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CALIPSO: Data User's Guide - Data Product Descriptions - Lidar Level 2 Polar Stratospheric Cloud (PSC) Version 1.x Product Ensemble


CALIPSO HOMECALIPSO User’s Guide HOMEData Products Description → Lidar Level 2 Polar Stratospheric Cloud Mask V1.x Product

Introduction

The CALIPSO Lidar Level 2 Polar Stratospheric Cloud (PSC) data product ensemble describes the spatial distribution and optical properties of PSC layers observed by the CALIPSO lidar. The product contains profiles of PSC presence, composition, optical properties, and meteorological information along CALIPSO orbit tracks. Each file contains data from all nighttime orbit segments from a single day reported on a 5-km horizontal by 180-m vertical grid. The PSC data ensemble is derived from the CALIPSO Lidar Level 1B data products using the PSC detection and composition classification algorithm described in Pitts et al. (2009) (PDF). In the current release, PSC detection is limited to nighttime CALIOP observations because higher levels of background light during daytime significantly reduce the signal-to-noise and, hence, the PSC detection sensitivity.

This is a standard only produced product.


Data Descriptions

In the text below we provide brief descriptions of the individual data fields reported in the CALIPSO Lidar Level 2 Polar Stratospheric Cloud data product ensemble. 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) Data Maturity
Number_Of_LIDAR_L1_File NA
L1_Input_Filenames NA
L1_Input_Start_Times NA
L1_Input_End_Times NA
Total_Scattering_Ratio_532_Threshold NA
Perpendicular_Attenuated_Backscatter_532_Threshold NA
Altitude NA
Latitude NA
Longitude NA
Profile_Time NA
Profile_UTC_Time NA
PSC_Feature_Mask Provisional
PSC_Composition Provisional
Temperature external
Potential_Temperature external
Total_Scattering_Ratio_532 Provisional
Perpendicular_Scattering_Ratio_532 Provisional
Particulate_Color_Ratio Provisional
Perpendicular_Attenuated_Backscatter_532 Provisional
Particulate_Depolarization_Ratio_532 Provisional
Total_Attenuated_Backscatter_532 Provisional
Particulate_Attenuated_Backscatter_532 Provisional
Tropopause_Height external
Orbit_Index NA


Time Parameters

Profile Time
Time at the profile locations, expressed in International Atomic Time (TAI). Units are in seconds, starting from January 1, 1993.

Profile UTC Time
Time expressed in Coordinated Universal Time (UTC), and formatted as ‘yymmdd.ffffffff”, where ‘yy” represents the last two digits of year, ‘mm” and ‘dd” represent month and day, respectively, and ‘ffffffff’ is the fractional part of the day.


Geolocation and Altitude Registration

Latitude
Latitude, in degrees, at the center point of the profile location.

Longitude
Longitude, in degrees, at the center point of the profile location.

Altitude
Altitudes at which the Level 2 PSC profile products are reported; consisting of 121 levels between approximately 8.3 and 30.1 km, with an interval of approximately 180 m. The altitudes are a subset of the standard lidar Level 1 profile altitudes. Units are in kilometers.


Meteorological Data

The Global Modeling and Assimilation Office (GMAO) produces the Meteorological data that has been interpolated to the CALIOP Level 1 measurement locations from the Goddard Earth Observing System Model (GEOS). To match the PSC data product grid, the GEOS data are smoothed to the 5-km horizontal resolution and interpolated to the 180-m vertical grid. During CALIPSO production, the version of the GMAO data changed. The table below describes the versions of the data.

GEOS Version Data Range File Description Reference
5.1 Jun 2006 - Sep 2009 Six-hourly gridded analyses GMAO-1001v6.1, File Specification for GEOS-5 DAS Gridded Output, 24 October, 2006.
5.2 Sep 2009 - Feb 2013 Six-hourly gridded analyses Rienecker et al., 2008
5.9 Mar 2013 - present Six-hourly gridded analyses GMAO Office Note No. 2 (Version 1.1), File Specification for GEOS-5 FP-IT, 11 December, 2012.
Tropopause Height (external)
Mean tropopause height (zt) above local mean sea level; derived from the meteorological data product provided to the CALIPSO project by the GMAO Data Assimilation System. Units are in kilometers.

Temperature (external)
Profiles of temperature, in Kelvin.

Potential Temperature (external)
Profiles of potential temperature, in Kelvin.


Profile Polar Stratospheric Cloud Properties

We have derived a set of PSC feature flags that includes information on (a) PSC presence (cloud or no cloud); (b) altitude location relative to the local tropopause; (c) the amount of horizontal averaging required for layer detection, and (d) the optical parameter used for detection (either scattering ratio 532 or perpendicular attenuated backscatter 532). In addition, there is a composition flag which indicates our best estimate of the PSC particle composition. These flags are reported for every 5-km horizontal x 180-m vertical resolution grid point in the PSC data product. For detected PSC layers, the values are replicated over the horizontal averaging scale required for detection (5, 15, 45, or 135 km). For non-PSC elements, the profiles are replicated over the largest horizontal averaging scale of 135 km.


PSC Feature Mask

The PSC Feature Mask provides information on PSC presence (cloud or no cloud detected), altitude location relative to the local tropopause, the amount of horizontal averaging required for layer detection, and the optical parameter used for detection (either scattering ratio 532 or perpendicular attenuated backscatter 532). The reported values signed integers comprised of three significant digits, defined as follows:

PSC_flag = N1N2N3
N1=N2=N3   =   0:   Missing or bad CALIPSO data
N1 = PSC presence flag
N1 < 0 : No cloud detected       or N1 > 0 : Cloud detected
N1 = -1       z < zt N1 = +1       z < zt
N1 = -2       zt <z < zt + 4km N1 = +2       zt < z < zt + 4km
N1 = -3       z > zt + 4km N1 = +3       z > zt + 4km
N1 =  0       No tropopause reported N1 =   0       No tropopause reported

 
 

N2 N3 = Horizontal averaging required and parameter used for detection
N2 N3 = 01 Detected at 5-km with R (Scattering ratio 532)
N2 N3 = 03 Detected at 15-km with R
N2 N3 = 09 Detected at 45-km with R
N2 N3 = 27 Detected at 135-km with R
N2 N3 = 02 Detected at 5-km with Β’perp (Perpendicular attenuated backscatter 532)
N2 N3 = 04 Detected at 15-km with Β’perp
N2 N3 = 10 Detected at 45-km with Β’perp
N2 N3 = 28 Detected at 135-km with Β’perp

PSC Composition

PSC composition reports information on the composition of the detected PSC. The composition is determined based on the observed lidar optical parameters in terms of scattering ratio and particulate depolarization ratio at 532 nm using the algorithm described by Pitts et al. (2009) (PDF) and Pitts et al. (2011) (PDF). The valid values for the PSC composition are:

Comp_flag = 0 No Cloud detected
Comp_flag = 1 Liquid Supercooled Ternary (sulfuric acid, water, nitric acid) Solution (STS) droplets
Comp_flag = 2 Mix1: STS + low number densities/volumes of Nitric Acid Trihydrate (NAT) particles
Comp_flag = 3 Mix2: STS + intermediate number densities/volumes of NAT particles
Comp_flag = 4 Water ice clouds
Comp_flag = 5 Mix2-enhanced: STS + high number densities/volumes of NAT particles
Comp_flag = 6 Wave ice: Mountain wave induced water ice clouds (R > 50)


Profile Optical Properties

We also report number of lidar optical properties associated with the PSC layers. These fields are reported for every 5-km horizontal x 180-m vertical resolution grid point in the PSC data product. For detected PSC layers, the values are replicated over the horizontal averaging scale required for detection (5, 15, 45, or 135 km). For non-PSC elements, the profiles are replicated over the largest horizontal scale of 135 km. Both total and molecular backscatter are corrected for two-way attenuation due to molecular scattering and ozone absorption, but not for attenuation due to overlying particulate layers.

Particulate backscatter coefficients are calculating by subtracting estimates of the appropriate molecular backscatter component from measured values. The molecular backscatter values are calculated using the GMAO molecular density profiles provided in the Level 1B data files and a theoretical value for the molecular scattering cross section as described in the CALIOP Level 1 ATBD (PDF). On a point-by-point basis, any derived parameter based on these (e.g. particulate color ratio and particulate depolarization ratio) can exhibit anomalously large, i.e. non-physical, absolute values. These have not been removed from the data products.


Total Scattering Ratio 532

Ratio of the total attenuated backscatter at 532 nm to the molecular backscatter at 532 nm. The total attenuated backscatter at 532 nm is based on the values reported in the Lidar Level 1B data products, averaged to 180-m vertical resolution and 5-, 15-, 45-, or 135-km horizontal resolution depending on the magnitude of successive averaging required for cloud detection (see Pitts et al., 2009 - PDF).


Perpendicular Scattering Ratio 532

Ratio of the perpendicular attenuated backscatter at 532 to the perpendicular molecular backscatter at 532. The perpendicular molecular backscatter is estimated as 0.0366% of the total molecular backscatter (CALIOP Level 1 ATBD - PDF). The perpendicular attenuated backscatter at 532 nm is based on the values reported in the Lidar Level 1B data products, averaged to 180-m vertical resolution and 5-, 15-, 45-, or 135-km horizontal resolution depending on the magnitude of successive averaging required for cloud detection (see Pitts et al., 2009 - PDF).


Particulate Color Ratio

Ratio of the 1064-nm to 532-nm particulate backscatter coefficients.


Perpendicular Attenuated Backscatter 532

Perpendicular component of the 532 nm total attenuated backscatter. The perpendicular attenuated backscatter at 532 nm is based on the values reported in the Lidar Level 1B data products, averaged to 180-m vertical resolution and 5-, 15-, 45-, or 135-km horizontal resolution depending on the magnitude of successive averaging required for cloud detection (see Pitts et al., 2009 - PDF). Units are per kilometer per steradian.


Particulate Depolarization Ratio 532

The particulate depolarization ratio, δp(z), is defined as the ratio of the perpendicular and parallel polarization components of particulate attenuated backscatter coefficient, calculated using the following equation:

        δp(z) = (Β’perp(z)-0.00366*Β’m(z))/( Β’tot(z)- Β’perp(z)-0.99634*Β’m(z))

Here Β’perp is the perpendicular attenuated backscatter, Β’tot is the total attenuated backscatter, Β’m is the total molecular attenuated backscatter derived from the GMAO density profile. The perpendicular and parallel components of the molecular backscatter are estimated as 0.0366% and 99.634% of the total molecular attenuated backscatter (CALIOP Level 1 ATBD - PDF).


Total Attenuated Backscatter 532

The total attenuated backscatter at 532 nm is based on the values reported in the Lidar Level 1B data products, averaged to 180-m vertical resolution and 5-, 15-, 45-, or 135-km horizontal resolution depending on the magnitude of successive averaging required for cloud detection (see Pitts et al., 2009 - PDF). Units are per kilometer per steradian.


Particulate Attenuated Backscatter 532

Particulate total attenuated backscatter at 532 nm calculated by subtracting estimates of the molecular attenuated backscatter component from the measured total attenuated backscatter coefficients reported in the Lidar Level 1B data products, averaged to 180-m vertical resolution and 5-, 15-, 45-, or 135-km horizontal resolution depending on the magnitude of successive averaging required for cloud detection (see Pitts et al., 2009 - PDF). Units are per kilometer per steradian.



Ancillary Parameters


Number of Lidar L1 Files

Number of Lidar Level 1B nighttime orbit files that were used to produce the PSC data product.


L1 Input Filenames

List of the names of the Lidar Level 1B nighttime orbit files that were used to produce the PSC data product.


L1 Input Start Times

Starting times of all the Level 1B nighttime orbit files that were used to produce the PSC data product.


L1 Input End Times

Ending times of all the Level 1B nighttime orbit files that were used to produce the PSC data product.


Total Scattering Ratio 532 Threshold

Array of 532-nm scattering ratio thresholds used in the PSC detection algorithm. The thresholds are calculated daily in five overlapping 100 K-thick potential temperature layers from 400 to 700 K at each of the four successive horizontal averaging scales (5, 15, 45, and 135 km). See Pitts et al. (2009) (PDF) for more detail.


Perpendicular Attenuated Backscatter 532 Threshold

Array of 532-nm perpendicular attenuated backscatter thresholds used in the PSC detection algorithm. The thresholds are calculated daily in five overlapping 100 K-thick potential temperature layers from 400 to 700 K at each of the four successive horizontal averaging scales (5, 15, 45, and 135 km). See Pitts et al. (2009) (PDF) for more detail.


Orbit Index

Array of orbit indices that can be used to associate each profile from the given day with a discrete orbit number ordered by time. Since there are at most 15 night profiles per day, the orbit index will range between 1 and 15, with the first night orbit assigned as 1 and the last night orbit assigned as 15.



References

GMAO-1001v6.1, File Specification for GEOS-5 DAS Gridded Output, 24 October, 2006.

GMAO Office Note No. 2 (Version 1.1), File Specification for GEOS-5 FP-IT, 11 December, 2012.

Pitts, M. C., L. R. Poole, and L. W. Thomason, “CALIPSO polar stratospheric cloud observations: second-generation detection algorithm and composition discrimination”, Atmos. Chem. Phys., 9, 7577-7589, 2009.
http://www.atmos-chem-phys.net/9/7577/2009/acp-9-7577-2009.pdf

Pitts, M. C., L. R. Poole, A. Dörnbrack, and L. W. Thomason, “The 2009-2010 Arctic polar stratospheric cloud season: a CALIPSO perspective”, Atmos. Chem. Phys., 11, 2161-2177, 2011.
http://www.atmos-chem-phys.net/11/2161/2011/acp-11-2161-2011.pdf

Rienecker, M. M., Suarez, M. J., Todling, R., Bacmeister, J., Takacs, L., Liu, H.-C., Gu, W., Sienkiewicz, M., Koster, R. D., Gelaro, R., Stajner, I., and Nielsenand, J. E.: “The GEOS-5 Data Assimilation System-Documentation of versions 5.0.1 and 5.1.0, and 5.2.0. NASA Tech. Rep. Series on Global Modeling and Data Assimilation”, ASA/TM-2008-104606, Vol. 27, 92 pp., 2008.



Data Quality Statements

 

Lidar Level 2 Polar Stratospheric Cloud Ensemble Information
Daily produced file consisting of night time only data.
Release Date Version Data Date Range Maturity Level
September 2013 1.00 June 13, 2006 to present Provisional

Summary Statement for the release of the CALIPSO Lidar Level 2 Polar Stratospheric Cloud Ensemble Product Version 1.00, September 2013

The CALIPSO Team is releasing Version 1.00 which describes the spatial distribution and optical properties of PSC layers observed by the CALIPSO lidar. This is the first release of this daily product.




NASA
Last Updated: August 05, 2020
Curator: Charles R. Trepte
NASA Official: Charles R. Trepte

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