  Several statistics-based detectors, based on unimodal matrix models, for
determining the number of sources in a field are designed. A new variance ratio
statistic is proposed, and its asymptotic distribution is analyzed. The
variance ratio detector is shown to outperform the alternatives. It is shown
that further improvements are achievable via optimally selected rotations.
Numerical experiments demonstrate the performance gains of our detection
methods over the baseline approach.
