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GLA09 Records: Release 28

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Cloud layer heights (GLA09) are determined from the 1064 nm and 532 nm channels. Heights from 532 nm are determined at four different sampling rates in the following order: 4 sec, 1 sec, 5 Hz, and 40 Hz. If a cloud layer height is found at 4 sec rate, then a search is performed at 1 sec rate. If a cloud layer height is found at 1 sec rate, then a search is performed at 5 Hz rate. Finally, if a cloud layer height is found at 5 Hz rate and the layer is below 4 km, then a search is performed at 40 Hz rate.

Cloud layer heights from 1064 nm are determined at 4 sec and 1 sec sampling rates. The search process is similar to that of 532 nm, whereby if a layer is found at 4 sec rate, then and only then, is the search performed at a 1 sec rate.

A maximum of 10 layers exists for each sampling rate, which imposes a limitation on the use of GLA09. At each resolution, a cloud layer flag indicates the number of layers detected, or the sum of the 532 nm layers plus the 1064 nm layers. These flags are "i_LRCL_Flag," "i_MRCL_Flag," "i_HRCL_Flag," and "i_FRCL_Flag."

Each layer also has a usage flag. The cloud layers found in the 532 nm data have a usage flag of "0," and the layers found in the 1064 nm data have a usage flag of "2"; thus, when looking at the 4 sec or 1 sec cloud layers in GLA09, you should view the usage flag to determine which channel was used to detect the layer. The layers detected from 532 nm will always be listed first, followed by the layers detected from 1064 nm. Duplication of layers may exist, meaning that a given layer is reported twice: once from 532 nm and once from 1064 nm, assuming that both channels are operating. If this occurs, the top and bottom of the layer should be slightly different, as two completely different algorithms are used to locate the layers; however, since the 532 nm channel is more sensitive than the 1064 nm channel, it should detect optically thin layers, resulting in some layers that were detected in 532 nm to go undetected in the 1064 nm channel.

A ground return search also runs for each of the four horizontal resolutions. The presence or absence of a ground return must be used to determine if the bottom of the last (lowest) discovered cloud layer is valid.

Follow the links in the table below to the Release 28 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 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: 10/01/08