Reverberation from explosive sounds detonated beneath uniform young summer sea-ice were recorded in September 1964 in the Arctic Archipelago. Backscattering strengths were obtained for three octave bands between 1.28 and 10.24 kcps, and for grazing angles between 10° and 70°. The reverberation measured is significantly lower than that measured under well-rotted polar pack ice in September 1963 [J. R. Brown, J. Acoust. Soc. Am. 36, 601–603 (L) (1964)], and a great deal lower than the results obtained by Milne in April [A. R. Milne, J. Acoust. Soc. Am. 36, 1551–1556 (1964)], under pressure-packed one-year ice. A strong dependence of under ice backscattering on surface roughness is thus indicated.