Validation of turbidity products EuroGOOS Conference, May 20-22, 2008, Exeter Session Observations...

Validation of turbidity productsEuroGOOS Conference, May 20-22, 2008, Exeter

Session Observations – OBS17 May 22, 2008

Validation of turbidity products in the Baltic derived from multi-sensors observations of ocean colour

Antoine Mangin1, Seppo Kaitala2, Stéphane Maritorena3, Odile Fanton d’Andon1, and Philippe Garnesson1

(1) ACRI-ST , (2) FIMR, (3) ICESS UCSB

Session Observations – May 22, 2008




Outline of this presentation

Background of Marcoast

Background of GlobColour

Validation over Baltic


Gulf of Finland



MarCoast Project: Presentation SERV10, 21 May by Planetek

GMES Service Element project (ESA Funding) The main goals are:

– the surveillance and monitoring of the marine and coastal environment – to deliver services at a European scale. – integration and Sustainability

was launched in 2005 and will be completed at the end of 2008.

Background, Marcoast Project



Background, MarCoast Project

ACRI-ST activities within Marcoast project:

-Ocean Colour Delivery Service (NRT/Archive MERIS/MODIS data) to other service providers

-Pan-European service of eutrophication statistics information

-Water quality indicator for EEA: see EuroGOOS poster P19

-Validation activities:Regional consistency assessment with in situ dataover Baltic sea in collaboration with FIMR

More on Marcoast: http://gmes-marcoast.com/



Background, Globcolour project 2005-2008

GlobColour: ESA DUE project i.e. driven by end users: IOCCG, IOCCP,UK Met-Office,

Achievements Provision of a long time-series (1997-2007) of consistently

calibrated and merged global ocean colour productsMERIS (ESA), SeaWiFS (NASA), MODIS-AQUA (NASA)

Validation and characterisation performed with available in situ observations

Future development: Global Ocean Colour Thematic Assembly Centre of the future EU GMES Marine Core Service (MyOcean)

More on Globcolour: www.globcolour.info

( Data available on line )



Validation with FIMR observations




Towards the turbidity validation …. through the

In situ monitoring route: Helsinki - Travemûnde

Turbidity is routinely measured and recorded during cruises

The Nephelometric Turbidity Unit (NTU) that is used is directly comparable to the scattering of particulate matter bp

Helsinki

Travemûnde




2006 20076 6.5 7 7.5 8 8.5

M onth

54

55

56

57

58

59

60

Latit

ude

0 .2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

6 6.5 7 7.5 8 8.5

M onth

54

55

56

57

58

59

60

Latit

ude

Travemûnde

Helsinki

Åland

Illustration of turbidity mapping

Well identified seasonalincrease of turbidity

Spatial and temporal uniformity of turbidity


Issues:High dissolved organic matter (CDOM) andTurbidity

High variability



0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12

Month

Ch

lro

ph

yll

a co

nce

ntr

atio

n (

mg

/m3)

Chla measured in Situ - source FIMR - 2003 Chla measured in Situ - source FIMR - 2004

Chla measured in Situ - source FIMR - 2005

Chl-a - Gulf of Finland – In situ obs. – Source : FIMR


High variability


Spring bloom

2005



Chl-a - Gulf of Finland MODIS/SeaWiFS standard algorithms – 1997-2006


High variability


Spring bloomis not captured

False summer bloom of Chl



0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12

Month

Ch

lro

ph

yll

a co

nce

ntr

atio

n (

mg

/m3)


Chla - case 2 waters - observed with MERIS - 2003





Chl-a validation - Gulf of Finland in situ / MERIS case 2


The Meris-Chla algorithm for Case 2 waters gives quite good fit with in situ data for the Gulf of Finland

But …

Spatial and temporalcoverage issue



GlobColourData merging


Why do ocean color data merging ?• Several simultaneous global ocean color missions• Several versions of the same product

Benefits:• Development of unified, consistent ocean color time-series from multiple sensors • Improved spatial and temporal coverage

• More diverse ocean color products with lower uncertainties

GlobColour :

• Access to products uncertainties

• Exploitation of all spectral bands from 412 nm to 670 nm.



GlobColourGSM algorithm

L wN() source 1 LwN() source 2 L wN() source n

LwN () uncertainties source 1 LwN () uncertainties source 2 LwN () uncertainties source n

[L wN() source 1, L wN() source 2, ..., LwN() source n]

LwN () uncertainties source 1, LwN () uncertainties source 2, ..., LwN () uncertainties source n[ ]

GSM01 MODEL INVERSION

wNL bb

bb= f(

a + )

wNL

SeaWiFSMODIS

[Chl] (443)acdm (443)bbp

DATA SOURCES

CONCATENATED ARRAYS

[Chl] confidence interval (443) confidence intervala cdm (443) confidence intervalb bp

RETRIEVALS

MERIS, MODIS, SeaWiFSLwN + Estimates of the uncertainties on input LwN (from sensors obs. characterisation)

Estimates of the model error (from NOMAD Database)

Estimates of Chla, bbp,

cdm + uncertainties on outputs (Co-variance matrix)




Inputs: In situ observations (Nomad)Results: very close to expectancy – no significant bias

0

10

20

30

40

50

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

Normalised std dev

Po

pu

lati

on

Results

Expected

Inputs: GC productsResults: very close to expectancy – a small bias is detected – the error estimates by GSM (with ad hoc inputs) is slightly underestimated.

Validation of turbidity products in the Baltic derived from multi-sensors observations of ocean colour GlobColour

Error estimates - Validation If the Chla error estimates is reliable

should be close to a standard normal distribution



GlobColourExample

GlobColour Chla-merged product – May,15 2006

GlobColour Chla-merged product relative uncertainties – May,15 2006

100

50

0




1009080706050403020100

%

GlobColourExample


bbp Error

August 7, 2007 – bbp



1009080706050403020100

%

GlobColourExample


bbp Error

March 26, 2007 – bbp



Some empirical laws are proposed between particle backscattering coefficient (bbp) and particle scattering coefficient (bp), e.g.,

bbp≈0.015 bp (in MERIS ATBD)

In other words it is there admitted that it exists a linear relationship between the two coefficients.

The challenging objective here is therefore to make the bridge between measured bp (through NTU) and EO-derived bbp in order to bring novel insights about the linearity of the relationship and wherever possible its suitability with respect to turbidity ranges.

Turbidity in Baltic – elements of validation


However, it should vary with size and nature of particulate matters, and consequently could vary with time and space.



1 2 1 4 1 6 1 8 2 0 2 2 2 45 4

5 6

5 8

6 0

Travemûnde

Helsinki

Extraction of a 3x3 GC macro-pixel each 10 km for available in situ truth

Turbidity in Baltic – elements of validation EO side

In situ side

2 4 6 8 10

0

1

2

3

4

5

Filtering:Bp<1,5 + removal of « obvious » artefacts

NT

U

Month


2006



In situ & GlobColour Time Series

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

4,00

4,50

5,00

0 5000 10000 15000 20000 25000 30000

Year 2006 - Observation Number

bp

In situ observation bbp (GlobColour)/0,015

Turbidity in Baltic – elements of validation


2006



Turbidity in Baltic – Confrontation EO (bbp) against in situ (bp)

GSM - GlobColour (EO) bbp vs In-situ bp


Year 2006No linear correlation

at annual scale

y = 0,0007x + 0,007

R2 = 0,002

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050

0 0,2 0,4 0,6 0,8 1 1,2 1,4

bp in situ observations

bb

p (

GS

M-

Glo

bC

olo

ur)





May 2006 y = 0,0115x - 0,0005

R2 = 0,36N=3039

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050

0 0,2 0,4 0,6 0,8 1 1,2 1,4


bb

p (

GS

M-

Glo

bC

olo

ur)

July 2006 y = 0,0091x + 0,007

R2 = 0,16N=4788

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050

0 0,2 0,4 0,6 0,8 1 1,2 1,4


bb

p (

GS

M-

Glo

bC

olo

ur)


Monthly scaleCorrelation exists …Still high (spatial) variability



September 2006

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050

0 0,2 0,4 0,6 0,8 1 1,2 1,4


bb

p (

GS

M-

Glo

bC

olo

ur)


….. and other sources for validation(Babin, Maritorena, personal com.)

to be compared to 0.015

GSM (in situ) vs In-situ


September 2006Bbp=0.0106 bp + 0.0005R2=0.39N=1012


Turbidity in Baltic (bp<2)September 1998 - Coastlooc campaign

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050

0 0,2 0,4 0,6 0,8 1 1,2 1,4

bp (555 nm) Coastloocs

bb

p (

GS

M)

Bbp=0.0109 bp + 0.01R2=0.15




First conclusions:

1. A simple linear relationship between bp and bbp cannot blindly be used as is in the Baltic sea.

2. On a monthly basis, a linear relationship between bbp and bp can be used to cross-check « observed bp » against « EO-derived bbp »

3. Still some work to sort out « valid » EO-derived information (e.g. by using exclusion threshold on standard deviation) and « valid » observation (e.g. by checking spatial and temporal consistencies).

4. Work will be expanded to previous observations (2003/2004/2005)




FIMR feedback on the service“The Meris-Chla algorithm for Case 2 waters and by extension GSM method gives quite good fit with in situ data for the Gulf of Finland (… quite problematic due to high variation of water quality parameters).”


The spring bloom estimate for the Western Gulf of Finland Year 2006 - Start April 8 - Duration 35 days

GlobColour GSM : Mean 8,06 mg/m3 - Peak 21,25 mg/m3 In situ (Helcom fact sheet) : Mean 13 mg/m3 - Peak 19,4 mg/m3

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Days after start of spring bloom

Glo

bC

olo

ur

GS

M C

hla

(m

g/m

3)



FIMR feedback on the service

” The service gives valuable information for the water quality evaluation of the Baltic Sea and reporting to HELCOM about the water quality status of the Baltic Sea.”


http://www.helcom.fi/environment2/ifs/ifs2007/secchi/en_GB/secchi/http://www.helcom.fi/environment2/ifs/ifs2007/en_GB/springbloom/

Validation of turbidity products EuroGOOS Conference, May 20-22, 2008, Exeter Session Observations...

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