Service Interruption

The NSIDC Web site and data services are currently having intermittent problems and may be unavailable. We are working to restore these services as soon as possible and apologize for any inconvenience this may cause. Please contact NSIDC User Services for assistance.

GLA10 Records: Release 33

View Record Table

GLA10 contains the optical inversion results from 532 nm backscatter and extinction cross sections, separated into cloud and aerosol components. It contains top and bottom heights of all the layers that were optically processed. These are the same heights detected by the 532 nm channel that were reported in GLA08 and GLA09. Cloud products such as backscatter, extinction, extinction-to-backscatter ratio (S), and cloud layer tops and bottoms, are reported at a 1 sec sampling rate, while aerosol products are reported at a 4 sec rate only. Polar stratospheric clouds (PSC) are part of the aerosol category.

To obtain the complete vertical optical structure, you should merge the aerosol and cloud components. For every atmospheric layer detected by 532 nm, an extinction-to-backscatter ratio (S) value is calculated or estimated, which reflects the current multiple scattering condition. This calculation is essential to complete the optical inversion. "True S" indicates conditions with no multiple scattering. The Aerosol True S Values flag ("i_aer4_sval1") refers to whether the calculated (flag = 2) or estimated (flag = 1) S value was used in the optical inversion process.

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 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 not stored in GLA10, but rather in GLA11. Each GLA10 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.

Cloud cross-section data from the 532 nm channel are stored as 1 sec average profiles from 20.4 km (bin 1) to -1 km (bin 280) above the geoid. The 532 nm channel aerosol cross section data are stored as 4 sec average profiles from 41.0 km (bin 1) to -1.0 km (bin 548). Each vertical bin is 76.8 meters thick. The extinction-to-backscatter ratio (S) values are recorded one value per layer. There are up to 10 cloud layers in each cloud profile (obtained from the 1 sec cloud layers detected by GLA09 using the 532 channel) and up to 9 aerosol layers in each aerosol profile (obtained from the 4 sec aerosol layers detected by GLA08 using the 532 channel). Active layers are not necessarily packed toward the front of the array sequence. For aerosols, the top three layer positions are reserved for layers above 20.4 km and the last (ninth) position is reserved for the PBL.

All the backscatter and extinction profiles have an associated composite flag variable that represents conditions in each layer that makes up the profile. The composite flag is made up of two main components: the layer quality flag and layer usage flag. In all cases, the quality flag is a categorized value of the percent error calculation. For backscatter cross section, the usage flag gives saturation status. For extinction cross section, the usage flag designates layer type category.

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_cld1_bs_prof Cloud backscatter cross section profile 160 i4b (280,4) 4480
i_cld1_ext_prof Cloud extinction cross-section profile 4640 i4b (280,4) 4480
i_aer4_bs_prof Aerosol backscatter cross-section profile 9120 i4b (548) 2192
i_aer4_ext_prof Aerosol extinction cross-section profile 11312 i4b (548) 2192
i_cld1_sval1 Cloud true S values from table 13504 i2b (10,4) 80
i_cld1_sval2 Cloud true S values from equation calculation 13584 i2b (10,4) 80
i_aer4_sval1 Aerosol true S values from table 13664 i2b (9) 18
i_aer4_sval2 Aerosol true S values from equation calculation 13682 i2b (9) 18
i_cld1_bot Medium-resolution cloud bottom 13700 i2b (10,4) 80
i_cld1_top Medium-resolution cloud top 13780 i2b (10,4) 80
i_cld1_grd_det Medium-resolution ground detection 13860 i2b (4) 8
i_aer4_bot Low-resolution aerosol layer bottom 13868 i2b (9) 18
i_aer4_top Low-resolution aerosol layer top 13886 i2b (9) 18
i_pbl4_grd_det Low-resolution aerosol layer ground detection 13904 i2b 2
i_spare2 Spares 13906 i1b 2
i_cld1_sval_uf Cloud true S values use flag 13908 i1b (20) 20
i_aer4_sval_uf Aerosol true S values use flag 13928 i1b (5) 5
i_spare3 Spares 13933 i1b (3) 3
i_cld1_bs_flag Cloud backscatter flag 13936 i1b (40) 40
i_cld1_ext_flag Cloud extinction flag 13976 i1b (40) 40
i_aer4_bs_flag Aerosol backscatter flag 14016 i1b (10) 10
i_aer4_ext_flag Aerosol extinction flag 14026 i1b (10) 10
i_spare4 Spares 14036 i1b 1
i_AttFlg3 Attitude flag 3 14037 i1b 1
i_timecorflg Time correction flag 14038 i2b 2
i_SolarAngle Solar angle 14040 i4b (4) 16
i_MRg_cldtop_temp Medium resolution 532 nm cloud top temperature 14056 i2b (10, 4) 80
i_MRg_cldtop_pres Medium resolution 532 nm cloud top pressure 14136 i2b (10, 4) 80
i_MRg_cldtop_relh Medium resolution 532 nm cloud top relative humidity 14216 i2b (10, 4) 80
i_MRg_cldbot_temp Medium resolution 532 nm cloud bottom temperature 14296 i2b (10, 4) 80
i_MRg_cldbot_pres Medium resolution 532 nm cloud bottom pressure 14376 i2b (10, 4) 80
i_MRg_cldbot_relh Medium resolution 532 nm cloud bottom relative humidity 14456 i2b (10, 4) 80
i_Aer_top_temp Aerosol layers temperature at top of layer at 532 nm 14536 i2b (9) 18
i_Aer_top_pres Aerosol layers pressure at top of layer at 532 nm 14554 i2b (9) 18
i_Aer_top_relh Aerosol layers relative humidity at top of layer at 532 nm 14572 i2b (9) 18
i_Aer_bot_temp Aerosol layers temperature at bottom of layer at 532 nm 14590 i2b (9) 18
i_Aer_bot_pres Aerosol layers pressure at bottom of layer at 532 nm 14608 i2b (9) 18
i_Aer_bot_relh Aerosol layers relative humidity at bottom of layer at 532 nm 14626 i2b (9) 18
i_Surface_temp Surface temperature 14644 i2b (4) 8
i_Surface_pres Surface pressure 14652 i2b (4) 8
i_Surface_relh Surface relative humidity 14660 i2b (4) 8
i_Surface_wind Surface wind speed 14668 i2b (4) 8
i_Surface_wdir Surface wind direction azimuth from north 14676 i2b (4) 8
i_aod_botht_4s Cloud free troposphere height 14684 i2b 2
i_spare5 Spares 14686 i1b (290) 290

Page last updated: 01/11/13