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:
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.
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:
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:
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.
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.
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
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.
Last Updated: January 22, 2021
Curator: Charles R. Trepte
NASA Official: Charles R. Trepte
