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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-172
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-172
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Jun 2019

Research article | 12 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Cloud Aerosol Transport System (CATS) 1064 nm Calibration and Validation

Rebecca M. Pauly1, John E. Yorks2, Dennis L. Hlavka1, Matthew J. McGill2, Vassilis Amiridis3, Stephen P. Palm1, Sharon D. Rodier4, Mark A. Vaughan5, Patrick A. Selmer1, Andrew W. Kupchock1, Holger Baars6, and Anna Gialitaki3 Rebecca M. Pauly et al.
  • 1Science Systems and Applications Inc., Lanham, 20706, USA
  • 2NASA Godard Space Flight Center, Greenbelt, 20771, USA
  • 3National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Application and Remote Sensing, Athens, Greece
  • 4Science Systems and Applications Inc., Hampton, 23666, USA
  • 5NASA Langley Research Center, 23618, USA
  • 6Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany

Abstract. The Cloud-Aerosol Transport System (CATS) lidar on board the International Space Station (ISS) operated from 10 February 2015 to 30 October 2017 providing range-resolved vertical backscatter profiles of Earth’s atmosphere at 1064 and 532 nm. The CATS instrument design and ISS orbit lead to a higher 1064 nm signal to noise ratio than previous space based lidars, allowing for direct 1064 nm calibration using the molecular normalization technique. Nighttime CATS Version 3-00 data were calibrated by normalizing the signal between 22–26 km above mean sea level to molecular profiles derived from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) re-analysis data. This altitude region was chosen primarily because the CATS data frame is −2 to 28 km AMSL due to the high CATS laser repetition rate. While this altitude region provides sufficient molecular scattering for the Rayleigh normalization technique, the aerosol loading in this altitude region must be quantified to improve the accuracy of the CATS nighttime calibration. Daytime CATS Version 3-00 data were calibrated through comparisons with nighttime thin, opaque, cirrus cloud layer integrated attenuated total backscatter (iATB).

The CATS nighttime 1064 nm attenuated total backscatter (ATB) uncertainties for clouds and aerosols are primarily related to the uncertainties in the Rayleigh normalization technique, which are estimated to be 7–10 %. Median CATS V3-00 1064 nm ATB relative uncertainty at night within cloud and aerosol layers is 7 %, consistent with these calibration uncertainty estimates. CATS median daytime 1064 nm ATB relative uncertainty is 21 % in cloud and aerosol layers, similar to the estimated 16–18 % uncertainty in the CATS daytime cirrus cloud calibration transfer technique. Coincident daytime comparisons between CATS and the Cloud Physics Lidar (CPL) during the CATS-CALIPSO Airborne Validation Experiment (CCAVE) project show good agreement in mean ATB profiles for clear-air regions. Eight nighttime comparisons between CATS and the PollyXT ground based lidars also show good agreement in clear-air regions between 3–12 km, with CATS having a mean ATB of 19.7 % lower than PollyXT. Agreement between the two instruments (∼7 %) is even better within an aerosol layer. Six-month comparisons of nighttime ATB values between CATS and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) also show that iATB comparisons of opaque cirrus clouds agree to within 19 %. Overall, CATS has demonstrated that direct calibration of the 1064 nm channel is possible from a space based lidar using the molecular normalization technique.

Rebecca M. Pauly et al.
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Short summary
The Cloud Aerosol Transport System (CATS) demonstrated that direct calibration of 1064 nm lidar data from a space borne platform is possible. By normalizing the CATS signal to a modeled molecular backscatter profile the CATS data was calibrated, enabling the derivation of optical properties of clouds and aerosols. Comparisons of the calibrated signal with airborne lidar, ground-based lidar, and space borne lidar all show agreement within estimated error bars of the respective instruments.
The Cloud Aerosol Transport System (CATS) demonstrated that direct calibration of 1064 nm lidar...
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