An apparatus comprises a subsurface sensor to be positioned in a wellbore formed in a subsurface formation, wherein the subsurface sensor is to detect subsurface measurements. The apparatus includes a processor and a machine-readable medium having program code executable by the processor to cause the processor to generate a combination of functions based on the subsurface measurements, wherein the combination of functions is a subset of functions from a library of functions. The program code is executable by the processor to cause the processor to determine at least one function parameter of at least one function of the combination of functions and determine at least one formation property of the subsurface formation based on the at least one function parameter.