In this paper, methods for improvement of surface/terrain aided navigation using an altimeter simulation model are introduced. The altimeter simulation model has been discussed in earlier publications and has been used to characterize the slant range errors of radar and laser altimeters, the simulation model has been validated on recorded flight test data. A method for in-flight measurement validity assessment using the simulation model is introduced and applied on recorded data in this paper. The information content of altimeter measurements below a flight path is analyzed regarding the horizontal correlation result. Criteria for beneficial measurement are derived and applied on a correlation algorithm. For in-flight beam steering, the criteria are extended for a multi-beam measurement application.