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Satellite derived sea surface temperature : a physical approach

University of British Columbia

In this study, a method of estimating atmospheric attenuation in the infrared remote sensing of sea surface temperature (SST) from National Oceanic and Atmospheric Administration (NOAA) meteorological satellites, by explicitly considering the physical processes involved, is developed. Unlike past methods which tend to rely on the inputs from the in situ data, this method which is entirely satellite derived, will be useful in the open oceans where in situ observations are sparse. Using Advanced Very High Resolution Radiometer (AVHRR), with atmospheric temperature and water vapor profiles from the TIROS Operational Vertical Sounder (TOVS), SST's are retrieved. TOVS sensors are carried by the same satellite as the AVHRR and provide simultaneous corrections for the AVHRR based SST estimates. SST, computed from sensor systems on NOAA-7, are compared with surface skin temperatures (from a PRT-5 infrared radiometer mounted on a ship) and subsurface temperature measurements. In addition to the physical method (AVHRR+TOVS), two additional split-window techniques (SWT) using channels 4 and 5 of the NOAA-7 AVHRR sensor, were investigated. These methods were: 1. Using AVHRR alone, and 2. Using AVHRR and data from the High-resolution Infrared Sounder (HIRS). The importance of scan angle correction and emittance effect to define the correct atmospheric path is discussed. The improvement in SST retrievals using sensor combinations is demonstrated with satellite versus ship skin temperature differences ranging from 0.63 to 0.89 °C for AVHRR alone, from 0.49 to 0.80 °C for AVHRR+TOVS, and from 0.39 to 0.56 °C for AVHRR+HIRS. The improved temperature accuracy with AVHRR+HIRS is due to the atmospheric water vapor correction possible with some of the HIRS channels. The effects of errors in TOVS derived atmospheric profiles upon the SST are significant, but using the SWT, these effects are reduced, improving the over all SST retrievals. Even though TOVS profiles cannot duplicate radiosonde observations in accuracy or in vertical resolution, their overall effect on the SST is found to be within the physical limitations of the satellite sensors. It is suggested that the physical method can effectively be used to generate coefficients, applicable to a given location, for a SWT method such as the AVHRR+HIRS, in order to achieve the required accuracy at a reduced computation time. The coefficients can then be updated for seasonal variations. Significant differences between ship skin and subsurface temperatures were observed with the mean deviation of -0.86 °C in the Pacific and —0.2°C in the Atlantic for a range of root-mean-square (RMS) temperature differences between 0.16 and 0.87 °C.

Text

2010-08-07

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http://hdl.handle.net/2429/27196

Oceanography

University of British Columbia

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