The sensor may be narrowband enough that part of your measured function is just whatever slice of the blackbody radiation curve it's seeing. If you factor that out, you might be back to mostly linear.

Polynomial and special function theory remains a vibrant area of mathematical research, interweaving classical algebra with advanced analysis. At its core, the study concerns algebraic expressions ...

Polynomial Threshold Function (PTF): A Boolean function represented as the sign of a real polynomial, used to model decision boundaries in high-dimensional spaces.