Ocean Color Chlorophyll (OC) v6

For a more up to date version, please go here.

---

updated 18 Mar 2010, OC4O modified to use 516 instead of 520 nm

---

The operational algorithm for deriving near-surface chlorophyll-a concentrations (OC; O'Reilly et al. 2000) was updated using in situ data from NOMAD version 2. NOMAD is a publicly available, global bio-optical data set constructed from data archived in SeaBASS. The data span a wide range of water types from coastal and offshore regions and were collected by participants in the NASA Ocean Biology &amp Biogeochemistry Program and by voluntary and international collaborators. The algorithm form describes the polynomial best fit that relates the log-transformed geophysical variable to a log-transformed ratio of remote-sensing reflectances. The polynomial form is consistent with past versions of OC.

requirements

* polynomials bisect the full dynamic range of the development data set
* OC4 = OC4E = OC4O = OC3S = OC3M = OC3C = OC3E = OC3O = OC2S = OC2M = OC2E = OC2O

algorithm

form:

* Rrs1 = blue wavelength Rrs (e.g., 443, 490, or 510-nm)
* Rrs2 = green wavelength Rrs (e.g., 547, 555, or 565-nm)
* X = log10(Rrs1 / Rrs2)
* chlor_a = 10^(a0 + a1_X + a2_X^2 + a3_X^3 + a4_X^4)

changes from operational:

* none, simply a revised fit to an updated in situ data set

v6 coefficients:

sensor	default *	blue	green	a0	a1	a2	a3	a4
OC4	SeaWiFS	Y	443>489>510	555	0.3272	-2.9940	2.7218	-1.2259	-0.5683
OC4E	MERIS	Y	443>489>510	560	0.3255	-2.7677	2.4409	-1.1288	-0.4990
OC4O	OCTS	Y	443>489>516	565	0.3325	-2.8278	3.0939	-2.0917	-0.0257
OC3S	SeaWiFS	N	443>489	555	0.2515	-2.3798	1.5823	-0.6372	-0.5692
OC3M-551	MODIS	N	443>489	550	0.2424	-2.5828	1.7057	-0.3415	-0.8818
OC3M-547	MODIS	Y	443>489	547	0.2424	-2.7423	1.8017	0.0015	-1.2280
OC3V	VIIRS	Y	443>486	550	0.2228	-2.4683	1.5867	-0.4275	-0.7768
OC3E	MERIS	N	443>489	560	0.2521	-2.2146	1.5193	-0.7702	-0.4291
OC3O	OCTS	N	443>489	565	0.2399	-2.0825	1.6126	-1.0848	-0.2083
OC3C	CZCS	Y	443>520	550	0.3330	-4.3770	7.6267	-7.1457	1.6673
OC2S	SeaWiFS	N	489	555	0.2511	-2.0853	1.5035	-3.1747	0.3383
OC2E	MERIS	N	489	560	0.2389	-1.9369	1.7627	-3.0777	-0.1054
OC2O	OCTS	N	489	565	0.2236	-1.8296	1.9094	-2.9481	-0.1718
OC2M-551	MODIS	N	489	550	0.2481	-2.2958	1.4053	-3.1299	0.6478
OC2M-547	MODIS	N	489	547	0.2500	-2.4752	1.4061	-2.8233	0.5405
OC2M-HI	MODIS (500-m)	Y	469	555	0.1464	-1.7953	0.9718	-0.8319	-0.8073

* Y indicates operational / default algorithm for each sensor within OBPG processing

algorithm development

OC4	OC3S	OC3M-551	OC3M-547
[](ocfit_oc4.png)	[](ocfit_oc3s.png)	[](ocfit_oc3m.png)	[](ocfit_oc3mr.png)
[](ocdens_oc4.png)	[](ocdens_oc3s.png)	[](ocdens_oc3m.png)	[](ocdens_oc3mr.png)

OC4E	OC4O	OC3E	OC3O
[](ocfit_oc4e.png)	[](ocfit_oc4o.png)	[](ocfit_oc3e.png)	[](ocfit_oc3o.png)
[](ocdens_oc4e.png)	[](ocdens_oc4o.png)	[](ocdens_oc3e.png)	[](ocdens_oc3o.png)

OC3V	OC3C	OC2S	OC2E
[](ocfit_oc3v.png)	[](ocfit_oc3c.png)	[](ocfit_oc2s.png)	[](ocfit_oc2e.png)
[](ocdens_oc3v.png)	[](ocdens_oc3c.png)	[](ocdens_oc2s.png)	[](ocdens_oc2e.png)

OC2O	OC2M-551	OC2M-547	OC2M-HI
[](ocfit_oc2o.png)	[](ocfit_oc2m.png)	[](ocfit_oc2mr.png)	[](ocfit_oc2mh.png)
[](ocdens_oc2o.png)	[](ocdens_oc2m.png)	[](ocdens_oc2mr.png)	[](ocdens_oc2mh.png)

algorithm verification: internal consistency

intercomparison of operational/default algorithms

intercomparison of 3-band algorithms

intercomparison of 2-band algorithms

algorithm verification: comparison with previous versions

operational OC4 and OC3M are v4 (SeaBAM); operational OC3S is v5 (NOMAD v1)

algorithm verification: comparison with Morel and Maritorena 2001

algorithm verification: level-2 match-ups

used NOMAD-free subset of SeaWiFS and MODIS-Aqua match-ups

SeaWiFS	MODIS-Aqua
[](ocval_swf.png)	[](ocval_mod.png)

Questions? Contact Jeremy Werdell
NASA Ocean Biology Processing Group