Asteroid 4197 (1982 TA)

Spectral Frequency Observations

4197 1982TA was first detected by radar on 23 October, 1996, by the 70 meter antenna at Goldstone, California. That day was devoted to cw (Doppler only) observations. A snapshot of an eleven minute integration on the real-time data display is shown at right.

The echoes were approximately 80 Hertz wide and centered several Hertz positive of the expected center frequency. This is not unusual for initial observations of an Earth-crossing asteroid. The integrated, optimally filtered signal-to-noise ratio for the several hours of observations on this date exceeded 160. Preliminary calibrations indicate a radar cross section of greater than 1 square kilometer and a circular polarization ratio (same sense to opposite sense) of 25 percent.

Variations in the locations of the edge frequencies of the echoes allow a preliminary estimate of the convex hull on the asteroid's pole-on silhouette. This fit can be improved with a more thorough search of the fitting parameter space. Important features are the minimum 3 km diameter and the relatively triangular shape which agrees with delay-Doppler images from the following days. Units of the hull in the lower left panel are km / cosine delta, where delta is the asteroid centered declination of the radar.

Continue to delay-Doppler imaging of 4197 1982TA