MTI Reflector

A Moving Target Indicator (MTI) is electronic circuitry that helps eliminate radar targets so that the radar display presents only those targets that are in motion.The MTI is physically located in the approach control facility.
An MTI reflector is a fixed device with the electrical characteristics of a moving target which is located at a known location and used to ensure alignment of radar video maps. The MTI reflector is located at a fixed distance from the radar antenna. Each radar antenna has more than one MTI reflector. This equipment operates in the following manner:

1. MTI causes the radar to display only moving targets to the controller. This has the effect of removing "ground clutter." Ground clutter is caused by radar reflecting off of trees, hills, buildings, and the other objects on the ground. Ground clutter makes it almost impossible to tell which reflections are aircraft and which are not.

2. Radar video maps allow controllers to associate radar targets with mapped points on the ground. However, the radar video maps may migrate over time. This is, for obvious reasons, bad.

3. Radar video maps portray things like airways, fixes, navigational aids, and airports. They also portray marks that correspond with features that can be used to ensure the map is properly aligned with the radar. However, most of these ground-based features are often filtered-out by MTI. Controllers may turn off MTI so they can see the features on the ground. However, there is no way to know for certain that the reflections from the ground are actually those that are meant to correspond to the marks on the map.

4. The MTI reflector uses electronics to fool the MTI into believing that the MTI reflector is a moving target. That MTI-created target shows up on the radar display vividly as though it were an aircraft. It will show, unambiguously, whether the MTI reflector is aligned with the radar video map.

MTI Reflector in the Approach Lights for runway 19R at Milwaukee, Wisconsin (KMKE)

Milwaukee MTI Reflector showing its orientation toward the radar in the upper left corner.