VESPA-22: a ground-based microwave spectrometer for long-term measurements of polar stratospheric water vapor

• Published in: Atmospheric measurement techniques Vol. 11; no. 2; pp. 1099 - 1117
• Main Authors: Mevi, Gabriele, Muscari, Giovanni, Bertagnolio, Pietro Paolo, Fiorucci, Irene, Pace, Giandomenico
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 23.02.2018; Copernicus Publications
• Subjects: Air bases; Altitude; Ambient temperature; Analysis; Blackbody; Body temperature; Calibration; Design and construction; Elevation; Emission; Emission lines; Environmental aspects; Instrument calibration; Integration; Intercomparison; Measurement; Meteorological satellites; Mixing ratio; Opacity; Optical equipment; Polar environments; Profiles; Resolution; Sensitivity; Sky; Spectra; Spectral sensitivity; Spectrometers; Telecommunications equipment; Temperature; Temperature effects; Vapor emission; Vertical profiles; Water; Water vapor; Water vapour; Weather; Weather conditions; Arctic region; Greenland
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-11-1099-2018

The new ground-based 22 GHz spectrometer, VESPA-22 (water Vapor Emission Spectrometer for Polar Atmosphere at 22 GHz) measures the 22.23 GHz water vapor emission line with a bandwidth of 500 MHz and a frequency resolution of 31 kHz. The integration time for a measurement ranges from 6 to 24 h, depending on season and weather conditions. Water vapor spectra are collected using the beam-switching technique. VESPA-22 is designed to operate automatically with little maintenance; it employs an uncooled front-end characterized by a receiver temperature of about 180 K and its quasi-optical system presents a full width at half maximum of 3.5.sup.∘ . Every 30 min VESPA-22 measures also the sky opacity using the tipping curve technique. The instrument calibration is performed automatically by a noise diode; the emission temperature of this element is estimated twice an hour by observing alternatively a black body at ambient temperature and the sky at an elevation of 60.sup.∘ . The retrieved profiles obtained inverting 24 h integration spectra present a sensitivity larger than 0.8 from about 25 to 75 km of altitude during winter and from about 30 to 65 km during summer, a vertical resolution from about 12 to 23 km (depending on altitude), and an overall 1σ uncertainty lower than 7 % up to 60 km altitude and rapidly increasing to 20 % at 75 km.