Scale used: the information bar at the bottom of the image (rows 964-1023) contains a scale bar labelled "1 um" (the label reads "1 um"; the instrument bar also shows a magnification text, which I read as approx. x5000 but did not need). The bar is exactly 53 px long (columns 1202-1254), so the scale is 1000 nm / 53 px = 18.9 nm per pixel (field of view about 24 um across the 1280 px width). The TIFF metadata carries only a 72 dpi default and no usable calibration.

Analysis: I analysed the SEM area above the info bar (rows 0-959), high-pass filtered it, and computed the 2D FFT and 1D projections. There is one dominant spectral peak (with its mirror) at a period of about 47-48 px (radial peaks 44.6-51.5 px, strongest 47.3 px); an angle-optimised projection gives 47.4 px.

Result: the dominant period is about 47.4 px x 18.9 nm/px = approx. 895 nm (roughly 0.9 um, range about 850-930 nm).

Orientation: the FFT peak lies along the horizontal frequency axis (wavevector about 3 degrees from the image x-axis), so the periodic ripples/lines run approximately vertically in the image (about 3 degrees off vertical, i.e. perpendicular to the horizontal x-axis), and are repeated along the horizontal direction.

RESULT: period = 895 nm
