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CALIPSO: Data User’s Guide - Data Product Descriptions - Lidar Level 3 Tropospheric Aerosol Profile Monthly Product Version 4.20


CALIPSO HOMECALIPSO User’s Guide HOMEData Products Description → Lidar Level 3 Tropospheric Aerosol Profile Monthly Product Version 4.20

Introduction

The CALIPSO lidar level 3 tropospheric aerosol profile product reports monthly mean profiles of aerosol optical properties on a uniform spatial grid. All level 3 parameters are derived from the version 4 CALIOP level 2 aerosol profile product and are quality screened prior to averaging. Eight level 3 data files are generated each month depending on sky condition and lighting condition (night and day are reported separately).

View the detailed data quality summary for this data product at: cal_lid_l3_tropospheric_apro_v4-20.php.



Organization of Level 3 Files

In order to keep level 3 file sizes manageable, eight different types of level 3 files are produced for eight unique combinations of sky conditions and lighting conditions (i.e., day vs. night).

Aerosol Data Files Produced
Sky Condition Lighting Condition
All Sky Night, Day
Cloud-Free Night, Day
Cloudy-Sky, Transparent Night, Day
Cloudy-Sky Opaque Night, Day

Statistics are reported in separate files corresponding to the relevant sky condition and lighting condition. Sky conditions describe the cloud occurrence frequency and location within the level 2 columns that are aggregated by level 3. There are four varieties of sky condition:

Description of the Four Sky Conditions
Sky Condition Description of Level 2 Data Usage
All Sky All level 2 columns are averaged, regardless of cloud occurrence
Cloud-Free Only cloud-free level 2 columns are averaged
Cloudy-Sky, Transparent Only level 2 columns containing transparent clouds are averaged
Cloudy-Sky Opaque Only level 2 columns containing opaque clouds are averaged

For the purposes of the level 3 tropospheric aerosol product, clouds detected at 5 km horizontal resolution or greater are used for screening; i.e., cloud-free columns do not contain clouds found at 5 km or coarser resolution, but they may contain clouds found at 1/3 km and 1 km horizontal resolution. These higher resolution clouds have been removed by the boundary layer cloud clearing algorithm prior to computing aerosol layer properties. Note that aerosol properties are never reported within clouds in any CALIPSO data product.

Temporal and Spatial Resolution

Statistics are aggregated with a temporal resolution of one month and are reported on an equal-angle grid with the following specifications.

Temporal and Spatial Resolution
Spatial Coverage Spatial Resolution
360° longitude (180°W to 180°E) 5° longitude
170° latitude (85°N to 85°S) 2° latitude
-0.5 km to 12 km altitude 60 m vertical

Based on the resolution of the grid above, level 3 quantities are reported in arrays having two, three, or four dimensions. The following table lists the sizes of all arrays of 2 dimensions or greater, excluding aerosol type distribution and aerosol spatial distribution arrays. Those arrays have similar dimensionality as the 3-D and 4-D arrays below, except the final dimension length depends on the purpose of the array. See product descriptions of those arrays for size descriptions.

Level 3 Array Sizes
Number of Dimensions Dimension Lengths
2-D num. latitudes x num. longitudes
(85 x 72)
3-D num. latitudes x num. longitudes x num. altitudes
(85 x 72 x 208)
4-D num. latitudes x num. longitudes x num. altitudes x num. percentiles *
(85 x 72 x 208 x 11)
* Number of percentiles is 11 because it contains the minimum, maximum, and the 10th, 20th, 30th, -, 90th percentiles.

Level 2 Input Data

The following table lists the versions of the level 2 data used as input for the version 4.20 level 3 tropospheric aerosol profile product.

CALIPSO Lidar Level 2 Input Data For Level 3 Tropospheric Aerosol Profile Product, V4
Level 2 Version Data Date Range
4.20 June 2006 - present

Quality Screening Strategy

Prior to generating level 3 statistics, all level 2 aerosol profile extinction samples are quality screened using filters designed to eliminate samples and layers that were detected or classified with very low confidence or that have untrustworthy extinction retrievals. Quality filters are described below. A more in-depth description of the quality filters and their impacts on version 3 level 3 statistics is given in Tackett et al., 2018.

  • CAD Score Filter. Only aerosol layers having cloud-aerosol discrimination (CAD) scores between -100 and -20 are used. Layers with CAD scores between 20 and -20 are often the result of erroneous layer detection triggered by noise. The lower confidence boundary of -20 was selected empirically by assessing the dependence of the number of layers rejected, the average extinction, and the propagated extinction uncertainties on the CAD score limit. This study revealed that varying the CAD threshold between -60 and -20 does little to remove large or negative extinction outliers or to reduce the propagated uncertainty. However, allowing aerosol layers with CAD scores closer to 0 does allow large and negative outliers into the extinction averages and increases the uncertainty.
  • Extinction QC Flag Filter. Only aerosol layers having extinction QC flag values of 0, 1, 16, or 18 are allowed. Extinction QC flag values of 16 and 18 correspond to layers classified as opaque where, in the former case, the retrieval completes successfully without adjusting the initial lidar ratio, and in the latter case, the lidar ratio is reduced to prevent the retrieval from diverging to infinity. Aerosol layers having extinction QC flag set to any other value are ignored since these retrievals show a greater propensity to exhibit erroneously large or negative values compared to aerosol layers with extinction QC = 0, 1, 16, or 18. Because errors in retrievals propagate downward, aerosol extinction samples at lower altitudes within the same profile are also rejected when an overlying aerosol layer exists with disallowed extinction QC flag values. Beginning in version 4 level 3, aerosol samples are also rejected beneath cloud layers having extinction QC ≠ 0, 1, or 2.
  • Extinction Uncertainty Filter. Only samples where aerosol extinction uncertainty is less than 99.9 km-1 are allowed. Uncertainty of 99.9 is a flag value assigned by the retrieval algorithm when the extinction uncertainty estimate has begun to diverge to infinity while iterating down the profile. In this case the retrieval results become unreliable and we exclude aerosol samples having extinction uncertainty equal to 99.9 and all aerosol samples at lower altitudes in the same profile since the untrustworthy extinction solution is propagated to lower altitudes as the retrieval proceeds downward.

    Sensitivity studies were conducted to assess if a more restrictive extinction uncertainty threshold is appropriate to reduce the occurrence of extinction outliers. For extinction uncertainty thresholds less than about 5 km-1 (uncertainty is expressed as an absolute uncertainty, not a relative uncertainty), we found that the propagated uncertainty had indeed been reduced, but the shape of level 3 mean extinction profiles had also changed in the lowest altitudes. This is because uncertainty increases at lower altitudes because errors are propagated from above. As a result, samples with relatively large aerosol extinction are selectively removed and the mean extinction is reduced in the lowest altitudes. To avoid changing the shape of the average extinction profile, all aerosol extinction uncertainty values are allowed except the flag value above (uncertainty = 99.9 km-1). Fortunately, just removing these samples reduces the number of extinction and extinction uncertainty outliers existing in level 3 statistics significantly.

  • Isolated 80 km Aerosol Layer Filter. Detection of layers averaged to 80 km is occasionally triggered by anomalous noise spikes, likely due to high energy particles impacting the lidar detectors. Aerosol layers detected at 80 km horizontal resolution that are not adjacent (either vertically or horizontally) to another aerosol layer and do not contain an embedded aerosol layer are excluded from quality screened level 3 statistics. Requiring that another aerosol layer is adjacent improves the confidence that a real aerosol layer exists in the region. These isolated 80 km layers tend to occur at higher altitudes and to have very low extinction values. Therefore excluding them removes sporadic extinction values which can be significant in the upper troposphere, but have little impact on the column AOD.
     
  • Misclassified Cirrus Fringe Filter. Occasionally, the tenuous edges of cirrus clouds are misclassified as aerosol by the cloud aerosol discrimination algorithm as shown in Figure 1 below. This happens most often for optically thin layers detected at 20 and 80 km horizontal resolutions. Because these cirrus fringes can skew the representativeness of true aerosol presence, aerosol layers adjacent to ice clouds are assumed to be misclassified clouds and are rejected. Specifically, aerosol layers above 4 km in altitude that are adjacent to an ice cloud (ice/water phase is randomly oriented or horizontally oriented) having cloud top temperature less than 0°C are rejected prior to computing level 3 statistics.
    Figure 1: Missclassified Cloud.
    Figure 1. CALIPSO level 2 vertical feature mask example showing where the fringe of cirrus clouds have been misclassified as aerosol. Orange, light blue, and green features have been classified as aerosol, cloud, and surface, respectively.
     
  • Undetected Near-Surface Aerosol Filter. At times the CALIPSO feature detection algorithm may not detect the entire vertical extent of surface attached aerosol layers. Often aerosol bases are assigned at 30 - 90 meters above the local surface due to overlying attenuation. If the aerosol base extension algorithm is invoked, the base is assigned to 90 meters above the local surface by default. This results in a low bias in the mean extinction profiles near the surface since "clear air" extinction is assumed to be 0.0 km-1 and undetected aerosol with non-zero extinction likely exists beneath these assigned bases.

    In order to avoid a low bias in level 3 mean aerosol extinction, for each level 2 profile, samples classified as "clear air" lying beneath the lowest quality screened aerosol layer whose base is below 250 meters are excluded from level 3 statistics; i.e., these values are not assumed to have clear air extinction of 0.0 km-1; they are ignored.

  • Negative Signal Anomaly Mitigation. A phenomenon dubbed a “negative signal anomaly” sometimes occurs when the level 1B attenuated backscatter becomes anomalously negative at the onset of an abrupt target such as the planetary surface or a dense cloud. Aerosol extinction can also become anomalously negative when attenuated backscatter affected by the anomaly is included within the extinction retrieval. Subsequent level 3 mean extinction would therefore exhibit a low bias near the surface where the negative signal anomaly is present. To mitigate the impact of this anomaly, all level 2 aerosol extinction within 60 meters of the planetary surface are excluded from level 3 calculations.

New Quality Filters in Version 4.20 Level 3

  • Cloud Layer Fraction Filter. Aerosol extinction samples having a Cloud Fraction > 28 (corresponding to 97%) are rejected to avoid cloud contamination. In the lower troposphere, level 2 extinction samples are comprised of at most 30 single shot attenuated backscatter measurements. Only the fraction of those measurements classified as aerosol are averaged together and ultimately contribute to the retrieved aerosol extinction within the 60 m vertical x 5 km horizontal resolution sample. The retrieved aerosol extinction can be spuriously large due to cloud contamination when most of the level 2 range bin is dominated by cloud attenuated backscatter. The level 2 Cloud Layer Fraction SDS, ranging from 0 to 30, is thereby used to determine the number of single shot values classified as cloud within an aerosol extinction sample. All aerosol samples having Cloud Layer Fraction exceeding the threshold are rejected, along with all aerosol extinction samples at lower altitudes within the same profile.
  • Misclassified Opaque Cloud Filter. Occasionally opaque clouds can be misclassified as opaque aerosol layers. This occurs most often underneath optically thick overlying cloud cover, which degrades the fidelity of the cloud-aerosol discrimination algorithm for lower layers. Because cloud contamination caused by an opaque clouds can significantly impact monthly mean aerosol extinction, opaque aerosol layers that are adjacent to opaque cloud layers are rejected.
  • Low Laser Energy Mitigation. Since September 2016, CALIOP has been experiencing low energy laser shots, primarily over the South Atlantic Anomaly (SAA) region. This behavior has significantly degraded the quality of affected profiles. In order to avoid impacting level 3 data quality, all level 2 profiles within the SAA region are excluded for data years 2017 onward. Figure 2 below illustrates the excluded region. More information on low energy laser shots is given on the CALIOP Data Advisory Page.
    Figure 2: Samples Searched.
    Figure 2. Samples searched by level 3 algorithm for June 2018 at night. No samples are searched in white regions.
  • References

    Tackett, J. L., D. M. Winker, B. J. Getzewich, M. A. Vaughan, S. A. Young and J. Kar, 2018: “CALIPSO lidar level 3 aerosol profile product: version 3 algorithm design”, Atmos. Meas. Tech., 11, 4129-4152, doi:10.5194/amt-11-4129-2018.

    Winker, D. M., J. L. Tackett, B. J. Getzewich, Z. Liu, M. A. Vaughan, and R. R. Rogers, 2013: “The global 3-D distribution of tropospheric aerosols as characterized by CALIOP”, Atmos. Chem. Phys., 13, 3345-3361, doi:10.5194/acp-13-3345-2013.



    Data Descriptions

    In the text below we provide brief descriptions of individual data fields reported in the CALIPSO vertical feature mask product. Where appropriate, we also provide an assessment of the quality and accuracy of the data in the current release. The data descriptions are grouped into several major categories, as follows:

    Additionally all the science data sets (SDSs) are listed in the table to the right, click on the SDS name to go directly to the description.

    Science Data Set (SDS)
    Longitude Midpoint
    Latitude Midpoint
    Altitude Midpoint
    Pressure Mean
    Pressure Standard Deviation
    Temperature Mean
    Temperature Standard Deviation
    Relative Humidity Mean
    Relative Humidity Standard Deviation
    Tropopause Height Minimum
    Tropopause Height Maximum
    Tropopause Height Median
    Tropopause Height Mean
    Tropopause Height Standard Deviation
    Meteorological Profiles Averaged
    Surface Elevation Minimum
    Surface Elevation Maximum
    Surface Elevation Median
    Land Samples
    Water Samples
    Days of Month Observed
    Initial Aerosol Lidar Ratio 532
    Initial Aerosol Lidar Ratio Uncertainty 532
    Extinction Coefficient 532 Mean [Dust, Polluted Dust, Elevated Smoke]
    Extinction Coefficient 532 Standard Deviation [Dust, Polluted Dust, Elevated Smoke]
    Extinction Coefficient 532 Percentiles
    AOD Mean [Dust, Polluted Dust, Elevated Smoke]
    AOD 63 Percent Below
    AOD 90 Percent Below
    Samples Searched
    Samples Averaged [Dust, Polluted Dust, Elevated Smoke]
    Samples Aerosol Detected Accepted [Dust, Polluted Dust, Elevated Smoke]
    Samples Aerosol Detected Rejected [Dust, Polluted Dust, Elevated Smoke]
    Samples Cloud Detected
    Aerosol Type
    Multiple Aerosol Type Count
    Number Layers Per Column [Dust, Polluted Dust, Elevated Smoke]
    Highest Aerosol Layer Detected [Dust, Polluted Dust, Elevated Smoke]
    Lowest Aerosol Layer Detected [Dust, Polluted Dust, Elevated Smoke]
    Layer Separation Minimum [Dust, Polluted Dust, Elevated Smoke]
    Layer Separation Maximum [Dust, Polluted Dust, Elevated Smoke]
    Layer Separation Median [Dust, Polluted Dust, Elevated Smoke]
    Layer Separation Mean [Dust, Polluted Dust, Elevated Smoke]
    Layer Separation Standard Deviation [Dust, Polluted Dust, Elevated Smoke]


    Spatial Coordinates

    Longitude_Midpoint (1-D array)
    Units: deg
    Format: Float_32
    Valid Range: -180.0...180.0
    Fill Value: No Fill Value
    Definition: Longitude, in degrees, at the latitude/longitude/altitude grid cell midpoint.

    Latitude_Midpoint (1-D array)
    Units: deg
    Format: Float_32
    Valid Range: -85.0...85.0
    Fill Value: No Fill Value
    Definition: Latitude, in degrees, at the latitude/longitude/altitude grid cell midpoint.

    Altitude_Midpoint (1-D array)
    Units: km
    Format: Float_32
    Valid Range: -0.5...12.1
    Fill Value: No Fill Value
    Definition: Altitude, in kilometers, at the latitude/longitude/altitude grid cell midpoint.

    Meteorological Context

    Pressure_Mean (external) (3-D array)
    Units: hPa
    Format: Float_32
    Valid Range: 1.0...1,086.0
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all pressures reported within the latitude/longitude/altitude grid cell in hectopascals; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Pressure_Standard_Deviation (external) (3-D array)
    Units: hPa
    Format: Float_32
    Valid Range: 0.0...15.0
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all pressures reported within the latitude/longitude/altitude grid cell in hectopascals; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Temperature_Mean (3-D array)
    Units: °C
    Format: Float_32
    Valid Range: -120.0...60.0
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all temperatures reported within the latitude/longitude/altitude grid cell in degrees C; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Temperature_Standard_Deviation (external) (3-D array)
    Units: °C
    Format: Float_32
    Valid Range: 0.0...10.0
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all temperatures reported within the latitude/longitude/altitude grid cell in degrees C; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Relative_Humidity_Mean (3-D array)
    Units: NoUnits
    Format: Float_32
    Valid Range: 0.0...1.5
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all relative humidity reported within the latitude/longitude/altitude grid cell, in percent; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Relative_Humidity_Standard_Deviation (external) (3-D array)
    Units: NoUnits
    Format: Float_32
    Valid Range: 0.0...0.4
    Fill Value: -9999.0
    Definition: Mean and standard deviation of all relative humidity reported within the latitude/longitude/altitude grid cell, in percent; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Tropopause_Height_Minimum (external) (2-D array)
    Tropopause_Height_Maximum (external) (2-D array)
    Tropopause_Height_Median (external) (2-D array)
    Topopause_Height_Mean (external) (2-D array)
    Units: km
    Format: Float_32
    Valid Range: 4.0...22.0
    Fill Value: -9999.0
    Definition: Statistics of all tropopause heights reported within the latitude/longitude grid cell in kilometers above local mean sea level; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Tropopause_Height_Standard_Deviation (external) (2-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...5.0
    Fill Value: -9999.0
    Definition: Statistics of all tropopause heights reported within the latitude/longitude grid cell in kilometers above local mean sea level; derived from the MERRA-2 data product provided to the CALIPSO project by the GMAO Data Assimilation System.

    Meteorological_Profiles_Averaged (2-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Number of 5 km horizontal resolution meteorological profiles averaged within the latitude/longitude grid cell.

    Surface Elevation and Overflight Parameters

    Surface_Elevation_Minimum (external) (2-D array)
    Surface_Elevation_Maximum (external) (2-D array)
    Surface_Elevation_Median (external) (2-D array)
    Units: km
    Format: Float_32
    Valid Range: -1.0...9.0
    Fill Value: -9999.0
    Definition: Surface elevation statistics for all columns reported in the latitude/longitude grid cell in kilometers above local mean sea level, obtained from the GTOPO30 digital elevation map (DEM).

    Land_Samples (external) (2-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Number of columns within the latitude/longitude grid cell having surface type at the lidar footprint classified as land (i.e., not water) by the International Geosphere/Biosphere Programme (IGBP). The IGBP surface types reported by CALIPSO are the same as those used in the CERES/SARB surface map.

    Water_Samples (external) (2-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Number of columns within the latitude/longitude grid cell having surface type at the lidar footprint classified as water by the International Geosphere/Biosphere Programme (IGBP). The IGBP surface types reported by CALIPSO are the same as those used in the CERES/SARB surface map.

    Days_Of_Month_Observed (2-D array)
    Units: NoUnits
    Format: Int_32
    Valid Range: 0...4,294,967,295
    Fill Value: No Fill Value
    Definition: The days of month observed flags are bit-mapped 32-bit floats indicating which calendar days of the month CALIPSO made observations within a latitude/longitude grid cell. Bits are set to true when CALIPSO makes an observation on that calendar day with the least significant bit corresponding to the first day of the month. Bit 1 is the least significant bit.

    For example, if CALIPSO made an observation within a grid cell on the 1st day of the month, then bit 1 would be set to true and if CALIPSO made an observation on the 2nd day of the month, then bit 2 would be set to true and so on. Based on CALIPSO"s orbit, a grid cell at the equator would have much fewer days set to true than a grid cell near the poles.


    Figure 3: days of month flag interpretation.
    Figure 3. Example of how to interpret Days of Month flag.

    Static Lidar Ratio Parameters

    Initial_Aerosol_Lidar_Ratio_532 (1-D array)
    Units: sr
    Format: Float_32
    Valid Range: 20.0...70.0
    Fill Value: No Fill Value
    Definition: Indicates estimated initial lidar ratios used in the level 2 retrievals, and their uncertainties, for each aerosol subtype in units of steradians. Retrieving aerosol extinction, backscatter and optical depth from CALIPSO measurements requires an estimate of the particulate extinction-to-backscatter ratio, known as the "lidar ratio". These initial estimates are based on the aerosol subtype of the layer being analyzed. The six values reported correspond to the six aerosol type that the automated classification system identifies: clean marine, dust, polluted continental/smoke, clean continental, polluted dust, elevated smoke, and dusty marine respectively. More information on the rationale for these estimates and their errors is discussed in the paper, 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, doi:10.5194/amt-11-6107-2018.

    Initial_Aerosol_Lidar_Ratio_Uncertainty 532 (1-D array)
    Units: sr
    Format: Float_32
    Valid Range: 2.0...30.0
    Fill Value: No Fill Value
    Definition: Indicates estimated initial lidar ratios used in the level 2 retrievals, and their uncertainties, for each aerosol subtype in units of steradians. Retrieving aerosol extinction, backscatter and optical depth from CALIPSO measurements requires an estimate of the particulate extinction-to-backscatter ratio, known as the "lidar ratio". These initial estimates are based on the aerosol subtype of the layer being analyzed. The six values reported correspond to the six aerosol type that the automated classification system identifies: clean marine, dust, polluted continental/smoke, clean continental, polluted dust, elevated smoke, and dusty marine respectively. More information on the rationale for these estimates and their errors is discussed in the paper, 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, doi:10.5194/amt-11-6107-2018.

    Aerosol Optical Parameters

    Extinction Coefficient 532 Mean [Dust, Polluted Dust, Elevated Smoke] (3-D array)
           (Units: km-1; Format: Float_32; Valid Range: 0.0...4.0; Fill Value: -9999.0)

    Extinction Coefficient 532 Standard Deviation [Dust, Polluted Dust, Elevated Smoke] (3-D array)
           (Extinction_Coefficient_532_Standard_Deviation - Units: km-1; Format: Float_32; Valid Range: 0.0...0.15; Fill Value: -9999.0)
           (all others - Units: km-1; Format: Float_32; Valid Range: 0.0...0.1; Fill Value: -9999.0)

    Extinction Coefficient 532 Percentiles (4-D array)
    Units: km-1
    Format: Float_32
    Valid Range: 0.0...0.4
    Fill Value: -9999.0
    Definition: Vertical profiles of mean and standard deviation for all quality screened lidar level 2 aerosol profile extinction coefficients, reported with the latitude/longitude/altitude grid cell in units of km-1. Percentiles is an 11-element array with the first value containing the minimum quality screened aerosol extinction coefficient within the grid cell and the last containing the maximum. Intermediate elements specify aerosol extinction coefficients corresponding to percentiles between 10% (element 2) and 90% (element 10). If the parameter name ends with "Dust", "Polluted Dust" or "Smoke", then only aerosol layers classified as the indicated subtype are used to compute statistics. Otherwise, all aerosol species are included in the statistics. An example of level 3 aerosol extinction percentiles are shown in Figure 3.

    In computing extinction statistics, regions identified as "clear air" by the feature finder are assumed to have an aerosol extinction coefficient of 0.0 km-1. This results in an underestimate of mean extinction, (see Section 4.1 of Tackett et al., 2018) but we believe the low bias is small in most cases at night. During daytime, the low bias may be larger where layers are not detected due to solar noise and high-albedo surfaces. This is being addressed in initial validation studies.

    Figure 4: extinction profile example.
    Figure 4. Example extinction percentiles for a single altitude bin at 4 km.

    AOD_Mean [_Dust, _Polluted_Dust, _Elevated_Smoke] (2-D array)
    Units: NoUnits
    Format: Float_32
    Valid Range: 0.0...5.0
    Fill Value: -9999.0
    Definition: Mean aerosol optical depth (AOD), calculated as the vertical integral of level 3 mean aerosol extinction coefficients.

    AOD_63_Percent_Below (2-D array)
    AOD_90_Percent_Below (2-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...12.0
    Fill Value: -9999.0
    Definition: Altitude in kilometers below which contains 63% or 90% of the total mean aerosol optical depth in the level 3 grid cell.

    Sample Counting Statistics

    Users may want to spatially or temporally aggregate these level 3 data. Therefore, the sample numbers required to correctly aggregate the statistics are included.

    Samples_Searched (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Reports the total number of atmospheric measurements made in each latitude/longitude/altitude grid cell, regardless of whether they were accepted, rejected, or ignored. It can be thought of as the number of chances that CALIOP had to measure an atmospheric feature. As such, range bins beneath the surface and range bins beneath opaque layers do not contribute to this number since CALIOP did not have a chance to measure beneath these features. Level 3 sample numbers are reported based on a 5 km horizontal x 30 meter vertical resolution grid to match resolution at which layers are reported in the level 2 aerosol and 5 km cloud layer products.

    Samples_Averaged [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Reports the number of samples contributing to the mean, standard deviation, and skew of aerosol extinction coefficients in each latitude/longitude/altitude grid cell. In computing these statistics, regions identified as "clear air" are assumed to have an aerosol extinction coefficient of 0.0 km-1. Therefore, the number of samples averaged includes both the aerosol extinction coefficients passing all quality assurance filtering criteria and the number of "clear air" extinction values in the grid cell. Level 3 sample numbers are reported based on a 5 km horizontal x 30 meter vertical resolution grid to match resolution at which layers are reported in the level 2 aerosol and 5 km cloud layer products.

    Samples_Aerosol_Detected_Accepted [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Reports the number of aerosol samples in each latitude/longitude/altitude grid cell that were detected and passed all quality assurance filtering criteria. However, this is not the number of samples that contributes to extinction and AOD statistics (excluding RMS uncertainty) because clear air extinction samples are included in those calculations (see Samples Averaged, above). For the case of RMS uncertainty, this is the number of samples used because only uncertainties from detected aerosol layers passing all quality assurance filtering criteria are propagated into level 3 RMS uncertainties. Level 3 sample numbers are reported based on a 5 km horizontal x 30 meter vertical resolution grid to match resolution at which layers are reported in the level 2 aerosol and 5 km cloud layer products.

    Samples_Aerosol_Detected_Rejected [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Reports the number of aerosol samples in each latitude/longitude/altitude grid cell that were detected but failed to pass our filtering criteria. These samples are ignored in all statistical calculations. Level 3 sample numbers are reported based on a 5 km horizontal x 30 meter vertical resolution grid to match resolution at which layers are reported in the level 2 aerosol and 5 km cloud layer products.

    Samples_Cloud_Detected (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Reports the number of 5 km x 30 m resolution range bins that are entirely cloudy (cloud layer fraction equals 100%) occurring in each latitude/longitude/altitude grid cell. Level 3 sample numbers are reported based on a 5 km horizontal x 30 meter vertical resolution grid to match resolution at which layers are reported in the level 2 aerosol and 5 km cloud layer products.

    Aerosol Type Distribution

    Aerosol_Type (4-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Histogram of aerosol type for each latitude/longitude/altitude grid cell. This array of seven integers counts the number of aerosol samples having the CALIPSO aerosol type clean marine, dust, polluted continental/smoke, clean continental, polluted dust, elevated smoke, and dusty marine, respectively for each latitude/longitude/altitude grid cell. Therefore this array has size num. latitudes x num. longitudes x num. altitudes x num. aerosol types (85 x 72 x 208 x 7).

    Multiple_Aerosol_Type_Count (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Histogram documenting occurrence of multiple aerosol types in each latitude/longitude grid cell. Each element of this 8-element array records the number of instances for which N different aerosol types were detected in the individual level 2 aerosol profiles within each latitude/longitude grid cell. N ranges from 0 (no aerosol detected in a column) to 6 (all six of the CALIPSO aerosol types were detected in a single column). Therefore this array has size num. latitudes x num. longitudes x num. aerosol types detected (85 x 72 x 8).

    Aerosol Spatial Distribution

    Number_Layers_Per_Column [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: NoUnits
    Format: Int_16
    Valid Range: 0...32,767
    Fill Value: -9999
    Definition: Histogram of the number of aerosol layers detected in the level 2 data products for each latitude/longitude grid cell. The first element of this 9-element array records the number of columns having zero aerosol layers. Similarly, the second element records the number of columns having one aerosol layer, and so on. The ninth array element records the number of columns having eight or more aerosol layers detected. Therefore this array has size num. latitudes x num. longitudes x num. aerosol detected (85 x 72 x 9).

    Highest_Aerosol_Layer_Detected [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...20.0
    Fill Value: -9999.0
    Definition: Distribution of highest aerosol layer top altitudes detected within each latitude/longitude grid cell in units of kilometers, reported as percentile arrays. Percentiles are 11-element arrays with the first value containing the minimum layer top altitude within the grid cell and the last containing the maximum. Intermediate elements specify layer top altitudes corresponding to percentiles between 10% (element 2) and 90% (element 10). Therefore this array has size num. latitudes x num. longitudes x num. percentiles (85 x 72 x 11).

    Lowest_Aerosol_Layer_Detected [_Dust, _Polluted_Dust, _Elevated_Smoke] (3-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...20.0
    Fill Value: -9999.0
    Definition: Distribution of lowest aerosol layer base altitudes detected within each latitude/longitude grid cell in units of kilometers, reported as percentile arrays. Percentiles are 11-element arrays with the first value containing the minimum layer base altitude within the grid cell and the last containing the maximum. Intermediate elements specify layer base altitudes corresponding to percentiles between 10% (element 2) and 90% (element 10). Therefore this array has size num. latitudes x num. longitudes x num. percentiles (85 x 72 x 11).

    Layer_Separation_Minimum [_Dust, _Polluted_Dust, _Elevated Smoke] (3-D array)
    Layer_Separation_Maximum [_Dust, _Polluted_Dust, _Elevated Smoke] (3-D array)
    Layer_Separation_Median [_Dust, _Polluted_Dust, _Elevated Smoke] (3-D array)
    Layer_Separation_Mean [_Dust, _Polluted_Dust, _Elevated Smoke] (3-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...20.0
    Fill Value: -9999.0
    Definition: Minimum, maximum, median, mean, and standard deviation of vertical separation distances between all detected aerosol layers in all columns within each latitude/longitude grid cell in units of kilometers. Layer separation is defined as the vertical distance between two aerosol layers that are separated by either clear air or cloud. Since there are can be more than two aerosol layers in a column, layer separation statistics are reported using 7-element arrays where the first element reports the separation statistics for columns where two aerosol layers are detected, the second element reports separation statistics for columns where three aerosol layers are detected, and so on. The seventh and last element reports separation statistics for columns where eight or more layers aerosol layers are detected. Therefore this array has size num. latitudes x num. longitudes x num. layers (85 x 72 x 7).

    Layer_Separation_Standard_Deviation [_Dust, _Polluted_Dust, _Elevated Smoke] (3-D array)
    Units: km
    Format: Float_32
    Valid Range: 0.0...5.0
    Fill Value: -9999.0
    Definition: Minimum, maximum, median, mean, and standard deviation of vertical separation distances between all detected aerosol layers in all columns within each latitude/longitude grid cell in units of kilometers. Layer separation is defined as the vertical distance between two aerosol layers that are separated by either clear air or cloud. Since there are can be more than two aerosol layers in a column, layer separation statistics are reported using 7-element arrays where the first element reports the separation statistics for columns where two aerosol layers are detected, the second element reports separation statistics for columns where three aerosol layers are detected, and so on. The seventh and last element reports separation statistics for columns where eight or more layers aerosol layers are detected. Therefore this array has size num. latitudes x num. longitudes x num. layers (85 x 72 x 7).

    File Metadata Parameters

    Product ID
    Parameter Name: Product_ID
    An 80-byte (max) character string specifying the data product name. For all CALIPSO lidar level 3 aerosol data products, the first portion of this string will be "CAL_LID_L3_Tropospheric_APro_" and the final portion of the string will indicate the sky condition, "AllSky" or "CloudFree", "CloudySkyTransparent", or "CloudySkyOpaque".

    Nominal Year Month
    Parameter Name: Nominal_Year_Month
    A six digit integer indicating the year and month when data within the level 3 file was measured by CALIPSO in the format yyyymm.

    Number of Level 2 Files Analyzed
    Parameter Name: Number_of_Level2_Files_Analyzed
    Integer indicating the number of level 2 granules analyzed to generate the level 3 file.

    Earliest Input Filename
    Parameter Name: Earliest_Input_Filename
    A 160-byte (max) character string specifying the filename of the first (by calendar day and time) level 2 aerosol profile granule analyzed within the month of the level 3 file.

    Latest Input Filename
    Parameter Name: Latest_Input_Filename
    A 160-byte (max) character string specifying the filename of the last (by calendar day and time) level 2 aerosol profile granule analyzed within the month of the level 3 file.

    Data Screening Script Filename
    Parameter Name: Data_Screening_Script_Filename
    A 160-byte (max) character string specifying the filename of the script containing configuration information and command sequences that were executed during the processing of the CALIPSO lidar level 3 data product.

    Data Screening Script File Contents
    Parameter Name: Data_Screening_Script_File_Contents
    A 5000-byte (max) character string containing configuration information and command sequences that were executed during the processing of the CALIPSO lidar level 3 data product. These commands define spatial boundaries and implement quality filters and are described by in-line documentation.

    List_of_Input_Files
    A 30,000-byte (max) character string containing the list of level 2 aerosol profile granules used to construct the level 3 file.


    Data Quality Statements

    Lidar Level 3 Tropospheric Aerosol Profile Products Information
    Release Date Version Data Date Range Production Strategy
    September 11, 2019 4.20 June 13, 2006 - present Standard


NASA
Last Updated: September 25, 2019
Curator: Charles R. Trepte
NASA Official: Charles R. Trepte

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