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CALIPSO HOMERESOURCESUser’s Guide HOME → Lidar Level 1.5 Data Product Descriptions

CALIPSO Data User’s Guide - Lidar Level 1.5 Data Product Description (Expedited V3.50 & Standard V1.00)


Introduction

The CALIPSO lidar level 1.5 data product contains profiles of attenuated backscatter and aerosol extinction coefficients for which clouds, overcast, surface, subsurface, and totally attenuated samples have been removed before being averaged to a 20 km horizontal resolution (see Table 1). This product is a synthesis of CALIPSO lidar level 1B and lidar level 2 aerosol profile products with the lidar level 2 vertical feature mask used for feature identification and screening. Thus, it is deemed a “level 1.5” product. The lower panel of figure 1 demonstrates that level 1.5 cloud-cleared attenuated backscatter is comprised solely of molecular and aerosol scattering.

Total attenuated backscatter plots.

Figure 1: Example of level 1 attenuated backscatter (top) and level 1.5 attenuated backscatter (bottom).

The level 1.5 data product is generated using two production strategies: standard and expedited. The standard production strategy uses the most recent CALIOP version 4 data as input, thus providing accurately calibrated attenuated backscatter and the benefits of the most sophisticated CALIOP scene classification algorithms. The expedited production strategy uses CALIOP version 3 expedited data products as input and is intended specifically for near-real time applications. While using the expedited calibration procedures (see Vaughan et al., 2011) and version 3 scene classification algorithm minimizes the latency between onboard data acquisition and data product release, the resulting data products are not as accurate as those derived from the version 4 standard data. Users are cautioned against the indiscriminate use of the expedited level 1.5 product as the basis for research findings, journal publications, and/or presentations at scientific conferences. Instead, users are encouraged to use the version 1 standard level 1.5 data product for research findings where near-real time use is not critical. Note that whereas the level 1.5 standard product can be ordered through the Atmospheric Science Data Center (ASDC) for the entire CALIOP data record, the level 1.5 expedited product is available only by subscription with only the most recent 30 days being available.



Resolution and Coverage



Table 1: The spatial resolution of the level 1.5 data product.
Altitude Region Spatial Resolution
-0.5 to 20.2 km 20 km horizontal x 60 m vertical
20.2 to 30.1 km 20 km horizontal x 180 m vertical


Input Data



Table 2: Lidar level 1 and level 2 input data for the level 1.5 products.
Level 1.5 Production Strategy and Version Level 1 and Level 2 Input Data
Standard V1.00 Standard V4.x
Expedited V3.50 Expedited V3.x


Algorithm Summary

The level 2 vertical feature mask is used to identify the occurrence of clouds, overcast, surface, subsurface, totally attenuated samples, and invalid features in full resolution profiles of level 1B attenuated backscatter coefficients and level 2 aerosol extinction coefficients. Thes undesirable features are then removed, and the remaining data is averaged to a uniform horizontal resolution of 20 km (equivalent to 60 consecutive laser pulses). Overcast is defined as all range bins beneath the highest cloud in a profile. Features in the stratosphere are handled differently, depending on the version of the input data. For standard version 4 input (i.e., the standard version 1 level 1.5 product), stratospheric aerosol layers having the subtype PSC aerosol are considered to be clouds, and thus removed, whereas volcanic ash, sulfate/other, and smoke layers are retained. For version 3 input (i.e., the expedited version 3.x level 1.5 product), stratospheric features are treated as clouds if they are located poleward of 60° or if their feature type QA flag is no confidence. Otherwise, they are classified as clear-air.

In order to avoid cloud contamination near cloud edges, the cloud mask derived from the CALIOP vertical feature mask is dilated vertically and horizontally by the distances in Table 3. Attenuated backscatter coefficients within the dilated cloud mask are removed prior to subsequent averaging. Similarly, attenuated backscatter coefficients within 30 m of the Earth’s surface are removed to avoid possible surface contamination. After screening, all remaining attenuated backscatter coefficients are then averaged to the resolutions given in Table 1. Feature types within each averaged profile are summarized by the L2_Feature_Type SDS.

Table 3: Cloud mask dilation amount.
Altitude Region Vertically Horizontally
20.1 - 30.2 km 180 m 5/3 km
8.2 - 20.1 km 60 m 1 km
-0.5 - 8.2 km 30 m 1/3 km

Important Notice: Since September 2016, CALIOP has been experiencing low energy laser shots, primarily over the South Atlantic Anomaly region that have significantly degraded the quality of the affected profiles. More information is given on the CALIOP Data Advisory Page. In order to help data users screen affected level 1.5 profiles, single shot laser energy statistics are provided for each 20 km-averaged profile. The most effective method for screening affected level 1.5 profiles is to exclude profiles based on the Minimum_Laser_Energy_532 SDS. Currently, the CALIPSO science team recommends removing profiles having a minimum laser energy < 0.08 J.



Product Descriptions

Descriptions of the individual data fields reported in level 1.5 are provided below. Note that some SDS records are only available for the V3 expedited level 1.5 product. 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. SDSs labeled as “external” originate from sources outside of the CALIPSO project.

Science Data Set (SDS)
Profile_Time
Profile_UTC_Time
Day_Night_Flag
Latitude
Longitude
Profile_ID
Laser_Energy_Statistics_532
Laser_Energy_Statistics_1064
Minimum_Laser_Energy_532
Molecular_Number_Density
Ozone_Number_Density
Pressure
Temperature
Tropopause_Height_Mean
Land_Water_Mask
Surface_Elevation_Mean
Surface_Elevation_StDev
Samples_Averaged
L2_Feature_Type
Extinction_QC_Flag_532 (V3 expedited only)
Total_Attenuated_Backscatter_532_Mean
Perpendicular_Attenuated_Backscatter_532_Mean
Attenuated_Backscatter_1064_Mean
Total_Attenuated_Backscatter_532_Median
Total_Attenuated_Backscatter_532_StDev
Perpendicular_Attenuated_Backscatter_532_Median
Perpendicular_Attenuated_Backscatter_532_StDev
Attenuated_Backscatter_1064_Median
Attenuated_Backscatter_1064_StDev
Total_Attenuated_Backscatter_532_Uncertainty
Perpendicular_Attenuated_Backscatter_532_Uncertainty
Attenuated_Backscatter_1064_Uncertainty
Extinction_Coefficient_532_Mean (V3 expedited only)
Extinction_Coefficient_532_Median (V3 expedited only)
Extinction_Coefficient_532_StDev (V3 expedited only)
Extinction_Coefficient_532_Uncertainty (V3 expedited only)
Calibration_Constant_Parallel_532
Calibration_Constant_Parallel_Uncertainty_532
Calibration_Constant_Perpendicular_532
Calibration_Constant_Perpendicular_Uncertainty_532
Calibration_Constant_1064
Calibration_Constant_Uncertainty_1064
Molecular_Model_Attenuated_Backscatter_532
Molecular_Model_Attenuated_Backscatter_1064


Column Time Parameters

Profile_Time
Units: sec
Format: Float_64
Valid range: 4.204E8...8.657E8
Definition: Time, expressed in International Atomic Time (TAI) at the temporal midpoint of each 20 km horizontal resolution profile (average time of the 30th and 31st consecutive laser shots). Units are in seconds, starting from January 1, 1993.

Profile_UTC_Time
Units: NoUnits
Format: Float_64
Valid Range: 60,426.0...200,608.0
Description: Similar to the Profile Time, but for time expressed in Coordinated Universal Time (UTC), and formatted as “yymmdd.ffffffff”, where “yy” represents the last two digits of the year, “mm” and “dd” represent the month and day, respectively, and “ffffffff” is the fractional part of the day.

Day_Night_Flag
Units: NoUnits
Format: Int_8
Valid Range: 0...2
Description: Indicates the lighting conditions at an altitude of ˜24 km above mean sea level; 0 = day and 1 = night. In lidar level 1.5 expedited profiles where the day/night terminator is crossed within the 20 km horizontal averaging interval, Day_Night_Flag is assigned a value of 2 for “day and night”. This occurs in the expedited products because expedited granules are 90 minutes in duration and contain data recorded at both day and night.

Geolocation and Altitude Registration

Latitude (midpoint)
Units: degree (°)
Format: Float_32
Fill Value: -9999.00 Valid Range: -90.0...90.0
Description: Geodetic latitude at the temporal midpoint of each 20 km horizontal resolution profile (average of laser footprint latitudes at the 30th and 31st consecutive laser shots).

Longitude (midpoint)
Units: degree (°)
Format: Float_32
Fill Value: -9999.00 Valid Range: -180.0...180.0
Description: Longitude at the temporal midpoint of each 20 km horizontal resolution profile (average of laser footprint longitudes at the 30th and 31st consecutive laser shots).

Profile Identification

Profile_ID (first and last)
Units: NoUnits
Format: Int_32
Valid Range: 1...228,630
Description: This integer is generated sequentially for each single-shot profile record in the level 1B products. Each profile ID is unique within each granule. For level 1.5 data products, only the first and last profile ID for each 20 km resolution profile are reported (corresponding to the 1st and 60th laser shots).

Laser Energy Information


Laser_Energy_Statistics_532
Laser_Energy_Statistics_1064
Units: Joules
Format: Float_32
Valid Range: 0.003...0.135
Description: Reports the minimum, maximum, mean, and median of all single-shot laser energies within each 20 km horizontal resolution profile for the indicated wavelength.

Minimum_Laser_Energy_532
Units: Joules
Format: Float_32
Valid Range: 0.003...0.135
Description: The 80 km distance matches the largest horizontal extent considered in CALIOP’s standard level 2 data analyses.

Profile Meteorological Data

Molecular_Number_Density (external)
Units: m-3
Format: Float_32
Fill Value: -9999.0
Valid Range: 8x1022...5x1025
Description: Mean molecular number density reported for the temporal midpoint of each range bin in each 20 km horizontal resolution profile (i.e., the average of the molecular number densities reported at the 30th and 31st consecutive single shot profiles for each range bin). Values are logarithmically interpolated from the 33 standard altitude levels reported in the lidar level 1B products (Met Data Altitudes) to the 400 standard altitude levels reported in the lidar level 1.5 product (Lidar Data Altitudes) prior to computing the temporal midpoint average. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Ozone_Number_Density (external)
Units: m-3
Format: Float_32
Fill Value: -9999.0
Valid Range: 1x1017...1x1019
Description: Mean ozone number density reported for the temporal midpoint of each range bin in each 20 km horizontal resolution profile (i.e., the average of the ozone number densities reported at the 30th and 31st consecutive single shot profiles for each range bin). Logarithmically interpolated from the 33 standard altitudes levels reported in the lidar level 1B products (Met Data Altitudes) to the 400 standard altitude levels reported in the lidar level 1.5 product (Lidar Data Altitudes) prior to computing the temporal midpoint average. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Pressure (external)
Units: millibars
Format: Float_32
Fill Value: -9999.0
Valid Range: 1.0...1086.0
Description: Mean pressure reported for the temporal midpoint of each range bin in the 20 km horizontal resolution profile (i.e., the average of the pressure reported at the 30th and 31st consecutive single shot profiles for each range bin). Values are logarithmically interpolated from the 33 standard altitude levels reported in the lidar level 1B products (Met Data Altitudes) to the 400 standard altitude levels reported in the lidar level 1.5 product (Lidar Data Altitudes) prior to computing the temporal midpoint average. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Temperature (external)
Units: °C
Format: Float_32
Fill Value: -9999.0
Valid Range: -120.0...60.0
Description: Mean temperature reported for the temporal midpoint of each range bin in the 20 km horizontal resolution profile (i.e., the average of the temperature reported at the 30th and 31st consecutive single shot profiles for each range bin). Values are linearly interpolated from the 33 standard altitude levels reported in the lidar level 1B products (Met Data Altitudes) to the 40 standard altitude levels reported in the lidar level 1.5 product (Lidar Data Altitudes) prior to computing the temporal midpoint average. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Tropopause_Height_Mean (external)
Units: km
Format: Float_32
Fill Value: -9999.0
Valid Range: 4.0...22.0
Description: Mean tropopause height for each 20 km horizontal resolution profile. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Surface Information

Land_Water_Mask
Units: NoUnits
Format: Int_8
Fill Value: -9
Valid Range: 0...7
Description: Reports the land-water mask value provided by the SDP toolkit at 5 km horizontal resolution. Hence, there are four values reported for each 20 km horizontal resolution profile. The values indicate the surface type at the lidar footprint, and are interpreted as follows:
0 = shallow ocean
1 = land
2 = coastlines
3 = shallow inland water
4 = intermittent water
5 = deep inland water
6 = continental ocean
7 = deep ocean

Surface_Elevation_Mean
Units: km
Format: Float_32
Valid Range: -1.0...9.0
Description: Average of the surface elevation above mean sea level of all laser footprints within each 20 km horizontal resolution profile. For the version 3 expedited level 1.5 product, the surface elevation is obtained from the GTOPO30 digital elevation map (DEM). For the version 1 standard level 1.5 product, a more accurate DEM developed by the CloudSat team is used.

Surface_Elevation_StDev
Units: km
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...9.0
Description: Standard deviation of the surface elevation above mean sea level of all laser footprints within each 20 km horizontal resolution profile. For the version 3 expedited product, the surface elevation is obtained from the GTOPO30 digital elevation map (DEM). For the version 1 standard level 1.5 product, a more accurate DEM developed by the CloudSat team is used.

Feature Spatial Information Within Column

Samples_Averaged
Units: NoUnits
Format: UInt_16
Valid Range: 0...360
Description: Number of full resolution samples averaged within each profile range bin after screening clouds, overcast, surface, subsurface, totally attenuated, and invalid features. Here, “full resolution” is taken to mean single shot (˜1/3 km) horizontally and 30 meters vertically. Since level 1.5 profile range bins are averaged to 20 km horizontal x 60 meters vertical, there are at most 120 full resolution samples averaged per lidar level 1.5 range bin below 20.2 km and at most 360 full resolution samples above 20.2 km.

L2_Feature_Type
Units: NoUnits
Format: UInt_8
Fill Value: 255
Valid Range: 0...29
Description: Reports the results of the CALIPSO level 2 layer detection and scene classification algorithms for tropospheric features within each lidar level 1.5 profile range bin. For each lidar level 1.5 profile range bin, a 4-element array of 8-bit unsigned integers is reported. Each of these four array elements corresponds to a 5 km horizontal x 60 m vertical segment of data that was considered for averaging. Values for L2_Feature_Type are as follows:

ValueL2 Feature TypeValueL2 Feature Type
0 invalid (bad or missing data)16 cloud-cleared clean marine
1 totally attenuated17 cloud-cleared dust
2 surface18 cloud-cleared polluted continental
3 subsurface19 cloud-cleared clean continental
4 cloud20 cloud-cleared polluted dust
5 clean marine21 cloud-cleared elevated smoke
6 dust22 cloud-cleared dusty marine
7 polluted continental23 cloud-cleared PSC aerosol
8 clean continental24 cloud-cleared volcanic ash
9 polluted dust25 cloud-cleared sulfate/other
10 elevated smoke26 cloud-cleared mixed aerosol
11 dusty marine27 “clear air”
12 PSC aerosol28 cloud-cleared “clear air”
13 volcanic ash29 overcast
14 sulfate/other  
15 mixed aerosol  

The aerosol types for dusty marine, PSC aerosol, volcanic ash, and sulfate/other only appear in version 1 standard level 1.5 data products because these aerosol types were not implemented until version 4.x of the CALIOP level 2 products (Kim et al., 2018).

Overcast is defined as all range bins beneath the highest cloud in a profile. The convention for defining clouds and overcast features with L2_Feature_Type is to classify the full vertical extent of the highest cloud in a profile as cloud (4). All range bins from the base of the cloud downward to the first range bin identified as either totally attenuated or the Earth’s surface are then classified as overcast.

Cloud-cleared aerosols refer to aerosols that have been detected after 1/3 km and/or 1 km horizontal resolution clouds have been cleared by the level 2 scene classification algorithms. Similarly, cloud-cleared “clear air” refers to segments of “clear air” where 1/3 km and/or 1 km resolution clouds have been cleared.

Mixed aerosols identify 20 km x 60 m resolution elements containing more than one aerosol type. Cloud-cleared mixed aerosols identify 20 km x 60 m resolution elements containing more than one aerosol subtype where at least one is cloud-cleared as defined above.

Note that stratospheric features are handled differently, depending on the version of the input data. For standard version 4 input (i.e., the standard version 1 level 1.5 product), stratospheric aerosol layers having the subtype PSC aerosol are screened as if they were clouds, but their L2_Feature_Types are still classified as PSC aerosol. Volcanic ash, sulfate/other, and smoke layers remain. For version 3 expedited input (i.e., the expedited version 3.x level 1.5 expedited product), stratospheric features are not reported. Instead stratospheric features between 60° N and 60° S having medium and high feature type QA confidence are reported as “clear air”; all other stratospheric features are assumed to be clouds. Poleward of 60°, all stratospheric features are assumed to be clouds (e.g., PSCs).

IMPORTANT: regions of data in the lidar level 1B and lidar level 2 aerosol profile products having L2_Feature_Type values of 0 through 4, 12, 23, and 29 are NOT INCLUDED when computing the cloud-cleared averaged data that is recorded in the attenuated backscatter and aerosol extinction coefficient profiles.

Profile QA Information

Extinction_QC_Flag_532 (V3 expedited only)
Units: NoUnits
Format: UInt_16
Fill Value: 32768
Valid Range: 0.0...5.3E-4
Description: Extinction QC flags are bit-mapped 16-bit integers reported for each profile range bin where an extinction solution was attempted. It summarizes the final state of the extinction attempt. For the level 1.5 products, the logical OR is computed from all aerosol extinction QC flags within each 20 km x 60 m resolution profile range bin.

Profile Attenuated Backscatter and Extinction Coefficients

Total_Attenuated_Backscatter_532_Mean
Perpendicular_Attenuated_Backscatter_532_Mean
Attenuated_Backscatter_1064_Mean
Units: km-1sr-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...5.3E-4
Description: For each variety of lidar level 1B attenuated backscatter coefficients listed above, this is the mean of those attenuated backscatter coefficients within each 20 km horizontal x 60 meter resolution level 1.5 profile range bin after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out.

Total_Attenuated_Backscatter_532_Median
Total_Attenuated_Backscatter_532_StDev
Perpendicular_Attenuated_Backscatter_532_Median
Perpendicular_Attenuated_Backscatter_532_StDev
Attenuated_Backscatter_532_Median
Attenuated_Backscatter_532_StDev
Units: km-1sr-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...5.3E-4
Description: For each variety of lidar level 1B attenuated backscatter coefficients listed above, these are the medians and standard deviations of the attenuated backscatter coefficients thate remain within each 20 km horizontal x 60 meter resolution level 1.5 profile range bin after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out. Since the lower troposphere (-0.5 km to 8.2 km) and upper troposphere (8.2 km to 20.2 km) are averaged to different resolutions in lidar level 1B products, the lower troposphere data are first averaged to upper tropospheric resolution prior to computing the median and standard deviation. Thus, below 20.2 km, the medians and standard deviations are derived from populations of screened attenuated backscatter coefficients having uniform spatial resolutions of 60 m vertically and 1 km horizontally. Similarly, above 20.2 km the medians and standard deviations are derived from data having a uniform spatial resolution of 180 m vertically and 5/3 km horizontally. Note that discontinuities in standard deviation and median attenuated backscatter can occur at range bins surrounding the 8.2 km altitude bin due to vertical shifting of downlinked level 0 data onto the standard lidar data altitude array. These discontinuities are replaced with fill values in level 1.5 products.

Total_Attenuated_Backscatter_532_Uncertainty
Perpendicular_Attenuated_Backscatter_532_Uncertainty
Attenuated_Backscatter_532_Uncertainty
Units: km-1sr-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...5.3E-4
Description: For each variety of lidar level 1B attenuated backscatter coefficients listed above, this is the uncertainty on the mean of attenuated backscatter coefficients that remain within each 20 km horizontal x 60 meter resolution level 1.5 profile range bin after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out.

Attenuated backscatter uncertainty is an estimate of random error based on level 1B noise scale factors (Liu et al., 2006 (PDF)). It is first calculated at nominal level 1B range resolution using procedures outlined in Uncertainties for Attenuated Backscatter (PDF) before the uncertainty on the mean σμ is calculated for each 20 km x 60 meter profile range bin using (Bevington & Robinson, 1992),

Equation 1.

Here, σi is the attenuated backscatter uncertainty at a level 1B profile range bin i, and N is the number of level 1B profile range bins within the 20 km x 60 m interval remaining after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out. Since the lower troposphere (-0.5 km to 8.2 km) and upper troposphere (8.2 km to 20.2 km) are averaged to different resolutions in lidar level 1B products, the lower troposphere uncertainties are first averaged to upper tropospheric resolution prior to computing the uncertainty on the mean. Thus, below 20.2 km, the uncertainty on the mean is derived from all valid 1 km x 60 m resolution attenuated backscatter coefficients within each 20 km x 60 m lidar level 1.5 profile range bin. Above 20.2 km, this statistic is the uncertainty on the mean of 5/3 km x 180 m resolution attenuated backscatter coefficients.


Extinction_Coefficient_532_Mean (V3 expedited only)
Extinction_Coefficient_532_Median (V3 expedited only)
Extinction_Coefficient_532_StDev (V3 expedited only)
Units: km-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...1.25
Description: Mean, median, and standard deviation of level 2 aerosol extinction coefficients at 532 nm after aerosol sammples in overcast skies have been removed. Since lidar level 2 aerosol profile products are reported uniformly at 5 km horizontal x 60 m vertical resolution, these statistics are the mean, median, and standard deviation of those screened 5 km x 60 m aerosol extinction coefficients within each 20 km x 60 m level 1.5 profile range bin. Currently, aerosol extinction coefficients are ony reported in the V3 expedited level 1.5 product because quality screening procedures for V4 aerosol extinction coefficients are still under development.

Extinction_Coefficient_532_Uncertainty (V3 expedited only)
Units: km-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 0.0...99.99
Description: Uncertainty on the mean of all lidar level 2 aerosol profile product extinction coefficients within each 20 km horizontal x 60 meter resolution level 1.5 profile range bin after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out.

Computed similar to attenuated backscatter uncertainties, except in this case the extinction coefficient uncertainty σi is reported by the level 2 aerosol profile products for each 5 km x 60 m profile range bin i. Thus, the uncertainty on the mean σμ is given by (Bevington & Robinson, 1992),

Equation 1.

Here, N is the number of lidar level 2 aerosol profile range bins within the 20 km x 60 m interval remaining after clouds, overcast, surface, subsurface, totally attenuated, and invalid features have been screened out.

Calibration Coefficients and Uncertainties

Calibration_Constant_Parallel_532
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 3.0E10...9.0E10
Description: Mean of the lidar parallel calibration constants at 532 nm within each 20 km horizontal resolution profile. Expedited calibration procedures are described in Vaughan et al. (2011).

Calibration_Constant_Parallel_Uncertainty_532
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 1.2E9...2.6E9
Description: Calibration constant uncertainties at 532 nm for the parallel lidar channel within each 20 km horizontal resolution profile, computed as

Equation 2.

where ΔC is the single-shot calibration uncertainty estimate for the parallel channel.

Calibration_Constant_Perpendicular_532
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 3.0E10...9.0E10
Description: Mean of the lidar perpendicular calibration constants at 532 nm within each 20 km horizontal resolution profile. Computed using equation 5.6 in Section 5.1.2 of the Lidar Level 1 ATBD (PDF). Expedited calibration procedures are described in Vaughan et al. (2011).

Calibration_Constant_Perpendicular_Uncertainty_532
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 1.2E9...2.6E9
Description: Calibration constant uncertainties at 532 nm for the perpendicular lidar channel within each 20 km resolution profile, computed as,

Equation 2.

where ΔC is the single-shot calibration uncertainty estimate for the perpendicular channel, computed using equation 5.17 in Section 5.2 of the Lidar Level 1 ATBD (PDF).

Calibration_Constant_1064
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 3.0E10...9.0E10
Description: Mean of the lidar parallel calibration constants at 1064 nm within each 20 km horizontal resolution profile. Expedited calibration procedures are described in Vaughan et al. (2011).
Calibration_Constant_Uncertainty_1064
Units: km3·sr·count
Format: Float_32
Fill Value: -9999.0
Valid Range: 1.2E9...2.6E9
Description: Calibration constant uncertainties at 1064 nm within each 20 km horizontal resolution profile, computed as

Equation 2.

where ΔC is the single-shot claibration uncertainty estimate. Expedited calibration procedures are described in Vaughan et al. (2011).

Molecular Model Attenuated Backscatter Profiles

Molecular_Model_Attenuated_Backscatter_532
Molecular_Model_Attenuated_Backscatter_1064
Units: km-1sr-1
Format: Float_32
Fill Value: -9999.0
Valid Range: 5E-4...2E-3
Description: Molecular attenuated backscatter coefficients at 532 nm and 1064 nm at the temporal midpoint of each 20 km horizontal resolution level 1.5 profile. For the version 3 expedited level 1.5 product, modeled atmospheric data is derived from the Global Modeling and Assimilation Office (GMAO) Forward Processing for Instrument Teams (FP-IT) global meteorological product. For the version 1 standard level 1.5 product, Modern Era Retrospective-Analysis for Research (MERRA-2) products are used.

Backscatter is computed by multiplying the modeled molecular number densities by the molecular backscatter cross section appropriate for the wavelength. Two-way transmittance due to molecules and ozone is obtained by first calculating extinction coefficients using the molecular extinction cross section and the ozone absorption cross section at the appropriate wavelength, converting these extinction coefficients to optical depths using trapezoidal integration, and then calculating two-way transmittance. Molecular model attenuated backscatter is the product of the calculated backscatter and two-way transmittance.

File Metadata Parameters

Product_ID
Units: NoUnits
Format: Char
Valid range: L1.5_LIDAR_Expedited (Version 3 expedited)
                    L1.5_LIDAR_Standard (Version 1 standard)
Description: An 80-byte (max) character string specifying the product name.

Date_Time_at_Granule_Start
Units: NoUnits
Format: Char
Valid range: 4/2006 - 12/2026
Definition: A 27-byte character string that reports the date and time at the start of the file orbit segment (i.e., granule) from the level 1B granule. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Date_Time_at_Granule_End
Units: NoUnits
Format: Char
Valid range: 4/2006 - 12/2026
Definition: A 27-byte character string that reports the date and time at the end of the file orbit segment (i.e., granule) from the level 1B granule. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Date_Time_at_Granule_Production
Units: NoUnits
Format: Char
Valid range: 4/2006 - 12/2026
Definition: A 27-byte character string that defines the date and time of the level 1.5 granule production. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Initial_Subsatellite_Latitude
Units: degree (°)
Format: Float_32
Valid Range: -90.0...90.0
Description: Reports the first subsatellite latitude of the level 1B granule.

Initial_Subsatellite_Longitude
Units: degree (°)
Format: Float_32
Valid Range: -180.0...180.0
Description: Reports the first subsatellite longitude of the level 1B granule.

Final_Subsatellite_Latitude
Units: degree (°)
Format: Float_32
Valid Range: -90.0...90.0
Description: Reports the last subsatellite latitude of the level 1B granule.

Final_Subsatellite_Longitude
Units: degree (°)
Format: Float_32
Valid Range: -180.0...180.0
Description: Reports the last subsatellite longitude of the level 1B granule.

Orbit_Number_at_Granule_Start
Units: NoUnits
Format: UInt_32
Valid Range: 1...232-1
Description: Reports the orbit number at the level 1B granule start time.

Orbit_Number_at_Granule_End
Units: NoUnits
Format: UInt_32
Valid Range: 1...232-1
Description: Reports the orbit number at the level 1B granule stop time.

Orbit_Number_Change_Time
Units: NoUnits
Format: Float_64
Valid Range: 60,426.0...261,231.0
Description: Reports the time at which the orbit number changes in the level 1B granule (TAI time converted to UTC time and stored in format: yymmdd.ffffffff).

Path_Number_at_Granule_Start
Units: NoUnits
Format: Int_16
Valid Range: 1...233
Description: Reports the path number at the level 1B granule start time.

Path_Number_at_Granule_End
Units: NoUnits
Format: Int_16
Valid Range: 1...233
Description: Reports the path number at the level 1B granule stop time.

Path_Number_Change_Time
Units: NoUnits
Format: Float_64
Valid Range: 60,426.0...261,231.0
Description: Reports the time at which the path number changes in the level 1B granule (TAI time converted to UTC time and stored in format: yymmdd.ffffffff).

GEOS_Version
Units: NoUnits
Format: Char
Definition: A 64-byte character that reports the version of the GEOS data product provided by the GMAO in the level 1B granule.

Level1_Filename
Units: NoUnits
Format: Char
Definition: A 160 byte character string reporting the filename of the lidar level 1B granule used to produce the level 1.5 granule.

Level2_VFM_Filename
Units: NoUnits
Format: Char
Definition: A 160 byte character string reporting the filename of the lidar level 2 vertical feature mask granule used to produce the level 1.5 granule.

Level2_APro_Filename
Units: NoUnits
Format: Char
Definition: A 160 byte character string reporting the filename of the lidar level 2 aerosol profile granule used to produce the level 1.5 granule.

Lidar_Data_Altitudes
Units: km
Format: Float_32
Valid Range: -0.5...30.1
Description: This HDF metadata field defines the altitudes of the 400 range bins to which the lidar level 1.5 profile products are registered. Altitudes extend from approximately -0.5 km to 30.1 km with a vertical resolution of 60 meters below 20.2 km and a vertical resolution of 180 m from 20.2 - 30.1 km.

Rayleigh_Extinction_Cross-section_532
Rayleigh_Extinction_Cross-section_1064
Units: m2
Format: Float_32
Definition: Reports the Rayleigh extinction cross-sections. The values are 5.167e-31 m2 and 3.127e-32 m2 for 532 nm and 1064 nm, respectively.

Rayleigh_Backscatter_Cross-section_532
Rayleigh_Backscatter_Cross-section_1064
Units: m2sr-1
Format: Float_32
Definition: Reports the Rayleigh backscatter cross-sections. The values are 5.930e-32 m2sr-1 and 3.592e-33 m2sr-1 for 532 nm and 1064 nm, respectively.

Ozone_Absorption Cross-section_532
Ozone_Absorption_Cross-section_1064
Units: m2
Format: Float_32
Definition: Reports the Ozone absorption cross-section at 532 nm and 1064 nm. The value is 2.728461e-25 m2 for 532 nm and 0.0 for 1064 nm.

Initial_Lidar_Ratio_Aerosols_532 (V3 expedited only)
Initial_Lidar_Ratio_Aerosols_1064 (V3 expedited only)
Units: sr
Format: Float_32
Definition: Reports the initial lidar ratios at 532 nm and 1064 nm wavelengths used for aerosol extinction retrievals in the lidar level 2 aerosol profile product.

Production_Script
Units: NoUnits
Format: Char
Definition: A 20,000 byte character string reporting the production script used when generating the level 1.5 product.


Data Quality Statements

Lidar Level 1.5 Product Information
Lidar Attenuated Backscatter
Release Date Version Data Date Range Production Strategy
March 1, 2019 3.50 March 1, 2019 - present Expedited
April 10, 2019 1.00 June 13, 2006 - present Standard


NASA
Last Updated: July 08, 2019
Curator: Charles R. Trepte
NASA Official: Charles R. Trepte

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