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ICESat/GLAS data products for Release-26 and earlier use only two digits of a three-digit release number slot (0XX) in the file names, with the first digit always being zero. For example, files in Release-26 contain 026 in their name, such as the following:
GLA15_026_2113_002_0407_0_01_0001.DAT
Beginning with Release-28, a YXX pattern for release numbers is used in file names. The Y portion (known as the Y-code) of this new three-digit naming convention ensures that similar Precision Orbit Determination (POD) and Precision Attitude Determination (PAD) procedures are completed for similarly-named elevation data products. The Y-code in the three-digit release number indicates the calibration level; the higher the Y-code, the greater the level of calibration. For each new release, the Y-code is assigned by the University of Texas Center for Space Research (UTCSR).
This change mostly concerns elevation products GLA06 and GLA12-15. Although present in other file names, the Y-code is not relevant for other data because the POD and PAD only affect the geolocation of the laser spot. Elevation data from different campaigns having the same Y-code may not necessarily have the same elevation quality (due to spacecraft instrumentation, orientation, and other factors affecting geolocation) but should be of reasonably similar quality.
The following table describes how to interpret the various Y-code values.
| Y-code | Description |
|---|---|
0 |
Predicted orbit; no PAD (for Level-1A products GLA01-GLA04) |
1 |
POD calibration Level 1; PAD calibration Level 1 |
2 |
POD calibration Level 2; PAD calibration Level 2 |
3 |
POD calibration Level 2; PAD calibration Level 3 |
4 |
POD calibration Level 2; PAD calibration Level 4 |
5-9 |
Reserved for future improvements |
Generally speaking, data with a higher Y-code are better than data with a lower Y-code. For example, data with Y-code = 4 are better than Y-code = 3 data.
The POD and PAD calibration levels are described in the following table.
| Calibration Level | Meaning |
|---|---|
| POD calibration Level 1 (near real-time) | Initial solution determined using rapid GPS solutions from IGS, rapid NOAA solar flux and geomagnetic indices, and preliminary IERS Earth orientation parameters. |
| POD calibration Level 2 | Solution incorporating final GPS, solar flux, geomagnetic, and Earth orientation products. |
| PAD calibration Level 1 (near real-time) | EKF solution using IST and gyro data, but without post-campaign-analysis compensation for IST bracket motion. |
| PAD calibration Level 2 | Includes interim pointing corrections. This is an intermediate step that was used during Laser 1 and Laser 2A and is reserved for future testing and analysis. |
| PAD calibration Level 3 | Includes a correction for IST bracket motion (LRS observations, modeled LRS, or an EKF-batch solution model), laser biases, and any other identified corrections. |
| PAD calibration Level 4 | Includes calibration corrections using ocean and RTW scans. |
See the ICESAT/GLAS CSR SCF Release Notes for Orbit and Attitude Determination (PDF, 244 KB) for a complete description of POD and PAD procedures, the calibration levels, and corresponding Y-codes for each release of each laser campaign.
The file names for GLAnn Level-1B and Level-2 data products generated prior to Release-28 will not be changed because they have been or will be replaced. Elevation products affected are GLA06 (Level-1B) and GLA12-15 (Level-2). The table below lists elevation products for releases prior to Release-28 along with their equivalent YXX release number. See The Attributes for ICESat Laser Operations Periods metadata table for more information about each release.
Release |
YXX Number |
|---|---|
12 |
112 |
13 |
113 |
14 |
214 |
17 |
217 |
18 |
318 |
19 |
319 |
21 |
421 |
22 |
322 |
24 |
424 |
26 |
426 |
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Supporting Cryospheric Research Since 1976 |
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