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CALIPSO HOMERESOURCESUser’s Guide HOME → Lidar Level 1 V4.10 Data Product Descriptions

CALIPSO Data User’s Guide - Lidar Level 1 V4.10 Data Product Description


Introduction

The CALIOP Level 1B data product contains a half orbit (day or night) of calibrated and geolocated single-shot (highest resolution) lidar profiles, including 532 nm and 1064 nm attenuated backscatter and depolarization ratio at 532 nm. The product released contains data from nominal science mode measurement.

The CALIOP Level 1B product also contains additional data not found in the Level 0 lidar input file, including post processed ephemeris data, celestial data, and converted payload status data.



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)
Profile_Time
Profile_UTC_Time
Profile_ID
Land_Water_Mask
IGBP_Surface_Type
Snow_Ice_Surface_Type
Day_Night_Flag
Frame_Number
Lidar_Mode
Lidar_Submode
Surface_Elevation
Surface_Saturation_Flag_532Par
Surface_Saturation_Index_532Par
Negative_Signal_Anomaly_Index_532Par
Surface_Saturation_Flag_532Perp
Surface_Saturation_Index_532Perp
Negative_Signal_Anomaly_Index_532Perp
Surface_Saturation_Flag_1064
Surface_Saturation_Index_1064
Negative_Signal_Anomaly_Index_1064
Laser_Energy_532
Perpendicular_Amplifier_Gain_532
Parallel_Amplifier_Gain_532
Perpendicular_Background_Monitor_532
Parallel_Background_Monitor_532
Depolarization_Gain_Ratio_532
Depolarization_Gain_Ratio_Uncertainty_532
Calibration_Constant_532
Calibration_Constant_Uncertainty_532
Total_Attenuated_Backscatter_532
Perpendicular_Attenuated_Backscatter_532
Perpendicular_RMS_Baseline_532
Parallel_RMS_Baseline_532
Laser_Energy_1064
Amplifier_Gain_1064
Calibration_Constant_1064
Calibration_Constant_Uncertainty_1064
Attenuated_Backscatter_1064
RMS_Baseline_1064
Molecular_Number_Density
Ozone_Number_Density
Temperature
Pressure
Relative_Humidity
Surface_Wind_Speeds
Tropopause_Height
Tropopause_Temperature
Noise_Scale_Factor_532_Perpendicular
Noise_Scale_Factor_532_Parallel
Noise_Scale_Factor_1064
Perpendicular_Column_Reflectance_532
Perpendicular_Column_Reflectance_Uncertainty_532
Parallel_Column_Reflectance_532
Parallel_Column_Reflectance_Uncertainty_532
QC_Flag
QC_Flag_2
Latitude
Longitude
Off_Nadir_Angle
Viewing_Zenith_Angle
Viewing_Azimuth_Angle
Solar_Zenith_Angle
Solar_Azimuth_Angle
Scattering_Angle
Surface_Altitude_Shift
Number_Bins_Shift
Spacecraft_Altitude
Spacecraft_Position
Spacecraft_Velocity
Spacecraft_Attitude
Spacecraft_Attitude_Rate
Subsatellite_Latitude
Subsatellite_Longitude
Earth-Sun_Distance
Subsolar_Latitude
Subsolar_Longitude


Attenuated Backscatter Profiles

Total_Attenuated_Backscatter_532
The total attenuated backscatter at 532 nm, β′532 in Section 6.2.2 of the Lidar Level I ATBD (PDF), is one of the primary lidar Level 1 data products. β′532 is the product of the 532 nm volume backscatter coefficient and the two-way optical transmission at 532 nm from the lidar to the sample volume. The construction of the 532 nm total attenuated backscatter from the two constituent polarization components is described in detail in Section 6 of the Lidar Level I ATBD (PDF). The attenuated backscatter profiles are derived from the calibrated (divided by calibration constant), range-corrected, laser energy normalized, baseline subtracted lidar return signal.

The 532 nm attenuated backscatter coefficients are reported for each laser pulse as an array of 583 elements that have been registered to a constant altitude grid defined by the Lidar Data Altitude field.

Note that to reduce the downlink data volume, an on-board averaging scheme is applied using different horizontal and vertical resolutions for different altitude regimes, as shown in the following table.

Table 1: Range Resolutions of Different Altitude Ranges for Downlinked Data
Altitude Range (km) Bin Number Horizontal
Resolution (km)
532 nm Vertical
Resolution (m)
1064 nm Vertical
Resolution (m)
Altitude Region
30.1 to 40.0 1-33 5 300 N/A 5
20.2 to 30.1 34-88 5/3 180 180 4
8.3 to 20.2 89-288 1 60 60 3
-0.5 to 8.3 289-578 1/3 30 60 2
-2.0 to -0.5 579-583 1/3 300 300 1

Uncertainties for the attenuated backscatter are not explicitly reported in the CALIOP Level 1 data products to save data volume, which would otherwise approximately double the Level 1 data volume. If needed, users can compute random errors for the attenuated backscatter products as described in Uncertainties for Attenuated Backscatter (PDF). IDL code for computing the attenuated backscatter uncertainties is contained in IDL Code for Uncertainty Calculations (PDF).

Perpendicular+Attenuated+Backscatter 532
This field reports the perpendicular component of the 532 nm total attenuated backscatter, as described in section 6 of the CALIPSO Lidar Level I ATBD (PDF). Profiles of the perpendicular channel 532 nm attenuated backscatter are reported in the same manner as are profiles of the 532 nm total backscatter. Profiles of the parallel component of the backscatter can be obtained by simple subtraction of the perpendicular component from the total.

Attenuated+Backscatter_1064
The attenuated backscatter at 1064 nm, β′1064, is computed according to equation 7.23 in section 7.2 of the Lidar Level I ATBD (PDF). Like β′532, β′1064 is one of the primary lidar Level 1 data products. β′1064 is the product of the 1064 nm volume backscatter coefficient and the two-way optical transmission at 1064 nm from the lidar to the sample volume. Profiles of the 1064 nm attenuated backscatter are reported in the same manner as are profiles of the 532 nm total backscatter. However, the first 34 bins of each profile contain fill values (-9999), because no 1064 nm data is downlinked from the 30.1 - 40 km altitude range.

Calibration Coefficients and Uncertainties

Calibration_Constant_532
This is the lidar calibration constant at 532 nm, as defined in section 3.1.2 of the Lidar Level I ATBD (PDF).

For the nighttime portion of an orbit, the 532 nm calibration constant is determined for each 55 km averaged profile (11 frames) by comparing the 532-parallel signals in 30 km to 34 km altitude range to a scattering model derived from molecular and ozone number densities provided by NASA’s Global Modeling and Assimilation Office (MERRA-2). This calculation uses equation 4.7 in Section 4.1.2.1 of the CALIPSO Lidar Level I ATBD (PDF). The computed 532 nm calibration constants are then smoothed over an interval of 1485 km using equation 4.8. A constant value of the calibration constant is applied to all single-shot profiles in each 55 km averaging region.

The calibration technique used during the nighttime cannot be used in the daytime portions of the orbits, because the noise associated with solar background signals (i.e., sunlight) degrades the backscatter signal-to-noise ratio (SNR) in the calibration region below usable levels. Therefore, for the daytime portion of the orbit, the calibration constants are derived by interpolating between values derived in the adjacent nighttime portions of the orbits.

Calibration_Constant_1064
The lidar calibration constant at 1064 nm, C1064, is determined by comparing 1064 nm signals to 532 nm signals in properly selected high cirrus clouds, using the procedure described in Section 7.1.2.2 of the CALIPSO Lidar Level I ATBD (PDF). For the current data release, the ratio of cirrus backscatter coefficients at 1064 nm and 532 nm is assumed to be uniformly 1. This assumption is being extensively assessed in on-going validation activities.

For each granule (day or night) a single, constant value (granule mean) for C1064 is derived by averaging all individual calibration constant estimates that were obtained. This granule mean serves as the calibration constant that is subsequently applied to all 1064 nm profiles in the granule.

We note that the procedure used in the 532 nm calibration cannot be applied for the 1064 nm measurements, because the molecular scattering at 1064 nm is ~16 times weaker than at 532 nm, and because the avalanche photodiode (APD) detector used in the 1064 nm channel has significantly higher dark noise than photomultiplier tube (PMTs) used in the 532 nm channels.

Calibration_Constant_Uncertainty_532
The uncertainty due to random noise for 532 nm calibration constant is computed based on the 532 nm noise scale factors using equation 4.24 in Section 4.3.2 of the CALIPSO Lidar Level 1 ATBD (PDF). Estimates of systematic errors, if any, are not included in this release. An extensive assessment of possible systematic errors is currently underway.

For nighttime calibrations, the uncertainty due to noise is estimated to be typically smaller than 1%. Additional systematic errors may arise from aerosol contamination of the calibration region (less than a few percent), and from large signal spikes seen frequently in the South Atlantic Anomaly (SAA) and occasionally outside the SAA region.

A stratospheric aerosol model is currently being developed to correct for the aerosol present in the calibration region. Upon completion, this model will be applied to calibration processing for subsequent data releases.

Large noise spikes can be present both in the lidar return signals and in the baseline signals. Baseline signals are determined on-board by calculating the mean signal value over 15000 data points (1000 15 meter samples in the 65 to 80 km altitude region from each of the 15 shots within a frame). This calculation is performed for each frame, and the resulting value is subtracted from each sample of all profiles in that frame. The presence of large outliers -- i.e., "spikes" -- in the backscatter signals in the calibration region tends to bias the calibration constant toward a larger value. On the other hand, the spikes present in the baseline region can cause and erroneous overestimate of the measured baseline signal, and the subsequent subtraction of this baseline value will thus introduce a bias in all data within the frame, causing it to be lower than it otherwise should be. This in turn tends to bias the calibration constant toward a smaller value. Threshold-based data filtering schemes are applied to 532 nm data to remove large spikes in the lidar signal prior to performing the nighttime calibration. Two threshold boundaries - a maximum and a minimum - are set. By excluding values outside this range, large signal excursions are effectively removed. Spikes with smaller magnitudes may remain, depending on the selection of the maximum threshold value. Perturbations to the calibration due to spikes in the baseline region can be only partly eliminated by this kind of threshold-based filtering scheme. However, by properly selecting the threshold limits, the impacts of spikes in the calibration region and the baseline region will cancel each other out to some degree. Preliminary comparisons of CALIOP's 532 nm attenuated backscatter coefficients, which are critically dependent on the accuracy of the calibration, with validation measurements acquired by the LaRC airborne high-spectral-resolution lidar (HSRL) and Goddard's airborne Cloud Physics Lidar (CPL) show consistency to within a few percent.

Because the daytime calibration constants are interpolated from nighttime values, the uncertainties contained in the nighttime calibration are transferred to daytime. Additional error may arise from the selection of interpolation scheme. In general, the uncertainty for daytime calibration constants is somewhat higher than the uncertainty for the nighttime values.

Calibration_Constant_Uncertainty_1064
This field reports the uncertainty in the 1064 nm calibration constant due solely to random noise contained in 1064 nm data. Systematic errors are not estimated in this release.

If a sufficient number of cirrus clouds are present in any granule, the uncertainty due to noise in the granule mean of the 1064 nm calibration constant can be very small. Larger systematic errors may arise from the assumption that the cirrus color ratio (the ratio of backscatter coefficients at 1064 nm and 532 nm) has a constant value of 1.0. A very preliminary study on the ratio of gain and energy-normalized, range-corrected signals (i.e., the quantity X defined in equations 3.7 and 3.8 in the CALIPSO Lidar Level I ATBD (PDF)) at 1064 nm and 532 nm in selected dense cirrus clouds shows a distribution having a width of exceeding 10% of the mean value.

Column Reflectance

Parallel_Column_Reflectance_532
Parallel column reflectance for 532 nm is reported for each lidar Level 1 profile.

Perpendicular_Column_Reflectance_532
Perpendicular column reflectance for 532 nm is reported for each lidar Level 1 profile.

Parallel_Column_Reflectance_Uncertainty_532
Not calculated for the current release; data products contain fill values in this field.

Perpendicular_Column_Reflectance_Uncertainty_532
Not calculated for the current release; data products contain fill values in this field.

Geolocation and Altitude Registration

Latitude
Geodetic latitude, in degrees, of the laser footprint on the Earth’s surface.

Longitude
Longitude, in degrees, of the laser footprint on the Earth’s surface.

Lidar_Data_Altitude
This is an HDF metadata field that defines the altitudes of the 583 range bins (refer to Table 1: Range Resolutions of Different Altitude Ranges for Downlinked Data) to which lidar Level 1 profile products are registered.

Number_Bins_Shift
Number bins shift contains the number of 30 meter bins the profile specific 30 meter array elements are shifted to match the lowest altitude bin of the fixed 30 meter altitude array. Profile specific altitude arrays are computed as a function of the actual spacecraft off-nadir angle, which varies slightly from the commanded spacecraft off-nadir angle. The fixed altitude array is computed using the commanded spacecraft off-nadir angle (0.3 or 3.0 degrees). The profile specific array elements may be shifted up or down.

Surface_Altitude_Shift
Surface altitude shift contains the altitude difference between the profile specific 30 meter altitude array and the fixed 30 meter altitude array at the array element that includes mean sea level. Profile specific altitude arrays are computed as a function of the actual spacecraft off-nadir angle, which varies slightly from the commanded spacecraft off-nadir angle. The fixed altitude array is computed using the commanded spacecraft off-nadir angle (0.3 or 3.0 degrees). The units are in kilometers and the values may be positive or negative. The difference is calculated as: Surface_Altitude_Shift = altitude (profile specific 30 meter mean sea level bin) - altitude (fixed 30 meter mean sea level bin).

Orbit_Number
Orbit Number consists of three HDF metadata fields that define the number of revolutions by the CALIPSO spacecraft around the Earth and is incremented as the spacecraft passes the equator at the ascending node. To maintain consistency between the CALIPSO and CloudSat orbit parameters, the Orbit Number is keyed to the Cloudsat orbit 2121 at 23:00:47 on 2006/09/20. Because the CALIPSO data granules are organized according to day and night conditions, day/night boundaries do not coincide with transition points for defining orbit number. As such, three parameters are needed to describe the orbit number for each granule as:
  • Orbit Number at Granule Start: orbit number at the granule start time
  • Orbit Number at Granule End: orbit number at the granule stop time
  • Orbit Number Change Time: time at which the orbit number changes in the granule
Path_Number
Path Number consists of three HDF metadata fields that define an index ranging from 1-233 that references orbits to the Worldwide Reference System (WRS). This global grid system was developed to support scene identification for LandSat imagery. Since the A-Train is maintained to the WRS grid within +/- 10 km, the Path Number provides a convenient index to support data searches, instead of having to define complex latitude and longitude regions along the orbit track. The Path Number is incremented after the maximum latitude in the orbit is realized and changes by a value of 16 between successive orbits. Because the CALIPSO data granules are organized according to day and night conditions, day/night boundaries do not coincide with transition points for defining path number. As such, three parameters are needed to describe the path number for each granule as:
  • Path Number at Granule Start: path number at the granule start time
  • Path Number at Granule End: path number at the granule stop time
  • Path Number Change Time: time at which the path number changes in the granule

Meteorological Data

Met_Data_Altitude
This is an HDF metadata field that defines the altitudes of the 33 range bins at which the ancillary meteorological data (i.e., molecular number density, ozone number density, temperature, and pressure, and relative humidity) are generated.

Molecular_Number_Density
Molecular number density, in units of molecules per cubic meter, reported for each lidar Level 1 profile at the 33 standard altitudes recorded in the Met Data Altitudes field. Molecular number density values are obtained from the ancillary meteorological data provided by the MERRA-2.

Ozone_Number_Density
Ozone number density, in units of molecules per cubic meter, reported for each lidar Level 1 profile at the 33 standard altitudes recorded in the Met Data Altitudes field. Ozone number density values are obtained from the ancillary meteorological data provided by the MERRA-2.

Pressure
Pressure, in millibars, reported for each lidar Level 1 profile at the 33 standard altitudes recorded in the Met Data Altitudes field. Pressure values are obtained from the ancillary meteorological data provided by the MERRA-2.

Relative_Humidity
Relative humidity reported for each lidar Level 1 profile at the 33 standard altitudes recorded in the Met Data Altitudes field. Relative humidity values are obtained from the ancillary meteorological data provided by the MERRA-2.

Surface_Wind_Speeds
Surface wind speeds, in meters per second, are reported for each lidar Level 1 profile as eastward (zonal) and northward (meridional) surface wind stress. Surface wind speed values are obtained from the ancillary meteorological data provided by the MERRA-2.

Temperature
Temperature, in degrees C, reported for each lidar Level 1 profile at the 33 standard altitudes recorded in the Met Data Altitudes field. Temperature values are obtained from the ancillary meteorological data provided by the MERRA-2.

Tropopause_Height
Tropopause height, in kilometers, reported for each lidar Level 1 profile. Tropopause height values are obtained from the ancillary meteorological data provided by the MERRA-2.

Tropopause_Temperature
Tropopause temperature, in degrees C, reported for each lidar Level 1 profile. Tropopause temperature values are obtained from the ancillary meteorological data provided by the MERRA-2.

Time_Parameters

Profile_Time
This field reports the International Atomic Time (TAI), in seconds, starting from January 1, 1993.

Profile Time UTC
This field reports the Coordinated Universal Time (UTC), 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.

Profile Identification

Frame Number
This field reports the number of a frame within the sequence of 11 frames making up a Payload Data Acquisition Cycle (PDAC). Each frame consists of 15 laser pulses. All 15 records in a frame have the same value of Frame Number.

Profile_ID
This is a 32-bit integer generated sequentially for each single-shot profile record. Each profile ID is unique within each granule.

Ancillary Data

Day_Night_Flag
This field indicates the lighting conditions at an altitude of ~24 km above mean sea level; 0 = day, 1 = night.

IGBP_Surface_Type
International Geosphere/Biosphere Programme (IGBP) classification of the surface type at the laser footprint. The IGBP surface types reported by CALIPSO are the same as those used in the CERES/SARB surface map. The CERES/SARB surface map table is below.

CERES/SARB Surface Map
Surface Index Surface Type   Surface Index Surface Type
1 Evergreen-Needleleaf-Forest   10 Grassland
2 Evergreen-Broadleaf-Forest   11 Wetland
3 Deciduous-Needleleaf-Forest   12 Cropland
4 Deciduous-Broadleaf-Forest   13 Urban
5 Mixed-Forest   14 Crop-Mosaic
6 Closed-Shrublands   15 Permanent-Snow
7 Open-Shrubland (Desert)   16 Barren/Desert
8 Woody-Savanna   17 Water
9 Savanna   18 Tundra

Land_Water_Mask
This is an 8-bit integer indicating the surface type at the laser footprint, with
0 = shallow ocean;
1 = land;
2 = coastlines;
3 = shallow inland water;
4 = intermittent water;
5 = deep inland water;
6 = continental ocean;
7 = deep ocean.

Snow_Ice_Surface_Type
Snow and ice coverage for the surface at the laser footprint. This data comes from the Air Force Weather Agency (AFWA). For all releases prior to version 4, data was obtained from the National Snow and Ice Data Center (NSIDC).

Surface_Elevation
This is the surface elevation at the laser footprint, in kilometers above local mean sea level, obtained from the CloudSat science team digital elevation map (DEM).

Lidar Operating Modes

Lidar_Mode
This is a 16-bit integer representing the operating mode of the lidar. For all Level 1B data, the lidar mode will have a value of 3, indicating that the lidar is in autonomous data acquisition mode.

Lidar_Submode
This is a 16-bit integer representing the operating submode of the lidar. For all Level 1B data, the lidar submode will have a value of 4, indicating that the lidar operating in its normal configuration.

Laser Energy and Instrument Gain Parameters

Parallel_Amplifier_Gain_532
This is the gain of the variable gain amplifier for the 532 nm parallel channel, in volts per volt.

Perpendicular_Amplifier_Gain_532
This is the gain of the variable gain amplifier for the 532 nm perpendicular channel, in volts per volt.

Amplifier_Gain_1064
This is the gain of the variable gain amplifier for the 1064 nm channel, in volts per volt.

Laser_Energy_532
This field reports the laser energy, in Joules, at 532 nm measured by the laser energy monitor for each shot.

Laser_Energy_1064
This field reports the laser energy, in Joules, at 1064 nm measured by the laser energy monitor for each shot.

Depolarization_Gain_Ratio_532
The depolarization gain ratio is the ratio of the opto-electric gains between the 532 perpendicular and the 532 parallel channels. This product is determined from the Polarization Gain Ratio (PGR) mode measurement, in which a pseudo-depolarizer is inserted into the optical path to generate equal backscatter intensities in both the 532 parallel and 532 perpendicular channels (see equation 5.8 in Section 5.1 of the CALIPSO Lidar Level I ATBD (PDF)).

During the first several months of the mission, the depolarization gain ratio has proved to be very stable, with values falling consistently between 1.02 and 1.05. The uncertainty in these measurements due to random noise is estimated to be smaller than 1% (see the Depolarization Gain Ratio Uncertainty 532, immediately below). Possible systematic errors have not yet been quantified; however, these are estimated to be small, and thus the measured depolarization gain ratio is considered highly reliable.

Depolarization_Gain_Ratio_Uncertainty_532
This field reports the uncertainty in Depolarization Gain Ratio Uncertainty 532 due to random noise. Values are computed based on the 532 nm noise scale factors (NSF) using equation 5.15 in Section 5.2 of the Lidar Level I ATBD (PDF). The uncertainty due to systematic errors is not included for this release, but is estimated to be small.

Instrument Characterization

Noise_Scale_Factor_532_Parallel
This field reports the NSF for each shot for the 532 nm parallel channel. This product is computed from daytime measurements of the Parallel RMS Baseline 532 and the Parallel Background Monitor 532.

Noise_Scale_Factor_532_Perpendicular
This field reports the noise scale factor (NSF) for each shot for the 532 nm perpendicular channel. This product is computed from daytime measurements of the Perpendicular RMS Baseline 532 and the Perpendicular Background Monitor 532. The theoretical basis for the calculation relies on the fact that the photons from solar background radiation follow a Poisson stochastic process (Liu et al., 2006 (PDF)). The procedure to compute the NSF is described in Section 8 of the Lidar Level I ATBD (PDF).

Noise_Scale_Factor_1064
This field reports the NSF for the 1064 nm channel. CALIOP does not measure the background signal level at 1064 nm, because the APD detector dark noise is dominant during both nighttime and daytime measurement. For this reason, the procedure to estimate the NSF for the 532 nm channels cannot be used for the 1064 nm channel. The 1064 nm NSF is therefore set to 0 for Version 1.10 of the CALIPSO lidar Level 1 product, which causes negligible error because, as above, the APD detector dark noise is the dominant error source.

Parallel_Background_Monitor_532
This field reports the background signal, in digitizer counts, for the 532 nm parallel channel.

Perpendicular_Background_Monitor_532
This field reports the background signal, in digitizer counts, for the 532 nm perpendicular channel. Background signals are measured at very high altitudes, where no backscattering signal will be returned from the atmosphere. Background signals include such things as detector dark current and background radiation signals (e.g., from daytime sunlight). In general, any lidar sample will include both an atmospheric scattering signal and the background signal. The latter is subtracted from lidar samples during data processing. For CALIOP, the background signal is computed on board and subtracted from the lidar data prior to downlink.

Parallel_RMS_Baseline_532
This field reports the RMS noise, in digitizer counts, of background signal in the 532 nm parallel channel.

Perpendicular_RMS_Baseline_532
This field reports the root mean square (RMS) noise, in digitizer counts, of the background signals from the 532 nm perpendicular channel The RMS noise is determined on-board for each laser pulse by computing the standard deviation of 1000 15 m samples acquired in the 65-80 km altitude range.

The random error contained in lidar measurements consists of two parts. One is due to the variation in the received laser scattering signal from the atmosphere. The other is due to the variation in the background signal. Both parts have to be taken into account when estimating the random error. The random error arose from the scattering signal can be estimated using the NSF. The random error due to the background signal is the measured RMS noise.

RMS_Baseline_1064
This field reports the RMS noise, in digitizer counts, of the background signal in the 1064 nm parallel channel. We note that the magnitude of the background signal at 1064 nm is not measured by CALIOP, because this quantity is dominated by the detector dark noise.

Lidar Surface Characterization

Surface_Saturation_Flag_532Par
Reports the likelihood that the surface signal in the 532 nm parallel channel is saturated. 0 = not saturated, 1 = possibly saturated, 2 = certainly saturated.

Surface_Saturation_Index_532Par
Reports the zero-based altitude index of the lowest range bin where the surface is either "possibly saturated" or "certainly saturated" for the 532 nm parallel channel. For profiles classified as "not saturated", a value of -1 is reported.

Negative_Signal_Anomaly_Index_532Par
Reports the zero-based altitude index of the lowest range bin where the negative signal anomaly is detected in the 532 nm parallel channel. For profiles where the negative signal anomaly is not detected, a value of -1 is reported.

Surface_Saturation_Flag_532Perp
Reports the likelihood that the surface signal in the 532 nm perpendicular channel is saturated. 0 = not saturated, 1 = possibly saturated, 2 = certainly saturated.

Surface_Saturation_Index_532Perp
Reports the zero-based altitude index of the lowest range bin where the surface is either "possibly saturated" or "certainly saturated" for the 532 nm perpendicular channel. For profiles classified as "not saturated", a value of -1 is reported.

Negative_Signal_Anomaly_Index_532Perp
Reports the zero-based altitude index of the lowest range bin where the negative signal anomaly is detected in the 532 nm perpendicular channel. For profiles where the negative signal anomaly is not detected, a value of -1 is reported.

Surface_Saturation_Flag_1064
Reports the likelihood that the surface signal in the 1064 nm channel is saturated. 0 = not saturated, 1 = possibly saturated, 2 = certainly saturated.

Surface_Saturation_Index_1064
Reports the zero-based altitude index of the lowest range bin where the surface is either "possibly saturated" or "certainly saturated" for the 1064 nm channel. For profiles classified as "not saturated", a value of -1 is reported.

Negative_Signal_Anomaly_Index_1064
Reports the zero-based altitude index of the lowest range bin where the negative signal anomaly is detected in the 1064 nm channel. For profiles where the negative signal anomaly is not detected, a value of -1 is reported.

Quality Check Flags

QC_Flag
This is an unsigned 32-bit integer with each bit indicating a specific error condition, as defined by Table 2.

The CALIPSO lidar data are averaged on-board the satellite, prior to being downlinked, using the variable averaging scheme shown in Table 1. Regions 1 and 2 contain single shot data (albeit at different vertical resolutions). In regions 3, 4, and 5, the downlinked data have been averaged to horizontal resolutions of, respectively, 3 shots, 5 shots, and 15 shots. The level 1 processing constructs Pseudo Single Shot Profiles (PSSP) by replicating the data from regions 3, 4, and 5, and then stacking data arrays from the different averaging regions. Two sets of QC flags, as shown in Tables 2 and 3, are computed for each one of these pseudo single shot profiles.

The laser energy assessments reported in QC Flag #1 are computed as follows:
  • the laser energies associated with bits 5, 6, 13, and 14 correspond to the laser energies for the genuine single shot portion (i.e., from regions 1 and 2) of each PSSP;
  • bits 15-19 are toggled on if any single shot within the horizontally averaged regions of a PSSP falls below the 'near zero energy' threshold; and
  • bits 20-24 are toggled on if any single shot within the horizontally averaged regions of a PSSP falls below the 'data quality' threshold.

For example, suppose that (a) the energies for shot #5 in a 15 shot frame fail the data quality threshold tests but are above the 'near zero' threshold; and (b) the energies for all other shots in the frame are normal. In this case, bits 5, 6, 13, and 14 in profiles 1-4 and 6-15 are all set to zero, to indicate acceptable laser energy. In profile #5, bits 5 and 6 are zero (because the energies were above the 'near zero' threshold) and bits 13 and 14 are one (because the energies were below the data quality threshold). Because the averaged data in region 3 of PSSP #4, #5, and #6 was constructed using the low energy data recorded for shot #5, bits 15 and 16 in these three profiles are set to one, whereas in the remaining profiles bits 15 and 16 are set to zero. Similarly, bits 17 and 18 are set to one for PSSP #1 - #5, and bit 19 is set to one for all profiles in the 15 shot frame.

Table 2: Bit assignments for the first QC Flag
Bits Interpretation
1 532 nm parallel channel missing
2 532 nm perpendicular channel missing
3 1064 nm channel missing
4 Not geolocated
5 Single shot 532 laser energy below calibration threshold (near zero energy)
6 Single shot 1064 laser energy below calibration threshold (near zero energy)
7 Historical value used for the depolarization gain ratio
8 Historical calibration constant used, 532 nm parallel channel
9 Historical calibration constant used, 532 nm perpendicular channel
10 Historical calibration constant used, 1064 nm channel
11 Averaged calibration constant used, 532 nm parallel channel
12 Averaged calibration constant used, 532 nm perpendicular channel
13 Single shot 532 laser energy below data quality threshold (low energy)
14 Single shot 1064 laser energy below data quality threshold (low energy)
15 Near zero 532 nm laser energy profile included in region 3 average
16 Near zero 1064 nm laser energy profile included in region 3 average
17 Near zero 532 nm laser energy profile included in region 4 average
18 Near zero 1064 nm laser energy profile included in region 4 average
19 Near zero 532 nm laser energy profile included in region 5 average
20 Low 532 nm laser energy profile included in region 3 average
21 Low 1064 nm laser energy profile included in region 3 average
22 Low 532 nm laser energy profile included in region 4 average
23 Low 1064 nm laser energy profile included in region 4 average
24 Low 532 nm laser energy profile included in region 5 average
25-32 Spare

QC_Flag_2
This is an unsigned 32-bit integer with each bit indicating a specific error condition, as defined by Table 3. QC Flag #1 contains an explanation of how bits are set for each Pseudo Single Shot Profile (PSSP).

Table 3: Bit assignments for the second QC Flag
Bits Interpretation
1 Reserve
2 Excessive underflows, 532 nm parallel channel in region 6*
3 Excessive underflows, 532 nm perpendicular parallel channel, region 6*
4 Excessive underflows, 1064 nm channel, region 6*
5 Excessive overflows, 532 nm parallel channel, region 6*
6 Excessive overflows, 532 nm perpendicular parallel channel, region 6*
7 Excessive overflows, 1064 nm channel, region 6*
8 Excessive overflows, 532 nm parallel channel, region 2
9 Excessive overflows, 532 nm perpendicular parallel channel, region 2
10 Excessive overflows, 1064 nm channel, region 2
11 LRE Flags in SAD packet indicate bad data, 532 nm parallel channel
12 LRE Flags in SAD packet indicate bad data, 532 nm perpendicular channel
13 LRE Flags in SAD packet indicate bad data, 1064 nm channel
14 Quality Flags in SAD packet indicate bad data, 532 nm parallel channel
15 Quality Flags in SAD packet indicate bad data, 532 nm perpendicular channel
16 Quality Flags in SAD packet indicate bad data, 1064 nm channel
17 Suspicious offset calculation, 532 nm parallel channel
18 Suspicious offset calculation, 532 nm perpendicular channel
19 Suspicious offset calculation, 1064 nm channel
20 Suspicious mean signal value, 532 nm parallel channel (any/all regions)
21 Suspicious mean signal value, 532 nm perpendicular channel (any/all regions)
22 Suspicious mean signal value, 1064 nm channel (any/all regions)
23 RMS noise out of range, 532 nm parallel channel
24 RMS noise out of range, 532 nm perpendicular parallel channel
25 RMS noise out of range, 1064 nm channel
26 Near surface meteorological parameters were remapped to DEM surface altitude
27 1064 nm calibration coefficients suspect due to low temperatures associated with power up
28-32 Spare
*Region 6 is the baseline subtraction region (see baseline signals in Calibration Constant Uncertainty 532).

Spacecraft Orientation

Off_Nadir_Angle
This is the angle of the viewing vector of the lidar off the nadir, in degrees. Since the beginning of operations in June 2006, CALIPSO has been operating with the lidar pointed at 0.3 degrees off-nadir (along track in the forward direction) with the exception of November 7-17, 2006 and August 21 to September 7, 2007. During these periods, CALIPSO operated with the lidar pointed at 3.0 degrees off nadir. Beginning November 28, 2007, the off-nadir angle was permanently changed to 3.0 degrees.

Scattering_Angle
This is the angle, in degrees, between the lidar viewing vector and the line of sight to the sun.

Solar_Azimuth_Angle
This field reports the azimuth angle from north of the line of sight to the sun, in degrees.

Solar_Zenith_Angle
This is the angle, in degrees, between the zenith at the lidar footprint on the surface and the line of sight to the sun.

Viewing_Azimuth_Angle
This field reports the azimuth angle from north of the lidar viewing vector, in degrees.

Viewing_Zenith_Angle
This is the angle, in degrees, between the lidar viewing vector and the zenith at the lidar footprint on the surface. This angle is close to Off Nadir Angle in value.

Spacecraft Position and Attitude

Earth-Sun_Distance
This field reports the distance from the Earth’s surface to the Sun, in AU.

Spacecraft_Altitude
This field reports the altitude, in kilometers above mean sea level, of the CALIPSO satellite.

Spacecraft_Attitude
This field reports the attitude data, expressed as a set of Euler angles in degrees, of the CALIPSO satellite. The Euler angles represent the rotation between orbital and spacecraft coordinates and expresses as roll, pitch, and yaw angles.

Spacecraft_Attitude_Rate
This field reports the changes of attitude data, in degrees per second, of the CALIPSO satellite.

Spacecraft_Position
This field reports the position, in kilometers, of the CALIPSO satellite. The position is expressed in Earth Centred Rotating (ECR) coordinate system as X-axis in the equatorial plane through the Greenwich meridian, the Y-axis lies in the equatorial plane 90 degrees to the east of the X-axis, and the Z-axis is toward the North Pole.

Spacecraft_Velocity
This field reports the velocity, in kilometers per second, of the CALIPSO satellite. The velocity is expressed in Earth Centred Rotating (ECR) coordinate system.

Subsatellite_Latitude
This field reports the latitude of the geodetic subsatellite point which is a point on the surface where the geodetic zenith vector (perpendicular to the surface tangent) points toward the satellite.

Subsatellite_Longitude
This field reports the longitude of the geodetic subsatellite point which is a point on the surface where the geodetic zenith vector (perpendicular to the surface tangent) points toward the satellite.

Subsolar_Latitude
This field reports the latitude of the geodetic subsolar point which is a point on the surface where the geodetic zenith vector (perpendicular to the surface tangent) points toward the sun.

Subsolar_Longitude
This field reports the longitude of the geodetic subsolar point which is a point on the surface where the geodetic zenith vector (perpendicular to the surface tangent) points toward the sun.

Metadata Parameters

Product_ID
This is an 80-byte character that describes the product name. This parameter has the entry "L1_Lidar_Science".

Date_Time_at_Granule_Start
This is a 27-byte character that defines the date and granule start time. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Date_Time_at_Granule_End
This is a 27-byte character that defines the date and granule end time. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Date_Time_at_Granule_Production
This is a 27-byte character that defines the date at granule production. The format is yyyy-mm-ddThh:mm:ss.ffffffZ.

Number_of_Good_Profiles
This is a 32-bit integer specifiying the number of good attenuated backscatter profiles contained in the granule.

Number_of_Bad_Profiles
This is a 32-bit integer specifiying the number of bad attenuated backscatter profiles contained in the granule.

Initial_Subsatellite_Latitude
This field reports the first subsatellite latitude of the granule.

Initial_Subsatellite_Longitude
This field reports the first subsatellite longitude of the granule.

Final_Subsatellite_Latitude
This field reports the last subsatellite latitude of the granule.

Final_Subsatellite_Longitude
This field reports the last subsatellite longitude of the granule.

Orbit_Number_at_Granule_Start
This field reports the orbit number at the granule start time.

Orbit_Number_at_Granule_End
This field reports the orbit number at the granule stop time.

Orbit_Number_Change_Time
This field reports the time at which the orbit number changes in the granule.

Path_Number_at_Granule_Start
This field reports the path number at the granule start time.

Path_Number_at_Granule_End
This field reports the path number at the granule stop time.

Path_Number_Change_Time
This field reports the time at which the path number changes in the granule.

Ephemeris_Files_Used
This is an 160-byte character that reports a maximum of two ephemeris files used in processing the spacecraft position and velocity.

Attitude_Files_Used
This is an 160-byte character that reports a maximum of two attitude files used in processing the spacecraft attitude and attitude rate.

GEOS_Version
This is an 64-byte character that reports the version of the MERRA-2 data product provided by the GMAO.

Percent_532-parallel_Bad
This field reports the percentage of bad 532 nm parallel attenuated backscatter profiles contained in the granule.

Percent_532-perpendicular_Bad
This field reports the percentage of bad 532 nm perpendicular attenuated backscatter profiles contained in the granule.

Percent_1064_Bad
This field reports the percentage of bad 1064 nm attenuated backscatter profiles contained in the granule.

Percent_532-parallel_Missing
This field reports the percentage of missing 532 nm parallel attenuated backscatter profiles in the granule.

Percent_532-perpendicular_Missing
This field reports the percentage of missing 532 nm perpendicular attenuated backscatter profiles in the granule.

Percent_1064_Missing
This field reports the percentage of missing 1064 nm attenuated backscatter profiles in the granule.

Cal_Region_Top_Altitude_532
This field reports the top altitude of the 532 nm calibration region.

Cal_Region_Base_Altitude_532
This field reports the base altitude of the 532 nm calibration region.

Lidar_Data_Altitude
This field defines the lidar data altitudes (583 range bins) to which lidar Level 1 profile products are registered.

Met_Data_Altitude
This field defines the met data altitudes (33 range bins) at which the ancillary meteorological data are generated.

Rayleigh Extinction_Cross-section_532
This field reports the 532 nm Rayleigh extinction cross-section. The value is 5.167e-31 m2.

Rayleigh_Extinction_Cross-section_1064
This field reports the 1064 nm Rayleigh extinction cross-section. The value is 3.127e-32 m2.

Rayleigh_Backscatter_Cross-section_532
This field reports the 1064 nm Rayleigh extinction cross-section. The value is 5.930e-32 m2·sr-1.

Rayleigh_Backscatter_Cross-section_1064
This field reports the 1064 nm Rayleigh extinction cross-section. The value is 3.592e-33 m2·sr-1.

Ozone_Absorption_Cross-section_532
This field reports the 532 nm Ozone absorption cross-section. The value is 2.728461e-25 m2.

Ozone_Absorption_Cross-section_1064
This field reports the 1064 nm Ozone absorption cross-section. The value is 0.0.


Data Quality Statements

Lidar Level 1B Profiles Information
Half orbit (Night and Day) geolocated, calibrated Lidar Profiles and Viewing Geometry Products
Release Date Version Data Date Range Production Strategy
November 8, 2016 4.10 June 13, 2006 - present Standard

Summary Statement for the release of the CALIPSO LIDAR Level 1 Version 4.10, November 08, 2016

View Detailed V4.10 Quality Statement.


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

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