SRA20 albedometer

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.

SRA20 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.