Leaving the weights of the different observation types (e.g. temperature obs, flow obs) causes bias towards high value observations (or residuals) in objective function. According to PESTPP4.2.4 manual
A simple procedure that often works well is to assign observations of different types to different observation groups, and to then use a utility program such as PWTADJ1 from the PEST suite to ensure that the contribution made to the objective function by each observation group is about the same as that made by any other observation group at the commencement of the inversion process.
When calibrating a surface water model, or when including contaminant concentrations as a component of the calibration dataset of a groundwater model, it may be useful for the magnitudes of weights to reflect the magnitudes of measurements.
Leaving the weights of the different observation types (e.g. temperature obs, flow obs) causes bias towards high value observations (or residuals) in objective function. According to PESTPP4.2.4 manual