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Abstract
The Aerological Observatory developed a new spectral sensitivity calibration system for broadband UV radiometers in the Japan Meteorological Agency (JMA) network. The system consists of an NIST lamp unit, a deuterium lamp unit, fore-optics, an iHR spectrometer, and rear-optics. NIST tungsten-halogen 1000W DXW and FEL lamps or a 30W deuterium lamp can be selected as the light source. A GR600 (GR1200) grating for UV produces light at a wavelength of 150 to 3000nm (150 to 1500nm), using minimum drive step size of 0.002nm. The theoretical spectral resolution depends on the kind of grating and slit width, (e.g. the theoretical spectral resolution is 2.5nm wavelength when GR600 was used at 0.5mm in slit width).
Tests using the system clarified the following. 1) Grating tests: UVB (UVA) outputs of a broadband UV radiometer (UV-S-AB-T) using GR1200 decrease 33% (25%) compared to the output using GR600; 2) Slit width tests: UVB (UVA) outputs can be produced by slit widths from 0.5 to 2.0mm (1.0 to 2.0mm); 3) Slit height tests: Outputs were recognized only at a slit height of open (15mm); 4) Lamp irradiance tests: High UVB and UVA irradiances are produced by FEL type NIST lamps; the deuterium lamp cannot be used in the UVA output test; 5) Wavelength position accuracy test: The wavelength position shifted less than 2nm when GR1200 was used. The GR1200 scanning by the spectrometer needs "calibrate menu" must be calibrated every time before tests.
The spectral sensitivity of the UV radiometer was determined by the system as followings. Spectral irradiances of the system could be calculated every 1nm (±0.5nm) from 280 to 400nm wavelength by scanning using the Brewer MKIII Spectrophotometer. The spectral irradiances produced remarkable spectral sensitivity of UV radiometer UV-S-AB-T (peak sensitivity at a wavelength of 301.0nm for UVB scanning and 359.0nm for UVA scanning). UVB responsivity of the instrument calculated by the spectral sensitivity was consistent with the value determined by NIST lamp calibration, but UVA responsivity differed by about 15%.
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