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GLA11 Records

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GLA11 contains the layer-by-layer optical results of the GLAS 532 nm atmospheric vertical profiles, i.e., the optical depth and multiple scattering factor separated into cloud and aerosol components. Polar stratospheric clouds are part of the aerosol category. To obtain the total column optical depth, you should add the aerosol and cloud components. For every atmospheric layer detected by 532 nm, a multiple scattering flag reflects the current multiple scattering condition.

GLA11 contains top and bottom heights of all the layers that were optically processed, separated into cloud and aerosol. All cloud products, including optical depth, multiple scattering factor, and layer tops and bottoms, are reported at a 1 sec sampling rate. These are the same layers as reported in GLA09. The aerosol products, output to GLA08, are reported at a 4 sec sampling rate.

The "ground detection" parameter refers to the height where the lidar sensed the ground. If the ground was not sensed, this parameter is set to "invalid." This parameter is useful for determining whether the last layer bottom sensed was a true bottom or if it marks the time when the lidar signal was extinguished. All layer locations are referenced from the geoid, and all extinction profiles were corrected for multiple scattering. The multiple scattering correction factor is stored in GLA11. Each GLA11 record is 4 sec long and contains one group of aerosol products and four groups of cloud products (one for each second). The time stamp refers to the J2000 time of the first shot of the record. J2000 time refers to the number of seconds since 01 January 2000 at 12:00 UTC.

The 532 nm cloud layer data are stored as 1 sec average values, and the 532 nm aerosol layer data are stored as 4 sec average values. The optical depth and multiple scattering factor values are recorded once per layer. There are up to 10 cloud layers in each cloud profile and up to nine aerosol layers in each aerosol profile; however, for the optical depth product, the nine layers are separated into eight elevated and one PBL height. Active layers are not necessarily grouped toward the front of the array sequence. For aerosols, the top three layer positions are reserved for layers above 20 km.

Optical depths for each layer have an associated composite flag variable that represents conditions in that layer. The composite flag is made up of two main components: a layer quality flag and a layer usage flag. In all cases, the quality flag is a categorized value of the percent error calculation. The usage flag designates layer type category. The "cloud multiple scattering warning flag" is a measure of multiple scattering intensity and is based on the total column optical depth. One value is calculated for each 1 sec profile.

Follow the links in the table below to the GLAS Atmosphere Data Dictionary for details of each record, including units and scaling factors. The GLAS science team created this dictionary. Units and scaling factors with a "d" indicate double-precision constants; for example, a value of "1.0d5" is equivalent to 100,000. The variable "pe/bin" represents photo electrons per bin.

The following codes are used to denote data types throughout the remainder of this document.

i1b: 1-byte integer
i2b: 2-byte (short) integer
i4b: 4-byte (long) integer
r4b: 4-byte real
r8b: 8-byte real

Values in parentheses indicate the record size, for example:

i2b (39): 39 records of 2-byte integers
i1b (48,40): 48-record x 40-record array of 1-byte integers

Nearly all integers are signed. Exceptions are noted in the following record table.

Page last updated: 08/11/11