Simon Calcutt

Abstract:

A radiometric experiment was conducted to investigate the thermodynamic behaviour of the H2O and CO2 pressure modulated cells of the Pressure Modulator Infrared Radiometer (PMIRR) which flew on "Mars Observer" in 1992. The wave forms and phases of the transmission, emission, pressure and piston position cycles, together with the mean absorption were, for the first time, all measured during the same experiment. The measured transmission and emission cycles were used to calculate the phase and amplitude of the temperature cycles and were found to be super-adiabatic for both cells, in reasonable agreement with a thermal diffusion model. Anomalies were seen in the H2O modulator driving frequency, as has been observed by other authors, but none were evident in the measured cell wave forms suggesting that the water vapour behaves as an ideal gas in the cell. © 1994.

Abstract:

We describe the design, the development, and the calibration of a radiometer to measure water vapor abundance in the middle atmosphere, using the solar occultation technique from an orbiting platform. The use of gas cells containing water vapor and carbon dioxide leads to a relatively simple, but sensitive, design. This radiometer is shown to be capable of detecting water vapor in the mesosphere, where, because of dissociation by the Sun, the amounts are very small, of the order of 1 part per 10(6) or less. A flight version of the instrument will be launched in 1992 on board the European Retrievable Carrier space platform, and the data will be employed for a better understanding of the Earth's water budget.

Abstract:

The fabrication of the filters for the two longest wave channels of the Pressure Modulator Infra-red Radiometer (PMIRR), launched in September 1992 on Mars Observer, was not possible using conventional multilayer dielectric techniques. Thus the extension of far-infrared/microwave mesh filter designs was investigated using a new dielectric spacing material. Test filters were designed and fabricated and, using their measured transmission spectra, a new model of the behaviour of resonant meshes in both air and dielectrics was developed. The low transmission of these filters in the end made them unsuitable for PMIRR but the model provides a useful design tool for future dielectric spaced filters providing a new, less absorbing dielectric can be found. © 1993.