A simplification of the JPDAM algorithm

The JPDAM (joint probabilistic data association for possibly merged measurements) algorithm has been developed to track targets in the same neighborhood in a cluttered environment, where the target-originated measurements could be unresolved (merged). The JPDAM algorithm evaluates for each measurement the probability that it originated from a single target, from two targets (i.e., it is a merged measurement), or from clutter. The original work used a relatively complicated expression for the probability density function (pdf) of a merged measurement. In this note, a simple approximation for the pdf of a merged measurement is derived. The results are easy to implement and can be used to significantly simplify the JPDAM algorithm. Some typographical errors from [2] are also corrected.