As part of the European Multi-Sensor Airborne Campaign on Snow and Ice 1995
(EMAC-95), the radar signatures of smooth low-salinity level ice in the Gu
lf of Bothnia were measured by means of a ship mounted scatterometer. The s
catterometer was operated at 1.25, 2.6, 5.4 and 10 GHz (L-, S-, C-, and X-b
and) at incidence angles from 20 degrees to 60 degrees. Various in situ sno
w and ice parameters were acquired during the field work. Utilising the ran
ging capabilities of the scatterometer system, the travel times of the rada
r returns are analysed at the different frequencies in order to locate the
dominant scattering contributions as a function of depth in the ice. Model
predictions which are based on the in situ snow and ice properties are comp
ared with the measured backscattering coefficients in order to determine th
e scattering mechanisms of the dominant radar returns. Experimental and mod
el results show that the backscattering responses at X-band are mainly caus
ed by volume inhomogeneities in the upper most part of the ice, and at C- a
nd S-band by the roughness of the snow-ice interface. At L-band, however, d
ominant radar returns can originate also from the interior of the ice, prob
ably from the ice-water interface, which is substantiated at smaller incide
nce angles. Implications of the presented results are discussed.