Follow the links in the table below to the GLAS Altimetry 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. Nearly all integers are signed; exceptions are noted below.
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
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.
| 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 J2000 | 4 | i4b(2) | 8 |
| i_transtime | One-way transmit time | 12 | i2b | 2 |
| i_spare1 | Spares | 14 | i1b(2) | 2 |
| i_deltagpstmcor | Delta GPS time correction | 16 | i4b | 4 |
| i_dShotTime | Laser shot time deltas (shots 2-40) | 20 | i4b(39) | 156 |
| i_lat | Spot coordinate data - latitude (uncorrected) | 176 | i4b(40) | 160 |
| i_lon | Spot coordinate data - longitude (uncorrected) | 336 | i4b(40) | 160 |
| i_elev | Spot surface elevation with respect to ITRF ellipsoid (uncorrected) | 496 | i4b(40) | 160 |
| i_spare43 | Spare 43 | 656 | i4b(12,40) | 1920 |
| i_sigmaatt | Attitude quality indicator | 2576 | i2b(40) | 80 |
| i_gval_rcv | Gain value used for received pulse | 2656 | i2b(40) | 80 |
| i_wfnoiseOb1 | 1064-nm background noise (alternative) | 2736 | i2b(40) | 80 |
| i_wfnoiseOb2 | 1064 nm background noise (standard) | 2816 | i2b(40) | 80 |
| i_sDevNsOb1 | Standard deviation of 1064-nm background noise (alternative) | 2896 | i2b(40) | 80 |
| i_sDevNsOb2 | Standard deviation of 1064-nm background noise (standard) | 2976 | i2b(40) | 80 |
| i_refRngNs | Reference Range | 3056 | i4b(40) | 160 |
| i_thRtkRngOff1 | Threshold retracker range offset (alternative) | 3216 | i4b(40) | 160 |
| i_thRtkRngOff2 | Threshold retracker range offset (standard) | 3376 | i4b(40) | 160 |
| i_minRngOff1 | Minimum range offset (alternative) | 3536 | i4b(40) | 160 |
| i_minRngOff2 | Minimum range offset (standard) | 3696 | i4b(40) | 160 |
| i_preRngOff1 | Preliminary uncorrected range offset (alternative) | 3856 | i4b(40) | 160 |
| i_preRngOff2 | Preliminary uncorrected range offset (standard) | 4016 | i4b(40) | 160 |
| i_centroid1 | Centroid retracker offset (alternative) | 4176 | i4b(40) | 160 |
| i_centroid2 | Centroid retracker offset (standard) | 4336 | i4b(40) | 160 |
| i_centroidInstr | Centroid retracker offset using max peak | 4496 | i4b(40) | 160 |
| i_areaRecWF1 | Area under received echo (alternative) | 4656 | i2b(40) | 80 |
| i_areaRecWF2 | Area under received echo (standard) | 4736 | i2b(40) | 80 |
| i_maxRecAmp | Max amplitude of received echo | 4816 | i2b(40) | 80 |
| i_maxSmAmp | Peak amplitude of smoothed received echo | 4896 | i2b(40) | 80 |
| i_reflctUncorr | Reflectivity not corrected for atmospheric effects | 4976 | i4b(40) | 160 |
| i_reflctuncmxpk | Reflectivity not corrected for atmospheric effects from max peak | 5136 | i4b(40) | 160 |
| i_tpCentX | LPA Centroid X | 5296 | i2b(40) | 80 |
| i_tpCentY | LPA Centroid Y | 5376 | i2b(40) | 80 |
| i_nPeaks1 | Initial number of peaks in received echo (alternative) | 5456 | i1b(40) | 40 |
| i_nPeaks2 | Initial number of peaks in received echo (standard) | 5496 | i1b(40) | 40 |
| i_parm1 | Parameters from the Gaussian fit to the received echo (alternative) | 5536 | i4b(19,40) | 3040 |
| i_parm2 | Parameters from the Gaussian fit to the received echo (standard) | 8576 | i4b(19,40) | 3040 |
| i_solnSigmas1 | Sigmas of fit parameters (alternative) | 11616 | i2b(19,40) | 1520 |
| i_solnSigmas2 | Sigmas of fit parameters (standard) | 13136 | i2b(19,40) | 1520 |
| i_wfFitSDev_1 | Received echo fit standard deviation (alternative) | 14656 | i2b(40) | 80 |
| i_wfFitSDev_2 | Received echo fit standard deviation (standard) | 14736 | i2b(40) | 80 |
| i_tpintensity | Transmit pulse intensity | 14816 | i4b(40) | 160 |
| i_tpazimuth | Transmit pulse azimuth | 14976 | i2b(40) | 80 |
| i_tpeccentricity | Transmit pulse eccentricity | 15056 | i2b(40) | 80 |
| i_tpmajoraxis | Transmit pulse major axis | 15136 | i2b(40) | 80 |
| i_skew1 | Skewness of received echo (alternative) | 15216 | i2b(40) | 80 |
| i_kurt1 | Kurtosis of received echo (alternative) | 15296 | i2b(40) | 80 |
| i_skew2 | Skewness | 15376 | i2b(40) | 80 |
| i_kurt2 | Kurtosis of received echo (standard) | 15456 | i2b(40) | 80 |
| i_WFqual | Received echo quality flag (view byte structure) | 15536 | i4b(40) | 160 |
| i_TxNrg | 1064 nm laser transmit energy | 15696 | i2b(40) | 80 |
| i_tpOrX | Pulse orientation | 15776 | i2b(40) | 80 |
| i_locTr | Centroid of transmitted pulse in time relative to gate 1 of transmitted waveform | 15856 | i4b(40) | 160 |
| i_parmTr | Parameters of the Gaussian fit to the transmitted pulse | 16016 | i4b(4,40) | 640 |
| i_sDevFitTr | Standard deviation of fit of transmitted pulse | 16656 | i2b(40) | 80 |
| i_skewTr | Skewness of transmitted pulse | 16736 | i4b(40) | 160 |
| i_maxTrAmp | Maximum amp of transmitted pulse | 16896 | i2b(40) | 80 |
| i_gval_tx | Gain value used for transmitted pulse - uncalibrated | 16976 | i2b | 2 |
| i_compRatio | Compression ratios | 16978 | i2b(2) | 4 |
| i_N_val | Value of N | 16982 | i2b | 2 |
| i_r_val | Value of r | 16984 | i2b | 2 |
| i_ElvuseFlg | Elevation use flag | 16986 | i1b(5) | 5 |
| i_spare3 | Spares | 16991 | i1b | 1 |
| i_ElvFlg | Elevation definition flag | 16992 | i1b(40) | 40 |
| i_spare49 | Spare 49 | 17032 | i1b(10) | 10 |
| i_timecorflg | Time correction flag | 17042 | i2b | 2 |
| i_APID_AvFlg | APID data availability flag | 17044 | i1b(8) | 8 |
| i_AttFlg2 | Attitude flag 2 | 17052 | i1b(20) | 20 |
| i_spare4 | Spares | 17072 | i1b | 1 |
| i_FrameQF | Altimeter frame quality flag | 17073 | i1b | 1 |
| i_OrbFlg | POD flag (orbit flag) | 17074 | i1b(2) | 2 |
| i_rngCorrFlg | Range correction flag | 17076 | i1b(2) | 2 |
| i_spare5 | Spares | 17078 | i1b(2) | 2 |
| i_beam_coelev | Co-elevation | 17080 | i4b | 4 |
| i_beam_azimuth | Azimuth | 17084 | i4b | 4 |
| i_AttFlg1 | Attitude flag 1 | 17088 | i2b | 2 |
| i_RMSpulseWd | RMS pulse width | 17090 | i2b(40) | 80 |
| i_satNdx | Saturation index | 17170 | i1b(40) | 40 |
| i_RecNrgAll | Received Energy signal begin to signal end | 17210 | i2b (40) | 80 |
| i_numIters | Number of iterations performed during fit | 17290 | i1b (40) | 40 |
| i_Spare6 | Spare 6 | 17330 | i1b(70) | 70 |
