Sunphotometer to Obtain Additional Aerosol Data in Niamey

 
Published: 15 August 2006

Located nearby the AMF ground instruments, the sunphotometer, in the foreground, requires an unobstructed hemispheric view of the sky to obtain its measurements.

In early August, a new Cimel sunphotometer (CSPHOT) was deployed at the ARM Mobile Facility site in Niamey, Niger, as part of the ongoing RADAGAST field campaign. The CSPHOT measures the solar and sky radiance at various wavelengths in the visible and near-infrared spectrum (340, 380, 440, 500, 670, 870, 936, 1020 nm). From these measurements, a number of aerosol properties, including aerosol optical depth, can be determined. It also has application to cloud property retrievals. Adding a CSPHOT to the AMF instrument suite at Niamey was identified as a high priority for both the ARM Aerosol and Cloud Properties Working Groups, as it provides the added benefit of complementing the measurements taken by the same instrument at the other ARM sites.

The CSPHOT has a 1.2 degree field of view and is comprised of three major components: (1) Cimel sun photometer, (2) Sutron Satlink satellite transmitter, and (3) solar panels to power the Cimel and the Satlink. The Cimel in turn is comprised of three subassemblies: (1) the sensor head, (2) the two-axis motor positioner, or “robot,” and (3) the control unit. The instrument points at the sun for certain measurements, and also scans the atmosphere on a regular basis. These data are used to infer the scattering properties and particle size of aerosols.

Measurements from the CSPHOT are acquired via satellite by the NASA Aerosol Robotic Network (AERONET) Project at Goddard Space Flight Center. There, the data are processed to obtain aerosol optical thickness, precipitable water vapor amount, and other aerosol parameters. Researchers can access the processed data from the AERONET web page, which also contains additional information about the CSPHOT instrument, its measurements, and the AERONET Project. Once checked for quality, the data is also made available through the ARM Data Archive.