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The Jet Propulsion Laboratory has developed a 170 GHz airborne radar for cloud and humidity remote sensing. Called VIPR (Vapor Inside-cloud Profiling Radar), the system uses differential absorption at closely spaced frequencies near the 183 GHz water vapor resonance to obtain range-profiling measurements of absolute humidity inside clouds, and partial-water- column measurements in clear skies. VIPR transmits around 300 mW over 167-174.8 GHz, has a system noise figure of 8 dB, and uses a 60-cm diameter aperture. The radar has been deployed both on the ground pointing toward zenith, and from an aircraft with nadir pointing. Based on architectures originally developed for submillimeter-wave security imaging, VIPR uses ultra-high-isolation transmit/receive duplexing with a single primary antenna. This approach achieves thermal noise limited sensitivity even while using frequency-modulated continuous-wave ranging methods, and even when the radar is mounted in an aircraft with its beam emerging from an open-air viewport. Here we present a validation measurement of VIPR’s ability to sense humidity in clear skies using ground reflection magnitudes at different altitudes and frequencies. These results have also motivated a new investigation of using a higher-frequency 557 GHz differential absorption radar for water vapor sensing in the low pressure, cold, and dry conditions on Mars. We have developed a 552-558 GHz RF source with several mW of output power that could be used for making local humidity measurements on Mars out to several kilometer ranges.

The magnetic susceptibility of chromium hydride increases from 3·5 × 10 −6 c.g.s. for pure Cr metal to 14·0 × 10 −6 c.g.s. at CrH 1·4 . On removal of hydrogen at room temperature the susceptibility remains high and this may be related to the formation of a defective hexagonal phase for CrH . The hexagonal phase can also exist for CrH >1·0 when it is probably metal deficient. The activation energy for the decomposition of chromium hydride is 2·36 ± 0·02 kcal/mole.

IN the past, the physical properties of transition metal hydrides have been studied almost exclusively, because the chemical properties appeared to be very similar to those of the parent metals. No clear picture of the nature of the hydrogen species in these compounds has emerged, as there is evidence from the physical properties to support protonic, covalent and anionic models1. This communication describes the reactions of a number of transition metals and their hydrides with organic acid–base and oxidation–reduction indicators.