def asignaltonoise(instack,dimension=0):
    m = mean(instack,dimension)
    sd = stdev(instack,dimension)
    return N.where(sd==0,0,m/sd)
Calculates signal-to-noise.  Dimension can equal None (ravel array
dataset/ETHPy150Open radlab/sparrow/src/main/python/third_party/stats.py/asignaltonoise