Richard P. Ingalls

Venus: Mapping the Surface Reflectivity by Radar Interferometry

The surface reflectivity of Venus obtained by radar interferometry at a wavelength of 3.8 centimeters has been mapped for a region extending approximately from -80� to 0� in longitude (Carpenters definition) and from -50� to +40� in latitude. The map is free from the twofold range-Doppler ambiguity because the interferometer fringe pattern makes possible the separation of two points of equal range and Doppler shift. The map presents many new features and clearly delineates features already observed. Most notably, the map shows large circular regions of significantly lower reflectivity than their surroundinigs.

The Case for the Radar Radius of Venus

The Venus radius of 6085 � 10 kilometers, deduced from combining observations made with the Venera 4 and Mariner V space probes is incompatible with the value of 6050 � kilometers determined from Earth-based radar mesurements.

Venus - Topography revealed by radar data.

Surface height variations over the entire equatorial region on Venus have been estimated from extended series of measurements of interplanetary radar echo delays. Most notable is a mountainous section of about 3-kilometer peak height located at a longitude of 100 degrees (International Astronomical Union coordinate system). The eastern edge has an average inclination of about 0.5 degrees, which is unusually steep for a large-scale slope on Venus. The resolution of the radar measurements along the surface of Venus varied between about 200 and 400 kilometers with a repeatability in altitude determination generally between 200 and 500 meters. The mean equatorial radius was found to be 6050.0�0.5 kilometers.

Radar observations of Icarus

Abstract The minor planet Icarus was observed with the 3.8-cm Haystack radar from 12 to 15 June 1968. Weak but significant echoes were detected indicating a radar cross section of about 0.1 km2, a radius of about 1 km, and an effective reflectivity of about 0.05. These results have an uncertainty of about a factor of 2.

Radar map of Venus at 3.8 cm wavelength

Abstract Radar echoes from Venus have been mapped at a wavelength of 3.8 cm from approximately 270° to 10° in longitude and −50° to +50° in latitude during the inferior conjunctions of 1969 and 1972. Observations made in April 1969 and again in June 1972 both show the same regions of high reflectivity as well as several large regions of low reflectivity.

Upper limit on the radar cross section of the comet Kohoutek

Abstract An attempt to observe radar echoes from the comet Kohoutek was made at a radio frequency of 7840 MHz ( λ ∼- 3.8 cm) on 12 January 1974 using the Haystack Observatory radar in Massachusetts. A search for an echo over a range of band-widths covering 2Hz to 66kHz yielded no positive result. The upper limit on the radar cross section is therefore approximately 10 4 B 1 2 km 2 , where B is the (unknown) bandwidth of the echo in Hertz. For B ⋍ 100 Hz , it follows that (i) the nucleus, if a perfect spherical reflector, must be less than 250 km in diameter, and (ii) the density of any millimeter-sized particles must be less than 1m −3 for a coma of diameter 10 4 km.