Scale used: the instrument information bar (image rows ~962-1023) contains a scale bar 53 px long (row 968-973, columns 1202-1254) labelled "1 um" (read by rendering the bar's pixel glyphs), i.e. about 18.9 nm per pixel. The image is 1280 x 1024 px; the structure analysis used the SEM part above the bar (rows 0-954). I could not fully confirm the magnification text, so the scale bar is the reference.

Analysis: 2D FFT (Hann window, zero-padded) of the SEM area shows one dominant spatial-frequency peak (plus harmonics/neighbours) at about 0.0210 cycles/px, i.e. a period of about 47.6 px (47.4-48.2 px from the peak centroid and the column-averaged profile). 47.6 px x 18.9 nm/px = about 900 nm.

Orientation: the wave vector points along the horizontal image axis (about 2 degrees from horizontal), so the periodic structures are stripe/ripple-like lines running essentially vertically in the image (about 2 degrees off vertical), repeating from left to right.

RESULT: period = 900 nm
