*4.3. Data Processing*

Raw data from a survey flight will be preliminarily processed by BOP before the next flight. The objectives of field data processing are to generate readable datasets of all instruments with corresponding PSTs, link all measurements to GPS positions, check the quality of the collected data, ensure all instruments functioned as designed and that data quality was su fficient to address the questions motivating the flight plan. The data processing system is set up at either the skiway camp or at Zhongshan Station and consists of two laptops for data processing, one or two QNAP (QNAP Systems, Inc.) RAIDs (redundant array of independent disks) for data storage and accessing, a printer and a tape driver for data archiving as well as a router and switch used to connect all the devices to a local network (Figure 3). Field data processing starts with downloading raw data from all media to an "orig" folder created in QNAP. Raw data are then converted into readable binary and ASCII files and separated by di fferent instrument streams and di fferent PSTs through a data breakout step (Figure 4). During the breakout step, each data stream from individual instruments is processed through custom code packages to improve the data quality and meet the demands of the data plotting and QC. For example, the IPR data are processed through down conversion, the removal of direct current o ffsets, pulse compression, coherent stacking and incoherent stacking. All measurements are linked with accurate time stamps, which can be traced to the GPS times and position with high accuracy. Data after the breakout step are saved in a "targ" folder. Finally, data from all instruments are plotted with the time and distance for each PST onto QC sheets to conveniently evaluate all data streams.

**Figure 3.** Field data processing, quality control and archiving system.

**Figure 4.** Flow chart of field data processing and quality control.

#### *4.4. Data Quality Control*

Data quality is checked after each flight by evaluating whether each device produced the expected data quality and, in parallel, whether the resulting data quality is su fficient to make the required interpretations of ice and subglacial geological conditions required by the motivating science questions behind the flight [18]. Device QC is checked with the data streams from four aircraft GNSS antennas, an Inertial Measurement Unit (IMU) and GNSS and magnetic base stations. Ice QC is checked with data streams from both the IPR high and low gain channels, the airborne GPS antenna at the aircraft CG and the IMU and laser altimeter are jointly analyzed. Geology QC is checked with data streams from the airborne gravimeter, magnetometer, IPR high gain channel and the airborne GNSS antenna at the CG. QC evaluations are made by BOP members based on a uniform data quality scale in four levels: good, moderate, poor and very poor (including data gaps). Joint interpretations by BOP and FOP members are made with particular emphasis on potential device problems that must be solved before another flight is possible or indications that lines must be re-flown due to poor flight conditions (e.g., excessive turbulence, clouds blocking laser data). QC records are printed in black and white and evaluations are hand-colored in four associated colors: blue = good, yellow = moderate, orange = poor, pink = very poor). A review sheet associated with the printed record is used for detailed notes during the review process.

#### *4.5. Data and Documents Archive*

All data uploaded to the "orig" and "targ" repositories including notes produced in flight and during the QC process are archived on magnetic storage tapes using a tape drive following the QC process. Four tapes are written after each flight including two redundant copies of each of the raw IPR and serial data (including all documents such as flight plans, flight notes, checklists and QC sheets). At the end of the season, the QNAP RAID and each set of tapes are shipped to PRIC using di fferent means for added robustness against cargo delays, lost luggage or other problems [18].

#### **5. Progress and Prospects**
