Abstract: The present invention provides a method and device for characterizing a physiological parameter. The method, in one application, uses one or more non-invasive sensors to collect patient data, and may also collect data on environmental conditions. At least some of the patient data has a direct relationship with the physiological parameter, that is, a change in the physiological parameter is reflected in the data set, although the magnitude of the physiological parameter may masked by noise, interference, or other environmental or patient influences. The direct patient data preferably has a generally linear relationship with the physiological parameter, and if not, the patient data is linearized according to an algorithm, table, or other adjustment process. These linearizing processes may be predefined, and may adaptively learn or adjust. A blind signal source process is applied to the linearized data to generate separated signals, and the signal associated with the physiological parameter is identified.