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Measurements of SST from infrared (IR) sensors are used extensively in the earth science community to monitor climate change, initialize weather models, and investigate air-sea interactions. Most often, the IR SSTs are calculated from observations made by the AVHRR instrument. IR SSTs suffer from three main problems. 1) They are unable to retrieve SSTs through clouds resulting in incomplete coverage and a “fair weather” bias. 2) Atmospheric aerosols from volcanic eruptions, fires, or dust storms can result in artificial cooling of large regions. 3) Undetected clouds cause biased retrievals.
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The ability to accurately measure SST using microwave imaging sensors was realized with the launch of the TRMM Microwave Imager (TMI) in November 1997. Extensive validation studies show these SSTs to be of extremely good quality with a standard deviation of 0.4° C from NDBC and TAO buoys. The atmosphere is 98% transparent at microwave frequencies, allowing virtually uninterrupted retrieval of SSTs. Microwave sensors capable of retrieving SSTs are planned for the next 20 years aboard the ADEOS 2, EOS PM, WindSat, GCOM B-1, and NPOESS platforms.
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A blended IR SST product (satellite IR SSTs and buoy SSTs) was developed by Dr. Richard Reynolds to address the shortcomings of IR SST data. Buoy SSTs are used to minimize artificial cooling from atmospheric aerosols and to correct for biases in the satellite sensor. Temporal and spatial averaging provides complete global oceanic coverage and eliminates cloud contamination. This blended SST product is used to initialize many weather and climate models. It is not as vulnerable to aerosol biasing as a standard IR SST, but has reduced spatial and temporal resolution as a result of the averaging. It is only available weekly on a 1° grid. There are some questions as to the accuracy of this product in areas devoid of buoy instrumentation.
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