Cloud-Aerosol Transport System (CATS) 1064 nm calibration and validation
<p>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 IS...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-11-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/6241/2019/amt-12-6241-2019.pdf |
| Summary: | <p>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 atmospheric calibration of the 1064 nm signals. Nighttime CATS version 3-00 data were calibrated by scaling the
measured data to a model of the expected atmospheric backscatter between 22
and 26 km a.m.s.l. (above mean sea level). The CATS atmospheric model is
constructed using molecular backscatter profiles derived from Modern-Era
Retrospective analysis for Research and Applications, Version 2 (MERRA-2)
reanalysis data and aerosol scattering ratios measured by the Cloud-Aerosol
Lidar with Orthogonal Polarization (CALIOP). The nighttime normalization
altitude region was chosen to simultaneously minimize aerosol loading and
variability within the CATS data frame, which extends from 28 to <span class="inline-formula">−2</span> km a.m.s.l. Daytime CATS version 3-00 data were calibrated through comparisons
with nighttime measurements of the layer-integrated attenuated total
backscatter (iATB) from strongly scattering, rapidly attenuating opaque
cirrus clouds.</p>
<p>The CATS nighttime 1064 nm attenuated total backscatter (ATB) uncertainties
for clouds and aerosols are primarily related to the uncertainties in the
CATS nighttime calibration technique, which are estimated to be
<span class="inline-formula">∼9</span>  %. Median CATS V3-00 1064 nm ATB relative uncertainty at
night within cloud and aerosol layers is 7 %, slightly lower than 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 Polly<span class="inline-formula"><sup>XT</sup></span> ground-based
lidars also show good agreement in clear-air regions between 3 and 12 km, with
CATS having a mean ATB of 19.7 % lower than Polly<span class="inline-formula"><sup>XT</sup></span>. Agreement
between the two instruments (<span class="inline-formula">∼7</span> %) is even better within an
aerosol layer. Six-month comparisons of nighttime ATB values between CATS
and CALIOP also show
that iATB comparisons of opaque cirrus clouds agree to within 19 %.
Overall, CATS has demonstrated that direct calibration of the<span id="page6242"/> 1064 nm
channel is possible from a space-based lidar using the atmospheric
normalization technique.</p> |
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| ISSN: | 1867-1381 1867-8548 |