The following pages provide sample pages of the Site Description Docum entation for the Bratt’s Lake Observatory.
The regional and local m aps of the area, the instrum ent field of view surveys, and the docum entation concerning the site location, operator, contacts etc. are m andatory. The general description of the site provides the data user inform ation to assess ground cover, how the instrum entation is installed, the m ethods used in calibration or if any special observational program s m ay be operational at the location that are not part of the BSRN program or not included in the archived data. The photographs can aid the user in understanding the type of land cover, general topography and how the instrum entation is installed.
Annex B Selected Instrumentation B 1. Instrument Specifications
B 1.1 Introduction
The inform ation found in this annex is based upon the use of particular instrum ents within the BSRN network. When used following the instructions given within the m anual, it is believed that these instrum ents can m eet the accuracy requirem ents specified by the BSRN. Other instrum entation m ay m eet these accuracies but have not been used within the program at the tim e of publication of this m anual.
The instrum ent specifications provided are those of the m anufacturers. Independent tests of the instrum ents have been m ade by a variety of laboratories and have been published in the open literature and through technical agencies such as the International Energy Agency. For further inform ation on any of these instrum ents the reader is advised to contact either a W MO Regional Radiation Centre or the m anufacturer directly.
The purpose in providing these specifications is to enable both data users and site scientists to gain inform ation about particular instrum ent configurations. For the form er, this should aid in gaining a better understanding of the data m easured by particular instrum ents; both strengths and weaknesses.
For the latter, the choice of an instrum ent for a particular site can be better determ ined by knowing what others use in sim ilar situations. Furtherm ore, by understanding the differences between instrum ents, questions concerning differences in data quality can be addressed.
The instrum ents are given in alphabetical order with the specifications provided by the m anufacturers.
W here possible, specifications comm on to each manufacturer are used. However, like most m anufactured goods, no standard m ethods of specifying all of the various attributes of an instrum ent have been adopted.
The International Standards Organization (ISO) (ISO 9060, Solar Energy - Specification and classification of instrum ents for m easuring hem ispherical solar and direct solar radiation) and the W MO (W MO No.
8, Com m ission on Instrum ents and Methods of Observation (CIMO) Guide to Instrum ents and Methods of Observation) has recom m ended som e guidelines, but these have yet to be universally accepted.
Tables B1 and B2 on pyranom eter specifications and pyrheliom eter specifications found in the ISO docum ent are provided below as a general guide on instrum ent quality.
Pyranom eters, pyrheliom eters and pyrradiometers have been categorized into three groupings depending
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upon the quality of the ins trum ent. T he ins trum ent mus t m eet all the specifications of a given c ategory before being classified within the category. T he highest category for pyranometers is the secondary standard because the m ost accurate determ ination of global irradiance is believed to be the sum of the direct beam irradiance as m easured by an absolute cavity radiometer and the diffuse solar irradiance as measured by a secondary standard pyranometer shaded from the sun by a disc.
Pyranometer Specification List
(a) Response to 200 W m net therm al radiation (ventilated)-2 (b) response to 5 K h change in am bient tem perature-1 Stability: percentage change in responsivity per year ± 0.8 % ± 1.8 % ± 3 % Non-linearity:
percentage deviation from the responsivity at 500 W m due-2 to change in irradiance within 100 W m to 1000 W m-2 -2
± 0.5 % ± 1 % ± 3 %
Directional response for beam radiation (the range of errors caused by assum ing that the norm al incidence responsivity is valid for all directions when m easuring, from any direction, a beam radiation whose norm al incidence irradiance is 1000 W m-2
± 10 W m-2 ± 20 W m-2 ± 30 W m-2
Spectral selectivity:
percentage deviation of the product of the spectral absorptance and the spectral transm ittance from the corresponding m ean within 0.3 :m and 3.0 :m
± 2 % ± 5 % ± 10 %
Tem perature response:
total percentage deviation due to change in am bient tem perature within in interval of 50 K
2 % 4 % 8 %
Tilt response:
percentage deviation form the responsivity at 0° tilt
(horizontal) due to change in tilt from 0° to 90° at 1000 W m-2 irradiance
± 0.5 % ± 2 % ± 5 %
Table B 1.1. Pyranom eter specification list from ISO 9060.
Pyrheliometer Specification List at 500 W m due to change in irradiance within-2 100 W m to 1000 W m-2 -2
± 0.2 % ± 0.5 % ± 2 %
Spectral selectivity:
percentage deviation of the product of the spectral absorptance and the spectral transm ittance from the corresponding m ean within 0.3 :m and 3.0 :m
± 0.5 % ± 1 % ± 5 %
Tem perature response:
total percentage deviation due to change in am bient tem perature within in interval of 50 K
± 1 % ± 2 % ± 10 %
Tilt response:
percentage deviation form the responsivity at 0°
tilt (horizontal) due to change in tilt from 0° to 90°at 1000 W m irradiance-2
± 0.2 % ± 0.5 % ± 2 %
Traceability: m aintained by periodic com parison with a prim ary standard Table B 1.2. Pyrheliom eter specification table from ISO 9060.
B 2. Pyranometers
B 2.1 Eppley Laboratory Model PSP Pyranom eter
The Precision Spectral Pyranom eter is designed for the m easurem ent of sun and sky radiation totally or in defined broad wavelength bands. It com prises a circular m ulti-junction wire-wound Eppley therm opile.
The therm opile has the ability to withstand severe m echanical vibration and shock. Its receiver is coated with Parson's black lacquer (non-wavelength selective absorption). This instrum ent is supplied with a pair of rem ovable precision ground and polished hem ispheres of Schott optical glass. Both hem ispheres are m ade of clear W G295 glass which is uniform ly transparent to energy between 0.285 to 2.8 µm . Other Schott coloured glass outer hem ispheres include clear (GG395), yellow (GG495), orange (OG530), red (RG630), and dark red (RG695). For special applications, other Schott glasses and Infrasil II quartz hem ispheres are available.
Included is a spirit level, adjustable levelling screws and a desiccator which can be readily inspected.
The instrum ent has a cast bronze body with a white enam elled guard disk and com es with a transit/storage case.
A calibration certificate traceable to the W orld Radiation Reference and a tem perature com pensation curve is included.
Specifications
Sensitivity: approx. 9 :V W m-1 2
Im pedance: approx. 650 S
Tem perature Dependence: ±l % over am bient tem perature range -20 to +40 °C tem perature com pensation of sensitivity (can be supplied over other ranges at additional charge)
Linearity: ±0.5% from 0 to 2800 W m-2
Response tim e: 1 second (1/e signal)
Cosine: ±1% from norm alization 0-70° zenith angle; ±3% 70-80° zenith
angle
Mechanical Vibration: tested up to 20 g's without dam age
Calibration: integrating hem isphere
Size: 5.75 inch diam eter, 3.75 inches high
W eight: 7 pounds
Orientation: Perform ance is not affected by orientation or tilt
B 2.2 Kipp & Zonen Delft BV CM11 Pyranom eters
The CM11 incorporates a 100-therm ocouple sensor, im printed on a thick-film substrate, housed under K5 glass dom es. The sensor is rotationally sym m etrical. A white screen prevents the body from heating up. The pyranom eter is supplied with a spirit level and screws for accurate levelling. A drying cartridge keeps the interior free from hum idity.
All pyranom eters are supplied with a calibration certificate which also shows the level of directional error.
Specifications
Response tim e < 15 s
tim e for 95 % response
Zero off-set when m easuring from any direction a beam radiation whose norm al incidence irradiation is 1000 W m )-2
Spectral selectivity ± 2 %
Glass dom es Schott K5 optical glass 2 m m thick,
30 m m and 50 m m outer diam eter
Desiccant Silicagel
Spirit level Sensitivity 0.1 degree
(bubble half out of the ring)
Coincident with base of the instrum ent.
Detector surface and base are coplanar within 0.1°
Materials Anodized alum inium case. Stainless steel screws in stainless steel bushes. W hite plastic screen of ASA
Drying cartridge PMMA
W eight 830 g
Cable length 10 m (standard)
Dim ensions 91.5 m m total height, 150 m m diam eter, 25 m m dom e height, 50 m m dom e diam eter
B 2.3 Kipp & Zonen Delft BV CM21/31 Pyranom eters
Suitable for the m easurem ent of solar irradiance on a plane surface.
- im proved specifications in com parison with the CM11.
- also available with quartz dom es (CM31) yielding a broader range and reduced offsets.
Essentially the pyranom eter CM21 has the sam e characteristics as the CM11. Som e of these specifications have been im proved: when m easuring from any direction a beam radiation whose norm al incidence irradiation is 1000 W m-2
Spectral selectivity ± 2%
percentage deviation of the product of spectral absorptance and spectral transm ittance from the corresponding m ean within 0.35 :m and 1.5 :m
Tem perature response ± 1%
percentage deviation due to change in am bient tem perature within an interval of -20 to +50 °C, relative to 20 °C.
Tilt response 0.25%
percentage deviation from the responsivity at 00 tilt (horizontal) due to change in tilt from 0° to 90°
at 1000 W m irradiance-2
Viewing angle 2 B sr
Irradiance 0 - 1400 W m (m ax.4000 W m )-2 -2
Spectral range 305-2800 nm (50% points)
335-2200 nm (95% points)
Sensitivity between 7 and 25 :V W m-1 2
Im pedance 40-100 Ohm
Receiver paint Carbon black
Glass dom es Schott K5 optical glass 2 m m thick, 30 m m and 50 m m outer diam eter
Desiccant Silicagel
Spirit level Sensitivity 0.1° (bubble half out of the ring) Coincide with base of the instrum ent. Detector surface and base are coplanar within 0.1°
Materials Anodized alum inium case Stainless steel screws in stainless steel bushes. W hite plastic screen of ASA
Drying cartridge PMMA
W eight 830 g
Cable length 10 m
Dim ensions 91.5 m m total height, 150 m m diam eter, 25 m m dom e height, 50 m m dom e diam eter
B 2.4 Kipp and Zonen Delft BV PYRANOMETER CM 31 (additions/changes to CM 21)
Spectral Range 200-4000 nm (50% points)
290-3500 nm (95% points)
Spectral selectivity m ax. 2% in the spectral range 300 to 3000 nm
Zero off-set + 4 W m-2
response to 200 W m-2
Directional response 5 W m-2 for beam radiation
Quartz dom es Infrasil II
B 2.5 Carter-Scott Middleton EP09 Pyranom eter
The EP09 sensor has an upwards facing black receiver disk with a radial heat conduction path for rapid response. An identical (reference) disk faces into the instrum ent body. The tem perature difference between the disks is a direct function of the intensity of radiation absorbed by the receiver disk. The disk tem perature is precisely determ ined with m iniature thin-film Platinum Resistance Elem ents which give the instrum ent exceptional linearity and stability. Zero offset and signal gain can be externally trim m ed via access holes in the base.
Spectral range 300 - 3000 nm (nom inal)
Signal output (responsivity) 1.00 m V/W m-2
Signal resolution < 1.0 W m-2
Zero point ( at 20 C )o ± 1.5 W m-2 Zero point tem perature coefficient < ± 0.05 W m / C-2 o
Calibration accuracy ± 2 % (factory certificate); traceable NATA Certificate available as extra cost option Operating tem perature -35 to +60 Co
Power supply requirem ent 5.5 to 14.5 VDC, 10 m A Measurem ent instrum ent
requirem ent -0.05 to +2.0 VDC, > 1MS
Standby m ode Shutdown input: 2 to 14.5 V
Standby current draw: 0.25 m A Startup settling tim e: 1.5s Herm etic seal integrity output OK = 0.5 to 1.0 V
(fail when approx. 5% RH at 20 C )o Fail = 0 to 0.2 V Tem perature output 10 m V/ C (0.20V = 20 C)o o
Bubble level resolution 0.1o
Desiccant Silica gel
Lead 6m ; 8-core
Mounting Central M10 hole, plus
pair M4 holes on 65m m P.C.D.
W eight 0.8 kg (excluding lead)
B 2.6 Eko MS-802 Pyranom eter
High precision pyranom eter for photovoltaic applications and other high precision m easurem ents The sensing elem ent consists of a wire-wound therm opile constructed of electroplated copper on constantan, covered with black paint that has a spectrally flat absorption response. It is protected from environm ent effects (wind, etc.) Using two concentric glass dom e covers.
Specifications
Directional response less than ± 10 W m-2
Tem perature response 1 % (within an interval for 50 C) o
Non-linearity ± 0.2 % (from 100 to 1000 W m )-2
Spectral range 300 to 2800 nm
B 2.7 Eppley Black and W hite Pyranom eter (Model 8-48)
The Black and W hite Pyranometer has a detector consisting of a differential therm opile with the hot-junction receivers blackened and the cold-junction receivers whitened. The receiver is of radial wire-wound plated construction with the black segm ents coated with a flat black coating and the white with Barium Sulfate.
Built-in tem perature com pensation with therm istor circuitry is incorporated to free the instrum ent from effects of am bient tem perature. A precision ground optical glass hem isphere of Schott glass W G295 uniform ly transm its energy from 0.285 to 2.8 :m .
Specifications
Sensitivity approx. 10 :V/W m-2
Im pedance approx. 350 Ohm s
Tem perature Dependence ± 1.5 % over am bient tem perature range -20 to +40 Co
Linearity ± 1.0 % from 0 to 1400 W m-2
Response tim e 5 seconds (1/e signal)
Cosine ± 2 % from norm alization 0-70 zenith angleo
± 5 % from norm alization 70-80 zenith angleo Mechanical Vibration tested up to 20 g’s without dam age
Calibration integrating hem isphere
Size 5.75 inch diam eter, 2.75 inches high
W eight 2 pounds
B 2.8 Schenk Star Pyranom eter
The m easuring principle of the star pyranom eter is the m easurem ent of, the tem perature difference between white and black painted sectors so that the result is not affected by am bient tem perature. A precisely cut dom e shields the sensing elem ents from environm ental factors.
A drying cartidge keeps the interior free from hum idity. An optional protective housing enables m easurem ents in cold weather.
Technical Data
Measuring range 0 to 1500 W m-2
Spectral sensitivity 0.3 to 3 :m
Output About 15 :V/W m or 4 ... 20 m A = 0 ... 1500 W m-2 -2
Im pedence About 35 Ohm
Am bient tem perature -40 C to +60 Co o
Resolution < 1 W m-2
Stability < 1% per year ( tem porary operation )
Cosine response < 3 % of the value, zenith angle 0 - 80o o
Azim uth response < 3 % of the value
Tem perature effect < 1 % of the value between -20 C to + 40 Co o
Linearity < 0.5 % in the range 0.5 to 1330 W m-2 Response tim e < 25 sec. (95%), < 45 sec. (99%)
W eight 1.0 kg
Cable 2-polar shielded, 3 m length
B 3. Cavity Radiometers and Pyrheliometers
B 3.1 Eppley Laboratory HF/AHF Cavity Radiom eter
The self-calibrating Absolute Cavity Pyrheliom eter has been a reference standard device for m any years.
The sensor consists of a balanced cavity receiver pair attached to a circular wirewound and plated therm opile.
The blackened cavity receivers are fitted with heater windings which allow for absolute operation using the electrical substitution m ethod, which relates radiant power to electrical power in SI units. The forward cavity views the direct solar beam through a precision aperture. The precision aperture area is nom inally 50 m m and is m easured for each unit. The rear receiver views an am bient tem perature blackbody. The2 HF radiom eter elem ent with baffle tube and blackbody are fitted into an outer tube which acts as the enclosure of the instrum ent. The instrum ent is weather proof when the window is m ounted. The m odel AHF has an autom atic shutter attached to the outer tube. A separate, m ounted window is supplied with each unit for continuous operation of the radiom eter, but at reduced accuracy. An adaptor is supplied for m ounting to Eppley solar trackers. The HF cavity radiom eter has been used for m easurem ent of the extraterrestrial solar radiation from the Nim bus 7 ( 14 years) and the LDEF (6 years) satellites and is space proven.
The operation of the cavity radiom eter, and the m easurem ent of the required param eters, is perform ed using the appropriate control box. The control functions include setting of the calibration heater power level, activation of the calibration heater, selection of the signals to be m easured and control of the m eter m easurem ent functions and ranges. The m easured param eters include the therm opile signal, the heater voltage and the heater current which is m easured as the voltage drop across a 10 LI precision resistor.
The instrum ent tem perature m ay also be m easured using an internally m ounted therm istor. The m eter resolution of 100 nV allows for a therm opile signal equivalent in radiation of approxim ately 0.1 W m .-2 Control boxes for m anual only, m anual and autom atic and autom atic only operation are available. The control box can operate either one radiom eter in the m easurem ent m ode or two radiom eters in the com parison m ode by changing from single to dual operations cable. Two cables are supplied with each unit. The autom atic operation allows for com puter control of all shuttering, calibration heating and m easurem ent functions.
Calculation operations and data storage are also possible under com puter control. Program s for independent, autom atic m easurem ent and cavity radiom eter com parison are supplied with autom atic units.
Although these are absolute devices, the radiom eters are com pared with the EPLAB reference cavity radiom eters which have participated in the EPC's and other inter-com parisons and are directly traceable to the W RR. The References are HF’s SN 14915 and SN 27798. The H F which is part of the W SG is SN 18748.
Specifications Radiom eter:
Sensor: 60 junction circular wirewound and plated therm opile with
balanced cavity receivers (. 350 S)
Cavity: Inverted cone within a cylinder coated with specular black paint.
em issivity $ 0.999
Aperture area: nom inal 50 m m : each m easured using precision pins 2 Field of view: 5° central; 1.6° unencum bered (0.8° slope); 8.5° m ax.
Heater resistance: 150 S (Approx.)
Irradiance sensitivity: I :V W m (approx)-1 2
Size: 5.5 in. diam eter at base; 13.32 in long without connector and
adaptor, 7 in x 5 in at shutter housing; 3.5 in. dia. outer tube
W eight 9.25 lb; 11.5 lb with tracker adaptor
W indow m aterial: Corning 7940
CONTROL BOX:
Size: 7 in. high x 17 in. wide x 16 in. deep
W eight: 23 lb (approx)
Power requirem ent: 115 VAC 60 @ or 230 VAC 50 Hz selectable
B 3.2 PMOD/PMO6
PMO-6 Absolute radiom eter (excerpted from Applied Optics, Vol. 25, Page 4173, Novem ber 15, 1986) The PMO6 radiom eter is based on the m easurem ent of a heat flux using an electrically calibrated heat flux transducer. The radiation is absorbed in a cavity which ensures a high absorptivity over the spectral -range of interest for solar radiom etry. The heat flux transducer consists of a therm al im pedance with resistance therm om eters to sense the tem perature difference across it. Heat developed in the cavity is conducted to the heat sink of the instrum ent and the resulting tem perature difference across the therm al im pedance is sensed. The sensitivity of the heat flux transducer is calibrated by shading the cavity and m easuring the tem perature difference while dissipating a known am ount of electrical power in a heater elem ent which is m ounted inside the cavity It is advantageous to determ ine the electrical power which is needed to produce the sam e tem perature difference as was observed with the cavity irradiated, because in this case the heat losses are the sam e during radiative and electrical heating—even if nonlinear effects are involved.
During practical operation of the instrum ent, an electronic circuit m aintains the tem perature signal constant by controlling the power fed to the cavity heater—independent of the m ode, that is, whether the cavity is shaded or irradiated. The substituted radiative power is then equal to the difference in electrical power as m easured during the shaded and irradiated periods, respectively.
Changes of the tem perature of the heat sink m ay also produce a tem perature signal. Therefore, two heat flux transducers with m atched tim e constants are com bined to form a differential heat flux transducer.
The temperature difference m easured between the two tops of the therm al im pedances is then—depending on the quality of the m atching—largely insensitive to changes of the tem perature of the heat sink.
The instrum ent m easures irradiance, hence its receiver area has to be accurately known. A precision aperture of nom inally 5-m m diam eter is placed in front of the prim ary cavity. A second aperture of 8.35-m m diam eter acting as a view-lim iting aperture and defining a field of view of 5/ is placed 95.4 m m in front of the precision aperture. This geom etry puts only a m oderate ~ 0.75/ requirem ent on the solar pointing.
All the apertures of the so-called m uffler are in the shadow of the view-lim iting aperture. The purpose of the m uffler is to reduce the sensitivity to wind effects and to increase the therm al m ass of the heat sink of the instrum ent.
The cavities are m ade of electro-deposited silver and are gold-plated on their outside. They are soldered
The cavities are m ade of electro-deposited silver and are gold-plated on their outside. They are soldered