Physics based RS algorithms for water quality parameters: Status and challenges. ZhongPing Lee

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1 Physics sed RS lgorithms for wter qulity prmeters: Sttus nd chllenges ZhongPing Lee Environmentl, Erth nd Ocen Sciences University of Msschusetts, Boston, MA EEOS UMssB Opticl Ocenogrphy L NASA Workshop for Remote Sensing of Costl & Inlnd Wter, June 20 22, 2012

2 Wter Qulity Prmeters WQPs: Physicl: SST, Turidity, Clrity, IOPs Geologicl : SPM TSM, TSS, POM, PIM Biologicl: Phytoplnkton chlorophyll, phycocynin,, virus, cteri Chemicl: ph, CDOM, hevy metls, pesticides, O 2, nutrients Cn these e sensed pssively?

3 ocen wter color

4 Quntify wter color rdince spectrum L w E d Remote sensing reflectnce sr 1 : L u 0 - E d 0 - R rs Lw,0 E,0 d r rs L E u d 0 0

5 The spectrl form of wter ocen color MERIS R rs [sr -1 ] MODIS SeWiFS Wvelength [nm] R rs WQPs CZCS

6 Algorithms for chlorophyll nd other WQPs: Gordon nd Morel 1983, emp Tssn 1993, emp Bukt et l 1995, semi Gitelson et l 1996, emp Hoge nd Lyon 1996, semi Crder et l 1999, semi Gower et l 1999, semi Khru nd Mitchell 1999, emp OC4 O Reilly et l 2000, emp OC3, emp Doerffer 1999, NN Dekker et l 2002, emp Mritoren et l 2002, semi Brndo et l 2003, semi Kutser et l 2005, emp Dll Olmo et l 2003, emp Devred et l 2005, semi Le et l 2009, emp Gilerson et l 2010, emp Binding et l 2012, semi Hu et l 2012, emp

7 Bsics of physics sed lgorithms empiricl Rrsλ Semi nlyticl lgeric or optimiztion explicit or implicit IOPs AOP IOP link Physicl iogeochemicl properties WQPs IOP WQP link

8 rs g g r 1 0 AOP IOP link Rrs model rs rs rs w L E rs r r R r n t t R rs G R The ultimte question: How to dequtely solve the Rrs eqution for WQPs?

9 Two sic strtegies: 1. Bottom up strtegy BUS: Assume we know the spectrl shpes of the opticlly ctive components 2. Top down strtegy TDS: Only need the spectrl shpe informtion when it is necessry

10 1. Bottom up strtegy BUS: rs G R p w λ = w λ + xi λ λ = w λ + xi λ Build up n Rrs spectrum lock y lock: dg ph w 2 1 dg ph w M M 4 3 o m w M M

11 R rs G w M 1 ph w M 2 M 3 dg m w M 4 M o 3 m M 4 o M 1 4 or M 1 3 re wvelength independent vriles! Then they could e derived y compring the modeled Rrs spectrum with the mesured Rrs spectrum. Spectrl rnges used for solutions e.g. exmples of BUS: The lue green domin: e.g., Hoge nd Lyon 1996, Crder et l 1999 The red infrred domin: e.g., Binding et l 2012 The entire spectrum spectrl optimiztion: e.g., Bukt et l 1995, Lee et l 1994,1996,1999, Mritoren et l 2002, Boss nd Roesler 2006, Brndo et l 2012 Key: Assume the spectrl shpes of the opticlly ctive components re well chrcterized!

12 BUS for opticlly shllow wters R L w E d rs E Lw d R rs = F[,,, H] H ottom : sorption : ck-scttering : ottom ledo H: ottom depth Wter property ottom property = M 5 ott R rs = F[M 1,M 2,M 3,M 4,M 5, H]

13 Wter properties efore correcting ottom Wter properties fter correcting ottom [mg m -3 ] [m -1 ] Lee et l 2007

14 2. Top down strtegy TDS: R rs G R rs & x Clrity Secchi depth, light depth, TSM/SPM, etc Remote sensing mesures the totl effect: Wter clrity or turidity is lso mesure of totl effect. Exmples of TDS: QAA Lee et l, 2002; Smyth et l 2006; Dorn et l 2007.

15 Bsics of TDS: 0.4 sorption coefficient m pure wter [C] = 0.03 [C] = 1.0 [C] = 5.0 λ wvelength nm For reference wvelength, λ 0, vrition of λ 0 is limited. Known λ 0, enles clcultion of λ 0 from R rs λ 0 ; propgte λ 0 to λ, then enles clcultion of λ from R rs λ. No need of spectrl model of x λ in this process! λ 0

16 Applictions of &: Secchi depth: Euphotic zone depth: Z eu =f &

17 The dt flow of QAA: r rs η 0 w 0 0 p 0 F2 rrs 0, 0, w 0 p p 0 0 Lee et l w 443 F3 rrs, p, w w ph ph dg dg ph ph dg dg

18 Contrst: BUS derives every component first, then simultneously derives the totl opticl property. BUS relies more on forwrd io opticl model TDS derives totl first, then decompose to seprte components. TDS relies more on Rrs mesurement

19 Quntifiction of product uncertinty We should not expect the sme error rs for the three pixels.

20 TDS mkes the uncertinty estimtion strightforwrd. Error propgtion theory: z f xi; i :1 N z N i1 z xi x i 2

21 Issues/chllenges? Rrsλ IOPs Physicl iogeochemicl properties WQPs AOP IOP link: Nerly universl IOP WQP link: Trnsfer coefficients re Regionl/temporl dependent 1. Get Rrs right!

22 After we get the right Rrs, different level of products fcing different chllenges/requirements λ 0 & λ 0 SPM Minimum requirement: spectrl shpe of p λ Z SD ; Z eu Require: spectrl shpe of ph λ nd g λ Require: mss-specific opticl properties Lee et l 2002

23 How to est prmeterize m,,, o ph dg? A. Derive them on the fly? e.g. Brndo et l 2012 B. Prmeterize them sed on regionl/temporl chrcteristics?

24 Thnk you!

Chl distribution of the global oceans (OBPG)

Chl distribution of the global oceans (OBPG) Chl distriution of the glol ocens OBPG / ] [ j i R R f Chl / i i i j j j j p j i p i j i f R R [Chl] is ctully n IOP product Remote-sensing reflectnce sr - : R L,0 E,0 d L E d The ultimte ojective of RS: