User notice: IceBridge Narrow Swath ATM L1B Elevation and Return Strength

The 2018 Antarctic and 2019 Greenland campaign data within the IceBridge Narrow Swath ATM L1B Elevation and Return Strength, Version 2 data set has been replaced with reprocessed files at the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC). The files originally delivered were discovered to have an error related to the application of the solid Earth tide correction within the timeframes of 10 October 2018 – 16 November 2018 and 03 April 2019 – 16 May 2019.

Description of the issue and the correction made to the data sets for the Fall 2018 Campaign:
The first release of the Operation IceBridge 2018 Antarctic ATM lidar data was delivered to NSIDC in Aug 2019. Subsequently a problem was identified related to the application of the solid Earth tide correction in the data-processing stage. The resulting errors in elevations varied in both space and time over wavelengths of hundreds of kilometers. The error was corrected, the data reprocessed, and the resulting change in position was computed. Over the entire campaign, the vertical change (reprocessing minus initial processing) varied between -10.3 cm and +14.4 cm. The mean change for each survey flight varied between -6.0 cm and +5.1 cm, with a root sum of squares (RSS) deviation from the mean of between 0.6 cm and 4.4 cm. The horizontal change was less than 15 cm throughout the campaign.

Description of the issue and the correction made to the data sets for the Spring 2019 Campaign:
The first release of the Operation IceBridge ATM lidar data was delivered to NSIDC in April 2020. At that time, a problem had been identified related to the application of the solid Earth tide correction in the data-processing stage. The resulting errors in elevations varied in both space and time over wavelengths of hundreds of kilometers. The error was subsequently corrected, the data reprocessed, and the resulting change in position was computed. Over the entire campaign, the vertical change (reprocessing minus initial processing) varied between -6.5 cm and +8.8 cm. The mean change for each survey flight varied between -1.8 cm and +2.8 cm, with a root sum of squares (RSS) deviation from the mean between 0.5 cm and 2.6 cm. The greatest magnitudes of vertical change tended to be at distances farthest from the staging airport (at Thule, April 03-23, 2019 or Kangerlussuaq, May 05-16, 2019). The horizontal change was less than 10 cm throughout the campaign.

In both campaigns, some files occurring at the beginning and ends of the data collection period (when the aircraft was a little higher during descent and climb out) failed quality checks and were omitted from the redelivery; the corresponding files originally ingested have been removed from the archive. If you accessed this data set between 10 October 2018 – 16 November 2018 and 03 April 2019 – 16 May 2019, we recommend downloading the updated files.

For a complete description of the original issues and these corrections, please reference the Errors and Limitations sections within each data set’s user guide.

Data set DOI: https://doi.org/10.5067/CXEQS8KVIXEI

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