This study concerns the experimental measurement of spray impingement onto walls and liquid films and the correct estimation of quantities required for modeling the impact phenomenon. The considerations introduced in this investigation are especially applicable when using the phase Doppler measurement technique, although the results also have relevance for the numerical simulation of such flows. When investigating impinging sprays the important parameters to be quantified include the deposition rate of the liquid onto the wall and characteristics of the splashed fraction—velocity, size and flux of the drops in the secondary spray. When applying the phase Doppler instrument to characterize spray/wall impingement, the measurement volume is usually placed a finite distance above the wall surface. The ingoing (primary) droplets are then distinguished from outgoing (secondary) droplets through the sign of the velocity component normal to the wall. It is demonstrated that the portion and size of the wall surface associated with the impinging drops or the secondary drops must be determined by analyzing the drop trajectories between the measurement position and the wall. If the tangential velocity of the drops is significant or if the wall surface is curved, then the flux densities referenced to particular wall surface areas can be significantly different when neglecting these trajectories. An appropriate evaluation procedure for improved estimates is introduced and described in detail.