A method of retrieving a temperature-depth profile in biological object from a set of multi-frequency microwave radiometric data has been developed. The method is a combination of model-fitting and Monte Carlo techniques and is capable of estimating a profile and its confidence interval as a function of the depth. We use 2#x3C3; -intervals as a measure of the precision of tissue temperature measurements. The method was tested and supported by an experiment in which temperature distributions in a muscle equivalent agar phantom were measured using a 5-band, 1-3.8 GHz radiometer with the brightness temperature resolution of 0.05-0.07 K. A typical result of the experiment showed that 2#x3C3; -intervals were 1 K or less for 0 z 3 cm, 1.4 K at z = 4 cm, and 3 K at z = 5 cm. A numerical simulation study was made using this technique to assess effects of the selection of measurement frequencies, number of frequency bands, brightness temperature resolution of radiometer and thickness of fat layer on the precision. Results indicated that 2#x3C3; -intervals of about 1.0 K or less over a 0-5 cm depth range could be achieved by a 6-band, 0.55-3.8 GHz radiometer with the brightness temperature resolution of 0.05 K.
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