Cassini RADAR Sequence Planning and Instrument Performance

Abstract

Abstract-The Cassini RADAR is a multimode instrument used to map the surface of Titan, the atmosphere of Saturn, the Saturn ring system, and to explore the properties of the icy satellites. Four different active mode bandwidths and a passive radiometer mode provide a wide range of flexibility in taking measurements. The scatterometer mode is used for real aperture imaging of Titan, high-altitude (around 20 000 km) synthetic aperture imaging of Titan and Iapetus, and long range (up to 700 000 km) detection of disk integrated albedos for satellites in the Saturn system. Two SAR modes are used for high-and medium-resolution (300-1000 m) imaging of Titan's surface during close flybys. A high-bandwidth altimeter mode is used for topographic profiling in selected areas with a range resolution of about 35 m. The passive radiometer mode is used to map emission from Titan, from Saturn's atmosphere, from the rings, and from the icy satellites. Repeated scans with differing polarizations using both active and passive data provide data that can usefully constrain models of surface composition and structure. The radar and radiometer receivers show very good stability, and calibration observations have provided an absolute calibration good to about 1.3 dB. Relative uncertainties within a pass and between passes can be even smaller. Data are currently being processed and delivered to the planetary data system at quarterly intervals one year after being acquired.

Saturn’s thermal emission at 2.2-cm wavelength as imaged by the Cassini RADAR radiometer

“…The Cassini RADAR instrument includes a radiometer that obtains measurements of externally generated (passive) radiation entering the receiver in all operating modes of the instrument, including the various radar modes during which internally-generated (active, or radar) signals are transmitted (Elachi et al, 2004;West et al, 2009;Janssen et al, 2009). The overall characteristics of the radiometer are given in Table 1.…”

Cassini SAR, radiometry, scatterometry and altimetry observations of Titan’s dune fields

“…Individual dunes are thus not resolved in this mode of operation. The normalized backscattering cross-section r 0 is measured with an error bar of $12% (West et al, 2009). During Cassini's nominal and extended missions, dune fields were observed over a wide enough range of incidence angles to support modeling the variations of backscatter with incidence angle.…”

Correlations between VIMS and RADAR data over the surface of Titan: Implications for Titan’s surface properties

“…Microwave radiometry and scatterometry measurements are very sensitive to the roughness and porosity of the upper few to tens of centimeters of the observed surface and to the dielectric permittivity of the surface material (e.g. Ulaby et al, 1981Ulaby et al, , 1982.…”