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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 9, 963-972, 2016
https://doi.org/10.5194/amt-9-963-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
08 Mar 2016
Development of a digital mobile solar tracker
Sunil Baidar1,2, Natalie Kille2,3, Ivan Ortega1,2, Roman Sinreich1, David Thomson2, James Hannigan4, and Rainer Volkamer1,2,3 1Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA
2Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, USA
3Department of Atmospheric and Oceanic Sciences (ATOC), University of Colorado, Boulder, CO 80309, USA
4National Center for Atmospheric Research (NCAR), Boulder, CO 80301, USA
Abstract. We have constructed and deployed a fast digital solar tracker aboard a moving ground-based platform. The tracker consists of two rotating mirrors, a lens, an imaging camera, and a motion compensation system that provides the Euler angles of the mobile platform in real time. The tracker can be simultaneously coupled to UV–Vis and Fourier transform infrared spectrometers, making it a versatile tool to measure the absorption of trace gases using solar incoming radiation. The integrated system allows the tracker to operate autonomously while the mobile laboratory is in motion. Mobile direct sun differential optical absorption spectroscopy (mobile DS-DOAS) observations using this tracker were conducted during summer 2014 as part of the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) in Colorado, USA. We demonstrate an angular precision of 0.052° (about 1/10 of the solar disk diameter) during research drives and verify this tracking precision from measurements of the center to limb darkening (CLD, the changing appearance of Fraunhofer lines) in the mobile DS-DOAS spectra. The high photon flux from direct sun observation enables measurements of nitrogen dioxide (NO2) slant columns with high temporal resolution and reveals spatial detail in the variations of NO2 vertical column densities (VCDs). The NO2 VCD from DS-DOAS is compared with a co-located MAX-DOAS instrument. Overall good agreement is observed amid a highly heterogeneous air mass.

Citation: Baidar, S., Kille, N., Ortega, I., Sinreich, R., Thomson, D., Hannigan, J., and Volkamer, R.: Development of a digital mobile solar tracker, Atmos. Meas. Tech., 9, 963-972, https://doi.org/10.5194/amt-9-963-2016, 2016.
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Short summary
We present development of a digital mobile solar tracker which can be coupled simultaneously to UV–Vis and FTIR spectrometers to measure trace gases in the atmosphere. We demonstrate an angular precision of 0.052º (about 1/10 of the solar disk diameter) during research drives and verify this tracking precision from measurements of the center to limb darkening (CLD, the changing appearance of Fraunhofer lines) in the mobile direct sun DOAS spectra.
We present development of a digital mobile solar tracker which can be coupled simultaneously to...
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