Sea surface slicks measured by SAR

The Synthetic Aperture Radar (SAR) systemcapabilit y to detect and characterise marine surface slicks was tested during the SAR-580 experiment in the northern Adriatic Sea, offshore the Venice coast, in October 1990. Two small artificial slicks of oleyl alcohol were produced in an area around the oceanographic platformof the Italian National Research Council (CNR). The oleyl alcohol produces a damping of the sea centimetric waves, which has been measured by an airborne two band (C and X) SAR, by a tower based 3 band (L, S and C) scatterometer and by a wave gauge, installed on board the platform, which measures the instantaneous sea surface elevation in the range fromgra vity up to capillary waves. The good agreement among measures proves that multi-frequency SAR is able to detect and characterise sea surface films. Slicks in SAR images taken during SIR-C/XSAR mission in 1994 have been analysed on the basis of these results and L-band measurements of spatial attenuation near the borders of the slicks have been done, in order to test the slicks detectability using single-band SAR images

(704) Interamnia: a transitional object between a dwarf planet and a typical irregular-shaped minor body

Context. With an estimated diameter in the 320–350 km range, (704) Interamnia is the fifth largest main belt asteroid and one of the few bodies that fills the gap in size between the four largest bodies with D > 400 km (Ceres, Vesta, Pallas and Hygiea) and the numerous smaller bodies with diameter ≤200 km. However, despite its large size, little is known about the shape and spin state of Interamnia and, therefore, about its bulk composition and past collisional evolution. Aims. We aimed to test at what size and mass the shape of a small body departs from a nearly ellipsoidal equilibrium shape (as observed in the case of the four largest asteroids) to an irregular shape as routinely observed in the case of smaller (D ≤ 200 km) bodies. Methods. We observed Interamnia as part of our ESO VLT/SPHERE large program (ID: 199.C-0074) at thirteen different epochs. In addition, several new optical lightcurves were recorded. These data, along with stellar occultation data from the literature, were fed to the All-Data Asteroid Modeling algorithm to reconstruct the 3D-shape model of Interamnia and to determine its spin state. Results. Interamnia’s volume-equivalent diameter of 332 ± 6 km implies a bulk density of ρ = 1.98 ± 0.68 g cm−3, which suggests that Interamnia – like Ceres and Hygiea – contains a high fraction of water ice, consistent with the paucity of apparent craters. Our observations reveal a shape that can be well approximated by an ellipsoid, and that is compatible with a fluid hydrostatic equilibrium at the 2σ level. Conclusions. The rather regular shape of Interamnia implies that the size and mass limit, under which the shapes of minor bodies with a high amount of water ice in the subsurface become irregular, has to be searched among smaller (D ≤ 300 km) less massive (m ≤ 3 × 1019 kg) bodies

"Sea wave spectra by electromagnetic techniques"

Sea wave measurements have been carried out in the Sicilian Channel using a navigational radar for the lower-frequency component and a teflon-coated wire (Goubau line) for the high-frequency component. The results are discussed and the continuity of the complete spectrum is clearly proved