5. The Benguela: Lesson Overview

Aims and objectives

This lesson looks at some of the techniques currently used to study plankton productivity in coastal upwelling systems. Using the The Benguela Current System as an example, the lesson demonstrates how Sea Surface Temperature (SST) data and ocean colour data may be used synergistically to provide information about upwelling events. By the end of this lesson you should be able to:

• create a colour composite suitable for illustrating the bright colour signature of coccolithophore blooms and sulphur eruptions, both common in the Benguela system,
• use meta-data information and Bilko formulae to convert 8-bit integer chlorophyll data to true chlorophyll concentrations
• apply MERIS and AATSR level 2 flags to mask areas affected by cloud
• create temporal composite images from several MERIS and AATSR scenes
• compare chlorophyll concentrations derived from measurements by different sensors
• investigate the relationship between sea surface temperaure and chlorophyll concentrations

Lesson content

1. Creating a colour composite of a coccolithophore bloom
2. Dealing with cloud in MERIS level-2 data
3. Using formulae to calculate chlorophyll
4. Creating an 8-day composite from MERIS data
5. Comparing MERIS and MODIS chlorophyll
6. Examining relationships between SST and chlorophyll
7. Summary and conclusions

Images used in this lesson

• MER_RR_1COLRA20030424~.N1
  Level 1 (top of atmosphere) scene from the MERIS sensor on Envisat, showing a coccolithophore bloom in the Benguela upwelling area on 24 April 2003.
• MER_RR_2COLRA200402~.N1
  Three MERIS Level 2 scenes from the southern Benguela region, showing a coastal upwelling event in early February 2004.
• l5_mod_a20040332004040~.HDF
  Level 3 MODIS images of chlorophyll and sea surface temperature from the same period as the MERIS images.