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.

Bernstein polynomial estimation provides a robust nonparametric technique for approximating both density and distribution functions. Based on the properties of Bernstein polynomials, which ...

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 ...

This function is a polynomial in two dimensions, with terms up to degree 5. It is nonlinear, and it is smooth despite being complex, which is common for computer experiment functions (Lim et al., 2002 ...

The conditional variance function in a heteroscedastic, nonparametric regression model is estimated by linear smoothing of squared residuals. Attention is focused on local polynomial smoothers.