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Although imaging radar is able to penetrate through sand to reveal subsurface geology in some areas, backscatter from the subsurface is influenced by attenuation of the signal by the sand. To study this modification of the backscatter, field measurements were coordinated with acquisition of AIRSAR images over the Mojave Desert, CA. Quad-polarized images at L- and C-bands were acquired along two orthogonal tracks over the Dumont Dunes area. A comparison of the backscatter at L-band to that at C-band for various areas reveals differences in the way that the sand affects the backscatter at the two wavelengths. To understand how radar attenuation by sand varies with radar frequency, a laboratory experiment was conducted to measure radar transmission through a sand target as a function of radar frequency and sand moisture. The frequency range covers X- through P-bands, and the moisture contents of the sand were 0.3, 4.7, and 10.7 percent by volume. Laboratory results quantify the difference in attenuation of the signal at L- and C-bands, allowing comparison AIRSAR data and field measurements in order to further understand how a sand cover modifies the radar signature of a surface.