Cassini Titan

Radar Mapper

(RADAR)

Aaron Russert

11 October 2011

http://photojournal.jpl.nasa.gov/jpeg/PIA01942.jpg 1

Why do RADAR?

• Titan’s atmosphere obscures surface features

• Methane is getting replenished, but from where?

• IR measurements are only sensitive for the top few cm

http://photojournal.jpl.nasa.gov/jpeg/PIA02238.jpg http://photojournal.jpl.nasa.gov/jpeg/PIA01532.jpg

2

RADAR Objectives

• Map Titan’s surface features beneath the clouds

• Look for liquid hydrocarbon concentrations (oceans and/or lakes)

• Create thermal emission maps of Titan, the icy moons, Saturn and the rings

3 C. Elachi, M. D. Allison, et al

RADAR Modes

• Imaging

– Synthetic Aperture Radar (SAR)

– Side looking

– Terrain mapping on Titan

• Altimetry

– Measure terrain beneath S/C

– Lower resolution, longer range

– Only elevation data

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2432

4

RADAR Modes

• Scatterometry

– “Low-resolution altimetry”

– Determines backscatter coefficient, 𝜎0

• Radiometry

– Passive mode

– Thermal noise received correlates to temperature

5 F. Paganelli et al

RADAR System

C. Elachi, M. D. Allison, et al 6

• RF subsystem in “Penthouse”

• Digital subsystem in Bay 11

• System mass: 43.3 kg

• 195 W transmitter

– Capacitor bank reduces peak draw to 30 W

• Total Power: 86 W

RADAR System

C. Elachi, M. D. Allison, et al

• Uses Cassini High Gain Antenna (HGA) dish

• Five separate feeds, five beams

• Ku band (13.78 GHz) for radar

7

RADAR System

• RADAR range based on “time of flight” of signals

• Burst of transmitted pulses then receive period then radiometry period

8 C. Elachi, M. D. Allison, et al

SAR

• Uses Doppler, range and phase information in side looking mode

• Images between 4,000 and 1,000 km

• 350 to 720 m resolution

• Variable bandwidth based on range

9 M. Richards, J. Scheer, and W. Holm

SAR

10

http://saturn.jpl.nasa.gov/multimedia/images/moons/images/IMG004347.jpg

Results

• Titan surface mapping

• Surface winds inferred from formations of dunes

• Distribution of hydrocarbon lakes investigated

11 http://photojournal.jpl.nasa.gov/jpeg/PIA13696.jpg

Results

12

http://photojournal.jpl.nasa.gov/jpeg/PIA11801.jpg

http://photojournal.jpl.nasa.gov/jpeg/PIA12037.jpg

Results

13 http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3760

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2614

References

1. C. Elachi, M. D. Allison, et al, “RADAR: The Cassini Titan Radar Mapper,” Space

Science Reviews, vol. 115 pp 71-110, 2004. 2. B. Stiles, Y. Gim, et al, “Ground Processing of Cassini RADAR Imagery of Titan,” Jet

Propulsion Laboratory, 2006. 3. F. Paganelli, M. Jansen, et al, “Titan's Surface from Cassini RADAR SAR and High

Resolution Radiometry Data of the First Five Flybys ,” Jet Propulsion Laboratory, 2007.

4. S. Wall, “The Cassini Radar Investigation,” Jet Propulsion Laboratory, 2008. 5. C. Elachi, E. Im, et al, “Cassini Titan Radar Mapper,” Proceedings of the IEEE, VOL.

79, NO. 6, 1991. 6. “Cassini Solstice Mission: RADAR Engineering and Technical Write-up”

[http://saturn.jpl.nasa.gov/spacecraft/cassiniorbiterinstruments/instrumentscassiniradar/instcassiniradardetails/] 11 Oct 2011

7. Richards, M. A., Jim Scheer, and William A. Holm. Principles of Modern Radar: Basic Principles. Raleigh, NC: SciTech Pub., 2010. Print.

14