2017 News & Events

Dan Murphy recognized for paper on Miniature Sun Photometer

20 April 2017

miniSASP radiometer assembly
The upward-looking radiometer (ULR) assembly. For scale, the dome is about 5 cm in diameter. For flights, a thin plastic moving cover rides in the slot in the dome. Photo: D. Murphy, NOAA

CSD Cloud & Aerosol Processes program lead Dr. Dan Murphy is recognized for a paper describing the miniature Scanning Aerosol Sun Photometer (miniSASP), a new instrument his team developed. The editors of Aerosol Science and Technology selected "A miniature scanning sun photometer for vertical profiles and mobile platforms" as one of several recent most notable papers.

The miniSASP primarily makes measurements of the vertical profile of aerosols. Atmospheric aerosols, which are tiny particles suspended in the air, can affect air quality and exert direct and indirect effects on climate. The primary way to do this is by absorbing or scattering light. The miniSASP measures aerosol optical depth, or how much direct sunlight is prevented from reaching the ground by aerosols. It is able to measure four different wavelengths of light.

The miniSASP instrument was designed to be deployed on either small balloons or Manta unmanned aircraft systems (UAS), since these measurements can't be accurately taken from the ground. Therefore, the instrument had to be small, lightweight, and consume minimal power. The current version weighs less than a pound and uses only 5 Watts of power. Since the payloads on balloons or UAS aren't always recovered, low cost was another important factor and the miniSASP costs only $2500, more than 10 times less than similar commercial instruments.

To meet these requirements, the instrument has several simplifications. One is that the miniSASP doesn't actively search for the sun based on where North is, like other larger instruments do. Instead, it calculates how high the sun should be in the sky using the latitude, longitude and the time of day. Knowing this, the instrument looks only at this elevation where the sun is, a much simpler process.

The instrument has already flown on Manta UAS in Norway and other missions, showing it can accurately collect data in the bottom few kilometers of the atmosphere.

Murphy, D.M., H. Telg, T.F. Eck, J. Rodriguez, S.E. Stalin, and T.S. Bates, A miniature scanning sun photometer for vertical profiles and mobile platforms, Aerosol Science and Technology, doi:10.1080/02786826.2015.1121200, 2016.


A miniature sun photometer has been developed that makes continuous almucantar scans to measure solar irradiance and sky radiance in four wavelength bands set by interference filters. It has a well-defined field of view and can rapidly compensate for a tilting platform. It weighs less than 400 g and has an average power consumption of less than 5 W. Together, these characteristics make it suitable for vertical profiles using small balloons or unmanned aircraft systems (UASs). Preliminary results are presented showing measurements of optical depth and the phase function of scattered sunlight. An optical depth of about 0.03 in a clean boundary layer was measurable with an accuracy of better than 0.01.