An intercomparison including 26 instruments, 7 recording devices, 3 calibration lamps and a staff of about 12 people needs thorough organisation. The Norwegian UV intercomparison was well prepared and planned. However, during the actual campaign and afterwards when preparing and analysing data, we discovered problems related to the measurements and to the data preparation and analysis. Below we have listed some points which should be considered in future intercomparisons.
The map
After a description of instruments and accessories from each participant has been communicated to the organiser, a map of the daylight measurement area should be made, showing
• the planned position of each instrument or instrument group.
• a suggestion for placement of cabels, PCs and desks for staff.
• corridors where operators can move without shading operating instruments.
When all instruments are installed and operating, a detailed photo documentation over the area should be made showing each instrument or group of instruments, as well as the platform horizon.
The schedule
It is not possible to make a time schedule in advance for an intercomparison consisting of daylight and lamp measurements. Daylight measurements must be carried out while the weather conditions are appropriate. Lamp measurements must have second priority and be conducted when weather conditions are poor or after the daylight measurements have been completed. Instead of an unflexible schedule, a daily schedule should be prepared each morning by the head of the intercomparison on the basis of the weather forecast and advice or requests from the participants. It is important that one person is in charge of the intercomparison and that she/he has the neccesairy authority to direct all activities during the day according to the schedule or ad hoc if unexpected difficulties arise.
The schedule should:
• secure that for daylight measurments, all instruments should operate and collect synchronous data (for a time interval containing all or as many as possible zenith angles).
• regulate activity near the instruments to guarantee continuous periods of daylight measurements free of shading or other disturbances from personnel working near or passing instruments.
The timing
Synchronous daylight data from the different instruments are crucial for further analyses. This point is especially important when the irradiation changes rapidly, due to passing clouds.
Moreover, different time standards should not be used. Therefore:
• All PCs, and personal watches should be synchronized to the seconds level each morning, midday and evening, collectively at pre-set times, and a common syncronisation logbook should be kept. Before each synchronisation any deviations should also be noted in the logbook. When the measurements have been completed, each participant should receive a copy of the logbook.
• Only local time should be used and recorded in the raw data files. The use of UTC or local normal time can be confusing and give rise to misunderstandings. It is simple to convert all data to UTC afterwards, in the data preparation process.
• Due to different routines for averaging the recorded measurements in the different recording systems, all prepared datafiles should contain precise information on recording algorithms.
The logbook
The importance of a detailed logbook for each individual instrument and recording system can hardly be emphasised enough. All procedures, activities and measurements conducted using any particular instrument should be recorded in detail in the logbook by the responsible person.
References:
Arvesen JC, Griffin RN, Pearson BD. 1969. Determination of extraterrestrial solar spectral irradiance from a research aircraft. Applied Optics 1969; 8: 2215-2232.
Dahlback A, Stamnes K. 1991. A new spherical model for computing the radiation field available for photolysis and heating at twilight. Planetary and Space Science 1991; 39: 671-683.
Dahlback A. 1996. Measurements of biologically effective UV-doses, total ozone abundance and cloud effects with multi-channel moderate filter instruments. Applied Optics 1996; 35:
6514-6521.
Hansen VT. 1984. Spectral distribution of solar radiation on clear days: a comparison between measurements and model estimates. Journal of Climate and Applied Meteorology 1984; 23: 772-780.
Hegg K. 1983. Daily values of global radiation, totally and divided in 5 wavelength bands, from 7 stations in the Nordic countries. Ås: Department of Physics and Meteorology, Agricultural University of Norway, 1983.
Hisdal V.1969. A comparative study of the spectral composition of the Zenith sky radiation. In:
Norwegian Polar Institute yearbook 1967. Oslo, 1969: 7-27.
Hisdal V. 1986. Spectral distribution of global and diffuse solar radiation in Ny-Ålesund, Spitsbergen. Polar Research 1986; 5: 1-27.
Johnsen B. 1996. UV monitoring in Norway: past, present and future. In: Diffey BL, ed.
Measurement and trends of terrestrial UVB radiation in Europe. Milano: OEMF, 1996: 93-101.
Johnsen B.1996. How to improve correlation of filter radiometer measurements and spectral scans during periods of unstable weather conditions. Suggestion for handling Nogic'96 data.
Presentation on a Workshop on ultraviolet radiation, Izaña (Tenerife) October 18, 1996.
Unpublished.
Josefsson W. 1991. The intercomparison of spectroradiometers at SMHI in Norrkøping 6-8 of August 1991. Norrkøping: Swedish Meteorological and Hydrological Institute (SMHI), Climate Section, 1991.
Koskela T. ed. 1994. The Nordic intercomparison of ultraviolet and total ozone instruments at Izaña from 24 October to 5 November 1993. Final report. Meteorological Publications. 27, Helsinki: Finish Meteorological Institute, 1994
Kostkowski HJ, Nicodemus FE. 1978. An introduction to the measurement equation. In:
Nicodemus FE, ed. Self-study manual on optical radiation measurements. Part 1; Consepts, Chapters 4 and 5. NBS TN 910-2. Washington DC: National Bureau of Standards, 1978: 58-104.
Kvifte G, Hegg K, Hansen VT. 1983. Spectral distribution of solar radiation in the Nordic countries, Journal of Climate and Applied Meteorology 1983; 22: 143-152.
Kvifte G. 1989. Værobservasjoner i Ås gjennom 125 år. In: Follominne, nr. 27: Årbok 1989 for Follo historie- og museumslag. Drøbak 1989: 58-67.
Opedal L.1996. UV-målinger med Brewer MKIV Ozone Spectrophotometer: Kalibrering og kvalitativ vurdering av målingene. Hovedfagsoppgave. Oslo: Fysisk Institutt, Universitetet i Oslo, 1996.
Pu Bu C R, Sigernes F, Gjessing Y. 1997. Ground-based measurements of solar ultraviolet radiation in Tibet: Preliminary results. In print june 1997. (Submitted to Geophysical Research Letters).
Schieldrup Paulsen H. 1966. Radiation observations in Bergen, Norway, 1965. Radiation Yearbook No. 1. Bergen: University of Bergen, Geophysical Institute, 1966.
Schieldrup Paulsen H. 1968. Radiation Observations in Bergen, Norway, 1967. Radiation Yearbook no. 3. Bergen: University of Bergen, Geophysical Institute, 1968.
Shumaker JF. 1979. Deconvolution. In: Nicodemus FE, ed. Self-study manual on optical radiation measurements: Part 1; Concepts, Chapters 7, 8 and 9. NBS TN 910-4. Washington DC: National Bureau of Standards, 1979: 35-90.
Skartveit A, Cleveland F, de Lange T. 1996. Radiation Observations in Bergen, Norway, 1995.
Radiation Yearbook no. 31. Bergen: University of Bergen, Geophysical Institute, 1996.
Stamnes K, Tsay S-C, Wiscombe WJ and Jayaweera K. 1988. Numerically stable algorithm for discrete-rdinate-method radiative transfer in multiple scattering and emitting layered media.
Applied Optics 1988; 27: 2502-2509.
Van Hoosier ME , Bartoe JDF, Brueckner GE, Prinz DK. 1988. Absolute solar spectral irradiance 120 nm -400 nm (Results from the SUSIM experiment on board Spacelab-2).
Astrophysical Letters and Communications 1988; 27: 163-168.
Appendix 1 UV-measuring activities up to 1995.
Table A1.1: UV-measuring activities conducted up to the spring of 1995.
Location Institution UV
instruments λ range, nm Period Spitsbergen,
Ny-Ålesund NPI TUVR
SL-501 295-385
290-380 1981→
1992→
Spitsbergen, Longyearbyen
University of Tromsø
Jobin-Yvon spectro.
300-600 short periods from 1985
Tromsø University Jobin-Yvon
spectro’s Brewer MKIII
300-600 280-366
1985→
1995→
Trondheim University SL-500* OL-752* PUV500U* PUV510S*
290-380 290-800 multibands multibands
1991→
1994→
short periods short periods Bergen University TUVR*
SL-501* PUV500U PUV510S
295-385 290-380 multibands multibands
1965→
1995→
short periods Oslo University
NILU
Brewer MKIV* SL-500* GUV511*
290-325 290-380 multibands
1990→
1991→
1992→
Ås University TUVS’s* 295-385 1977→
Finse,
Hardangervidda
NRPA SL-501* 290-380 1992→
* participated in the Norwegian intercomparison meeting, June 5-9 1995.
Appendix 2: Participating institutions’s UV-measuring activities. Agricultural University of Norway
A meteorological station was established at the Agricultural University of Norway at Ås in 1870 (Kvifte 1989). The purpose of the station was to study the interaction between the weather/climate and agricultural production. During the early years, measurements were restricted to parameters such as air and soil temperature, humidity and wind velocity (Table A2.1). Since approximately 1950, these measurements have been extended to include solar radiation. These meteorological data are currently used to develop weather forecasts which target agricultural activities such as irrigation and fertilizer application.
Broadband ultraviolet (290–385 nm) measurements have been conducted at Ås since 1977. The measurements were commenced in conjunction with a joint research project between the five Nordic countries (Kvifte et al. 1983). The aim of the project was to chart the spectral distribution of solar radiation in the Nordic area in order to provide agronomists studying the effects of radiation on plant growth and crop yield with data. Radiation (385–2800 nm) was measured with Eppley spectral pyranometers equipped with different glass filters. Eppley TUVR radiometers were used to measure UV radiation in the wavelength band 290–385 nm.
Even though the project was terminated in 1981, field observations have continued at Ås. The UV data has been used in several studies of agricultural production. In addition, the data has been used to assess atmospheric models for radiative transfer (Hansen 1984).
Table A.2.1 Meteorological measurements at the Agricultural University of Norway, Ås.
Quantity measured Derived quantities and comments
Current instrument Time series start 1 global irradiation Eppley Precision Pyranometer 1950 2 diffuse irradiation Eppley Precision Pyranometer 1966 3 global irradiation
down (reflected) irradiation balance (1− 3) albedo (3⁄1)
Eppley Precision Pyranometer 1966 1983 4 radiation energy
balance
Radiation Energy Balance System /
Pyranometer 1960
5 PAR photosynthetic active radiation LI-COR Quantum sensor 1977 6 irradiation UV
(295 - 385 nm)
Eppley Ultra-Violet Pyranometer 1977 7 irradiation GG14 blue (385-495nm) (1−6−7) Eppley Precision Pyranometer 1977 8 irradiation RG2 green (495-630nm) (7− 8) Eppley Precision Pyranometer 1977 9 irradiation RG8
IR (695-2800nm) red (630-695nm) (8−9) Eppley Precision Pyranometer 1977 10 # sunshine hours
pr day
sunshine recorder 1897-1982
11 precipitation manual/ITF 1863
12 snow # days with snow & snow depth
manual 1874
13 relative humidity hair hygrometer 1874
14 air temperature temp., min. and max. temp. PT100 1874 15 temperature
grass level minimum temperature mercury thermometer 1969 16 soil temperature 25 cm depth mercury thermometer 1896-1960 17 soil temperature 5, 10, 20, 50, 100 cm depth PT100 1960 18 soil temperature 2 cm depth PT100 1983
19 soil heat flux EKO/CN-81H 1983
20 evaporation Vibrating Wire Gauge/ITF 1961-64, 96 21 wind speed maximum / minimum Windmaster Ultrasonic Anemometer 1882 22 wind direction Windmaster Ultrasonic Anemometer 1874 23 air pressure Vaisala/Digital Barometers PTA200 1885
University of Bergen, Geophysical Institute.
As part of a long term program (Schieldrup Paulsen 1967, Skartveit et al. 1996), hourly global UV radiation is recorded at Bergen by Eppley Total Ultraviolet Radiometers (290 - 385 nm) since 1967. This program includes measurements of (all-wave solar) global, diffuse and direct beam radiation, sunshine duration, and downward atmospheric radiation.
Global UV radiation is measured at Bergen by a multichannel filter (305 - 380 nm) instrument (GUV#9270) since February 1996, as part of the Norwegian UV monitoring network.
Furthermore, since July 1995, hourly global UV-B (erythemal) radiation is recorded hourly by a Solar Light UV Biometer 501A, while global, diffuse and direct beam radiation at seven wavelength passbands between 415 and 940 nm are recorded by a Multi Filter Rotating Shadowband Radiometer since autumn 1996.
Since summer 1996, UV radiation is recorded at 3648 m a.s.l. in Lhasa, Tibet by a multi-channel filter (305 - 340 nm) instrument (NILUV) (Pu Bu et al., in print).
Norwegian Radiation Protection Authority (Statens Strålevern)
With the ratification of National regulations for solarium appliances and sunlamps in 1983, Ultraviolet Radiation became part of NRPA’s general responsibility for public radiation safety.
A diodearray spectrograph was purcased in 1984 and the establishing of an optical laboratory started. In 1992 NPRA installed a SL-501 MED-meter at Finse 1200 metres above sea level, 600N. In 1994 a spectroradiometer from Macam Photometrics Ltd was purcased and later upgraded for solar measurements. The instrument is now installed in the optical laboratory for measurements of artificial UV-sources as e.g. sunlamps.
The plans for establishing a solar UV-monitoring network started in 1989. Late 1994 the health- and environmental authorities decided to establish a UV-monitoring network in Norway. In cooperation with State Pollution Control Authroity represented by NILU, NRPA is responsible for coordinating the UV-monitoring activities. NRPA is responsible for UV monitoring at four of the seven locations, for calibration of the UV-network instruments and for the evaluation and reporting of health relevant data. Facilities and routines for instrument calibration and characterization have been established at the optical laboratory. A spectroradiometer from Bentham has later been installed on a platform on the roof of NRPA, and has since April 1997 been regularly measuring global and diffuse solar radiation for the wavelength region 290-450nm. The reference GUV#9273 and Bentham will be running side by side, whenever the GUV is not occupied for other calibration purposes.
Norwegian Institute for Air Research
NILU has been involved in UV related research since 1990. In 1992-1994 NILU established a network of multi channel GUV instruments in Southern Chile from 53S to 33 S. This
Chilean/Norwegian project was financed by the Norwegian Ministry of Environment. In 1994 a new project with funding from the Norwegian Ministry of Environment was started in
Southern Chile. This project focuses on UV effects on terrestrial plants in Torres del
Paine national park in Southern Chile at 51S. NILU has developed a new multi channel filter instrument and a network of seven instruments was established in the national park in 1995.
NILU is responsible for three of the multi channel GUV instrument in the Norwegian UV monitoring network. Radiative transfer modelling has since 1990 played an important role and has been used to interpret UV measurements.
Norwegian University of Science and Technology, Department of Physics, Lade At NTNU UV has been measured since 1991. A solar light model 500 meter has been measuring MED-UV in one minutes intervals. The instrument has participated in two intercomparisons, Norrkoping 1993 and Helsinki 1996. In addition, temperature within the instrument and on the green filter has been measured.
In 1994 a spectroradiometer, Optronic 752 started to measure global spectral UV. The wavelength range and frequency of spectra has been changed during this periode. The
instrument has also been modified during this period with respect to temperature stabilisation and input optic. The main change occured in 1996 when the integrating sphere was replace by an optical fiber. At the moment the instrument is measuring from 290 nm to 400 nm with 0.5 nm steps every ten minute. The instrument has participated in four intercomparisons,
Norrköpong 1991, Izana 1993 and 1996, Oslo 1995.
Since 1996 a multichannel instrument GUV 511, part of the Norwegian UV network has been given minute values of UV in five different channels. This instrument participated in one intercomparison, Oslo 1995 and is ones a year compared with a travelling standard.
Anxillary measurements with pyranometer and pyrheliometer has been performed since 1991.
These instruments give minute values. Out door temperature and wind is also measured.
A multichannel instrument for underwater measurements (PUV500 and PUV510) has been used for shorter campaign studies were high timeresolution measurements has been carried out(scale within seconds). This instrument has been used for underwater measurements University of Oslo, Physics Department.
University of Tromsø, Auroral Observatory.
Appendix 3
Table A3.1 Adress list for the participants of the interkomparison meeting
Name E-mail Phone Fax Institute and address
Berit Kjeldstad Berit.Kjeldstad@phys.ntnu.no +4773591995 +4773591852 NTNU
The Norwegian University of Science and Technology NTNU (earlier University of Trondheim)
Department of Physics, Lade N-7034 Trondheim
Oddbjørn Grandum oddgra@alfa.avh.unit.no NTNU
Gry Storsveen grysto@james.avh.unit.no NTNU
Trond Morten Thorseth trotho@alfa.avh.unit.no +4773591869 +4773591852 NTNU
Arne Dahlback arne@nilu.no +4763898177 +4763898050 NILU
Norwegian Institute for Air Research Instituttveien 18, 2007 Kjeller
Tore Perssen +4777645731 +4777645580 UiTø
University of Tromsø, Auroral Observatory POB 953, 9001 Tromsø
Trond Svenøe Trond@phys.uit.no,
trond.svenoe@nilu.no +4777606970 UiTø
From '96 working at NILU in Tromsø Strandtorget 2B, POB 1245, 9001 Tromsø Finn Tønnessen Finn.tonnessen@fys.uio.no +4722855673 +4722855671 UiO
University of Oslo, Physics Dept.
POB 1048 Blindern, 0316 Oslo Lars Opedal Lars.opedal@fys.uio.no +4722855662 +4722855671 UiO Cecilia Futsæther c.futsaether@itf.nlh.no +4764948752 +4764948810 NLH
Agricultural University of Norway Dept. of Agricultural Engeneering POB 5065, 1432 ås
Arne Auen Grimnes arne.grimnes@itf.nlh.no +4764949582 +4764948810 NLH, Institutt for Tekniske Fag
Oddvar Haga itas@itas.nlh.no +4764949839 +4764942033 ITAS
Instrumenttjenesten at NLH
Arvid Skartveit arvid@gfi.uib.no +4755582602 +4755589883 UiB
University of Bergen, Geophysical Institute Allégaten 70, 5020 Bergen
Tor de Lange Lange@gfi.uib.no +4755582687 UiB
Bjørn Johnsen bjorn.johnsen@nrpa.no +4767162549 +4767147407 NRPA
Norwegian Radiation Protection Authority POB 55, Grini Næringspark 13
1345 Østerås Merete Hannevik Merete.Hannevik@nrpa.no +4767162565 +4767147407 NRPA Oddbjørn Mikkelborg Oddbjorn.Mikkelborg@nrpa.no +4767162540 +4767147407 NRPA
Frank Bason soldata@bason.da.diatel.dk +4586841196 +4586841597 Soldata AS, 8600 Silkeborg, Denmark
Appendix 4: Instrument spesifications.
Table A4.1: Spectroradiometers.
Institution UiO NTNU NRPA
Spectroradiometer Brewer Mk IV Optronic OL-752 Macam Photometrics SR99
Type of monochromator Fastie-Ebert scanning spectroradiometer
Rowland-circle scanning spectro.
Rowland-circle scanning spectro.
Focal length [mm] 160 100 100
Gratings plane/concave ruled/holographic lines/mm
blaze wavelength
1 plane r 1200
300nm, 3'rd order
2 concave h 1200
350nm, 1'th order
2 concave h 1200
350nm, 1'th order
Bandwidth, FWHM [nm] 0.59 1.5 1.3
Wavelength range 290-325(342) + 420-510
200-800 200-800 Front optics Teflone diffusor Integrating sphere Teflone diffusor on optical
light guide Photomultiplier EMI 9789QA S-20 response Hamamatsu R3896
Weather proof y y y
Temperature stabilized
optics n y y (24°C±1)
Irradiance calibration
traceable to NIST-SciTec NIST-Eppley Lab NIST-Swedish Testing and Res. Inst.
Main standard lamp Eppley FEL EN75 Eppley Lab FEL? GE DXW#5
Table A4.2. Eppley ultraviolet radiometers (290 - 385 nm).
Reference name Factory supplied calibration factor (Wm-2 per mV) Purchase year Owner
E-13814 12.4 1975 NLH (ITAS)
E-13815 10.6 1975 NLH (ITAS)
E-15728 4.59 1977 NLH (ITF)
E-30072 4.88* 1994 UiB
* Temperature coefficient (0.1% per degree Celcius between -40°C to +25°C) supplied by Eppley Laboratory, Inc.
Table A4.3. PAR instruments.
Reference
name Instrument Purchase
year Owner GUV#9222 GUV-511 #9222. Biospherical Instruments PAR channel 1993 NILU PUV510S PUV510 "surface". Biospherical Instruments PAR channel 1994 NTNU PUV500U PUV500 "under water". Biospherical Instruments PAR channel 1994 NTNU NLH89 LiCor Li-189SR Quantum sensor, #QR789-7502 PAR single unit 1977 NLH NLH90 LiCor Li-190SR Quantum sensor, #QR790-7502 PAR single unit 1977 NLH Table A4.4 Solar Light instruments.
Reference name Instrument Purchase year SL-501 NRPA SL-501 UV-Biometer #0587 1992
SL-501 UiB SL-501 UV-Biometer #1489 1995 SL-500 UiO SL-500 Robertson-Berger meter 1989
Table A4.5 Delta-T and Kipp&Zonen singleband radiometers.
Instrument λpeak [nm]
FWHM [nm]
Factory supplied calibration factor [Wm-2 per mV]
Calibration year
Owner Kipp&Zonen CUVB1
s/no. 952001
306 2.4 -2.7855E-4 1995 ITAS (NLH) Kipp&Zonen
CUV3 s/no. 950005
360 315-378 3.5587 1995 ITAS (NLH)
Delta-T 313 26 10 1993 ITAS (NLH)
Table A4.6 Multiband filter radiometers from Biospherical Instruments Co.
Instrument λcenter nominal [nm]
FWHM nominal [nm]
Calibration factor by manufacturer (Solar intercomparison
with SUV-100 in San-Diego) [V/µW]
Dark current
Calibration year
Network location
#9270 305 313
320 340 380
10
"
"
"
"
0.5531 -0.1928 -0.1066 -0.0818 -0.0457
-0.003220 -0.001308 0.001150 0.000617 0.000853
1995 Bergen
#9271 305 313
320 340 380
10
"
"
"
"
0.4244 -0.2074 -0.1231 -0.0861 -0.0455
0.005291 -0.001555 -0.002856 -0.000856 -0.001553
1995 Landvik
#9272 305 313
320 340 380
10
"
"
"
"
0.6234 -0.2060 -0.1158 -0.0832 -0.0481
-0.018348 -0.001750 0.000457 -0.000010
0.001973
1995 Kise
#9273 305 313
320 340 380
10
"
"
"
"
0.5733 -0.1844 -0.1102 -0.0783 -0.0482
-0.005178 -0.001693 -0.000432 -0.001701 0.000487
1995 NRPA, Oslo
#9274 305 313
320 340 380
10
"
"
"
"
0.4088 -0.1913 -0.1247 -0.0834 -0.0481
-0.011120 0.000632 -0.001708 -0.000648 0.000662
1995 Trondheim
#9275 305 313
320 340 380
10
"
"
"
"
0.4899 -0.2069 -0.1239 -0.0772 -0.0443
0.007057 0.001445 -0.000145 -0.001235 -0.000264
1995 Ny-Ålesund
#9276 305 313
320 340 380
10
"
"
"
"
0.3439 -0.2011 -0.1063 -0.0701 -0.0434
-0.005369 -0.001817 0.003259 0.001052 -0.002197
1995 Tromsø
#9222*) 308 320 340 380 PAR
10
"
"
"
400-700
1.455647 -0.109043 -0.109528 -0.0422 -9.657562
-0.004759 0.001275 -0.003405
0.002306 -0.000162
1993 (?) Blindern, Oslo
*) Note: Calibration by lamp, whereas the other are solar calibrated towards SUV-100.
1 .3 n m F W HM in s tru m e n ta l lin e p ro file (Hg -s c a n with M a c a m )
0.00001 0.0001 0.001 0.01 0.1 1
-4 -3 -2 -1 0 1 2 3 4
W a v e le n g th fr o m c e n te r o f lin e [n m ]
Fig. A4.1 Instrumental line profile (slit function) of the Macam spectroradiometer, as recorded by scanning the 253.7nm emission line of a mercury lamp.