Land SeaFresh Water Test

All observation locations are checked against a global, high-resolution land/sea database. Observation locations surrounded by water in all directions are accepted, and observation locations surrounded by land in all directions are discarded. For observations very near the coast a fuzzy land/sea boundary check is used. Observation locations are accepted if, in any one direction, the otherwise over-land location is next to a water point. Relaxation of the land/sea discrimination allows for resolution errors of the land/sea database and precision errors in the reporting of observation latitude and longitude positions over the GTS. Fuzzy land/sea tests are useful when ships provide observations while parked at a dock, or when instruments are deployed on piers very close to the coast. Note that the land/sea test must also distinguish observation locations in fresh- and seawater locations. Lake surface temperatures are routinely provided in remotely sensed satellite data streams, and in situ fixed buoys are located in many large lake systems, such as the Great Lakes in the U.S. Remotely sensed and in situ lake surface temperatures have unique error characteristics and need to be distinguished as such in the quality control. Remotely sensed lake surface temperatures are routinely used in analyses of lower boundary conditions in Numerical Weather Predictions (NWP) systems.

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