Radio echo observations of Venus and Mercury at 23 CM wavelength
Abstract
Radar observations in 1964 of the planets Venus and Mercury conducted at the Millstone Hill radar ob- servatory are presented. The radar equipment employed for this work, together with details of its operation, and the data gathering and reduction procedures are described. Venus was observed from March to October at approximately weekly intervals. The distance to Venus was determined with an accuracy of about +75 km at the beginning and end of this period and +1.5 km throughout June and July. The velocity of Venus with respect to the earth was also measured, the accuracy varying between +10 to +1 cm/sec. These values are tabulated here and are currently being employed to refine some of the elements of the orbits of earth and Venus and the value for the astronomical unit. Echoes from Mercury were obtained on five days around the inferior conjunction occurring on 30 April 1964. The radar cross section appeared to be about 10% of the projected area of the disk. The radar cross section for Venus had an average value of 15%, which is close to most other values at meter and decimeter wavelengths. The scattering properties of Venus were explored using a variety of pulse lengths in order to fully resolve different regions. It is concluded that Venus has a surface that is considerably smoother than the moon's. The average slope of surface elements in the range of about S to 50 m across appears to be 8 . There are, however, regions that are distinctly rough and cause a lowering of the radar cross section when rotated under the subradar point. By contrast, Mercury appears somewhat rougher than the moon. Attempts to obtain echoes from NIars during opposition in 1965 are briefly summarized. A statistically significant echo was obtained after integrating the signals for four nights.
- Publication:
-
The Astronomical Journal
- Pub Date:
- September 1965
- DOI:
- 10.1086/109772
- Bibcode:
- 1965AJ.....70..486E