Home > Guidance > Journal of the Aerological Observatory > Vol.66
| Title | Author | |
|---|---|---|
| Foreword | in Japanese | Michio Hirota |
| Frontispiece | in Japanese | Mariko KUMAMOTO, Toyoo ABE and Masashi SATO |
| Time Variation of Cold Air Mass by Aerological Data of Tateno, December in 2005 | in Japanese | Mariko KUMAMOTO, Toyoo ABE and Masashi SATO |
| The Correction and Trend of Surface Ozone Data in Tsukuba | in Japanese | Takeo UENO and Hirotoshi BABA |
| Trends of the Radioactivity Sonde Observation Data and the Consideration of Change Factors | in Japanese | Shogo INOUE, Hiroki SHIOZURU, Hideyuki MIZOBATA, Junken OKUYAMA and Masami IWABUCHI |
| Re-evaluation of N-value from Umkehr Observation | in Japanese | Koji MIYAGAWA |
| Comparison Analysis of Vertical Ozone Profile by Re-evaluated Umkehr Observation and Ozonesonde Observation | in Japanese | Koji MIYAGAWA |
| The Influence of Clouds on Surface UV Radiation | in Japanese | Matsumi TAKANO |
| Diffuse Spectral UVB Observation using Brewer Spectrophotometer and New Automated Shadow Unit | [Abstract] | Mahito ITO |
| Development of External Lamp Test Unit for Broadband UV Radiometer | [Abstract] | Mahito ITO and Matsumi TAKANO |
| Some Tests Results of Skye SKU 430 UV Radiometer | [Abstract] | Mahito ITO |
| Improvement of the Grating Sunphotometer PGS-100 and its Effect | in Japanese | Osamu IJIMA |
| On the Net-Radiometer CNR1 (Part IV) - Tests Results of Ventilating Equipment Developed for CNR1 - | in Japanese | Katsue NAGAI and Hiroshi NAGANUMA |
A diffuse Brewer spectrophotometer for continuous operation through seasons was developed by replacing the previous manual shadowing device (Ito : 2005b) with automated shadow unit controlled by computer. In this paper, the system of the automated shadow unit, the setup procedures, and the results of diffuse spectral UVB measurements carried out for six months from August 2005 to January 2006 are presented. They are summarized as follows: 1) The new diffuse system is comprised of black shade ball, rotating frame, automatic rotating unit, binding frame and control PC (set indoors). The whole system was mounted on Brewer MKII #058. Shading of UV quartz dome is bimodal, i.e. intermittent mode and continuous mode. In the intermittent mode, three sets of shade/open time sequences can be programmed in an hour. 2) Shadow effect of the rotating frame was confirmed to be negligible comparing with global Brewer MKII #052 on a clear sky day. 3) Monthly maximum diffuse UVB irradiance ratio (diffuse UVB / global UVB) of 0.908 was observed in October and the minimum of 0.845 in December during the observation period. Average over six monthly means of diffuse UVB irradiance ratio was 0.871 contrasting to 0.552 for diffuse solar irradiance ratio (diffuse solar / global solar). 4) As for daily diffuse UVB irradiance ratio, the minimum of lower limit envelope appeared as 0.62 around early September, which increased toward winter season and reached 0.78. On the other hand, diffuse solar irradiance ratio had the minimum of 0.18 with no significant seasonal dependence during the period. 5) Monthly spectral diffuse UVB irradiance ratio had clear seasonal change and commonly indicated the negative linear dependence on wavelength. 6) Correlation between diffuse UVB ratio and diffuse solar ratio clarified the significantly different behavior of UVB and solar radiation in the atmosphere.
To monitor and correct the responsivity change of broadband UV radiometer, an external lamp unit, together with the operation method, was developed at the Aerological Observatory in Tsukuba. The accuracy of this unit including the operation methodology was tested periodically in parallel with the comparison with NIST lamp test results from January to December in 2005. The results are summarized as follows: 1) The external lamp unit using 50W halogen lamp was effectively used for global (upward facing) and reflected (downward facing) UV radiometer in the observation field. By changing the mount of lamp house, the unit could be attached to some kinds of UV radiometers (Kipp & Zonen UV-S-AB-T and EKO MS212WF). 2) Optimal warm-up time of the lamp seemed to be about 20 minutes, which was derived through many experimental tests. 3) Irradiance stability of 0.1%(±0.05%) was achieved by controlling the voltage of the power supply within the range from 11.999 to 12.001V. 4) Comparison experiments were carried out over a year to test the usefulness of the unit and the operation method developed. The result showed that the average responsivities of UV radiometer traced in the field by the external lamp unit using three 50W lamps agreed well within 1% with those determined by indoor NIST lamp tests using six 1000W lamps.
It was demonstrated that periodical application of the external lamp test unit and the operation method system developed can serve as a practical measure to assure the reliability and consistency of UV monitoring network with broadband UV radiometers.
A small broadband UV radiometer, SKU 430 was manufactured by Skye Instrument Ltd. in UK. To evaluate the performance of the radiometer, some tests were carried out using NIST lamps, optical filters and the calibration system, as well as outdoor comparison with Brewer MKIII spectrophotometer. The results are summarized as follows: 1) NIST lamp tests by eight lamps showed that the error of calibrated responsivity was less than 4%, bearing in mind that irradiance error of lamp is about 2%. The responsivity changed by +3.5% during three months under solar radiation, and +0.4% in a month in the dark room. 2) NIST lamp tests were repeated by changing the distance between the lamp and the detector surface to find the optimum distance for calibration. The result was that the calibration of the instrument could be properly performed at the distance from 30 to 70 cm with errors of -1.4 to +0.8%. 3) Cosine response deviation from the ideal value of 1/cosZ was under -5% at the zenith angle (Z) from 0 to 35 degrees, under -10% from 35 to 60 degrees, and about -20% at Z = 70 degrees, respectively. The azimuth response test indicated that the best azimuth position (AZ) to minimize the effect of directional response was AZ =180 degrees (south side). 4) Tests using sixteen kinds of optical filters suggested that about 85% of total output was attributed to the wavelength range of UVB from 280 to 315nm. 5) Water pool on the flat detector surface produced the output decrease of 22% at a maximum. 6) Outdoor comparison between SKU 430 calibrated by NIST lamp and Brewer MKIII showed that the irradiance ratio of SKU 430 to Brewer MKIII scattered around 1.8 at noon for clear sky.
Compact and low-priced, the SKU 430 demonstrated good performance comparable to other UV radiometers such as UV-S-AB-T and MS212WF. Water holding tendency of the flat detector surface is recommended to be improved for all-weather meteorological use.