Refractivity of Carbon Dioxide Under Simulated Martian Conditions

Abstract

The refractivity of carbon dioxide has been measured at 2.26 GHz under simulated Martian conditions and at standard temperature and pressure. In the temperature range of 150° to 190°K, at pressures from 2 to 25 millibars, the refractivity per molecule per cm2 is 1.78 × 10−17 ± 0.06 when scaled by the ideal gas law. The measurements include pressures and temperatures which are within 30°C of the sublimation curve. This result is slightly lower than the best measurements previously obtained near standard temperature and pressure at other frequencies (1.8345 × 10−17 ± 0.0003) and at 2.26 GHz under standard conditions by the authors (1.8413 × 10−17 ± 0.005). It is concluded that the scaled refractivity of CO2 in the range of temperatures and pressures stated above may be a few percent lower than under standard conditions. These results do not significantly alter the conclusions regarding the atmosphere of Mars as measured by the radio occultation method.