【记录】CALIPSO Lidar Level 1B产品介绍

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【记录】CALIPSO Lidar Level 1B产品介绍

CALIPSO Quality Statements Lidar Level 1B Profile Products Version Releases: 3.01, 3.02, 3.30

Attenuated Backscatter Profiles

Total Attenuated Backscatter 532

Perpendicular Attenuated Backscatter 532

Attenuated Backscatter 1064

Calibration Coefficients and Uncertainties

Column Reflectance

Geolocation and Altitude Registration

Latitude

Longitude

Lidar Data Altitude

Number Bins Shift

Surface Altitude Shift

Orbit Number

Path Number

Meteorological Data

Time Parameters

Profile Identification

Ancillary Data

Day Night Flag

IGBP Surface Type

Land Water Mask

NSIDC Surface Type

Surface Elevation

CALIPSO Quality Statements Lidar Level 1B Profile Products Version Releases: 2.01, 2.02

CALIPSO Quality Statements Lidar Level 1B Profile Products Version Releases: 3.01, 3.02, 3.30

CALIOP_L1ProfileProducts_3-01-v02.pdf

Attenuated Backscatter Profiles

Total Attenuated Backscatter 532

The total attenuated backscatter at 532 nm，β’532n Section 6.2.2 of the Lidar Level I ATBD (PDF),是主要的激光雷达一级数据产品之一。β’532是是532nm体积后向散射系数和532nm处的双向光学透射的乘积。Lidar Level I ATBD (PDF)第6节详细描述了来自两个组成偏振分量的532nm总衰减后向散射的构造。衰减的反向散射剖面是从校准的(除以校准常数)、距离校正的、激光能量归一化的、基线减去激光雷达返回信号中得到的。

532nm衰减后向散射系数被记录在每个激光脉冲的对应的583个元素的阵列中，对应于由激光雷达数据高度字段定义的恒定高度网格（元数据中Lidar Data Altitudes字段中记录）。（）

为了减少下行链路数据量，对不同的高度范围使用不同的水平和垂直分辨率，如下表所示。

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.

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

532nm总衰减后向散射的垂直分量。垂直通道532nm衰减后向散射的轮廓以与532nm总后向散射的轮廓相同的方式记录。反向散射的平行分量的轮廓可以通过从总量中简单地减去垂直分量来获得。

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

Column Reflectance

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

这是一个HDF元数据字段，定义激光雷达1级剖面产品注册到的583个距离仓的高度(请参考表1:下行链路数据的不同高度范围的距离分辨率)。

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 offnadir 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

Orbit 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

Time Parameters

Profile Identification

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.

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.

NSIDC Surface Type

Snow and ice coverage for the surface at the laser footprint; data obtained from the National Snow and Ice Data Center (NSIDC).

Surface Elevation

这是从GTOPO30数字高程图（DEM）获得的激光足迹的表面高程，以高于当地平均海平面的公里为单位。

This is the surface elevation at the laser footprint, in kilometers above local mean sea level, obtained from the GTOPO30 digital elevation map (DEM).