ISOPLETHS OF CHLOROPHYLL IN RADIANCE SPACE

1. ISOPLETHS OF CHLOROPHYLL IN RADIANCE SPACE Janet W. Campbell, Timothy S. Moore, and Mark D. Dowell Ocean Process Analysis Laboratory University of New Hampshire Durham, NH 03824-3525 USA Santa Fe, New Mexico November 21, 2002 This work was supported by a NASA MODIS Team contract (NAS5-96063) and NASA grant (NAG5-6289).

2. According to a ratio algorithm…. Isopleths of chlorophyll are lines passing through the origin in the plane defined by the two radiances used in the ratio. • CZCS • OC2 • OC3M • OC4 • Lw(443):Lw(550) • R(490):R(555) • max[R(443),R(490)]:R(555) • max[R(443),R(490),R(510)]:R(555)

3. According to a semi-analytic algorithm … Isopleths of chlorophyll generally do not pass through the origin in planes defined by two radiances. • Gordon et al. 1988 • Garver & Siegel, 1997 • Carder et al. 1999

4. In this presentation, I will…. • Demonstrate this by comparing • Garver & Siegel (1997) algorithm • OC4 algorithm (O’Reilly et al. 2000) • Show that covariance among optically active constituents reconciles this inconsistency.

5. Ratio algorithms are strongly supported by empirical data….

6. Chl = 0.01 0.1 0.3 1 3 10 30 Isopleths of chlorophyll for the OC4 algorithm

7. Semi-analytic Model of Garver & Siegel, 1997 l b ( ) b l R ( ) ~ Gordon et al. 1988 rs l + l a ( ) b ( ) b Pope & Fry, 1997 Bricaud et al. 1995 S = 0.02 p = 1

8. 3-D “constituent space” maps into 2-D reflectance plane bbp=bbp(555) max. Rrs(l) Chl Rrs(555) adm=acdm(443)

9. p=2 to 0 Chl = 0 %adm = 0 Pure Seawater bbp = 0 Chl = 10 mg m-3 %adm = 80% Feasible Points in 490 vs. 555 Reflectance Plane

10. Measured Chl SeaBAM Data

11. Chl = 0.01 0.1 0.3 1 3 10, 30 Maximum reflectance bbp isopleths Isopleths of Chl in the OC4 plane, holding %adm = 35%

12. bbp isopleths Chl = 0.3 isopleths varying %adm between 0 and 90%

13. %adm = 0 10 35 50 65 80 90 Chl = 0.3 isopleths varying %adm between 0 and 90% Tracing points along the OC4 Chl = 0.3 isopleth, adm increases as bbp decreases. OC4

14. Chl = 0 Chl = 0.1 Chl = 1 %adm = 0% 10% 50%10% 75% 30% Chl = 10 90% SeaBAM data for Chl = 0.1, 1 and 10

15. Chl = 0.01 0.1 0.3 1 3 10 30 Isopleths of chlorophyll for the OC4 algorithm The Garver&Siegel model was inverted to derive the relationship between adm and bbp along the OC4 isopleths of Chl.

16. Relationship between adm and bbp required to reconcile OC4 and Garver&Siegel model

17. Measured Chl SeaBAM Data

18. Chl < 0.05Chl = 0.1Chl = 1Chl = 10

19. CONCLUSIONS • According to semi-analytic models for Case 1 waters, optical properties are governed by three variables (Chl, adm, bbp). Chl isopleths in radiance space do not pass through the origin. • Empirical evidence supports ratio algorithms in which Chlisopleths do pass through the origin. • Covariance between adm and bbp reconciles this discrepancy.

20. CONCLUSIONS (cont.) • The nature of the relationship between adm and bbp depends on the trophic state: • In oligotrophic waters, there is a negative correlation between adm and bbp. • In eutrophic waters, the correlation is zero or positive. • This might contain a clue as to the nature of the particles that scatter light in the different ocean environments.

21. NOMAD Data

22. Measured Chl SeaBAM Data