The Baseline Surface Radiation Network Station (BSRN) contributes to knowledge of the Earth’s radiation budget by monitoring background short-wave and long-wave radiative components and their changes. BSRN radiometers measure direct, diffuse, and global components of down-welling irradiance. Upwelling radiance is also measured.
The PEARL BSRN site is currently listed as closed. However, the equipment has continued to operate and data has been collected continuously. Data was submitted to the BSRN archive from Fall 2007 to the end of 2011. Subsequent data has been archived by CANDAC but not submitted to the BSRN archive.
The reported quantities are:
Shortwave Downwelling radiance —- SWD
Longwave Downwelling radiance —- LWD
Direct radiance —————————– DIR
Diffuse radiance —————————- DIF
The instruments are mounted on an azimuth-elevation tracker. The Direct component is measured with a pyrheliometer mounted on the elevation arm as shown above. Pyranometers are used to measure both the diffuse and the global contributions. The Diffuse pyranometer is shaded by a ball held at the proper distance to block the solar disk so that none of the direct component arrives at the sensor. This ensures that any energy arriving on the Diffuse pyranometer comes by an indirect path. The Global pyranometer is not blocked and contains both the direct and indirect components. Not shown is a global infrared pyrgeometer.
The sensor in the pyrheliometer is a thermopile with a spectral response of 280-4000 nm. The pyranometers also use thermopiles as their active elements. The pyranometers typically have a spectral response of better than 300-3000 nm. The pyrgeometer has a spectral response of approximately 4 to 40 µm.
The BSRN instruments measure the components of the solar driven radiation input to the Earth’s surface. The figure from 13 June 2011 shows a typical clear sky 24 hours of daylight “summer” case. The 5 June 2011 plot shows the impact of a full cloud cover, with the direct measurement going to zero. Note that the SWD measurement is still significant as is the LWD. The impact of sporadic cloud cover is seen in the 09 June 2011 plot, showing the decrease in the DIR component and the increase in the LWD component, and the impact of the surrounding topography can be seen in the 14 April 2011 plot. Only the portion indicated as having the solar elevation be below zero should be dark.
BSRN data can be used to monitor the impacts of anything that change the amount of solar radiation reaching the Earth’s surface. These effects include cloud fraction, cloud thickness, aerosol extinction (smoke, etc.) and possibly others.