o h ee OWT amewo ks, namely by Jackson e al. (2017);
Moo e e al. (2014), and Hie onymi e al. (2017); u he mo e, A4O
popula es mos classes, including hype -eu ophic cases. C2RCC
also achie es >95% use ul esul s o he h ee OWT amewo ks,
bu has ailing e ie als o in ense cyanobac e ial blooms. Fo he
OWT me hod by Jackson e al. (2017), he eflec ances o
POLYMER a e bes classifiable; his OWT scheme was de eloped
on he basis o such da a. POLYMER also gi es mos ly well-
classifiable esul s o M14, bu alls o o H17. The gene al
classifiabili y o R
s
om IPF is compa able o POLYMER, bu
conside ing he ecommended alid-pixel-exp ession, he
sui abili y o IPF o OWT classifica ion is insu ficien .
ACOLITE-DSF is e y ocused on wa e s wi h high
concen a ions o non-algal pa icles; he e a e significan
p oblems a low ma ine eflec ances, limi ing b oad applica ion in
he OWT con ex . The esul s o all AC me hods, o he mos pa ,
could no be well-classified using he OWT sys em o Bi e al.
(2019), and Bi e al. (2021), which has i s ocus o applica ion on
inland wa e s; ye compa isons wi h in si u da a sugges ha he
ough shape o R
s
is well ep oduced by mos ACs.
So a , OWT algo i hms ha e ocused oo much ei he on
ma ine o limnological applica ions; o a comp ehensi e
usabili y, missing classes should be added. The classifica ion
schemes o Hie onymi e al. (2017) p o ides a good basis, as i
includes ep esen a i e classes o ocean, coas al and inland wa e s.
Howe e , his me hod in pa icula shows ha e o ole ances
should be inc eased in o de o achie e be e classifiabili y o AC
esul s, which is he basis o a ully comp ehensi e exploi a ion o
an OWT sys em. The ocusing o an OWT sys em on he spec al
shape, h ough log- ans o med no maliza ion, inc eases he
sensi i i y o noise and small inaccu acies, and hus leads o
educed classifica ion pe o mance. I is gene ally ad an ageous i
Hie onymi e al. 10.3389/ ma s.2023.1129876
F on ie s in Ma ine Science on ie sin.o g19
he OWT classifica ion sys em is aligned wi h he pe o mance
spec um o he a mosphe ic co ec ion and ice e sa.
Da a a ailabili y s a emen
The en OLCI scenes used in his wo k we e sa ed as Ne CDF
files along wi h all he esul s o he fi e a mosphe ic co ec ion
models and made a ailable a he open eposi o y Zenodo
(Hie onymi e al., 2023). The da a can be ound online a : h ps://
doi.o g/10.5281/zenodo.7567534.
Au ho con ibu ions
MH concep ualized he s udy, p epa ed, and w o e he o iginal
d a . MH, ES, DB, CL, and DM we e in cha ge o he da a cu a ion
and sa elli e da a p ocessing. SB pe o med independen OWT
analysis. DM pe o med independen ma ch-up analysis. MH and
ES conduc ed he spa ial-spec al s udies. MH, KS, CB, FS, QV, and
DM deli e ed backg ound in o ma ion on a mosphe ic co ec ion
me hods. All au ho s con ibu ed o he a icle and app o ed he
submi ed e sion.
Funding
The Helmhol z Associa ion wi h he esea ch p og am Ea h
and En i onmen (PoF IV) unded his s udy. Addi ional suppo
was p o ided by he He eon-I
2
Bp ojec Phy oDi eand he
Eu opean Cope nicus Ma ine En i onmen Moni o ing Se ice
(EU, 77-CMEMS-TAC-OC). Mo eo e , his wo k benefi ed om
achie emen s o he ollowing p ojec s: Coas Colou (ESA), OC-
CCI (ESA), SEOM-C2X (ESA), OC-BPC (EUMETSAT), and
WEnMAP (BMWi & DLR, 50EE1718).
Acknowledgmen s
This wo k is based on ee and open sa elli e da a om he
Eu opean Union’s Cope nicus P og amme p o ided by ESA and
EUMETSAT. In addi ion, in si u da a om AERONET-OC we e
used, o whichwe hank hePIs:G.Zibo di,S.Ahmed,A.Gile son,S.
K a ze ,T.Sch oede ,H.Feng,H.M.Sosik,A.Weidemann,B.Gibson,
and R. A none. Mo eo e , D. Vans eenwegen, he Flemish Ma ine
Ins i u e, and POM Wes -Vlaande en a e hanked o he ins alla ion,
ope a ion and p o ision o PANTHYR da a. We also hank R.
Rö ge s,H.K asemann,C.Maze an,M.Pe e s,M.Bö che ,andV.
B ando o inspi ing discussions and suppo . Finally, we would like o
hank he edi o , J.A. Concha, and h ee expe s o hei ho ough
e iew o he pape and help ul commen s.
Conflic o in e es
Au ho s KS, DM, CL, and CB a e employed by he company
B ockmann Consul GmbH, Ge many. Au ho FS is employed by
he company HYGEOS, F ance.
The emaining au ho s decla e ha he esea ch was conduc ed
in he absence o any comme cial o financial ela ionships ha
could be cons ued as a po en ial conflic o in e es .
The handling edi o JC decla ed a pas co-au ho ship wi h he
au ho QV and e iewe IC decla ed a pas collabo a ion wi h he
au ho DM o he handling edi o .
Publishe ’s no e
All claims exp essed in his a icle a e solely hose o he au ho s
and do no necessa ily ep esen hose o hei a filia ed o ganiza ions,
o hose o he publishe , he edi o s and he e iewe s. Any p oduc
ha may be e alua ed in his a icle, o claim ha may be made by i s
manu ac u e , is no gua an eed o endo sed by he publishe .
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Appendix 1
APPENDIX FIGURE A1
O e iew o all en OLCI scenes used (Table 2) in e ical nea -side pe spec i e. RGB images c ea ed om L
TOA
. Ma ked in ed a e he 100x100 pixel
a eas o es ima ing spa ial homogenei y (Table 4). The image sec ions in Figu e 2 a e shown in o ange.
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