# Presentation: 530037

## Slide 1

## Collaborators and Team Members (*students)

- Dr. Mark D. Dowell
- Timothy S. Moore
- Hui Feng*
- Seung-Hyun Son*
- Joe Salisbury*
- Doug Vandemark*
- Gillian Fairchild*

*This work is supported under a MODIS Instrument Team contract (NAS5-96063) and a grant from NASA’s Office of Earth Science Oceanography Program (NSG5-6289).*

## Slide 3

## The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was launched in August 1997.  It continues to operate and produce  ocean color and land color data.

- The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was launched in August 1997.  It continues to operate and produce  ocean color and land color data.

## 30 day composite ocean chlorophyll and land normalized difference vegetation index (NDVI)

- <date/time>

## Why so many MODIS chlorophylls?  

- What’s the difference?
- 	Originally there were 2 algorithms:
- “Case 1” waters:	Chlor_MODIS (Clark)
- 	This is an empirical algorithm based on the 443:551 band ratio .... following the CZCS approach
- “Case 2” waters:	Chlor_a_3 (Carder)
- This is a semi-analytic (model-based) inversion algorithm.  This approach is required in optically complex “case 2” (coastal) waters.

## This algorithm was based on regression involving  HPLC chlorophyll(s).  n=93, r2=0.915, std error of estimate = 0.047.  

- Chlor_MODIS December 2000

- This algorithm was based on regression involving  HPLC chlorophyll(s).  n=93, r2=0.915, std error of estimate = 0.047.

## This “semi-analytic” algorithm accounts for pigment packaging effects in nutrient-replete and nutrient-deplete conditions.

- Chlor_a_3 December 2000

## 	More recently a 3rd algorithm was added:

- 	More recently a 3rd algorithm was added:
- “SeaWiFS-compatible”	Chlor_a_2 (Campbell)
- 	This is an empirical algorithm using the 443:551 and 488:551 band ratios whichever is greater.
- SeaWiFS algorithm		OC4.v4 (O’Reilly)
- 	This is an empirical algorithm using the 443:555, 490:555 and 510:555 band ratios whichever is greater.

## This “SeaWiFS compatible” algorithm is based on the same data set used to parameterize the SeaWiFS algorithm.

- Chlor_a_2 December 2000

## Slide 11

## Slide 12

## SeaWiFS December 2000

## Slide 14

## Slide 15

## SeaWiFS Chlorophyll

## Slide 17

## Slide 18

## Our approach is to test algorithms using in-situ data  

- _In-situ Data_:  We have combined three in-situ data sets of reflectance and chlorophyll data for a total of n = 1,229 stations.

- Subset of the original SeaBAM data which had measurements at 443, 490, and 510 nm (n = 539)
- COASTLOOC data from European coastal waters (n = 324)
- AMT cruise data obtained from SeaBAS (n = 366)

## Chlor_a_2  Chlorophyll (OC3M)

**In-situ chlorophyll (mg m****-3****)**

**Bias = -0.03**
**RMS = 0.29**

## SeaWiFS Chlorophyll (OC4.v4)

**SeaWiFS Chlorophyll (OC4.v4)**

**In-situ chlorophyll (mg m****-3****)**

**Bias = -0.05**
**RMS = 0.27**

## SeaWiFS  Chlorophyll

**SeaWiFS  Chlorophyll**

**Chlor_a_2  Chlorophyll (OC3M)**

## MODIS Chlorophyll:  May 8, 2000 10:45 am

## SeaWiFS Chlorophyll:  May 8, 2000 11:51 am

## Slide 25

## CONCLUSIONS

- MODIS and SeaWiFS chlorophylls agree reasonably well.  RMS ~ 0.2 log units
- RMS ~ 0.3 log units when comparing MODIS or SeaWiFS with in-situ chlorophyll measurements.
- The differences (Chlor_a_3 vs. SeaWiFS) can be explained in terms of pigment packaging, or surface layer drift (e.g. Liu et al. 2001).
- The Chlor_a_2 product is ready to be validated after the next reprocessing.  By definition, if it is compatible with SeaWiFS, then it is valid.