Two-dimensional contour plot of snow depth ( t
) and snow density ( ρ
) for PRN 18. The plot has contour values of the SE of the QNA output values produced by the 112 input pair combinations of snow depth and density using a QNA. The minimum SE value of 0.760 dB (black square) is produced by an 11.7-cm-thick snow layer with a snow density of 0.09 g∙cm-3 (SWE = 1.05 g cm-2).