variety of emission sources and atmospheric processes will act to produce air masses with a typical, identifiable aerosol 'type'. This is an idealization, but one that allows us to classify aerosols based on observations and location in a way to gain insight into the geographic distribution of aerosol types and constrain the possible values of Sa for use in aerosol extinction retrievals. The aerosol subtype product is generated downstream of the cloud-aerosol discrimination (CAD) scheme and, therefore, depends on the cloud-aerosol classification scheme in a very fundamental way. If a cloud feature is misclassified as aerosol, the aerosol subtype algorithm will identify this 'aerosol' as one of the aerosol subtypes. The user must exercise caution where the aerosol subtype looks suspicious or unreasonable. Such situations can occur with some frequency in the southern oceans and the polar regions.

## Cloud and aerosol extinction profiles

The CALIOP cloud and aerosol profiles of extinction and backscatter are released as beta products. Cloud profiles are reported at a horizontal resolution of 5 km; aerosol profiles are reported at a horizontal resolution of 40 km. These products contain a number of known errors and, in their current form, cannot be used as standalone products. The current products contain no data quality information, and hence must be used in conjunction with the Cloud and/or Aerosol Layer Products and/or the Vertical Feature Mask Product, which contain data quality parameters and confidence flags. Data assessment and screening procedures have not yet been developed. Because of this, the profile data product is considered to be not appropriate for scientific publication but is released to users for evaluation and to provide feedback to the CALIOP algorithm development team. PLEASE NOTE: users of the CALIOP extinction and backscatter profile data should read and thoroughly understand the information provided in the Profile Products Data Quality Summary. This summary contains an expanded description of the extinction retrieval process from which the layer optical depths are derived and provides essential guidance in the appropriate use of all CALIOP extinction-related data products. Validation and improvements to the profile products QA are ongoing efforts, and additional data quality information will be included with future releases.

## Cloud and aerosol optical depths

Because comprehensive data assessment and screening procedures have not yet been developed, the CALIOP cloud and aerosol optical depths reported in the V2.01 data release are not considered appropriate for scientific publication. The data is being released as a beta quality product, for evaluation by the user community, and to provide feedback to the CALIOP algorithm development team.

## Data Quality Statement for CALIPSO's Version 1.10 Lidar Level 2 Data Product Release

Data Version: 1.10

Data Release Date: December 8, 2006

Data Date Range: June 13, 2006 to November 11, 2007

The CALIPSO vertical feature mask (VFM) data product reports a single 16-bit integer for each lidar altitude resolution element in the data stream downlinked from the satellite. Upon decoding each of these bit-mapped integers, users will obtain information describing layer location (both vertically and horizontally), layer type, and the amount of horizontal averaging required for the layer to be detected.

Given the accuracy of the CALIPSO altitude registration, the layer heights reported in the Lidar Level 2 Cloud and Aerosol Layer Products and the VFM appear to be quite accurate. In optically dense layers, the lowest altitude where signal is observed is reported as the base. In actuality, this point may lie well above the true base. In this release, the layers which are reported represent a choice in favor of high reliability over maximum sensitivity. Weakly scattering layers sometimes will go unreported, in the interest of minimizing the number of false positives.

A preliminary version of the algorithm to discriminate cloud and aerosol has been used in this release. Overall, the algorithm performance is fairly good at labeling cloud as cloud and somewhat less successful in labeling aerosol as aerosol. Several types of misclassifications are fairly common and should be watched for. The most common misclassification is portions of dense aerosol layers being labeled as cloud. The algorithm operates on individual profiles, so small regions within an aerosol layer are sometimes labeled as cloud. These misclassifications are often
apparent from study of Level 1 browse images. Actual clouds occurring within aerosol layers appear to be correctly classified as cloud most of the time. Additionally, portions of the bases of some cirrus clouds are mislabeled as aerosol, and some tropospheric polar clouds are erroneously labeled as aerosol. Improvements to the cloud/aerosol discrimination algorithm are underway and misclassifications should be greatly reduced in future data releases.

# Appendix 1

Prior to November 28, 2007, CALIPSO was nominally pointed in a 'near nadir' direction (actually at ~0.3° off nadir, to avoid the full force of specular reflections from still waters and horizontally oriented ice crystals). In that pointing configuration, the CALIOP browse images – as shown below – correctly represented both the spatial distribution of clouds and aerosols, and the optical effects of overlying layers on the atmosphere below.

<figure><img src="image_33.png" /></figure>

As a result of the change to pointing 3° off-nadir, with the tilt being in the same plane as the satellite velocity vector (i.e., along track, rather than cross track), the spatial distribution of layers is not exactly what is shown in the standard browse images. A more faithful representation might look like this...

<figure><img src="image_34.png" /></figure>

There are several aspects of this change that could be of interest to data users:
1. While there is now a 3° vertical shear in the spatial distribution of clouds and aerosols (i.e., as shown above), the optical effects of overlying layers are still correctly represented by the original, upright images that are being shown on our web pages.

2. The altitudes reported in all products are still measured with respect to a nadir viewing instrument, and thus users need not (and should not) make any corrections for pointing angle.

3. The laser footprint locations reported in the data products give the latitude and longitude coordinates of the beam location on the Earth at mean sea level.

4. The horizontal offset between any two points in the vertical can be computed using 'triangle trig'. If the vertical distance is V, the horizontal offset, Δh, between the upper and lower points is Δh = V·tan(3°).

5. Version 2 of the data products includes a new 'Spacecraft_Position' SDS that contains all of the spacecraft attitude information required to vertically collocate the CALIPSO and CloudSat profiles. This was included at the request of the CloudSat team, specifically for the continued production of their GeoProf products.

6. In general, the optical properties reported for measurements of aerosols and water clouds are not expected to change as a function of the change in pointing angle. However, the properties reported for individual ice clouds will change by some varying amount, depending on the concentration of horizontally aligned ice crystals present in the cloud. Among the changes that can be anticipated are

* a reduction in the maximum values of integrated attenuated backscatter measured at both wavelengths;

* an increase in the minimum depolarization ratios associated with strongly scattering ice clouds;

* a small change in the proportion of clouds classified as ice versus those classified as water; and

* an increase in the minimum lidar ratios retrieved for strongly scattering ice clouds.

## References

Avery, M. A., R. A. Ryan, B. J. Getzewich, M. A. Vaughan, D. M. Winker, Y. Hu, A. Garnier, J. Pelon, and C. A. Verhappen, 2020: CALIOP V4 Cloud Thermodynamic Phase Assignment and the Impact of Near-Nadir Viewing Angles, *Atmos. Meas. Tech.*, **13**, 4539–4563, https://doi.org/10.5194/amt-13-4539-2020.

Burton, S. P., R. A. Ferrare, M. A. Vaughan, A. H. Omar, R. R. Rogers, C. A. Hostetler, and J. W. Hair, 2013: Aerosol Classification from Airborne HSRL and Comparisons with the CALIPSO Vertical Feature Mask, *Atmos. Meas. Tech.*, **6**, 1397–1412, https://doi.org/10.5194/amt-6-1397-2013.

Chand, D., T. L. Anderson, R. Wood, R. J. Charlson, Y. Hu, Z. Liu, and M. Vaughan, 2008: Quantifying above-cloud aerosol using spaceborne lidar for improved understanding of cloudy-sky direct climate forcing, *J. Geophys. Res.*, **113**, D13206, https://doi.org/10.1029/2007JD009433.

Haarig, M., R. Engelmann, H. Baars, B. Gast, D. Althausen and A. Ansmann, 2025: Discussion of the spectral slope of the lidar ratio between 355 nm and 1064 nm from multiwavelength Raman lidar observations, *Atmos. Chem. Phys.*, **25**, 7741–7763, https://doi.org/10.5194/acp-25-7741-2025.

Heymsfield, A. J., D. Winker, and G.-J. van Zadelhoff, 2005: Extinction-ice water content-effective radius algorithms for CALIPSO, *Geophys. Res. Lett.*, **32**, L10807, https://doi.org/10.1029/2005GL022742.

Heymsfield, A., D. Winker, M. Avery, M. Vaughan, G. Diskin, M. Deng, V. Mitev, and R. Matthey, 2014: Relationships between Ice Water Content and Volume Extinction Coefficient from In Situ Observations for Temperatures from 0° to -86°C: Implications for Spaceborne Lidar Retrievals, *J. Appl. Meteor. Climatol.*, **53**, 479–505, https://doi.org/10.1175/JAMC-D-13-087.1.
Holz, R. E., S. Platnick, K. Meyer, M. Vaughan, A. Heidinger, P. Yang, G. Wind, S. Dutcher, S. Ackerman, N. Amarasinghe, F. Nagle, and C. Wang, 2016: Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals, *Atmos. Chem. Phys.*, **16**, 5075–5090, https://doi.org/10.5194/acp-16-5075-2016.

Hu, Y. M. Vaughan, Z. Liu, B. Lin, P. Yang, D. Flittner, W. Hunt, R. Kuehn, J. Huang, D. Wu, S. Rodier, K. Powell, C. Trepte, and D. Winker, 2007: The depolarization-attenuated backscatter relation: CALIPSO lidar measurements vs. theory, *Opt. Express*, **15**, 5327–5332, https://doi.org/10.1364/OE.15.005327.

Hu, Y., M. Vaughan, Z. Liu, K. Powell, and S. Rodier, 2007: Retrieving Optical Depths and Lidar Ratios for Transparent Layers Above Opaque Water Clouds From CALIPSO Lidar Measurements, *IEEE Geosci. Remote Sens. Lett.*, **4**, 523–526, https://doi.org/10.1109/LGRS.2007.901085.

Hunt, W. H, D. M. Winker, M. A. Vaughan, K. A. Powell, P. L. Lucker, and C. Weimer, 2009: CALIPSO Lidar Description and Performance Assessment, *J. Atmos. Oceanic Technol.*, **26**, 1214–1228, https://doi.org/10.1175/2009JTECHA1223.1.

Kar, J., K.-P. Lee, M. A. Vaughan, J. L. Tackett, C. R. Trepte, D. M. Winker, P. L. Lucker, and B. J. Getzewich, 2019: CALIPSO Level 3 Stratospheric Aerosol Product: Version 1.00 Algorithm Description and Initial Assessment, *Atmos. Meas. Tech.*, **12**, 6173–6191, https://doi.org/10.5194/amt-12-6173-2019

Kim, M.-H., A. H. Omar, J. L. Tackett, M. A. Vaughan, D. M. Winker, C. R. Trepte, Y. Hu, Z. Liu, L. R. Poole, M. C. Pitts, J. Kar, and B. E. Magill, 2018: The CALIPSO Version 4 Automated Aerosol Classification and Lidar Ratio Selection Algorithm, *Atmos. Meas. Tech.*, **11**, 6107–6135, https://doi.org/10.5194/amt-11-6107-2018.

Liu, Z., R. Kuehn, M. Vaughan, D. Winker, A. Omar, K. Powell, C. Trepte, Y. Hu, and C. Hostetler, 2010: The CALIPSO Cloud And Aerosol Discrimination: Version 3 Algorithm and Test Results, 25th International Laser Radar Conference (ILRC), 5–9 July 2010, St. Petersburg, Russia; see https://www.researchgate.net/publication/285685007.

Liu, Z., J. Kar, S. Zeng, J. Tackett, M. Vaughan, M. Avery, J. Pelon, B. Getzewich, K.-P. Lee, B. Magill, A. Omar, P. Lucker, C. Trepte, and D. Winker, 2019: "Discriminating Between Clouds and Aerosols in the CALIOP Version 4.1 Data Products", *Atmos. Meas. Tech.*, **12**, 703–734, https://doi.org/10.5194/amt-12-703-2019.

Lopes, F. J. S., E. Landulfo, and M. A. Vaughan, 2013: Evaluating CALIPSO's 532 nm lidar ratio selection algorithm using AERONET sun photometers in Brazil, *Atmos. Meas. Tech.*, **6**, 3281–3299, https://doi.org/10.5194/amt-6-3281-2013.

Lu, X., Y. Hu, Z. Liu, S. Rodier, M. Vaughan, C. Trepte, and J. Pelon, 2017: Observations of Arctic snow and sea ice cover from CALIOP lidar measurements, *Remote Sens. Environ.*, **194**, 248–263, https://doi.org/10.1016/j.rse.2017.03.046.

Lu, Z., X. Liu, Z. Zhang, C. Zhao, K. Meyer, C. Rajapakshe, C. Wu, Z. Yang and J. E. Penner, 2018: Biomass smoke from southern Africa can significantly enhance the brightness of stratocumulus over the southeastern Atlantic Ocean, *PNAS*, **115**, 2924–2929, https://doi.org/10.1073/pnas.1713703115.

Mace, G. G., S. Benson and Y. Hu, 2020: On the Frequency of Occurrence of the Ice Phase in Supercooled Southern Ocean Low Clouds Derived from CALIPSO and CloudSat, *Geophys. Res. Lett.*, **47**, e2020GL087554, https://doi.org/10.1029/2020GL087554.

McGill, M. J., M. A. Vaughan, C. R. Trepte, W. D. Hart, D. L. Hlavka, D. M. Winker, and R. Kuehn, 2007: Airborne validation of spatial properties measured by the CALIPSO lidar, *J. Geophys. Res.*, **112**, D20201, https://doi.org/10.1029/2007JD008768.

Papagiannopoulos, N. and 15 coauthors, 2016: CALIPSO climatological products: evaluation and suggestions from EARLINET, *Atmos. Chem. Phys.*, **16**, 2341–2357, https://doi.org/10.5194/acp-16-2341-2016.
Platt, C. M. R., D. M. Winker, M. A. Vaughan and S. D. Miller, 1999: Backscatter-to-Extinction Ratios in the Top Layers of Tropical Mesoscale Convective Systems and in Isolated Cirrus from LITE Observations, *J. Appl. Meteor. Climatol.*, **38**, 1330–1345, https://doi.org/10.1175/1520-0450(1999)038<1330:BTERIT>2.0.CO;2.

Powell, K. A., C. A. Hostetler, Z. Liu, M. A. Vaughan, R. E. Kuehn, W. H. Hunt, K. Lee, C. R. Trepte, R. R. Rogers, S. A. Young, and D. M. Winker, 2009: CALIPSO Lidar Calibration Algorithms: Part I - Nighttime 532 nm Parallel Channel and 532 nm Perpendicular Channel, *J. Atmos. Oceanic Technol.*, **26**, 2015–2033, https://doi.org/10.1175/2009JTECHA1242.1.

Powell, K. A., M. A. Vaughan, R. R. Rogers, R. E. Kuehn, W. H. Hunt, K-P. Lee, and T. D. Murray, 2010: The CALIOP 532-nm Channel Daytime Calibration: Version 3 Algorithm, 25th International Laser Radar Conference (ILRC), 5–9 July 2010, St. Petersburg, Russia; see https://www.researchgate.net/publication/391011856.

Rajapakshe, C., Z. Zhang, J. E. Yorks, H. Yu, Q. Tan, K. Meyer, S. Platnick and D. M. Winker, 2017: Seasonally Transported Aerosol Layers over Southeast Atlantic are Closer to Underlying Clouds than Previously Reported, *Geophys. Res. Lett.*, **44**, https://doi.org/10.1002/2017GL073559.

Redemann, J. and 68 coauthors, 2021: An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol–cloud–radiation interactions in the southeast Atlantic basin, *Atmos. Chem. Phys.*, **21**, 1507–1563, https://doi.org/10.5194/acp-21-1507-2021.

Rodriguez, J. V., R. C. Verhappen, C. Weimer, C. R. Trepte and T. E. Cayton, 2022: Charged Particle Fluxes Associated with CALIPSO Low Laser Energy Shots, *IEEE T. Nucl. Sci.*, **69**, 2146–2153, https://doi.org/10.1109/TNS.2022.3204715.

Ryan, R. A., M. A. Vaughan, S. D. Rodier, J. L. Tackett, J. A. Reagan, R. A. Ferrare, J. W. Hair, and B. J. Getzewich, 2024: Total Column Optical Depths Retrieved from CALIPSO Lidar Ocean Surface Backscatter, *Atmos. Meas. Tech.*, **17**, 6517–6545, https://doi.org/10.5194/amt-17-6517-2024.

Tackett, J., M. Vaughan, J. Lambeth, and A., Garnier, 2022: Critical Improvements to CALIOP Boundary Layer Cloud-Clearing in Version 4.5, 2022 CALIPSO/CloudSat Science Team Meeting, 12–14 September 2022, Fort Collins, CO USA, https://ntrs.nasa.gov/citations/20220013563.

Tackett, J. L., J. Kar, M. A. Vaughan, B. Getzewich, M.-H. Kim, J.-P. Vernier, A. H. Omar, B. Magill, M. C. Pitts, and D. Winker, 2023: The CALIPSO version 4.5 stratospheric aerosol subtyping algorithm, *Atmos. Meas. Tech.*, **16**, 745–768, https://doi.org/10.5194/amt-16-745-2023.

Tackett, J. L., R. A. Ryan, A. E. Garnier, J. Kar, B. Getzewich, X. Cai, M. A. Vaughan, C. R. Trepte, R. Verhappen, D. M. Winker and K.-P. A. Lee, 2025: Mitigating Impacts of Low Energy Laser Pulses on CALIOP Data Products, *EGUsphere* [AMTD], https://doi.org/10.5194/egusphere-2025-2376, accepted for publication.

Toth, T. D., J. Zhang, J. R. Campbell, J. S. Reid, Y. Shi, R. S. Johnson, A. Smirnov, M. A. Vaughan, and D. M. Winker, 2013: Investigating Enhanced Aqua MODIS Aerosol Optical Depth Retrievals over the Mid-to-High Latitude Southern Oceans through Intercomparison with Co-Located CALIOP, MAN, and AERONET Datasets, *J. Geophys. Res.*, **118**, 4700–4714, https://doi.org/10.1002/jgrd.50311.

Toth, T. D., J. R. Campbell, J. S. Reid, J. L. Tackett, M. A. Vaughan, J. Zhang, and J. W. Marquis, 2018: Minimum Aerosol Layer Detection Sensitivities and their Subsequent Impacts on Aerosol Optical Thickness Retrievals in CALIPSO Level 2 Data Products, *Atmos. Meas. Tech.*, **11**, 499–514, https://doi.org/10.5194/amt-11-499-2018.

Toth, T. D., M. Clayton, Z. Li, D. Painemal, S. Rodier, J. Kar, T. Thorsen, R. Ferrare, M. Vaughan, J. Tackett, H. Bian, M. Chin, A. Garnier, E. Welton, R. Ryan, C. Trepte and D. Winker, 2025: Mapping CALIPSO Marine and Dusty Marine Aerosol Lidar Ratios using MODIS AOD Constrained Retrievals and GOCART Model Simulations, *EGUsphere* [AMTD], https://doi.org/10.5194/egusphere-2025-2832, accepted for publication.
Vaughan, M., K. Powell, R. Kuehn, S. Young, D. Winker, C. Hostetler, W. Hunt, Z. Liu, M. McGill, and B. Getzewich, 2009: Fully Automated Detection of Cloud and Aerosol Layers in the CALIPSO Lidar Measurements, *J. Atmos. Oceanic Technol.*, **26**, 2034–2050, https://doi.org/10.1175/2009JTECHA1228.1.

Vaughan, M., R. Kuehn, J. Tackett, R. Rogers, Z. Liu, A. Omar, B. Getzewich, K. Powell, Y. Hu, S. Young, M. Avery, D. Winker, and C. Trepte, 2010: Strategies for Improved CALIPSO Aerosol Optical Depth Estimates, 25th International Laser Radar Conference (ILRC), 5–9 July 2010, St. Petersburg, Russia, https://ntrs.nasa.gov/citations/20100026019

Vaughan, M., K.-P. Lee, A. Garnier and B. Getzewich, 2016: Improvements to the CALIOP Surface Detection Algorithm, CALIPSO CloudSat Science Team Meeting, 1-3 March 2016, Newport News, VA USA, https://doi.org/10.13140/RG.2.2.21628.04481.

Venkata, S. L. and J. A. Reagan, 2016: Aerosol Retrievals from CALIPSO Lidar Ocean Surface Returns, *Remote Sens.*, **8**, 1006, https://doi.org/10.3390/rs8121006.

Yang, P., L. Bi, B. A. Baum, K.-N. Liou, G. W. Kattawar, M. I. Mishchenko, and B. Cole, 2013: Spectrally Consistent Scattering, Absorption, and Polarization Properties of Atmospheric Ice Crystals at Wavelengths from 0.2 to 100 µm, *J. Atmos. Sci.*, **70**, 330–347, https://doi.org/10.1175/JAS-D-12-039.1.