Scale: the info bar (JEOL-style, "SEI 10.0kV x5,000 WD 10.0mm") shows a scale bar labelled "1 um". The bar is 53 px long (columns 1202-1254), so 1 um = 53 px, i.e. about 18.9 nm per pixel (image 1280 x 1024 px, SEM area = rows 0-960).

Method: the SEM area was high-pass filtered and windowed, then analysed by 2D FFT and by zero-padded row-averaged 1D spectra. The dominant spectral peak is at about 27 cycles per 1280 px, along the horizontal (x) direction (kx ~ 27, ky ~ 1). That gives a period of about 47-49 px (mean ~48 px) in the image, consistent across different row blocks.

Period = 48 px x 18.9 nm/px = about 905 nm (roughly 0.9 um; range 890-920 nm).

Orientation: the spatial-frequency vector points along the image x axis (about 3 degrees from horizontal), so the periodic structures (ripples/lines) run vertically, i.e. along the image y axis (about 90 degrees from the x axis, tilted only a few degrees), repeating from left to right.

RESULT: period = 905 nm
