SST computes the Celsius temperature for every pixel in an image, regardless of whether it represents land or water; however, only the temperature values for oceans will be precise. Temperature values for land, cloud, or inland water bodies can be used as rough indicators if necessary, but in general should be ignored.
For mid-ocean sea surface temperatures, SST typically provides about 0.5 degree Celsius accuracy, given ideal data sets. Temperature accuracy is generally dependent on atmospheric conditions and land proximity. Water vapour content (single most important factor), pollution, and strong winds are some of the conditions that can affect temperature accuracy. Temperature calculations near land are also of lesser accuracy due to the high land temperatures and extra atmospheric pollutants. The McClain coefficients can be used to compensate for these conditions; however, it is often difficult or impossible to get precise McClain coefficients for a specific scene or set of circumstances.
The default McClain coefficients used by SST are for mid-ocean, sunny sky, low wind conditions. This is a reasonable set of assumptions since this is about the only set of atmospheric conditions that actually lets you see the sea surface.
For 8-bit AVHRR tape formats, the MIT program must be used to import the raw AVHRR image. The resultant image is typically less than 2048 pixels wide (half-scan data). The text segment generated by MIT has a slightly different format than that generated by FIMPORT or MIAVHRR (for 10-bit AVHRR data). The main difference is that the MIT text segment has a FIRSTPIXEL line indicating the original pixel position of the first pixel in the image. When SST finds a FIRSTPIXEL line in the text segment of the input image, it assumes that it is working with LAC/HRPT data. In particular, SST assumes that the original image is 2048 pixels wide. This assumption is important for the satellite zenith angle calculations (which are pixel position dependent).
For 10-bit AVHRR data, SST expects the input image to be 2048 or 409 pixels wide (LAC/HRPT or GAC data, respectively). Any other image widths will result in an error.