1. A computer-implemented method of constructing a model of a target object, the method comprising causing a computer to execute instructions for: receiving an input signal from a source, the input signal containing data describing the target object and a plurality of parameters, the input signal having a noise portion; selecting a group of initial parameters from the plurality; estimating a nonparametric probability distribution function (pdf) comprising a linear combination of a set of square-integrable basis functions; computing a quadratic likelihood functional (QLF) of the form L = ∫  x [ 1 2 f ( x , θ ) 2 - f ( x , θ ) ∑ i δ ( x - x i ) ] where θ represents the parameters, x represents the positions of the observations, and ƒ(x, θ) is the pdf; evaluating a fit of the initial parameters to the data based on the QLF; iteratively optimizing the QLF by selecting a new group of parameters and evaluating the fit of the new group of parameters into a predetermined condition is achieved; and generating an output comprising a model of the target object constructed using optimized parameters.