Cassini RADAR Instrument for Titan Surface Mapping and Analysis Jeff S. Hall Kansas University December 9 th, 2014

Titan Largest moon of Saturn, 2 nd largest moon in solar system, (~  2576 km) – Bigger than ours, bigger even than Mercury. Only Ganymede bigger. Thought to be biggest until atmosphere realized. Only body with surface liquids other than Earth – Methane cycle similar to water cycle on Earth…methane clouds, precipitation, seas/lakes of methane, ethane, and rivers. Drop size ~2x typical, falls as slowly as snow. Average 94K on surface. Water present as ice, liquid under surface. Ice cryovolcanism. Atmosphere is ~95% nitrogen, ~5% methane primary 2 nd gas. Surface is obscured visibly by orange organonitrogen haze. Pressure 1.45x Earth. Only significant absorber is ammonia with GHz resonance.

Atmosphere

Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981) unable to penetrate haze. Cassini RADAR built primarily for Titan (secondary Enceladus, icy moons, Saturn) – GHz, 86 W TWTA. Powered by plutonium Radioisotope Thermoelectric Generators, stored bursts on capacitor banks. Max 7% duty cycle. – Dual 1.8 G SSDs. Collects data 15 hours, transmits to Earth 9 hours at 7.2 GHz kbps ~1 Gb to Goldstone 34 m (also other DSN), kbps ~4 Gb Goldstone 70 m. Primary mission , Equinox , Solstice Recent discoveries Kraken Mare changes; next run December 10 th (tomorrow.) Radiometry 125 MHz BW. Integrations 0.5, 1s. (  T < 0.1K) Scatterometry MHz BW (high SNR for best performance in case of low RCS zones) Altimetry 4.25 MHz BW (~35 m range resolution) Imaging MHz or 0.85 MHz BW, depending on altitude and SNR requirements Data Rates 1 kbps (radiometer only) 30 kbps (altimeter, scatterometer/radiometry) 365 kbps (SAR, usually limited to ~250 kbps) Doppler…+/-0.6 MHz. Need to shift chirp center frequency.

RADAR Runs

Radiometry km Highest BW, 125 MHz Integration usually 1 s Variance better than 0.1 K Two polarization angles km footprint Noise diode, resistive reference. Calibration Sun, planets, CMB, M17, Cassiopeia-A, Taurus-A, Orion-A… 3 hr warm-up of receiver for stable noise, gain.

Scatterometry km altitude PRF set to 1.2 kHz BW MHz km footprint Scan for multiple incidence angles Set to transmit 8 pulses, receive 14 pulse repetition intervals Additional intervals for echo buffer as beam footprint through high incidence angles exceeds time margin; noise calibration 30 kb/s data rate Compare with Arecibo 2380 MHz scatterometry data. You read that right. Scatterometry data from Earth and not just full disc; rough surface features too. 8 AU or 1.2 billion km range at opposition. >2 hr round trip time. …563 dB two-way loss factor Best that Earth offers. 305 m diameter, ~72 dB antenna gain, 1 MW transmitter, and one heck of a long integration time.

Altimetry km PRF 5 kHz BW 4.25 MHz Range resolution 35 m km footprint 0.14 ms pulse length 15 pulses (almost fills echo data buffer), range spread m 30 kb/s data rate

SAR/InSAR km. LowSAR: BW MHz, 1 MHz sampling) HiSAR: BW 0.85 MHz, 2 MHz sampling 5-26 km footprint. Range limited to 2400 km before too degraded. 250 kbps data rate SARtopo mode using multiple feeds, small interferometric usefulness for overlapping patterns. SARstereo multiple pass overlapping, better SAR interferometry. North Pole

Bright feature on Kraken Mare Plumbing coastal depths of Kraken Mare Ligeia Mare changes

Methane Clouds over Ligeia Mare (Go into Slide Show mode for Animation

Sotra Facula cryovolcano (1000 m peaks)

References West, Anderson, Boehmer, Borgarelli, Callahan, Elachi, Yonggyu Gim, Hamilton, Hensley, Janssen, Johnson, Kelleher, Lorenz, Ostro, Roth, Shaffer, Stiles, Wall, Wye, and Zebker. "Cassini RADAR Sequence Planning and Instrument Performance." IEEE Transactions on Geoscience and Remote Sensing 47.6 (2009): Web. Stofan, E. R., Wall S. D., Stiles B. W., Kirk, R. L., West, R. D., Callahan, P.S., “Cassini RADAR User’s Guide”, Jet Propulsion Labatory Elachi, C., Allison, M. D., Borgarelli, L., Encrenaz, P., Im, E., Janssen, M. A., Johnson, W. T., Kirk R. L., Lorenz, R. D., Lunine, J. I., Muhleman, D. O., Ostro, S. J., Picardi, G., Posa, F., Rapley, C. G., Roth, L. E., Seu, R., Soderblom, L. A., Vetrella, S., Wall, S. D., Wood, C. A., Zebker, H. A., “RADAR: The Cassini Radar Mapper”, University of Boulder Laboratory for Atmospheric and Space Physics, “Cassini Solstice Mission”, Sultan-Salem, Ahmed, Tyler, G. Leonard, “Revisiting Titan’s Earth-based Scattering Data at 13 cm”, Geophysical Research Letters, Vol. 34, L12201, (2007)