  In this work, the issue of obtaining consistent parameter estimators for
nonlinear regression models where the regressors are second-order modulus
functions is explored. It is shown that consistent instrumental variable
estimators can be obtained by estimating first and second-order moments of
non-additive environmental disturbances' probability distributions as nuisance
parameters in parallel to the sought-after model parameters, conducting
experiments with a static excitation offset of sufficient amplitude and forcing
the instruments to have zero mean. The proposed method is evaluated in a
simulation example with a model of a marine surface vessel.
