Far-infrared measurements of trace gases

A better detector system was developed for far infrared spectroscopy by usng cryogenic technology to cool bolometric detectors to approximately 0.4K. Technical assistance was provided to two submillimeter infrared balloon experiment (SIBEX) flights which demonstrated the diagnostic capability of far IR emission spectroscopy. It is estimated that more than a hundred spectral emission features were detected which are not due to the main emitting gases O3, O2, and H2O. The trace species sources for many features still remain unidentified and the spectra obtained during the SIBEX flights present a new source of information on stratospheric composition

Tunable far infrared studies of molecular parameters in support of stratospheric measurements

Lab studies were made in support of far infrared spectroscopy of the stratosphere using the Tunable Far InfraRed (TuFIR) method of ultrahigh resolution spectroscopy and, more recently, spectroscopic and retrieval calculations performed in support of satellite-based atmospheric measurement programs: the Global Ozone Monitoring Experiment (GOME), and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)

Measurement of stratospheric HBr using high resolution far infrared spectroscopy

Far infrared spectral features of HBr have been observed in the stratospheric emission spectrum using a balloon borne high resolution Fourier transform spectrometer equipped with a high sensitivity detector specially designed for this purpose. The value of 1.6±0.6 parts per trillion in volume for the HBr mixing ratio has been retrieved, from the global‐fit analysis of 121 spectra, in the 25–36.5 km altitude range. The result is briefly compared with models and previous assessments

Evaluation of composite bolometers at 0.4 kelvin

Composite bolometer structures have provided the most sensitive IR detectors for operation at helium-4 temperatures of 1.5K. Below 1.5K the electrical and thermal properties change significantly and the performance characteristics cannot be accurately extrapolated for composite bolometers at helium-3 temperatures of 0.4K. The paper deals with experimentally assessed performance of composite bolometers at 0.4K. It is found that sensitivity estimates derived from electrical or load curve properties can overestimate the responsivity to radiation by several orders of magnitude depending upon a particular material behavior. For many near-millimeter applications background power levels are several nanowatts and the associated photon noise plus Johnson and phonon noise components impose a fundamental detection limit of about 5 x 10 to the -15thW/Hz to the -1/2. We have successfully fabricated composite bolometers which at 0.4 K and millimeter wavelengths achieve a noise equivalent power of 7 x 10 to the -15thW/Hz to the -1/2 coupled with a large absorbing area (0.3 sq cm) and a fast response time (2 msec.)

The submillimetre and millimetre spectrum of NGC 5128

Our observations define the millimetre and submillimetre spectrum of the central 80 arcsec of NGC 5128 and show that in the submillimetre region the spectrum displays a radical departure from what, at longer wavelengths, appears to be non-thermal synchrotron emission. The observed submillimetre excess is probably the Rayleigh-Jeans tail of thermal emission from warm dust in the dark lane, which may be heated by an extended distribution of young stars and possibly partly by the nuclear source itself

The Queen Mary College/University of Oregon photometer for submillimetre continuum observations

Recent advances in FIR detection and filter technology form the basis of a new multiband submillimetre photometer. The instrument provides a selection of filters to match the atmospheric transmission windows between 300 μm and 1.4mm wavelength, and uses a composite Ge bolometric detector cooled by 3He cryogenics to 0.35 K. It is designed primarily for use at the f/35 focus of the United Kingdom Infrared Telescope (UKIRT) and, in common with user instruments, is mounted on the UKIRT multiport photometer cage. This configuration allows use of the chopping secondary mirror for sky cancellation and of the TV optical system for either on- or off-axis guiding. Further, IR to millimetre wavelength coverage can be achieved in a single night by the use of several common focus photometers. Under good atmospheric conditions, the system achieves a noise-equivalent flux density (NEFD) of about at 1.1 mm, and about 10 Jy Hz− at 400μm.‡ These figures represent the best sensitivities yet reported at these wavelengths

Far-infrared radiometer to map OH in the middle atmosphere

A baseline design is evaluated for a far-infrared radiometer to map global concentration profiles of OH from a satellite platform. The instrument performance is modeled using the spectral database and radiative transfer models developed from recent balloon-based studies of the upper atmosphere. The results indicate that the OH concentration can be measured by limb sounding with 10-percent accuracy in the region of its peak concentration near 40 km, but with useful data for the altitude range between 25 and 120 km. The resolution is 3.5 km in the vertical and 500 km in the horizontal direction. The same technique in principle can be expanded in a multichannel mode to address other related species, e.g. H2O, O3, and HO2, which have accessible rotational emission features in the far-infrared spectral region