Summary And Conclusions

In situ temperature observations do not provide adequate global coverage; therefore, additional data sources are needed to supplement these traditional observations. Satellite borne infrared observations have been tried for years (Davis and Tarpley 1983), but cloud contamination continues to resist filtering. Although passive microwave measurements have considerably lower resolution than the infrared or visible observations, they provide a viable option. Fortunately, clouds are not much problem in the microwave spectrum; although there is the issue of variable emissivity of the radiating surface. We addressed this variation by understanding the radiating characteristics of numerous surfaces and made dynamic emissivity adjustments as a consequence of the surface type of each observed signal. Spatially and temporally coincident SSM/I observations and in situ data were used to develop regression equations to estimate the emissivity adjustments. Each adjustable surface type within the SSM/I data has a different set of parameters and goodness of fit with respect to the shelter height temperatures.

An independent high-resolution data set was used to validate the accuracy and precision of the satellite derived surface temperature anomalies. Both the satellite and reference time series had similar distributions around their mean, and the difference between the two anomaly fields had a standard variance of 0.76°C with low kurtosis and skewness. The spatial correlation over the time series was 0.92 and temporal correlation over the study area generally exceeded 0.80. There was some spatial and temporal auto-correlation in the residual, but it is at an acceptable level.

The present blended global surface temperature product is clearly better than any one of the sources alone. For example, insights into the climate can be obtained by seeing the transition between SST and continental air temperatures which in some instances is very smooth and in other cases have abrupt changes. The SSM/I-derived temperatures provide dramatically improved coverage over in situ data in some climatologically important areas and at the same time the SSM/I temperatures are improved by anchoring the monthly anomalies on in situ observations. Blended together, the three sources of data provide near-global coverage.

The BWI had strong correspondence with precipitation measurements through many important agricultural areas of the globe. The relationship between the two variables generally increased as precipitation was aggregated across the concurrent and previous months. This indicates that the BWI measures upper level soil moisture, and it provides valuable information across many areas of the world where in situ are not available. The BWI does not represent soil moisture with much accuracy over densely vegetated surfaces, since the satellite can not see the ground through the vegetative cover.

Products of global surface temperature anomalies and surface wetness can be obtained from the world wide web at 7777/plwebapps/plsql/ssmimain. These are available in near real time by the 15th day of the following month. The historical anomaly fields are also available from the January 1992 to the present. The data also be accessed free of charge from the web by going through the site listed above.

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