secondary standard albedometer
SRA20 albedometer is an instrument that measures global and reflected solar radiation and the solar albedo, or solar reflectance, with the highest accuracy. It is composed of two SR20 secondary standard pyranometers with thermopile sensors; the upfacing one measuring global solar radiation, the downfacing one measuring reflected solar radiation. SRA20 complies with the latest ISO and WMO standards.
Albedo, also called solar reflectance, is defined as the ratio of the reflected to the global radiation. The solar albedo depends on the directional distribution of incoming radiation and on surface properties at ground level. Albedos of typical surfaces range from about 4 % for fresh asphalt, and 15 % for green grass to 90 % for fresh snow.
Using SRA20 albedometer is easy. The instrument is composed of two SR20 secondary standard pyranometers; the upfacing one measuring global solar radiation, the downfacing one measuring reflected solar radiation. The irradiance in W/m2 in each direction is calculated by dividing the pyranometer output, a small voltage, by the sensitivity. The sensitivity of both pyranometers is provided on the SRA20 product certificate. The working principle and specifications of the pyranometers can be found in the SRA20 user manual. We recommend to use SRA20 in particular in applications where the highest measurement accuracy is required. SRA20’s analogue output is in millivolt. SRA20 can be connected directly to commonly used datalogging systems.
Albedometers are used for general meteorological observations, building physics, roof reflectance studies, climate studies and solar collector testing. A common application is for outdoor solar radiation balance measurements as part of a meteorological station. This application requires horizontal levelling; a bubble level and a mounting rod are included. SRA20 is suited for use in extreme climates.The incorporated heater reduces measurement errors caused by frost and dew.
- high-accuracy meteorological observations
- building physics, roof reflectance studies
- extreme climates (tropical / polar)
SRA20 albedometer design
SRA20 consists of two identical pyranometers model SR20, one facing up, one facing down. The albedometer body is equipped with a 15 x 10-3 m diameter rod for mounting purposes. A sun screen is part of the delivery too. SRA20, including its sun screen fixation, connector and desiccant holder, is very robust. The albedometer has an incorporated heater and a temperature sensor. SRA20 can be ordered optionally with longer cable, and with a Pt100 temperature sensor instead of an internal heater and instead of a 10 kΩ thermistor.
Applicable instrument-classification standards are ISO 9060 and WMO-No. 8. Calibration is according to ISO 9847 and ASTM G207-11.
- SRA20 with Pt100 temperature sensor instead of internal heater and 10 kΩ thermistor
- longer cable, in multiples of 5 m, cable lengths above 20 m in multiples of 10 m
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- global solar radiation and reflected solar radiation
- Optional measurand
- albedo or solar reflectance
- Optional measurand
- net solar radiation
- Included sensors
- 2 x identical ISO 9060 secondary standard pyranometer
- analogue millivolt
- Temperature sensor
- Pt100 or 10 kΩ thermistor included
- mounting rod with 15 x 10-3 m diameter included
- Calibration uncertainty
- < 1.2 % (k = 2)
- Calibration traceability
- to WRR
- Measurement range
- 0 to 2000 W/m2
- Spectral range
- 285 to 3000 x 10-9 m
- Sensitivity (nominal)
- 15 x 10-6 V/(W/m2)
- Rated operating temperature range
- -40 to +80 °C
- Temperature response
- < ± 1 % (-10 to +40 °C)
< ± 0.4 % (-30 to +50 °C) with correction in dataprocessing
- Temperature response test and directional response test of individual instrument
- reports included
- Standard cable length
- 5 m (see options)