Comparison of chlorophyll in the Red Sea derived from MODIS-Aqua and in vivo fluorescence

- The 1st comparison of MODIS-Aqua and in situ chlorophyll in the Red Sea.
- We evaluate the performance of two satellite chlorophyll algorithms in the Red Sea.
- Results support the use of ocean colour data in the Red Sea.
- Results support the development of regional algorithms for the Red Sea.

The Red Sea is a unique marine environment but relatively unexplored. The only available long-term biological dataset at large spatial and temporal scales is remotely-sensed chlorophyll observations (an index of phytoplankton biomass) derived using satellite measurements of ocean colour. Yet such observations have rarely been compared with in situ data in the Red Sea. In this paper, satellite chlorophyll estimates in the Red Sea from the MODIS instrument onboard the Aqua satellite are compared with three recent cruises of in vivo fluorometric chlorophyll measurements taken in October 2008, March 2010 and September to October 2011. The performance of the standard NASA chlorophyll algorithm, and that of a new band-difference algorithm, is found to be comparable with other oligotrophic regions in the global ocean, supporting the use of satellite ocean colour in the Red Sea. However, given the unique environmental conditions of the study area, regional algorithms are likely to fare better and this is demonstrated through a simple adjustment to the band-difference algorithm.