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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_pad_angle||PAD angle||44||i4b (4)||16|
|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_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_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_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|
Page last updated: 01/11/13