# Product Tutorial on Sea Surface Temperature (SST)

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## Chapter III: Brief history of SST measurements

### Table of Contents

- Brief history of SST measurements

### Brief history of SST measurements

Sea surface temperatures have been measured for over one hundred years, first using instruments on shorelines, ships and buoys. Such observations provide limited spatial and temporal coverage, as illustrated from the next two figures that show measurements taken between the 31st August and the 6th September 1997. Figure 2 shows ship-based and Figure 3 shows buoy measurements (most having sensors at about a 1-meter depth or placed at regular intervals along a tether line).

Fig. 2: SST measurements taken from a ship between the 31st August and the 6th September 1997

Fig. 3: SST measurements taken from buoys between the 31st August and the 6th September 1997

The constraint of the limited spatial and temporal coverage provided by local observations could be overcome with the use of satellite technology; using infrared remote sensing from satellite, the spatial complexity of the sea surface features signatures could be revealed. The computation of SST from infrared satellite data started in the mid-1970's using the primary instrument called the Scanning Radiometer (SR) on NOAA's polar orbiting weather satellites with an 8 km spatial resolution. The first (1978) Advanced VHRR (AVHRR) had 4 channels that included a mid-range infrared (3.7 μm in channel 3) with a single thermal infrared channel at 11 μm. The 1 km resolution of the AVHRR and its improved radiometric fidelity promised some improvements in the computation of SST. It was realized that atmospheric water vapor markedly attenuates the 11 μm infrared signal from the sea surface and that some way of correcting the AVHRR data for this effect was needed. It was decided to modify the AVHRR to add another thermal infrared channel (~12 μm) that was affected more strongly by atmospheric water vapor attenuation. The difference between the 11 and 12 μm thermal infrared channels would provide an estimate of the water vapor content in the atmosphere which could be corrected for in the SST algorithm. This formulation, called the "split-window", has been used in the majority of the SST algorithms developed (McMillin and Crossby, 1984). Since the 1980's, most of the information about global SST has originated from satellite observations. (source: https://doi.org/10.1175/1520-0477(2001)082<2773:ESSTFI>2.3.CO;2).

Source: Images from http://www2.hawaii.edu/~jmaurer/sst/#intro