FY 2003

ATLAS module temperature bias due to solar heating

A'Hearn, P.N., H.P. Freitag, and M.J. McPhaden

NOAA Tech. Memo OAR PMEL-121, NTIS: PB2003-101593, NOAA/Pacific Marine Environmental Laboratory, Seattle, WA, 24 pp (2002)

Some near-surface temperature measurements from NextGeneration Autonomous Temperature Line Acquisition Systems (NX ATLAS) moorings between 1996 and 2001 have been found to be at times biased by solar heating. The bias is maximum near the sea surface around noon local time and has been observed at depths down to 75 m. Sea surface temperature sensors mounted immediately beneath the buoy at 1 m are not exposed to direct sunlight and thus not subject to similar solar heating. The bias is estimated to have a typical maximum of about 0.13°C at 20 m, the depth of the shallowest sensor on most moorings. Temperature sensors at 5 m and 10 m on some specially instrumented moorings may have larger biases. Modifications to the instrumentation and deployment procedures have reduced solar heating bias to 0.01°C or less. These improvements were first introduced in April 2000 and have been used on all moorings deployed since January 2001. The recovery of potentially biased instrumentation was completed in December 2001. A list of when and where data may be biased is given in the appendix.