The ATM instrument package includes suites of lidar, GPS, and attitude measurement subsystems. The instrument package is installed onboard the aircraft platform and calibrated during ground testing procedures. Installation mounting offsets, the distances between the GPS and attitude sensors and the ATM lidars, are measured using surveying equipment. One or more ground survey targets, usually aircraft parking ramps, are selected and surveyed on the ground using differential GPS techniques. Prior to missions, one or more GPS ground stations are established by acquiring low rate GPS data over long time spans. Approximately one hour prior to missions, both the GPS ground station and aircraft systems begin data acquisition. During the aircraft flight, the ATM instrument suite acquires lidar, GPS, and attitude sensor data over selected targets, including several passes at differing altitudes over the selected ground survey calibration sites. The aircraft and ground systems continue to acquire data for one hour post-mission. Instrument parameters estimated from the surveys of calibration sites are used for post-flight calculation of laser footprint locations. These parameters are later refined using inter-comparison and analysis of ATM data where flight lines cross or overlap.

12 and 13 April 2010: 
During collection of IceBridge ATM Greenland data on 12 and 13 April 2010, hydraulic oil progressively leaked from the forward landing gear on the DC8 aircraft. The oil was blown back along the bottom of the fuselage and across the nadir window through which the ATM was transmitting and receiving the laser signal. The ATM signal was attenuated, and data in part of the scan is missing as a result. The problem developed during the flight and worsened through time. The ATM still acquired more than half of the shots throughout the scan. The net effect of this problem is to decrease the number of shot returns logged, the same as if the laser power was reduced. To the user this will appear as a reduced point density on the ground. This issue will not affect the accuracy of the data. In the Antarctic 2010 campaign, fuel leakage degraded the signal in a similar fashion.

The flight on 28 April 2012 traversed the notoriously turbulent regions over Greenland's southeast glaciers. During the flight, two planned glaciers were skipped due to concern about expected severe turbulence. The survey data spans roughly 11:15 to 18:20 UTC. On the approach to Ikerssuaq glacier at 16:56:19.5 (GPST=60994.5 secs), both the ATM T3 and T4 instruments quit recording data within 0.1 second of each other. T3 resumed at 16:57:05.3, whereas T4 did not resume for the rest of that day's flight. After this event, the flight followed the Ikerssuaq flow line, then traversed directly west across the icesheet back to the Kangerlussuaq airport. The data gap spans 46 seconds, from the fjord up to about 500 m elevation on the Ikerssuaq glacier. The T4 data quit during the creation of the file 20120428_165532.ATM4BT4.F1.qi. The T4 data are being supplemented by the these narrow swath files of T3 data from the latter part of the survey:

20120428_165449.atm4cT3.F1.qi
20120428_170030.atm4cT3.F1.qi
20120428_170524.atm4cT3.F1.qi
20120428_171019.atm4cT3.F1.qi
20120428_171514.atm4cT3.F1.qi
20120428_172008.atm4cT3.F1.qi
20120428_172503.atm4cT3.F1.qi
20120428_172957.atm4cT3.F1.qi
20120428_173452.atm4cT3.F1.qi
20120428_173947.atm4cT3.F1.qi
20120428_180815.atm4cT3.F1.qi
20120428_181219.atm4cT3.F1.qi
20120428_181619.atm4cT3.F1.qi

The above files can be found with the IceBridge Narrow Swath ATM L1B Qfit Elevation and Return Strength 2012 Greenland data. For details on the ATM 4BT3 and 4BT4 instruments, see the Sensor Or Instrument Description section, and the ILNSA1B data set documentation.

No data for 14 April 2015:
On 14 April 2015, the ATM wide-scan instrument suffered a failure in the scanning mechanism and did not collect data for that mission.

Fall 2015 Campaign:
For the Fall 2015 ATM data, some ATM elevations are adjusted slightly (~10 cm) to compensate for a systematic anomaly related to the ATM scanner azimuth. The overall mean elevation is not changed, but some elevations around the scan are adjusted upward or downward as a function of scanner azimuth. For further details on the adjustment method, see Yi et al. (2015).

Fall 2016 Campaign:
On 07 November 2016, the ATM wide-scan lidar (ATM6aT6) suffered a laser system failure and did not collect any usable ILATM1B data for that flight. However, the ATM narrow-scan lidar (ATM5bT5) operated normally. Generally, data from the narrow-scan instrument are only provided for sea ice flights, where the smaller off-nadir angle is beneficial for lead detection. In this case however, ILNSA1B data were made available for the flight on 07 November 2016 as a substitute for the missing ILATM1B data.

Fall 2018 and Spring 2019 Campaigns (10/10/2018 to 05/16/2019):
As compared to most other Operation IceBridge ATM laser altimetry data sets, this particular data set has certain limitations in accuracy that result from a recently identified problem related to the application of the solid Earth tide correction in the data processing stage. This error can cause long-wavelength errors in elevations that are less than decimeter in magnitude and which vary in both space and time. The error wavelength is typically hundreds of kilometers, so it should not significantly affect most analyses of this data set, but it can be smaller because it depends on the number and position of base stations used for the trajectory solution and on other factors including moon phase. The error only affects the 2018 DC-8 Antarctic and 2019 P-3 Arctic Spring ATM data sets published at NSIDC DAAC. Resolution of this error is in progress, and a future version of this data set will eliminate it. The user should consider the elevation issue in any scientific interpretation or other use of the data set. Users are requested to report their findings about data quality to NSIDC User Services, to be forwarded to the ATM team, for information and comment before publication or reporting elsewhere.