The Processing of Altimetric Data (PAD) System for Cassini RADAR (original) (raw)
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Altimetry by Cassini Radar: Processing and Simulation
2009
The Cassini mission, that is a joint NASA/ESA/ASI effort, has recently offered the unique possibility of exploring Titan, the largest moon of Saturn, that is the only satellite in the solar system to host an appreciable atmosphere, which unfortunately made the surface below very difficult to be observed from the Earth with optical instruments. In fact, a smoggy haze, mostly composed of aerosols resulting from photochemistry between methane and hydrogen and other hydrocarbons, completely envelops the satellite. The Radar Altimeter of the Cassini Mission to Titan operates in a transition region between pulse and beam-limited condition. Due to the specific observation geometry, low values of mispointing angle have been found to significantly affect altimeter impulse response. This involves a non-conventional formulation of the system response which has been the main goal of this research doctorate. An analytical model of the average return power waveform, valid for near-nadir altimetry...
Advanced processing of altimetry Cassini radar data
2011 MICROWAVES, RADAR AND REMOTE SENSING SYMPOSIUM, 2011
The Cassini RADAR is a Ku band multimode instrument capable of providing topography information of Titan's surface when operating in altimetry mode. During the last six years (January 2005 to 2011) Cassini has performed 71 Titan's fly-bys and several observations have been collected in Altimetry mode. These profiles have shown Titan's surface complexity. Along track profile resolution can be improved by processing data in a coherent approach. This paper describes an advanced processing applied to the raw Altimetric Cassini radar data (LBDR, Long Burst Data Record). The processing is based on the well known Doppler/Delay algorithm. Results show an improvement respect to the existing ABDR (Altimeter Burst Data Record) products in terms of along track resolution and SNR .
Cassini RADAR Sequence Planning and Instrument Performance
IEEE Transactions on Geoscience and Remote Sensing, 2000
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.
Radar: The Cassini Titan Radar Mapper
Space Science Reviews, 2004
The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn's icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn's atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.
The Cassini-Huygens Mission
The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35 • across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5 • across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 µ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn's many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising.
Covariance Analysis of Cassini Titan Flyby using SAR and Altimetry Data
AIAA/AAS Astrodynamics Specialist Conference and Exhibit, 2006
The Cassini spacecraft is equipped with a radar system that provides Synthetic Aperture Radar (SAR) and altimetry data types for scientific purposes. The radar operates in these modes during close flybys of Titan; due to operations constraints, ground-based radiometric navigation data are unavailable. This paper discusses a covariance study of Titan flybys using both SAR and altimetry data as additional navigation observables and show the possibility of improving the trajectory reconstruction during these flybys. Realistic measurement accuracies and trajectory model are considered; the result that there is a possible improvement of planar motion estimation by an order of magnitude.
AIAA Guidance, Navigation, and Control Conference, 2015
This paper discusses the implementation challenges and lessons learned from radar and radio science pointing observations during the Cassini mission at Saturn. Implementation of the precise desired pointing reveals key issues in the ground system, the flight system, and the pointing paradigm itself. To achieve accurate pointing on some observations, specific workarounds had to be implemented and folded into the sequence development process. Underlying Cassini's pointing system is a remarkable construct known as Inertial Vector Propagation.
Impact of aerosols present in Titan's atmosphere on the CASSINI radar experiment
Icarus, 2003
Simulations of Titan's atmospheric transmission and surface reflectivity have been developed in order to estimate how Titan's atmosphere and surface properties could affect performances of the Cassini radar experiment. In this paper we present a selection of models for Titan's haze, vertical rain distribution, and surface composition implemented in our simulations. We collected dielectric constant values for the Cassini radar wavelength (∼ 2.2 cm) for materials of interest for Titan: liquid methane, liquid mixture of methane-ethane, water ice, and light hydrocarbon ices. Due to the lack of permittivity values for Titan's haze particles in the microwave range, we performed dielectric constant (ε r ) measurements around 2.2 cm on tholins synthesized in laboratory. We obtained a real part of ε r in the range of 2-2.5 and a loss tangent between 10 −3 and 5 × 10 −2 . By combining aerosol distribution models (with hypothetical condensation at low altitudes) to surface models, we find the following results: (1) Aerosol-only atmospheres should cause no loss and are essentially transparent for Cassini radar, as expected by former analysis.
Saturn Satellites as Seen by Cassini Mission
Earth Moon and Planets, 2009
In this paper we will summarize some of the most important results of the Cassini mission concerning the satellites of Saturn. The Cassini Mission was launched in October 1997 on a Titan IV-Centaur rocket from Cape Canaveral. Cassini mission was always at risk of cancelation during its development but was saved many times thanks to the great international involvement. The Cassini mission is in fact a NASA-ESA-ASI project. The main effort was made by NASA, which provided the launch facilities, the integration and several instruments; ESA provided the Huygens probe while ASI some of the key elements of the mission such as the high-gain antenna, most of the radio system and important instruments of the Orbiter, such as the Cassini Radar and the visual channel of the VIMS experiment. ASI contributed also to the development of HASI experiment on Huygens probe. The Cassini mission was the first case in which the Italian planetology community was directly involved, developing state of the art hardware for a NASA mission. Given the long duration of the mission, the complexity of the payload onboard the Cassini Orbiter and the amount of data gathered on the satellites of Saturn, it would be impossible to describe all the new discoveries made, therefore we will describe only some selected, paramount examples showing how Cassini’s data confirmed and extended ground-based observations. In particular we will describe the achievements obtained for the satellites Phoebe, Enceladus and Titan. We will also put these examples in the perspective of the overall evolution of the system, stressing out why the selected satellites are representative of the overall evolution of the Saturn system. Cassini is also an example of how powerful could be the coordination between ground-based and space observations. In fact coordinated ground-based observations of Titan were performed at the time of Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the in situ observations by the probe with the general view provided by ground-based measurements. Different telescopes operating at different wavelengths were used, including radio telescopes (up to 17-tracking of the Huygens signal at 2040 MHz), eight large optical observatories studying the atmosphere and surface of Titan, and high-resolution infrared spectroscopy used to observe radiation emitted during the Huygens Probe entry (Witasse et al. J. Geophys. Res. 111:E07S01, 2006).