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GLA09 Records: Release 33

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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 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.


Name Short Description Byte Offset Data Type Total Bytes
i_rec_ndx GLAS record index 0 i4b 4
i_UTCTime Transmit time of first shot in frame in J2000 (referenced from noon on 01 January 2000) 4 i4b (2) 8
i_beam_coelev Co-elevation 12 i4b (4) 16
i_beam_azimuth Azimuth 28 i4b (4) 16
i_pad_angle PAD angle 44 i4b (4) 16
i_spare0 Spares 60 i1b (40) 40
i_AttFlg1 Attitude flag 100 i2b (4) 8
i_lat Profile location, latitude 108 i4b (4) 16
i_lon Profile location, longitude 124 i4b (4) 16
i_OrbFlg Orbit flag 140 i1b (2,4) 8
i_surfType Region type 148 i1b (4) 4
i_LidarQF Lidar frame quality flag 152 i2b (4) 8
i_spare2 Spares 160 i1b (8) 8
i_topo_elev Topographic elevation of surface above geoid 168 i4b (4) 16
i_atm_dem DEM value at current location from 1 km x 1 km grid 184 i4b (4) 16
i_LRcld_bot Low-resolution cloud bottom 200 i2b (10) 20
i_LRcld_top Low-resolution cloud top 220 i2b (10) 20
i_LRcld_grd Low-resolution ground detection 240 i2b 2
i_spare3 Spares 242 i1b (2) 2
i_MRcld_bot Medium-resolution cloud bottom 244 i2b (10,4) 80
i_MRcld_top Medium-resolution cloud top 324 i2b (10,4) 80
i_MRcld_grd Medium-resolution ground detection 404 i2b (4) 8
i_MRcld_pct Percentage of saturated bins in medium-resolution cloud layers 412 i1b (10,4) 40
i_HRcld_bot High-resolution cloud bottom 452 i2b (10,20) 400
i_HRcld_top High-resolution cloud top 852 i2b (10,20) 400
i_HRcld_grd High-resolution ground detection 1252 i2b (20) 40
i_FRcld_bot Full-resolution cloud bottom 1292 i2b (160) 320
i_FRcld_top Full-resolution cloud top 1612 i2b (160) 320
i_FRcld_grd Full-resolution cloud ground detection 1932 i2b (160) 320
i_FRg_grd_sig Full-resolution ground return signal at 532 nm 2252 i4b (160) 640
i_FRir_grd_sig Full-resolution ground return signal at 1064 nm 2892 i4b (160) 640
i_LRCL_Flag Low-resolution cloud layers flag (view byte structure) 3532 i1b (11) 11
i_MRCL_Flag Medium-resolution cloud layers flag (view byte structure) 3543 i1b (37) 37
i_HRCL_Flag High-resolution cloud layers flag (view byte structure) 3580 i1b (185) 185
i_FRCL_Flag Full-resolution cloud layers flag (view byte structure) 3765 i1b (220) 220
i_AttFlg3 Attitude flag 3 3985 i1b 1
i_timecorflg Time correction flag 3986 i2b 2
i_FRir_cldtop Full resolution 1064 cloud top 3988 i2b (160) 320
i_FRir_qaFlag Full resolution 1064 quality flag 4308 i1b (160) 160
i_FRir_intsig Full resolution 1064 integrated signal 4468 i2b (160) 320
i_SolarAngle Solar angle 4788 i4b (4) 16
i_LRir_cld_top Elevation of top of cloud layers detected in 1064 nm at low resolution 4804 i2b (10) 20
i_LRir_cld_bot Elevation of bottom of cloud layers detected in 1064 nm at low resolution 4824 i2b (10) 20
i_LRir_QAflag Low resolution 1064 nm cloud layer QA flag 4844 i1b (10) 10
i_LRir_cldtop_temp Temperature of top of cloud layers detected in 1064 nm at low resolution 4854 i2b (10) 20
i_LRir_cldtop_pres Pressure of top of cloud layers detected in 1064 nm at low resolution 4874 i2b (10) 20
i_LRir_cldtop_relh Relative humidity of top of cloud layers detected in 1064 nm at low resolution 4894 i2b (10) 20
i_LRir_cldbot_temp Temperature of bottom of cloud layers detected in 1064 nm at low resolution 4914 i2b (10) 20
i_LRir_cldbot_pres Pressure of bottom of cloud layers detected in 1064 nm at low resolution 4934 i2b (10) 20
i_LRir_cldbot_relh Relative humidity of bottom of cloud layers detected in 1064 nm low resolution 4954 i2b (10) 20
i_MRir_cld_top Elevation of top of cloud layers detected in 1064 nm at medium resolution 4974 i2b (10, 4) 80
i_MRir_cld_bot Elevation of bottom of cloud layers detected in 1064 nm at medium resolution 5054 i2b (10, 4) 80
i_MRir_QAflag Medium resolution 1064 nm cloud layer QA flag 5134 i1b (40) 40
i_MRir_cldtop_temp Temperature of top of cloud layers detected in 1064 nm at medium resolution 5174 i2b (10, 4) 80
i_MRir_cldtop_pres Pressure of top of cloud layers detected in 1064 nm at medium resolution 5254 i2b (10, 4) 80
i_MRir_cldtop_relh Relative humidity of top of cloud layers in 1064 nm at medium resolution 5334 i2b (10, 4) 80
i_MRir_cldbot_temp Temperature of bottom of cloud layers detected in 1064 nm at medium resolution 5414 i2b (10, 4) 80
i_MRir_cldbot_pres Pressure of bottom of cloud layers detected in 1064 nm at medium resolution 5494 i2b (10, 4) 80
i_MRir_cldbot_relh Relative humidity of bottom of cloud layers detected in 1064 nm at MR 5574 i2b (10, 4) 80
i_LRg_cldtop_temp Low resolution 532 nm cloud top temperature 5654 i2b (10) 20
i_LRg_cldtop_pres Low resolution 532 nm cloud top pressure 5674 i2b (10) 20
i_LRg_cldtop_relh Low resolution 532 nm cloud top relative humidity 5694 i2b (10) 20
i_LRg_cldbot_temp Low resolution 532 nm cloud bottom temperature 5714 i2b (10) 20
i_LRg_cldbot_pres Low resolution 532 nm cloud bottom pressure 5734 i2b (10) 20
i_LRg_cldbot_relh Low resolution 532 nm cloud bottom relative humidity 5754 i2b (10) 20
i_MRg_cldtop_temp Medium resolution 532 nm cloud top temperature 5774 i2b (10, 4) 80
i_MRg_cldtop_pres Medium resolution 532 nm cloud top pressure 5854 i2b (10, 4) 80
i_MRg_cldtop_relh Medium resolution 532 nm cloud top relative humidity 5934 i2b (10, 4) 80
i_MRg_cldbot_temp Medium resolution 532 nm cloud bottom temperature 6014 i2b (10, 4) 80
i_MRg_cldbot_pres Medium resolution 532 nm cloud bottom pressure 6094 i2b (10, 4) 80
i_MRg_cldbot_relh Medium resolution 532 nm cloud bottom relative humidity 6174 i2b (10, 4) 80
i_LRg_SourceFt Low resolution data 532 nm source function 6254 i2b 2
i_MRg_SourceFt Medium resolution data 532 nm source function 6256 i2b (4) 8
i_HRg_SourceFt High resolution data 532 nm source function 6264 i2b (20) 40
i_LRir_SourceFt Low resolution data 1064 nm source function 6304 i2b 2
i_MRir_SourceFt Medium resolution data 1064 nm source function 6306 i2b (4) 8
i_Surface_temp Surface temperature 6314 i2b (4) 8
i_Surface_pres Surface pressure 6322 i2b (4) 8
i_Surface_relh Surface relative humidity 6330 i2b (4) 8
i_Surface_wind Surface wind speed 6338 i2b (4) 8
i_Surface_wdir Surface wind direction azimuth from north 6346 i2b (4) 8
i_PBL_Layer_ht PBL Layer Height from Met Data 6354 i2b (4) 8
i_Spec_Humid Specific Humidity 6362 i2b (4) 8
i_Temp2mAbvGrnd Temperature 2m Above Ground Level 6370 i2b (4) 8
i_Total_CloudCov Total Cloud Cover 6378 i2b (4) 8
i_blow_snow_ht Blowing snow height 6386 i2b (20) 40
i_blow_snow_od Blowing snow optical depth 6426 i2b (20) 40
i_blow_snow_erd Blowing snow range delay 6466 i2b (20) 40
i_blow_snow_conf Blowing snow confidence 6506 i1b (20) 20
i_atm_char_flag Atmosphere Characterization Flag 6526 i2b (4) 8
i_atm_char_conf Atmosphere Characterization Flag Confidence 6534 i2b (4) 8
i_spare4 Spares 6542 i1b (402) 402

Page last updated: 01/11/13