A Global Dataset of Monthly Satellite data: SST and Chlorophyll-a concentration

By Mati Kahru, mkahru@ucsd.edu

A value-added monthly global dataset has been compiled of the best-available data of SST and chlor_a.

The SST dataset consist of two parts:

·        Earlier SST data is from the MCSST 18-km dataset from November-1981 to 1985. It has been made by compositing the weekly daytime data downloaded from ftp://podaac.jpl.nasa.gov/pub/sea_surface_temperature/avhrr/mcsst/data/weekly/day/ with a WAM script wam_composite. The data were also remapped to start at longitude -180 at the left column (instead of 0 degrees longitude) to be compatible with other datasets. Only the period  of 1981-1984 is actually needed and the 1985 data from MCSST is only provided for a comparison with the more accurate Pathfinder version 5 data.


  • Later SST data is derived from AVHRR Oceans Pathfinder Global 4km Equal-Angle All SST V5 (NOAA)  (#216) ascending mode (Kilpatrick et al., 2001) downloadable from ftp://podaac.jpl.nasa.gov/pub/sea_surface_temperature/avhrr/pathfinder/data_v5/monthly/ascending/4km/. Using the WAM program wam_screen_pf  the actual SST data and the corresponding quality datasets were screened and only the best quality pixels were retained (the lower-quality pixels were converted to zero). This monthly dataset starts with January-1985 and currently ends with May-2004. More monthly data will be added when they become available.


The chlorophyll-a concentration dataset consists of three parts (from three different sensors):


  • The 1978-November to 1986-June data is derived from the Coastal Zone Color Scanner (CZCS) water-leaving radiances as processed by Feldman et al (1989). The radiances were then processed with the OC3 algorithm of O’Reilly et al (1998). This version of the CZCS data was first reported and used in Kahru and Mitchell (2000). It was reported by Kahru and Mitchell (2004) that this version of the CZCS data corresponds better to in situ match-ups in the California Current than both the original and the other reprocessed CZCS datasets. For example, Gregg and Conkright (2002) and Antoine et al. (2003) have produced newer versions of the CZCS dataset using different algorithms and assumptions but the match-ups from the California Current do not show their superiority.


  • 1996-November to 1997-June period is based on the OCTS data as reprocessed by NASA and slightly modified by using pixel value 0 for the missing pixels.


  • 1997-September to 2004-December is based on the standard SeaWiFS (Reprocessing 4, software version 2.4) Mapped Level-3 data that have been slightly modified. For both the OCTS and SeaWiFS data the missing-value pixels of 255 have been replaced with a pixel value of 0 (using a script wam_replace_pixel_values). In all other respects the data is not modified.
  • 2005-January and forward is based on the standard MODIS-Aqua (software version 2.8) Mapped Level-3 data at either 4 km or 9 km resolution.




Antoine et al., EOS Trans. AGU, 84: 301, 2003.

Feldman, G., N. Kuring, C. Ng, W. Esaias, C. McClain, J. Elrod, N. Maynard, D. Endres, R. Evans, J. Brown, S. Walsh, M. Carle, and G. Podesta, Ocean color: Availability of global data set, EOS Trans. AGU, 70, 634-641, 1989.

Gregg W. and M. E. Conkright, J. Geophys. Res., 106: 2499-2515, 2001.

Gregg et al., Applied Optics 41: 1615-1628.

Gregg, W. and M. E. Conkright. 2002. Decadal changes in global ocean chlorophyll. Geophysical Research Letters 29 (15): 10.1029/2002GL014689.

Kahru, M., B.G. Mitchell, Influence of the 1997-98 El Niño on the surface chlorophyll in the California Current, Geophysical Research Letters, Vol. 27, No. 18, 2937-2940, 2000.

Kahru, M., B.G. Mitchell, Long-term trends in satellite-derived ocean color: validation of various algorithms in the California Current. Abstract XXXXX-XX, 2004 Ocean Sciences Meeeting, ASLO/AGU, XX-XX Feb 2004, Honolulu, Hawaii, 2004.

Kilpatrick, K.A., G.P. Podesta, and R.H. Evans, Overview of the NOAA/NASA AVHRR Pathfinder algorithm for sea surface temperature and associated matchup database, J. Geophys. Res., 106, C5, 9179-9197, 2001.

O’Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru, and C.R. McClain, Ocean color chloro-phyll algorithms for SeaWiFS, J. Geophys. Res., 103: 24,937-24,953, 1998.