The Improved lnitialization Inversion (3I) procedure is a physico-statistical algorithm for retrieving meteorological parameters from TIROS-N satellite data at a special resolution of 100 × 100 km. This procedure accounts for the physics of the phenomena involved, explicitly taking into consideration the local properties of each terrain observed, such as surface elevation, surface emissivity, percentage of water, and viewing angle. Considerable effort is put into the optimization of the initial guess solution which is retrieved from a large precomputed TOVS Initial Guess Retrieval (TIGR) data set. TIGR describes the physical and statistical properties of a large number of well-sampled atmospheric situations with which the observed situation may be compared. Retrieval of the initial guess also relies upon operational forecast of the temperature and gepotential altitude of the lowest atmospheric levels. The quality of the initial solution obtained is demonstrated by the fact that only one iteration with the retrieval scheme is required to get the final solution. Preliminary comparisons for the ALPEX Intensive Observing Period of 4 and 5 March 1982 show a satisfactory agreement with conventional data and, in particular, a much better agreement in the 500–1000 mb pressure range than that recently found by Gruber and Watkins.

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