Light absorption by aerosols is a key component to atmospheric extinction, and affects a number of processes relevant to the Navy. Satellite and other remotely sensed measurements can be strongly impacted by aerosols, obscuring targets and/or confounding interpretation of data products. Directed energy applications, including weapon and communication systems, are also impacted by absorption, which affects processes such as thermal blooming. There is currently a lack of reliable, sensitive aerosol absorption instrumentation capable of operating in challenging field environments and at wavelengths needed for measurements relevant to the Navy, including in the infrared region of the electromagnetic spectrum. To address this need, we propose commercial development of a proven system based on photoacoustic technology, originally developed at NOAA and further enhanced by researchers at the University of Wyoming. The system is readily adaptable to the wavelengths of interest and has a proven track record for providing highly accurate, sensitive measurements of light absorption in the visible, including measurements from airborne platforms. In Phase I we successfully evaluated the performance characteristics of several candidate optical systems (lasers, mirrors) that were implemented in the existing Wyoming instrument hardware. We tested a novel calibration approach that will greatly simplify operation of the instrument in the field by non-specialists. In Phase II base period, we will focus on miniaturizing and improving instrument laser, optics, flow, and temperature control to develop a man-portable instrument that can be used in rapid response field site or aircraft applications and allows for improved closed cell performance for coarse aerosol. We will design and fabricate a working prototype instrument with integrated calibration. We will conduct laboratory evaluation including environmental testing by first verifying performance in laboratory environment and investigating response to coarse mode aerosol and then demonstrate the prototype at Navy field sites with a commercial instrument. In Phase II option period, we will refine extinction measurement approach for higher sensitivity, which would broaden applications for the instrument by adding capability to measure extinction and single scattering albedo at ambient conditions. We will conduct long-term calibration material evaluation to verify that our proposed calibration material remains stable over long periods of storage and allows testing of different storage conditions. We will also conduct flight testing on manned aircraft to test performance of the system in an aircraft environment, which is a desired capability of the system. We will attempt to integrate the system into UAS and test the integrated UAS system to solve need for a rapid responsive system capable of measuring atmospheric conditions over a range of altitudes and demonstrate operational capabilities of the aircraft system.
Benefit: Development of a robust, sensitive instrument to measure aerosol absorption will provide a range of benefits to the Navy, other federal agencies, and the broader public. Light absorption by aerosols is an important component of climate change, with light absorbing aerosols having a strong warming impact on the atmosphere. Current research lacks a reliable method for measuring atmospheric absorption, critical for evaluating global models that predict future climate. Unlike greenhouse gases, aerosols have short atmospheric lifetime, making them stronger candidates for emission reduction scenarios. Light absorbing particles also affect atmospheric visibility, and current measurements designed to monitor and improve visibility in protected areas lack accurate measurements needed to inform policy choices. Finally, there are few, if any, commercial instruments on the market sufficient for measuring absorption from airborne platforms at high time resolution, which our proposed instrument would be able to deliver. The instrument would have immediate commercial applications in meeting a long-standing need in the atmospheric research community for a high performing, reliable instrument. In the longer term, it is possible that light absorbing aerosols will be regulated due to their impact on climate. If so, there would be a large demand for aerosol absorption instrumentation for monitoring and emissions testing, both large commercial markets. The instrument we develop here would feature technology that could be translated into a simplified, less sensitive version to address monitoring requirements, and the integrated calibration system we will develop would be critical for establishing a standard measurement approach that can be deployed continuously.
Keywords: directed energy, atmosphere, aerosol, Dust, Absorption, photoacoustic, soot
