However, some train detection situations can be much more challenging. Cargo trains have a varied assortment of cars, including flatbeds of multiple heights, and cars carrying radar-absorbing targets such as wood or coal. In the case of radar-absorbing targets, a retroreflective mode sensor can be used, as it will detect the loss of the reference signal due to the radar-absorbing target. The reference target can be a concrete or brick wall on the other side of the train, such as in tunnels, or the sensor can be aimed down at the tracks, using the tracks as a reference target. Stand-alone radar targets can also be mounted on posts opposite the sensor. If using a strong reference target, the retroreflective sensor can be mounted lower to the ground since it has a narrower effective beam pattern, allowing it to detect empty flatbed cars.
There are also high-gain, intrinsically narrow-beam FMCW radar antennas that can also be mounted lower to the ground without seeing the tracks, allowing them to reliably detect empty flatbed cars in adjustable-field mode, without requiring a reference target.
Another solution to the variety of train cars — which has already been implemented in several underground and aboveground train lines — is simply to use many radar sensors periodically spaced along the tracks. Then even if one sensor misses an empty flatbed, neighboring sensors will still pick up the presence of the train.
In today’s tough economical climate and due to an increased focus on lowering people’s environmental footprints, more and more people are opting to regularly use various types of mass transportation. The resulting increased demand on existing trains, subways and light rails, as well as the construction of new modes of mass transit, make reliable detection and tracking methods more important than ever before.
Ashley Wise is a development engineer at Banner Engineering.