Lesson 4: Global sea surface temperature

For centuries sea surface temperature (SST) has been used by mariners to locate strong ocean currents such as the Gulf Stream. In the late 1700´s early charts of the North Atlantic Ocean were emerging which clearly detailed the location of the Gulf Stream, largely determined by sharp changes of SST. At this time the measurement of SST was considered an instrument of navigation. Measurements of SST were inconsistent in methodology and highly biased towards shipping routes in the Northern Hemisphere, in significant areas of the global ocean (e.g., Southern Ocean), few if any observations existed.

This situation changed dramatically in the late 1960´s when satellite platforms carrying accurate radiometer systems capable of imaging global SST became operational. The images were revolutionary, revealing for the first time the highly dynamic character of the global ocean. SST image data showed intense mesoscale activity, ocean gyres, large frontal zones, and many ocean current systems. The distribution and character of these global SST patterns was found to be highly dynamic having seasonal, annual, inter-annual and decadal signatures depending on the geographic location. The character of large-scale SST patterns is now considered common knowledge in the ocean and atmospheric sciences but it should be remembered that it was only after regular high-resolution global coverage of SST provided by operational satellites that the modern era of oceanography truly began.

The data used in this tutorial is from the Along Track Scanning Radiometer (ATSR-2) instrument, a four channel, dual view, self calibrating, spatially co-registered, infrared radiometer having spectral channels centred at 1.6, 3.7, 10.8 and 11.5µm (Edwards et al. 1990). Several innovative features in the instrument design ensure that the ATSR delivers exceptional sensitivity and stability of calibration. The ATSR is capable of measuring the sea surface temperature to an accuracy of +/- 0.3K from over 800km above the ocean surface!

This Bilko tutorial uses a time series of SST observations derived from the European Remote Sensing satellite 2 (ERS-2) ATSR to investigate the spatial and temporal character of the major global patterns of SST. Manipulating this time series, the character of SST observations in a number of regions is investigated using a variety of techniques that allow qualitative and quantitative information to be extracted from the SST data.

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