NRL 7333

RbRb = 1- = 1- 1+ 1+

22

Non- LinearNon- Linear

b1- b2q3b1- b2q3

We developed improved SeaWIFS coastal ocean color algorithms to derived inherent optical properties, based on relationships between absorption, scattering and remote sensing reflectance. The linear remote sensing reflectance to scattering: absorption ratio (bb/a) is the basis for open ocean algorithms where absorption (predomoninantly from chlorophyll) is greater than backscattering. In coastal waters, where backscattering from sediment can dominate absorption, a non-linear and spectral dependence occurs between the reflectance and the backscatter: absorption ratio. These nonlinear influencesinfluences affect not only the in water optical algorithms, but they are also coupled with the atmospheric correction in coastal waters. The removal of water leaving radiance in the near-IR (765 and 865 nm) is especially necessary in coastal waters. The non-linear relationship is used in estimating the water leaving radiance in the near-IR through an iterative pixel-by-pixel process using the 670 nm water leaving radiance. We used SeaWIFS imagery and insitu measurements to evaluate the effects the non-linear relationships have on coastal algorithms where backscattering dominates the absorption. We compare these new products with the more standard NASA products and we highlight areas where regional differences are greatest (bays, estuaries).

Improved Algorithms for Retrieving Optical Properties in Coastal Waters from Ocean Color SensorsImproved Algorithms for Retrieving Optical Properties in Coastal Waters from Ocean Color Sensors

R. A. ArnoneR. A. Arnone11, R. W. Gould, R. W. Gould11, P. A. Martinolich, P. A. Martinolich22, S. Ladner, S. Ladner33, A. W. Weidemann, A. W. Weidemann11, and V. Haltrin, and V. Haltrin11 1. Naval Research Laboratory, SSC, MS 2. Neptune Sciences SSC. MS 3. Planning Systems Inc, SSC. MS1. Naval Research Laboratory, SSC, MS 2. Neptune Sciences SSC. MS 3. Planning Systems Inc, SSC. MS

Where are These RelationsWhere are These Relations Used in Remote Sensing AlgorithmsUsed in Remote Sensing Algorithms

- NIR – Iteration - NIR – Iteration Coupled Ocean – Atm AlgorithmCoupled Ocean – Atm Algorithm

- extension of Gordon- atm into - extension of Gordon- atm into Coastal waters by Lu765 = 0 Coastal waters by Lu765 = 0

- Bio – optical Algorithms - Bio – optical Algorithms bb and a(total) bb and a(total)

bb ~ RRS bb ~ RRS

MISSISSIPPI Bight- SeaWIFS processing April 18,2001 MISSISSIPPI Bight- SeaWIFS processing April 18,2001

ChlorophyllOC4

Objective : Objective : - Determine the affect of linear and non-linear relationships - Determine the affect of linear and non-linear relationships

Which IOP’s (backscattering and absorption) have on reflectance. Which IOP’s (backscattering and absorption) have on reflectance.

RRS ~ bb/a ~ bb/(a+bb) RRS ~ bb/a ~ bb/(a+bb)

- Apply these relationships to SeaWIFS processing and determine their affect- Apply these relationships to SeaWIFS processing and determine their affectCoastal and offshore waters. Coastal and offshore waters. Chlorophyll, backscattering (550) and Total AbsorptionChlorophyll, backscattering (550) and Total Absorption

- Determine where (water type) and how magnitude these relationships - Determine where (water type) and how magnitude these relationships affect Ocean Color “SeaWIFS” Algorithms. affect Ocean Color “SeaWIFS” Algorithms.

b0-b1 - b0-b1 - b1- b2q3b1- b2q3

b1-b2q4b1-b2q4

b2-q3-b2q4b2-q3-b2q4

Maxium Maxium Non linear Non linear b2q3-b2q6b2q3-b2q6

bb_555_arnonebb_555_arnone

b0-b1 – b0-b1 – b1-b2-q3b1-b2-q3 b1-b2q4b1-b2q4

Total AbsorptionTotal Absorption““Carder”Carder”

b0-b1- Oc4 b0-b1- Oc4

b1-b2q4b1-b2q4 b1-b2q6b1-b2q6

b2q3-b2q4b2q3-b2q4 b2q4-b2q6b2q4-b2q6

SummarySummary

A linear g –RRS relationship effectively changes the Q-value in A linear g –RRS relationship effectively changes the Q-value in the non-linear relationship. Q changes from +3.14 to 6.0 the non-linear relationship. Q changes from +3.14 to 6.0 with increasing “g” in coastal waters.. with increasing “g” in coastal waters.. Insitu shows high variability of the RRS - “g” relationshipInsitu shows high variability of the RRS - “g” relationship

associated with non-linear and bb-b relationshipassociated with non-linear and bb-b relationshipSignificant differences occur in SeaWIFS products (bb) in high scattering water (coastalSignificant differences occur in SeaWIFS products (bb) in high scattering water (coastal and shelf waters ) that are associated with Q. Small changes in CHL and “a”.and shelf waters ) that are associated with Q. Small changes in CHL and “a”. Improved algorithms will require estimate of Q in coastal waters for bb products.Improved algorithms will require estimate of Q in coastal waters for bb products.

Origin of the Remote Sensing Reflectance? Origin of the Remote Sensing Reflectance?

Rb = 0.33 bb a+ bb

Rb= Diffuse ReflectanceRb= Diffuse Reflectance

Linear Linear 1-g1-g

= = 1+2g + g (4+5g)1+2g + g (4+5g)

g = bb g = bb a + bba + bb

Where Where

Haltrin Appl. Opt. 37, 3773-3774 (1998)Haltrin Appl. Opt. 37, 3773-3774 (1998)

Q= 3.14 a = 0.1778Q = 4 a = 0.1357Q = 6 a = 0.0950

Remote Sensing Reflectance

Conversion of Rb to RRS for non-linear

RRS = F T 2 bb Q n 2 a+bb

0.0510.051 typicallytypically gg

RRS = 1 T2 Rb Q n2

Q= Changes in Water typeQ= Changes in Water type

Use the Non-linear Rb and Convert to the RRSUse the Non-linear Rb and Convert to the RRS

Changes from bb/a to bb/(a+bb) is significant in High scattering (bb) waters.

Insitu Observations in Coastal WatersInsitu Observations in Coastal Waters90 stations 90 stations - RRS – ASD (Above water) RRS - RRS – ASD (Above water) RRS - absorption – ac9- absorption – ac9 - bb – ac9 converted b to bb (Petzold) - bb – ac9 converted b to bb (Petzold)

bb to b *53 (1.97%) bb to b *53 (1.97%) (Source of Error) (Source of Error)

Insitu data from different Insitu data from different Cruises Cruises Large variability in coastal Large variability in coastal Waters. Waters. Influence of Influence of

Q variability ?Q variability ?bb –b conversion ?? bb –b conversion ??

Spectral Dependence of Insitu Spectral Dependence of Insitu - 550 nm 440 nm 670 nm - 550 nm 440 nm 670 nm Red has lower “g” from attenuationRed has lower “g” from attenuationGreen has largest variation in coastal Green has largest variation in coastal Waters. Waters.

g = g = bb/abb/a

bb Q =3.14bb Q =3.14 a+bba+bb

bb Q =4.0bb Q =4.0 a+bba+bb

bb Q =6.0bb Q =6.0 a+bba+bb

bbbb(a+bb)(a+bb)LinearLinear LinearLinear Non-linearNon-linear Non-linearNon-linear Non-linearNon-linear

SeaWIFS Imagery was processes using the SeaWIFS Imagery was processes using the NIR – which is a coupled ocean - atmospheric NIR – which is a coupled ocean - atmospheric Correction (Gordon) . We varied the linear – and Correction (Gordon) . We varied the linear – and non-linear RRS with different Q parameters and non-linear RRS with different Q parameters and determined the affect on coastal optical products. determined the affect on coastal optical products. 1. Chlorophyll - NASA –OC4 algorithms1. Chlorophyll - NASA –OC4 algorithms 2. bb550 – Arnone algorithms 2. bb550 – Arnone algorithms 3. absorption 440 Total – Carder Algorithm3. absorption 440 Total – Carder Algorithm

The coupled ocean-atm algorithm is triggered by The coupled ocean-atm algorithm is triggered by the Lu670 where high scattering has significant the Lu670 where high scattering has significant influence on the Lt765 and Lt865, which are used influence on the Lt765 and Lt865, which are used for atmospheric correction. for atmospheric correction.

Therefore, the nonlinear RRS and g will affect Therefore, the nonlinear RRS and g will affect coastal waters products and not offshore waters. coastal waters products and not offshore waters.

DifferencesDifferences

DifferencesDifferences

bb in denominator decrease bb in denominator decrease Chl in coastal watersChl in coastal waters Non linear with Q=3, Non linear with Q=3,

Increases Chl.Increases Chl.Little change with Q=4,6Little change with Q=4,6

bb in denominator increases bb in denominator increases bb in coastal watersbb in coastal waters Non linear with Q=3, Non linear with Q=3,

Decrease bbDecrease bbLarger decrease with Q=4,6Larger decrease with Q=4,6

Changes in bb productChanges in bb productAre significant with Are significant with Q changes.Q changes.

Changes in “a total” productChanges in “a total” productAre similar with non-linear Are similar with non-linear Q changes.Q changes.

bb in denominator decrease bb in denominator decrease chl in coastal waterschl in coastal waters

Variation in the bb/b relationshipVariation in the bb/b relationshipillustrates the changing Q parameter.illustrates the changing Q parameter.Currently using ~2%. Currently using ~2%. Volume Scattering Functions (VSF) Volume Scattering Functions (VSF) show high variability in different water show high variability in different water types.types.This is responsible for high insitu scatter.This is responsible for high insitu scatter.

Currently 0.019Currently 0.019

Linear Relationship Used Linear Relationship Used Current Semi Analytical algorithms Current Semi Analytical algorithms

Backscattering

AbsorptionRrsRrs = 0.051= 0.051

bb ~ bbw + bbp

at ~ aw + a + ad + ag

water phytoplankton detrituscolored dissolvedorganic matter

Backscattering

Absorption

?? ??bbt bbt at at

Remote Sensing Remote Sensing Reflectance Reflectance

Insitu - ComparisonsInsitu - Comparisons

DifferencesDifferences

Changing Changing from Q=3-6from Q=3-6Decreases bbDecreases bb

Changes inChanges inQ – Little Q – Little Affect on Affect on ChlorophyllChlorophyll

For Contact: For Contact:

Robert ArnoneRobert ArnoneHead Ocean Optics SectionHead Ocean Optics SectionNaval Research Laboratory Naval Research Laboratory Stennis Space Center, MS 39529Stennis Space Center, MS 39529 arnone@nrlssc.navy.mil(228) 688-5268(228) 688-5268

http://www7333.nrlssc.navy.milhttp://www7333.nrlssc.navy.mil

OS52A-0530OS52A-0530