The Optical Characteristics of the Fore-Optics and the Calibration for. Direct-Sun UV Observation with Brewer Spectrophotometers

Transcription

1 The Optical Characteristics of the Fore-Optics and the Calibration for Direct-Sun UV Observation with Brewer Spectrophotometers Mahito ITO * Abstract The UV network of JMA has been made the direct sun UV observation by ss.rtn (ss-observation) since 199, but the constants of Brewer Spectrophotometers for the actual measurement could not be calibrated. In this paper, constant calibration method by using the NIST lamp calibration system was developed for the ss-observation and its accuracy was clarified, after the clarification of the optical characteristics of the fore-optics of Brewer MKIII #174 (BR#174). Results were summarized as follows. 1. The optical characteristics of the fore-optics, QW of quartz window, ZE of zenith prism, IR of iris, FW#2 of filter wheel #2 and FW#1 of filter wheel #1, with BR#174: (1) Transmittance of QW was indicated as approx. 88 %. (2) Photon counts were decreased to approx. 3 % by a change of NIST lamp irradiation angle, ZA NIST, of 1. Measurement error at an angle of ZA NIST against to the ZA ZE in this tests could be estimated as within ± %. (3) Irradiance ratio of "Open" to "Close" at IR positions was indicated approx (4) The transmittances of FW#2 at every position from P to P5 were differed 7 % (at P2 position) to 32 % (at P4 position) from the specified values. Their transmittances were not in constant at all wave-lengths. (5) Regarding the transmittances of FW#1, spectral characteristics differ vastly at every position from P to P5. 2. Calibration for the ss-observation: (1) The instrument constant of responsivities for the ss-observation could be calibrated at every filters of FW#2, from the filter positions of P to P4, and at every zenith angles, from to 9 per 1, by the test. (2) The ss-observation results of the direct UV of DH SS Cor with BR#174 using above instrument constant were agreed within ±1 % to the results of the direct UV of DH UX which was calculated from the global UV of GL UX with BR#173 and the diffuse UV of DF UX with BR#174. The ss-observation should be abolished, since the accuracy of the direct UV of DH SS Cor by ss-observation was lower than the accuracy of the direct UV of DH UX calculated by ux-observations of the global UV of GL UX and the diffuse UV of DF UX, and also because the ss-observation requires continuous controls of the zenith prism motor, the micrometer motor and the azimuth trucker motor that causes heavy loads to those motors. However the method of above calibration for ss-observation is useful for the ss-observation data analysis in the past, moreover the DF UX observation using the automated shadow unit is very important for the high precision clarification of the direct UV. 1. Introduction The UV observations with Brewer Spectrophotometer can produce the GL UV of global spectral UV by uv.rtn (uv-observation of double scans at the wavelength from 29. to 325. per.5nm), the GL UX of global spectral UV by ux.rtn (ux-observation of single scan at the wavelengths from to 363. per.5 nm) and the DR SS of direct sun spectral UV by ss.rtn (ss-observation). In the later ss-observation, Brewer MKII of single type scans at the wavelengths from 29. to 325. per.5nm and Brewer MKIII of double type scans at the wavelengths from 29. to 363. per.5 nm as single scan. Although the ss-observations had been continued in JMA UV network since 199, the instrument constant of Brewer for the observation still could not be calibrated in globally. In this paper, calibration method for the instrument constant by using JMA NIST lamp calibration system (Ito: 22) was developed after the clarification * Ozone and Radiation Division, Aerological Observatory, JMA. of the fore-optics with Brewer MKIII#174 (BR#174). On the other hand, three type observations of the GL UV/UX, the DF UV/UX and the RF UV have been continued at ever half an hour, and 3 minutes, at Aerological observatory, Tsukuba (Ito: 24, 25a, b, 26, 27). The DH UV at Tsukuba can be calculated as "GL UV/UX-DF UV/UX ", as follows. (1) GL UV/UX : global spectral UV by uv.rtn and ux.rtn. (2) DF UV/UX : diffuse spectral UV by uv.rtn and ux.rtn. (3) RF UV : reflected spectral UV by uv.rtn. (4) DH UV/UX : direct (horizontal) spectral UV by "(1)-(2)". UVirradiances from (1) to (4) are shown as the horizontal element. The observation of the DRss at Tsukuba also has been carried out at 8 minute per every hour (Ito et al.: 1991, JMA: 1993, Ito et al.: 22), as follow. (5) DH SS : direct (horizontal) spectral UV by ss.rtn. UV irradiance of (5) as the horizontal element is transformed from DRss as the direct element. DHss = DRss * cos ZA. (DRss : direct spectral UV by ss.rtn. ZA: zenith angle.)

2 高層気象台彙報第 69 号 211 JMA NIST lamp calibration system 回折格子 String (Vertical axis) NIST lamp (1 W DXW type) Zenith prism 1 Adjustment of calibration system Rotating axis of ZE Imitation lamp Measure 5. cm Lazar beam 3 Adjustment of rotating axis of zenith prism Lazar beam Fig. 1 Top view of Brewer Spectrophotometer. The figure was modified one of Kipp&Zonen (26). Table 1 Positions of fore-optics for ss-observation by ss.rtn. 2 Adjustment of lazar beam Adjustmentscrews for lazar beam Fig. 2 Optical adjustment methods for the test using JMA NIST lamp calibration system. Quartz Window Zenith Prism Iris Filter Wheel #2 Filter Wheel #1 QW ZE IR FW#2 FW#1 f: Neutral Density Factor Filter P : f =. (----) P : film polarizer (horizontal) UV Direct sun: NIST lamp use Open P1 : f =.5 (1/3.16) P1 : quartz diffuser (transiucent) or ZA = to 9 or P2 : f = 1. (1/1) P2 : blocked aperture (opaque) no use (UV: -9 ) Close P3 : f = (1/31.6) P3 : clear aperture (transparent) P4 : f = 2. (1/1) P4 : quartz diffuser; ND of f=2. (transiucent) P5 : f = 2.5 (1/316) P5 : film polarizer (vertical) UVdome Diffuser Quartzwindow ZA= QW (Ex.) step ZA=3 (Ex.) step Positions by ss.rtn ZA=6 (Ex.) step The accuracy of the instrument constant for ss-observation can be estimated by the comparisons between the data of DH UV and the data of DH SS. MKIII BR#174 and MKII BR#34 were used for generating the instrument constant. This paper shows the example of BR#174. Please refer McElroy et al. (28), Kipp&Zonen (1996, 28a, b), and etc for all of the technical terms, used in this paper. 2. The optical characteristics of the fore-optics 2. 1 Test methods In the ss-observation, measurements has been done by allowing direct sun pass through QW (quartz window), ZE (zenith prism), IR (iris), FW#2 (filter wheel #2), and FW#1 (filter wheel #1) of the fore-optics, and by bringing each of above optical systems in operation automatically. The top of view of optical system and the positions of fore-optics for ss-observation are shown in Fig.1 and Table 1. The ss-observation uses the positions of QW, ZE, IR, FW#2 and FW#1 shown as dark color in Table 1. The optical characteristics of all positions included ss-observation positions are tested as follows. Control software for the calibration (Renovation of control software) Software of ss.rtn for ss-observation controls (1) ZE positions according to the zenith angle of the observation time, (2) FW#2 positions ZA=88.47 (Ex.) 277. step ZA=-9 (Ex.) 289. step レーザー照射 UV prism MKII Zenith prism ZE MKIII 36 = 2816 step 2972 step 1 = step step Adjustment using lazar beam ZA=18 (Ex.) -23. step sllamp hg lamp ZA=177.6 (Ex.) step ZA=9 (Ex.) 681. step Fig. 3 Adjustments of ZA ZE of the zenith prism and ZA NIST of the NIST lamp. according to the degree of solar irradiance intensity, and (3) AZ (azimuth trucker) positions according to the azimuth of the observation time, in automatically. Their positions of (1) and (3) are controlled as the second tick away. Therefore, the tests in this paper cannot use the software of ss.rtn. The new software of "ut.rtn" which can control to select the test positions of the ZE and the FW#2 was produced as a modified uv/ux.rtn. In the following data analysis, the data were corrected by the dark counts correction, the instrument responsivity correction and etc. (Ito et al.: 1991). Irradiation angle of NIST lamp, ZA NIST The irradiation angles of NIST lamp to the ZE, ZA NIST, can be

3 ブリューワー分光光度計前置光学系の光学特性と直射波長別紫外域日射観測のための常数校正 2 15 UVAB TUV no cover, close, f=, dffuser Photon Counts/s ZA=3 Cover use, Close P () P1 (256) ZA=3 No Cover, Close P () P1 (256) coveruse, close, f=, diffuser no cover, close, f=, dffuser coveruse, close, f=, diffuser Fig. 4 Transmittance of quartz window, ''QW'' of BR#174. Upper and lower figures show the photon counts and the photon counts ratio, respectively. ''Cover" means the quart window. <Positions> ZA ZE: 3, IR: Close, FW#2: P, FW#1: P1 controlled by the rotating frame of the NIST lamp calibration system with an angle meter. The center position of the rotating frame can be adjusted at the center position of the rotating ZE using a laser beam shown in Fig.2. The angle error of ZA NIST estimated under.1 (±.5 ) by the accuracy of the angle meter. (c) Observation angle of ZE, ZA ZE was The tests need to adjust the angle between "the irradiation angle of NIS lamp, ZA NIST " and "the observation angle of ZE, ZA ZE " in high accuracy. The ZE motor step numbers are set up to 2,972 steps per 36 with MKIII Brewer and 2,816 steps per 36 with MKII Brewer in Fig.3. The step numbers per 1 are as follows. The angle error of ZA ZE was estimated under.1, because the ZE motor is controlled by the unit of 1/1 step. ZE motor step number to the zenith angle of 1. MKIII: 1 => step MKII : 1 => step Adjustments of ZA NIST and ZA ZE were done after the methods, (1) a leveling of Brewer, (2) a confirmation of light axis through the ZE using leveling laser, (3) an adjustment of the NIST lamp calibration system, (4) a horizontal moving of Brewer and (5) a final leveling of Brewer. The following tests of the sections of 2.2 to 2.6 were done at a locked ZE angle of ZA=3, using ut.rtn at the wavelengths from to 363. per.5 nm with MKIII Brewer and from 29. to 325. per.5 nm with MKII Brewer. The 1.5 UVB UVAB TUV UVB Zenith Angle UVB TUV UVAB Zenith Angle Fig. 5 Measurement error by the incident error of NIST lamp beam at ZA NIST of 3. The incidence angles are from 25 to 35 per 1. Upper and lower figures show the photon counts and the photon counts ratio to the ones at ZA NIST of 3, respectively. UVB, TUV and UVAB mean the total irradiance at wavelength, 29 to 315, 29 to 325 and 39 to 36 nm, respectively. <Positions> ZA ZE: 3, IR: Close, FW#2: P, FW#1: P1 data were calculated as the average of three scans and corrected by the trend of irradiance change of the NIST lamp Transmittance test of quartz window, QW The UV transmittance of Quartz window, QW, was clarified as Fig.4 using the NIST lamp calibration system. In case QW was not fitted ("IR no QW "), UV irradiance increases in approx. 13 % compare to the irradiance of "IR QW " (with fitting QW), at almost all wavelengths from to 363. nm. Therefore, the transmittance of QW was calculated as approx. 88 % as follows. Transmittance of QW Ir no QW / Ir QW = 33 Ir QW / Ir no QW =.883 (1) 2. 3 Measurement error of zenith prism, ZE The measurement error at zenith angle of the zenith prism, ZE, was tested by changing of NIST lamp irradiation angle, "ZA NIST ", at a fixed zenith angle, "ZA ZE " of 3. The results were shown as Fig.5. The photon counts were decreased to approx. 3 % by the change of ZA NIST of 1. Therefore, the measurement error at an angle of ZA NIST against to the ZA ZE in the tests could be considered within ±%, because the angle error of ZA NIST was estimated under.1 (±.5 ) in former section of

4 高層気象台彙報第 69 号 open, f=, diffuser close, f=, diffuser 4 2 close, f=, diffuser close, f=.5, diffuser close, f=1, diffuser close, f=, diffuser close, f=2, diffuser close, f=2.5, diffuser open, f=, diffuser ZA=3 Close P () P1 (256) ZA=3 Open P () P1 (256) close, f=, diffuser Fig. 6 Differences of photon counts at the IR (iris) positions, open/close, of BR#174. Upper and lower figures show the photon counts and the photon counts ratio, respectively. <Positions> ZA ZE: 3, IR: Open/Close, FW#2: P, FW#1: P1 Ratio of tested transmittances to respective specified values close, f=.5, diffuser close, f=, diffuser close, f=1, diffuser P 1/1 P1 1/3.16 P2 1/1 P3 1/31.6 P4 1/1 P5 1/316 close, f=, diffuser close, f=2.5, diffuser close, f=2, diffuser P () P1 (64) P2 (128) P3 (192) P4 (256) P5 (32) f=. f=.5 f=1. f= f=2. f=2.5 Specific Tested / Incident errors of NIST lamp irradiation angle = 3 % / 1 Measurement errors <± % (2) 2. 4 Irradiance tests of iris, IR The irradiances, "Ir CLOSE " and "Ir OPEN ", through the iris, IR, are different from the close position to the open position. The difference of irradiance was tested and clarified as Fig.6. The irradiance ratio of "Ir OPEN " to "Ir CLOSE " could be calculated approx , at all wavelengths from to 363. nm. IR photon counts ratio at the positions of "Open" to "Close" Ir OPEN / Ir CLOSE = (3) 2. 5 Transmittance of filter wheel #2, FW#2 The filter wheel #2, FW#2, has six attenuating filters, with the specified transmittances of 1/1, 1/3.16, 1/1, 1/31.6, 1/1, 1/316, at the positions of to 6. They were tested to confirm their transmittances. The results were shown in Fig.7. Their transmittances indicated the maximum difference of 1 % against to the specified values, and differed at every wavelength too. Therefore, all the filters need to be calibrated in the after mentioned ss-observation. The transmittance ratios of FW#2 to the specified values Results / Specified values =.68 at P4 to 93 at P3 (4) Fig. 7 Transmittances of filter wheel, FW#2, of BR#174 at every position from P to P5. Upper figure shows the photon counts. Middle figure and lower table show the ratio of tested transmittances to specified values, respectively. <Positions> ZA ZE: 3, IR: Close, FW#2: P to P5, FW#1: P Irradiance characteristics of filter wheel #1, FW#1 The filter wheel #1, FW#1, has six variant filters, film polarizer (horizontal), quartz diffuser (translucent), blocked aperture (opaque), clear aperture (transparent), quartz diffuser (ND of f=2. (translucent)), film polarizer (vertical), at the positions of to 6. They were tested to clarify their irradiance characteristics. The results were shown in Fig.8. The photon counts through their filters were different at every wavelength. 3. Calibration for ss-observation (ss.rtn) 3. 1 Test methods The direct sun in ss-observation comes through (1) quartz window of QW, (2) zenith prism of ZE, (3) iris of IR, (4) filter wheel #2 of FW#2 and (5) filter wheel #1 of FW#1 in order, and conducted into the spectrometer, as described in Table 1. The positions of QW, IR and FW#1 are always fixed, but other positions of ZE and FW#2 are dependent on the zenith angle and the intensity of the direct sun irradiance at the observation time. The specified value of FW#2 could not be used by the test results in section 2.5, and the test of ZE in section 2.3 was carried out only at

5 ブリューワー分光光度計前置光学系の光学特性と直射波長別紫外域日射観測のための常数校正 close, f=, clear close, f=, polarizer(h) close, f=, diffuser close, f=, diffuser close, f=, plolariser(v) close, f=, polariser(h) close, f=, diffuser close, f=, clear close, f=, plolariser(v) close, f=, diffuser ZA=3 Close P () P1 (256) ZA=3 Close P () P (32) ZA=3 Close P () P3 (128) ZA=3 Close P () P4 (64) ZA=3 Close P () P5 () Fig. 8 Differences of filter wheel, FW#1, of BR#174 at every position from P to P5. Upper and lower figures show the photon counts and the photon counts ratios to the tested value at the position of P1, respectively. <Positions> ZA ZE: 3, IR: Close, FW#2: P, FW#1: P to P5 a zenith angle ZA=3. Therefore, individual test and calibration of (4) FW#2 and every zenith angles of (2) ZE is necessary, in order to calibrate the constant for ss-observation. Under this circumstance, all 6 pieces of attenuation filters were individually tested at each zenith angle from -1 to 1 per 1, by using ut.rtn. Same as the test in the section 2, data were calculated as average of three scans and corrected by the trend of irradiance change of NIST lamp Test results The test results are described in Fig.9. Upper figures show the photon counts, middle figures done the photon counts ratios to the result at ZA=, and lower figures done the photon counts, at every wavelengths from 29. to 363. per.5 nm, respectively. Their figures showed the results at the positions of FW#2, P (f=1/1), P1 (f=1/3.16), P2 (f=1/1), P3 (f=1/31.6), P4 (f=1/1), P5 (f=1/316), (f: specified neutral density factor), from left side. The photon counts were different at every zenith angles and every attenuation filters. The degrees of irradiance intensity indicated the order at every zenith angles, e.g. ZA at position of P: 8 > 7 > 6 > 5 > -1 > 4 > > 3 > 1 > 2 > 9, due to the polarization properties of every spectrometers and the difference of transmittance of the quartz window at every zenith angles. The maximum irradiance ratio to the irradiance at ZA of indicated approx. at ZA of 8, and the minimum one indicated approx..8 at ZA of 2. The photon counts at ZA of 9 showed very low intensity, because most of the direct sun to the zenith prism was cut by the flame of quartz window. Therefore, the photon counts at ZA of 9 was estimated a larger intensity than the photon counts at ZA of Spectral responsivities for ss-observation Spectral responsivities as the instrument constant for ssobservation were calculated at every attenuating filters and at every zenith angles, ZAs, per 1. The responsivity ratios at every ZAs per 1 against to the responsivity at ZA of were calculated by the interpolation of the ratios at every ZAs of 1 in section 3.2. On the other hand, the spectral responsivities using absolute irradiances must be produced by the NIST lamp calibration method at the distance of 5 cm, from the observation surface to the NIST lamp filament. The observation surface in ss-observation is estimated as the prism surface of ZE or the quartz window surface. However, the distance from their surfaces to the NIST lamp filament cannot be measured in high accuracy. In this test, the spectral responsivities were calibrated by the methods at two distances from the rotation axis of ZE to the NIST lamp filament, : the distance of 5 cm and the distance of 62 cm (by the parallel shifting from the normal position upper UV dome) in Fig.1, at every attenuating filters and at ZA of. Based on the relation of to, all spectral responsivities at the distance of could be calibrated at every ZAs from to 9 per 1. The spectral responsivities could be calibrated at every attenuating filters, and at every ZAs from to 9 per 1 by the above mentioned methods by using S-179 NIST lamp. Their results are shown in Fig.11. The responsivity at attenuating filter of P5 was not necessary in the ss-observation. The errors (amplitude) of spectral responsivities increased at darker attenuating filters (P P4), because of the smaller photon counts Observation results using the spectral responsivities Direct spectral UV of "DH SS " by ss.rtn is produced by the conversion from the direct element to the horizontal element of the observation results using the responsivities in section 3.3. On the other hand, the direct spectral UV of "DH UX " is calculated by "GL UX " and "DF UX " as "DH UX =GL UX-DF UX ". Accuracy of responsivities is estimated by the comparison between DH SS and DH UX. Their instruments and the observation time are shown as follows. ss-observation (DH SS transformed from DRss) BR#174: every 8 min ± 4 min ux-observation (DH UX =GL UX-DF UX ) GL UX BR#173: every 3 min ± 4 min BR#174: every 3 min ± 4 min DF UX

6 高層気象台彙報 第 69 号 211 FW#2: P (c) FW#2: P2 FW#2: P1 3 1 (d) FW#2: P3 3 (e) FW#2: P4 (f) FW#2: P Zenith Angle Zenith Angle Wave length (nm) Fig. 9 Photon counts and photon count ratios of BR#174 at the six positions, P to P5, of FW#2, and at the zenith angles, 1 to 1 per 1. Upper figures show the photon counts, middle figures done the photon counts ratios to the result at ZA=, and lower figures done the photon counts, at every wavelengths from 29. to 363. nm per.5 nm, respectively. <Positions> ZAZE: 1 to 1, IR: Close, FW#2: P to P5, FW#1: P2 FW#2: P Responsivity μ(w/cm2/nm)/counts (c) FW#2: P2 FW#2: P1 25 (d) FW#2: P (e) FW#2: P Fig. 11 Responsivities of BR#174 for ss-observation at the five positions, P to P4, of FW#2, and the zenith angles, to 9 per 1. <Positions> ZAZE: to 9, IR: Close, FW#2: P to P4, FW#1: P2 3 Irradiance (uw/m2) 5 Irradiance (uw/m2) L.S.T. (hour) L.S.T. (hour) L.S.T. (hour) UVB (DH ss) TUV (DH ss) UVAB (DH ss) UVB (DH ss Cor) TUV (DH ss Cor) UVAB (DH ss Cor) UVB (DH ux) TUV (DH ux) UVAB (DH ux) (d) DH obs Cor/DH calc in 256 JD 2. ZA=5 ZA=7 ZA=4 ZA=4 ZA=5 ZA=7 Irradiance Ratio Irradiance (uw/m2) (c) UVAB in 256 JD TUV in 256 JD UVB in 256 JD L.S.T. (hour) UVB (DH ss Cor/DH ux) TUV (DH ss Cor/DH ux) UVAB (DH ss Cor/DH ux) Fig. 12 Example of daily variation of direct UV, the DHSS by ss-measurement, the DHSS Cor after correction, and the DHUX by GLUX and DFUX observations. Upper figures, to (c), show the integrated UVB (29. to 315. nm), TUV (29. to 325. nm) and UVAB (29. to 363. nm), respectively. Gray, violet and red color lines indicate the DHSS, the corrected DHSS Cor by K= 2.35, and DHUX, respectively. Lower figure, (d), shows the irradiance ratios of DHSS Cor / DHUX, as UVB of orange line, TUV of light blue line and UVAB of dark blue line.

7 ブリューワー分光光度計前置光学系の光学特性と直射波長別紫外域日射観測のための常数校正 NIST Lamp NIST Lamp Table 2 Examples of daily total irradiance ratio, DH SS Cor / DH UX. DH SS Cor by ss-observation with BR#174, and DH UX by ux- observations of GL UX (global UV) and DF UX (diffuse UV) with BR#173 and BR#174, respectively. (c) 5 cm UV Dome Teflon Diffuser 62 cm 5 cm Quartz Window ZA= ZA=3 JD M/D/Y UVB TUV UVAB 253 Sep. 9, Aug. 6, Sep. 12, UVB: 29 to 315 nm. TUV: 29 to 325 nm. UVAB: 29 to 363 nm. of NIST lamp calibration, especially the distance, is important. UV Prisn Zenith Prism Fig. 1 Distance for the NIST lamp calibration. shows the distance of 5 cm between NIST lamp filament and zenith prism (rotating axis) at the test, shows the distance of 62 cm between NIST lamp filament and zenith prism (rotating axis) for the calibration, and (c) shows the distance of 5 cm between NIST lamp filament and Teflon diffuser for the UV normal calibration. The example of the comparative results in 256 JD, 29, after the correction by the difference of observation time was shown in Fig.12. Upper figures shows the integrated UVB (29. to 315. nm), the integrated TUV (29. to 325. nm) and (c) the integrated UVAB (29. to 363. nm), respectively. Gray, violet and red color lines indicate the DH SS, the corrected DH SS Cor by the correction factor of K= 2.35, and DH UX, respectively. The correction factor of "K" was defined as a representative daily total ZA=6 ZA=9 irradiance ratio of DH SS / DH UX of about 2.35 as follows. DH SS / DH UX = 2.35 <2.35: Correction factor K> DH SS Cor = DH SS * 2.35 (5) Lower figure (d) in Fig.12 shows the daily irradiance ratios of DH SS Cor /DH UX, using above expression (5). Orange line, light blue line and dark blue line indicate the ratios of UVB, TUV and UVAB, respectively. The irradiance ratios shows a pattern of "UVAB > TUV > UVB". The three examples of daily total irradiance ratio of "DH SS Cor / DH UX " of UVB, TUV and UVAB are shown in Table 2. The results produced the error of ±1 % between "DH SS Cor " by ss-observation and "DH UX " by the global and diffuse observations, as the following expression (6). Daily total irradiance ratio DH SS Cor / DH UX =.954 to 28 (±1 %) (6) The correction factor "K" mentioned arose from the method of the NIST lamp calibration. However, the degree of the correction factor could not be clarified by the difference of the NIST lamp calibration distances in this paper. In the future, the reconsideration of the method 4. Conclusion In this paper, after the optical characteristics of the fore-optics with Brewer MKIII #174 (BR#174) were clarified, the calibration method of instrument constant for the direct sun UV observation by ss.rtn (ss-observation) using the NIST lamp calibration system was developed, and the accuracy of the calibration was verified as follows. (1) The optical characteristics of the fore-optics, QW of quartz window, ZE of zenith prism, IR of iris, FW#2 of filter wheel #2 and FW#1 of filter wheel #1, with BR#174 The transmittance of QW was indicated as approx. 88 %. The photon counts were decreased to approx. 3 % by a change of NIST lamp irradiation angle, ZA NIST, of 1. The measurement error at an angle of ZA NIST against to the ZA ZE in the tests was estimated as within ± %. The irradiance ratio of "Open" to "Close" at IR positions was indicated as approx The transmittances of FW#2 at every positions from P to P5 were differed from 7 % (at P2 position) to 32 % (at P4 position) against the specified values. Their transmittances were not in constant at all wave-length. The transmittances of FW#1 showed variety of different spectral characteristics at every positions from P to P5 (2) Calibration for the ss-observation The instrument constant for the ss-observation could be calibrated at every filters of FW#2, from the filter positions of P to P4, and at every zenith angles, from to 9 per 1, by the test. The ss-observation results of the direct UV of DH SS Cor with BR#174 using above instrument constant were agreed within ±1 % to the results of the direct UV of DH UX which calculated from the global UV of GL UX with BR#173 and the diffuse UV of DF UX with BR#174. The ss-observation should be abolished, since the accuracy of the direct UV of DH SS Cor by ss-observation was lower than the accuracy of the direct UV of DH UX calculated by ux-observations of the global UV of GL UX and the diffuse UV of DF UX, and also because ss-observation requires continuous operation of the zenith prism motor, the micrometer motor and the azimuth trucker motor

8 高層気象台彙報第 69 号 211 that causes heavy loads to those motors. However the method of above calibration for ss-observation is useful for the ss-observation data analysis in the past ss-observation data analysis, moreover the DF UX observation using the automated shadow unit is very important for the high precision clarification of the direct UV. Acknowledgment We would like to thank the staff of Experimental Studies Division of MSC (Meteorological Service of Canada) and Aerological Observatory of JMA (Japan Meteorological Agency). References Ito, M., T. Sato, T. Shimokihara, O. Taira, and K. Miyagawa (22): Introduction of new Brewer spectrophotometers MKIII for the UV-B observation network, JMA. Jour. of Aerological Observatory, 62, Ito, M. (22): Development of new NIST lamp calibration system and the directional (cosine / azimuth) responses of Brewer spectrophotometer. Jour. of Aerological Observatory, 62, Ito, M. (24): Reflected spectral UVB observation on the ground surface using modified Brewer spectrophotometer. Jour. of Aerological Observatory, 64, Ito, M. (25a): Diffuse spectral UVB routine observation using Brewer spectrophotometer and simple shadow unit. Jour. of Aerological Observatory, 65, Ito, M. (25b): Reflected spectral UVB routine observation on the ground surface using modified Brewer spectrophotometer at Tsukuba in 24. Jour. of Aerological Observatory, 65, Ito, M. (26): Diffuse spectral UVB observation using Brewer spectrophotometer and new automated shadow unit. Jour. of Aerological Observatory, 66, Ito, M. (27): Reflected and diffuse spectral UV observation using Brewer spectrophotometer. Jour. of Aerological Observatory, 67, Ito, T., T. Ueno, R. Kajihara, M. Shitamichi, T. Uekubo, M. Ito and M. Kobayashi (1991): Development of monitoring technique of ultraviolet irradiance on the ground - an assesment of UV-B increase due to ozone depletion based on spectral observations -. Jour. of Meteorological Reseaerch, 43, JMA (1993):The manual for ultraviolet observation. JMA, 83pp. Kipp & Zonen (1996): Brewer MKIII Spectrophotometer Final Test Record, BR#174. Kipp & Zonen Inc., 75pp. Kipp & Zonen (28a): Brewer MKIII Spectrophotometer Operators Manual. Kipp & Zonen Inc., 132pp. Kipp & Zonen (28b): Brewer MKIII Spectrophotometer Service Manual. Kipp & Zonen Inc., 125pp. McElroy, C.T., V. Savastiouk and T. Grajnar (28): Standard operating procedures manual for the Brewer Spectrophotometer, Ver. D.1. Environment Canada, 138pp. ブリューワー分光光度計前置光学系の光学特性と直射波長別紫外域日射観測のための常数校正 要旨 伊藤真人 * 気象庁におけるブリューワー分光光度計 (Brewer Spectrophotometer) を使用した紫外域日射観測網では, 全天波長別紫外域日射観測 (uv- 観測, ux- 観測 ) のほかに直射波長別紫外域日射観測 (ss- 観測 ) を 199 年より実施している. しかし, 従来その ss- 観測用の測器常数を校正することが できなかった. 本稿では,NIST ランプ検定装置と Brewer MKIII #174 (BR#174) を用い,Brewer の前置光学系の光学特性を明らかにし,ss- 観 測のための常数校正方法の開発を試みた. 結果は以下のとおりである. 1. BR#174 の前置光学系 (QW: 傾斜窓,ZE: 選択プリズム,IR: 絞り装置,FW#2: フィルター #2,FW#1: フィルター #1) の光学特性 (1) 傾斜窓 QW の透過率は約 88% となった.(2) 選択プリズム ZE では,NIST ランプの照射角度 1 の変化で約 3% の照度差が認められた. そのため当試験における ZE の設定角度と NIST ランプ照射角度とのちがいによる照度誤差は ±% 以内と推定できる.(3) 絞り装置 IR の Open 位置での照度は,Close 位置での照度の約 2.56 倍となる.(4) FW#2 の透過率は,P~P5(P:,P1: 1/3.16,P2: 1/1,P3: 1/31.6,P4: 1/1, P5: 1/316) の各位置において, 規定値に対し最小 7%(P2 位置 )~ 最大 32%(P4 位置 ) 異なる. またこれらの透過率は, 波長特性を有して異なる. (5) FW#1 の透過率は,P~P5(P: 水平方向偏光板,P1: すり水晶板,P2: 暗板,P3: 素通し板,P4: 減衰すり水晶板,P5: 垂直方向偏向板 ) の 各位置において個々に分光特性が大きく異なる. 2. ss- 観測のための常数校正 (1) 当試験により,ss- 観測のための測器常数は,FW#2 の P~P4 位置のフィルター毎に太陽天頂角 ~9 の 1 毎に校正することができた. (2) 上記測器常数を使用した BR#174 の ss- 観測による直射紫外域日射量 (DH SS Cor: 水平面成分 ) は, 全天紫外域日射量 (GL UX ) から散乱紫外域日 射量 (DF UX ) を除去した直射紫外域日射量 (DH UX: 水平面成分 ) に対し,±1% 程度の誤差となった. 以上により,ss- 観測による直射紫外域日射量 (DH SS Cor ) の観測精度は, 全天紫外域日射量 (GL UX ) と散乱紫外域日射量 (DF UX ) の 2 つの ux- 観測 から得られる直射紫外域日射量 (DH UX ) より精度が悪いことが明らかとなった. また ss- 観測では ZE モータ,MI モータ,AZ モータの常時作 動による負荷が大きく, これらのことからも今後 ss- 観測を廃止し, 全天紫外域日射観測を継続させるとともに, 自動遮蔽装置を使用した散 乱紫外域日射観測を充実させることが重要である. ただし過去の ss- 観測データを解析するためには, 上記の校正による方法が有益と考えられる. * 気象庁高層気象台観測第三課