Write a short note on:
1) Parabolic sand dunes or barchans ?
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Parabolic sand dunes

U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. ... Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts.

Explanation:

Barchans

Barchans are a crescent-shaped shifting sand dune. Barchans face the wind predominantly from one direction. They are found in sandy deserts.

answer; they use longitude and latitude and   global grid system; good luck