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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 frame 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 | Coordinate data, latitude, specific to ice sheet range | 176 | i4b(40) | 160 |
| i_lon | Coordinate data, longitude, specific to ice sheet range | 336 | i4b(40) | 160 |
| i_elev | Ice sheet surface elevation | 496 | i4b(40) | 160 |
| i_PADPoint | PAD pointing unit vector in ICRF | 656 | i4b(6,40) | 960 |
| i_PODFixedPos | Position orbit vector in ICRF | 1616 | i4b(6,40) | 960 |
| i_sigmaatt | Attitude quality indicator | 2576 | i2b(40) | 80 |
| i_Azimuth | Local azimuth | 2656 | i4b | 4 |
| i_SolAng | Solar incidence angle | 2660 | i4b | 4 |
| i_tpintensity_avg | Transmit pulse intensity - frame average | 2664 | i4b | 4 |
| i_tpazimuth_avg | Transmit pulse azimuth - frame average | 2668 | i2b | 2 |
| i_tpeccentricity_avg | Transmit pulse eccentricity - frame average | 2670 | i2b | 2 |
| i_tpmajoraxis_avg | Transmit pulse major axis - frame average | 2672 | i2b | 2 |
| i_Spare2 | Spares | 2674 | i1b(2) | 2 |
| i_gdHt | Geoid | 2676 | i2b(2) | 4 |
| i_erElv | Solid earth tide elevation (at first and last shot) | 2680 | i2b(2) | 4 |
| i_spElv | Tide elevations, specific | 2684 | i2b(4) | 8 |
| i_ldElv | Load tide elevation | 2692 | i2b(4) | 8 |
| i_ocElv | Ocean tide elevation (at first and last shot) | 2700 | i2b(2) | 4 |
| i_wTrop | Range correction - wet troposphere | 2704 | i2b(2) | 4 |
| i_dTrop | Range correction - dry troposphere | 2708 | i2b(40) | 80 |
| i_surfType | Region type (view byte structure) | 2788 | i1b | 1 |
| i_Spare3 | Spares | 2789 | i1b(3) | 3 |
| i_DEM_elv | DEM elevation | 2792 | i4b(40) | 160 |
| i_refRng | Reference range | 2952 | i4b(40) | 160 |
| i_TrshRngOff | Threshold retracker range offset | 3112 | i4b(40) | 160 |
| i_isRngOff | Ice sheet range offset | 3272 | i4b(40) | 160 |
| i_SigEndOff | Signal end range offset | 3432 | i4b(40) | 160 |
| i_cntRngOff | Centroid range offset | 3592 | i4b(40) | 160 |
| i_reflctUncorr | Reflectivity not corrected for atmospheric effects | 3752 | i4b(40) | 160 |
| i_reflCor_atm | Reflectance correction, atmosphere | 3912 | i4b | 4 |
| i_maxSmAmp | Peak amplitude of smoothed received echo | 3916 | i2b(40) | 80 |
| i_SigmaElv | Sigma of elevation | 3996 | i2b(40) | 80 |
| i_numPk | Number of peaks found in the return | 4076 | i1b(40) | 40 |
| i_kurt2 | Kurtosis of the received echo (standard) | 4116 | i2b(40) | 80 |
| i_skew2 | Skewness | 4196 | i2b(40) | 80 |
| i_IceSheetRuf | Ice sheet roughness | 4276 | i2b(40) | 80 |
| i_IsSlopeEmp | Ice sheet slope - echo | 4356 | i2b(40) | 80 |
| i_IsRngLast | Ice sheet range offset using last peak | 4436 | i4b(40) | 160 |
| i_IsRngFst | Ice sheet range offset using first peak | 4596 | i4b(40) | 160 |
| i_IceSVar | Standard deviation of the ice sheet Gaussian fit | 4756 | i2b(40) | 80 |
| i_ElvuseFlg | Elevation use flag (view byte structure) | 4836 | i1b(5) | 5 |
| i_atm_avail | Atmosphere availaility flag (view byte structure) | 4841 | i1b | 1 |
| i_erd | Estimated range delay | 4842 | i2b | 2 |
| i_rdu | Range delay uncertainty | 4844 | i2b | 2 |
| i_cld1_mswf | Cloud multiple scattering warning flag (view byte structure) | 4846 | i1b | 1 |
| i_MRC_af | Medium resolution cloud availability flag (view byte structure) | 4847 | i1b | 1 |
| i_SurfRuf_slpQF | Surface roughness and slope quality flag (view byte structure) | 4848 | i1b(40) | 40 |
| i_ElvFlg | Elevation definition flag (view byte structure) | 4888 | i1b(40) | 40 |
| i_rng_UQF | Range offset quality/use flag (view byte structure) | 4928 | i2b(40) | 80 |
| i_atmQF | Atmosphere flag (view byte structure) | 5008 | i1b(10) | 10 |
| i_timecorflg | Time correction flag (view byte structure) | 5018 | i2b | 2 |
| i_APID_AvFlg | APID data availability flag (view byte structure) | 5020 | i1b(8) | 8 |
| i_AttFlg2 | Attitude flag 2 (view byte structure) | 5028 | i1b(20) | 20 |
| i_spare5 | Spares | 5048 | i1b | 1 |
| i_FrameQF | Altimeter frame quality flag (view byte structure) | 5049 | i1b | 1 |
| i_OrbFlg | POD flag (orbit flag) (view byte structure) | 5050 | i1b(2) | 2 |
| i_rngCorrFlg | Range correction flag (view byte structure) | 5052 | i1b(2) | 2 |
| i_CorrStatFlg | Correction status flag (view byte structure) | 5054 | i1b(2) | 2 |
| i_beam_coelev | Co-elevation | 5056 | i4b | 4 |
| i_beam_azimuth | Azimuth | 5060 | i4b | 4 |
| i_AttFlg1 | Attitude flag 1 (view byte structure) | 5064 | i2b | 2 |
| i_Spare6 | Spares | 5066 | i1b(2) | 2 |
| i_DEM_hires_src | High Resolution Source Flag (view byte structure) | 5068 | i1b (40) | 40 |
| i_DEM_hires_elv | High Resolution Elevation | 5108 | i2b (40) | 80 |
| i_satNdx | Saturation Index | 5188 | i1b (40) | 40 |
| i_satElevCorr | Saturation Elevation Correction | 5228 | i2b (40) | 80 |
| i_satCorrFlg | Saturation Correction Flag (view byte structure) | 5308 | i1b (40) | 40 |
| i_satNrgCorr | Saturation Energy Correction | 5348 | i2b (40) | 80 |
| i_satPwdCorr | Saturation Pulse Width Correction | 5428 | i2b (40) | 80 |
| i_gval_rcv | Gain Value used for Received Pulse | 5508 | i2b (40) | 80 |
| i_RecNrgAll | Received Energy signal begin to signal end | 5588 | i2b (40) | 80 |
| i_FRir_cldtop | Full Resolution 1064 Cloud Top | 5668 | i2b (40) | 80 |
| i_FRir_qaFlag | Full Resolution 1064 Quality Flag (view byte structure) | 5748 | i1b (40) | 40 |
| i_FRir_ODflg | Full Resolution 1064 Optical Depth Flag | 5788 | i1b (40) | 40 |
| i_FRir_intsig | Full Resolution 1064 Integrated Signal | 5828 | i2b (40) | 80 |
| i_msRngCorr | Multi-Scatter Range Correction | 5908 | i2b (40) | 80 |
| i_msCorrFlg | Multi-Scatter Range Correction | 5988 | i1b (40) | 40 |
| i_Surface_temp | Surface Temperature | 6028 | i2b | 2 |
| i_Surface_pres | Surface Pressure | 6030 | i2b | 2 |
| i_Surface_relh | Relative Humidity | 6032 | i2b | 2 |
| i_maxRecAmp | Max Amplitude of Received Echo | 6034 | i2b (40) | 80 |
| i_sDevNsOb1 | Standard deviation of 1064 nm background noise (alternate) | 6114 | i2b (40) | 80 |
| i_pctSAT | Percent Saturation | 6194 | i1b (40) | 40 |
| i_spare7 | Spares | 6234 | i1b (366) | 366 |
