NRL 7333 Rb = 1-  1+  1+  2 Non- Linear b1- b2q3 influences 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 influences 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 Sensors R. A. Arnone 1, R. W. Gould 1, P. A. Martinolich 2, S. Ladner 3, A. W. Weidemann 1, and V. Haltrin 1 1. Naval Research Laboratory, SSC, MS 2. Neptune Sciences SSC. MS 3. Planning Systems Inc, SSC. MS 1. Naval Research Laboratory, SSC, MS 2. Neptune Sciences SSC. MS 3. Planning Systems Inc, SSC. MS Where are These Relations Used in Remote Sensing Algorithms Used in Remote Sensing Algorithms - NIR – Iteration - NIR – Iteration Coupled Ocean – Atm Algorithm - extension of Gordon- atm into - extension of Gordon- atm into Coastal waters by Lu765 = 0 - Bio – optical Algorithms - Bio – optical Algorithms bb and a(total) bb ~ RRS bb ~ RRS MISSISSIPPI Bight- SeaWIFS processing April 18,2001 Chlorophyll OC4 Objective : - Determine the affect of linear and non-linear relationships 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 Coastal and offshore waters. Chlorophyll, backscattering (550) and Total Absorption Chlorophyll, 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. b0-b1 - b0-b1 - b1- b2q3 b1- b2q3 b1-b2q4 b1-b2q4 b2-q3-b2q4 Maxium Non linear b2q3-b2q6 b2q3-b2q6 bb_555_arnone bb_555_arnone b0-b1 – b0-b1 – b1-b2-q3 b1-b2-q3 b1-b2q4 b1-b2q4 Total Absorption “Carder” b0-b1- Oc4 b0-b1- Oc4 b1-b2q4 b1-b2q4 b1-b2q6 b2q3-b2q4 b2q4-b2q6 b2q4-b2q6 Summary  A linear g –RRS relationship effectively changes the Q-value in the non-linear relationship. Q changes from to 6.0 the non-linear relationship. Q changes from to 6.0 with increasing “g” in coastal waters.. with increasing “g” in coastal waters..  Insitu shows high variability of the RRS - “g” relationship associated with non-linear and bb-b relationship  Significant 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. Origin of the Remote Sensing Reflectance? Rb = 0.33 bb a+ bb Rb= Diffuse Reflectance Linear 1-g 1-g  = 1+2g + g (4+5g) 1+2g + g (4+5g) g = bb g = bb a + bb a + bbWhere Haltrin Appl. Opt. 37, (1998) Q= 3.14 a = Q = 4 a = Q = 6 a = Remote Sensing Reflectance Conversion of Rb to RRS for non-linear RRS = F T 2 bb Q n 2 a+bb typically typically g RRS = 1 T 2 Rb Q n 2 Q= Changes in Water type Use 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 Waters 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 Cruises Large variability in coastal Waters. Influence of Q variability ? bb –b conversion ?? Spectral Dependence of Insitu nm 440 nm 670 nm nm 440 nm 670 nm Red has lower “g” from attenuation Green has largest variation in coastal Waters. g = g = bb/a bb/a bb Q =3.14 bb Q =3.14 a+bb a+bb bb Q =4.0 bb Q =4.0 a+bb a+bb bb Q =6.0 bb Q =6.0 a+bb a+bb bb bb(a+bb) LinearLinear Non-linearNon-linearNon-linear SeaWIFS Imagery was processes using the NIR – which is a coupled ocean - atmospheric Correction (Gordon). We varied the linear – and non-linear RRS with different Q parameters and determined the affect on coastal optical products. 1. Chlorophyll - NASA –OC4 algorithms 1. Chlorophyll - NASA –OC4 algorithms 2. bb550 – Arnone algorithms 2. bb550 – Arnone algorithms 3. absorption 440 Total – Carder Algorithm 3. absorption 440 Total – Carder Algorithm The coupled ocean-atm algorithm is triggered by the Lu670 where high scattering has significant influence on the Lt765 and Lt865, which are used 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. Differences Differences bb in denominator decrease bb in denominator decrease Chl in coastal waters Non linear with Q=3, Increases Chl. Little change with Q=4,6 bb in denominator increases bb in denominator increases bb in coastal waters bb in coastal waters Non linear with Q=3, Decrease bb Larger decrease with Q=4,6 Changes in bb product Are significant with Q changes. Changes in “a total” product Are similar with non-linear Q changes. bb in denominator decrease bb in denominator decrease chl in coastal waters chl in coastal waters Variation in the bb/b relationship illustrates the changing Q parameter. Currently using ~2%. Volume Scattering Functions (VSF) show high variability in different water types. This is responsible for high insitu scatter. Currently Linear Relationship Used Current Semi Analytical algorithms Backscattering Absorption Rrs = b b ~ b bw + b b p a t ~ a w + a  + a d + a g waterphytoplanktondetritus colored dissolved organic matter Backscattering Absorption ? ? bbt bbt at at Remote Sensing Reflectance Insitu - Comparisons Differences Changing from Q=3-6 Decreases bb Changes in Q – Little Affect on Chlorophyll For Contact: Robert Arnone Head Ocean Optics Section Naval Research Laboratory Stennis Space Center, MS (228)