1 Planetary Radar Basics 4 th NAIC/NRAO School on Single-Dish Radio Astronomy July 2007, Green Bank, WV Greg Black (Univ. of Virginia)

2 Observables Measure echo strength vs. frequency, time delay, polarization: Surface properties (strength & poln.)  Surface properties (strength & poln.)  –Density –Dielectric constant –Roughness Shape (resolved in f and t) Shape (resolved in f and t) –Topography –Rotation state Astrometry (absolute bulk f and t) Astrometry (absolute bulk f and t) –Radial position and velocity

3 Technique 1: Doppler only (CW) Transmit single frequency Echo is spread in frequency - Doppler-shifted by rotation. (Harmon et al. 1982) Mars

4 Radar Equation Echo power: Noise power: Noise RMS fluctuations: P t = transmit power R = target distance  = target cross section B = target bandwidth cmPowerkWGainK/Jy Arecibo – S Goldstone – X Arecibo – P

5 Technique 2: Delay-Doppler Transmit a series of pulses: (Pulse Repetition Period) Each echo is dispersed in time: Align in range: sample of each range bin every PRP: Fourier transform each range bin:

6 Radar ‘image’ of spherical targets: Much more complicated for non-spherical targets. Technique 2: Delay-Doppler

7 Venus: Delay-Doppler Image ( Campbell et al.)

8 Asteroid Radar Radar Image Shape model  (Ostro et al. 1995)(Hudson et al. 2005)

9 Misc. Rings of Saturn: Comet: (Nicholson et al. 2005) ( et al.19??)

10 Mars: specular + diffuse Single scattering off surface, rocks. Europa: no specular. Multiple subsurface scattering in ice. (Harmon et al. 1982) Radar Spectra