Articles | Volume 9, issue 11
Research article
14 Nov 2016
Research article |  | 14 Nov 2016

Simulation of submillimetre atmospheric spectra for characterising potential ground-based remote sensing observations

Emma C. Turner, Stafford Withington, David A. Newnham, Peter Wadhams, Anna E. Jones, and Robin Clancy

Abstract. The submillimetre is an understudied region of the Earth's atmospheric electromagnetic spectrum. Prior technological gaps and relatively high opacity due to the prevalence of rotational water vapour lines at these wavelengths have slowed progress from a ground-based remote sensing perspective; however, emerging superconducting detector technologies in the fields of astronomy offer the potential to address key atmospheric science challenges with new instrumental methods. A site study, with a focus on the polar regions, is performed to assess theoretical feasibility by simulating the downwelling (zenith angle = 0°) clear-sky submillimetre spectrum from 30 mm (10 GHz) to 150 µm (2000 GHz) at six locations under annual mean, summer, winter, daytime, night-time and low-humidity conditions. Vertical profiles of temperature, pressure and 28 atmospheric gases are constructed by combining radiosonde, meteorological reanalysis and atmospheric chemistry model data. The sensitivity of the simulated spectra to the choice of water vapour continuum model and spectroscopic line database is explored. For the atmospheric trace species hypobromous acid (HOBr), hydrogen bromide (HBr), perhydroxyl radical (HO2) and nitrous oxide (N2O) the emission lines producing the largest change in brightness temperature are identified. Signal strengths, centre frequencies, bandwidths, estimated minimum integration times and maximum receiver noise temperatures are determined for all cases. HOBr, HBr and HO2 produce brightness temperature peaks in the mK to µK range, whereas the N2O peaks are in the K range. The optimal submillimetre remote sensing lines for the four species are shown to vary significantly between location and scenario, strengthening the case for future hyperspectral instruments that measure over a broad wavelength range. The techniques presented here provide a framework that can be applied to additional species of interest and taken forward to simulate retrievals and guide the design of future submillimetre instruments.

Short summary
Observations of the submillimetre part of the electromagnetic spectrum have previously been the domain of the astronomical community. However, new technological advances in the superconducting detectors field are offering the atmospheric sciences unexplored opportunities to perform useful spectroscopy in this region, exploiting existing radio telescope sites. Example simulations at six sites are presented for HBr, HOBr, HO2 and N2O showing the need for broad high-resolution measurements.