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GLA01 Records: Release 33

View GLA01 Main Record Table
View GLA01 Long Record Table
View GLA01 Short Record Table

GLA01 data records consist of three types: main records, long records, and short records. All types have the same physical length of 4660 bytes so users can read the files with FORTRAN or other suitable program, using a direct-access format. The record type indicator is contained in bytes 11 and 12 of each record. Normally a main record is followed by either two short records or five long records, depending on the number of samples telemetered for that frame (1 sec) of data. When waveform information is missing, however, it is possible to have only a main record without any long or short records following it.

Follow the links in the table below to the GLAS Altimetry Data Dictionary for details of each parameter, 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. Nearly all integers are signed; exceptions are noted below.

When comparing data from different products, the record index is consistent as long as all products represent the same release of data. If you want to compare different products with different releases, you should update your oldest product to the latest release. For example, if you want to compare data from a GLA05 Release-12 file and GLA12 Release-18 file, you should order a new GLA05 Release-18 file to replace the older release. The ICESat/GLAS Data Releases page describes characteristics and temporal coverage of each version of data.

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


GLA01 Main Record

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_gla01_rectype GLA01 record type 12 i2b 2
i_spare1 Spares 14 i2b 2
i_dShotTime Laser shot deltas (shots 2-40) 16 i4b(39) 156
i1_pred_lat Predicted geodetic latitude of the laser footprint 172 i4b 4
i1_pred_lon Predicted geodetic longitude of the laser footprint 176 i4b 4
i_RespEndTime Ending address of range reponse 180 i4b(40) 160
i_LastThrXingT Last threshold crossing location for selected filter 340 i4b(40) 160
i_NextThrXing Next to last threshold crossing location for selected filter 500 i4b(40) 160
i_EchoPeakLoc Echo peak location 660 i4b(40) 160
i_EchoPeakVal Echo peak value 820 i2b(40) 80
i_wt_fact_filt Filter weight factors 900 i4b(6,40) 960
i_filtr_thresh Selected filter threshold value 1860 i2b(40) 80
i_time_txWfPk Transmit pulse peak location 1940 i4b(40) 160
i_TxWfStart Starting address of transmit pulse sample 2100 i4b(40) 160
i_TxNrg_EU 1064 nm laser transmit energy 2260 i4b 4
i_RecNrgAll_EU 1064 nm laser received energy from all signals above threshold 2264 i4b(40) 160
i_RecNrgLast_EU 1064 nm laser received energy 2424 i4b(40) 160
i_txWfPk_Flag Transmit waveform peak status flag (view byte structure) 2584 i1b(40) 40
i_InstState Instrument state 2624 i4b 4
i_APID_AvFlg APID data availability flag 2628 i1b(8) 8
i_FiltNumMask Filter selection mask 2636 i4b 4
i_HOff DEM offset 2640 i4b(2) 8
i_ADBias Altimeter digitizer bias 2648 i4b(2) 8
i_RminRmax Range window start and stop 2656 i4b(2) 8
i_WMinMax Window size 2664 i4b(2) 8
i_ObSCHt Onboard height of spacecraft 2672 i4b 4
i_engineering Engineering data 2676 i2b(12) 24
i_compRatio Compression ratios 2700 i2b(2) 4
i_N_val Value of N 2704 i2b 2
i_r_val Value of r 2706 i2b 2
i_ADdetOutGn Transmitted gain 2708 i2b 2
i_DEMmin DEM minimum 2710 i2b 2
i_DEMmax DEM maximum 2712 i2b 2
i_tx_wf Sampled transmit pulse waveform 2714 i1b(48,40) unsigned 1920
i_OrbFlg Orbit flag 4634 i1b(2) 2
i_EchoLandType Echo land type 4636 i1b 1
i_RngSrc_Flag Range data source (view byte structure) 4637 i1b 1
i_timecorflg Time correction flag 4638 i2b 2
i_TxFlg Transmit pulse flag 4640 i1b(5) 5
i_GainShiftFlg Gain shift flag 4645 i1b(5) 5
i_spare2 Spares 4650 i1b(10) 10


GLA01 Long Record

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 4 i4b(2) 8
i_gla01_rectype GLA01 record type 12 i2b 2
i_spare1 Spares 14 i2b 2
i_filtnum Filter number 16 i1b(8) 8
i_shot_ctr Shot counter 24 i2b(8) 16
i_statflags Range window status word 40 i4b(8) 32
i_gainSet1064 AD gain setting 72 i2b(8) 16
i_4nsPeakVal 4 ns filter peak value 88 i2b(8) 16
i_8nsPeakVal 8 ns filter peak value 104 i2b(8) 16
i_4nsBgMean Background mean value 120 i2b(8) unsigned 16
i_4nsBgSDEV Background standard deviation 136 i2b(8) unsigned 16
i_samp_pad Echo sample padding 152 i2b(8) 16
i_comp_type Echo compression type 168 i1b(8) 8
i_rng_wf 1064 nm range waveform 176 i1b(544,8) unsigned 4352
i_gainStatus Gain status bits 4528 i1b(8) 8
i_NumCoinc Number of coincidences for selected filter 4536 i1b(8) 8
i_rawPkHt Height of peak in raw waveform 4544 i1b(8) 8
i_spare2 Spares 4552 i1b(108) 108


GLA01 Short Record

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 4 i4b(2) 8
i_gla01_rectype GLA01 record type 12 i2b 2
i_spare1 Spares 14 i2b 2
i_filtnum Filter number 16 i1b(20) 20
i_shot_ctr Shot counter 36 i2b(20) 40
i_statflags Range window status word 76 i4b(20) 80
i_gainSet1064 AD gain setting 156 i2b(20) 40
i_4nsPeakVal 4 ns filter peak value 196 i2b(20) 40
i_8nsPeakVal 8 ns filter peak value 236 i2b(20) 40
i_4nsBgMean Background mean value 276 i2b(20) unsigned 40
i_4nsBgSDEV Background standard deviation 316 i2b(20) unsigned 40
i_samp_pad Echo sample padding 356 i2b(20) 40
i_comp_type Echo compression type 396 i1b(20) 20
i_rng_wf 1064 nm range waveform 416 i1b(200,20) unsigned 4000
i_gainStatus Gain status bits 4416 i1b(20) 20
i_NumCoinc Number of coincidences for selected filter 4436 i1b(20) 20
i_rawPkHt Height of peak in raw waveform 4456 i1b(20) 20
i_spare2 Spares 4476 i1b(184) 184

Page last updated: 01/11/13