Using LabVIEW and PXI in the Harsh Antarctic to Investigate Glaciers and Ice Sheets

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"During the AGAP project, the PXI chassis rugged design survived the harsh Antarctic environment overcoming the -30°C ambient temperatures and high vibration levels from the aircraft."

- Carl Robinson, British Antarctic Survey

The Challenge:
Investigating the inner workings of glaciers and ice sheets by studying the nature of the ice.

The Solution:
Using LabVIEW graphical programming to design the user interface, acquire data, manage system configuration, record the radar ice depth soundings and provide a real time display, and combine with PXI modular instrumentation, and other components to deliver not only a stable radar platform but also a glaciological research tool.

Carl Robinson - British Antarctic Survey

It became apparent in the 1960s that radar could be used to investigate the inner workings of glaciers and ice sheets, and the UK has been at the forefront of developing technologies that facilitate high-quality science. Current programmes designed to analyze the ice require knowledge of what lies within and beneath ice sheets. Researchers must study the nature of the ice and survey isochronal layers to understand the effect of the structure and orientation of ice crystals on flow dynamics and the role of subglacial water and bedrock roughness on fast glacier flow. The previous British Antarctic Survey (BAS) radar system was out-dated and unable to provide the data scientist needed. Therefore, our application required a new system that utilised modern digital acquisition and processing to improve the depth sounding capabilities and provide improved vertical and spatial resolution so that aperture synthesis could be performed.

Using LabVIEW, NI PXI and other components such as a Radstone board with a custom FPGA, the new radar was created. LabVIEW graphical programming environment was used to design the user interface, analyze acquirde data, manage system configuration, record the radar ice-depth soundings and provide real-time data display. The system uses PXI modular hardware closely integrated with software to replace the radar system developed in the 90s. LabVIEW provided the flexibility to deliver not only a stable radar platform but also a glaciological research tool.

 The British Antarctic Survey

Cambridge-based BAS, a component of the Natural Environment Research Council, is a world leader in research into global environmental issues. With an annual budget of around £45 million, five Antarctic Research Stations, two Royal Research Ships and five aircraft, BAS undertakes an interdisciplinary research programme and plays an active and influential role in Antarctic affairs. BAS has joint research projects with over 40 UK universities and has more than 120 national and international collaborations.

Antarctica: the Last Frontier on Earth

 Antarctica is one of the least understood continents on Earth. It is the coldest, windiest, highest-elevated continent with over 99 % of its surface submerged beneath thick ice. There is increasing international awareness of the pivotal role that Antarctica plays in the global climate and geodynamic systems. The stability of the Antarctic ice sheet in a warming climate is of significant societal relevance because of its repercussions on the rise of global sea-levels. Though, if all Antarctica’s ice melted, sea-level would rise by over 60 metres.

Antarctica Aerogeophysics Research

Airborne geophysics is a prime tool to explore ice sheets and image subglacial environments, and to study associated geological features. BAS is at the forefront in airborne geophysical survey having developed an enhanced aero-geophysical platform which combines ice-sounding radar, aeromagnetic and aerogravity sensors. The platform is installed in a ski-equipped De Havilland DH-6 Twin Otter which is capable of operating from remote field camps off un-groomed runways.

The new ‘in house’ radar utilises LabVIEW and is capable of surveying ice surface, ice thickness, bedrock configurations, internal ice layering, and subglacial lakes. The radar system has successfully explored three key regions of Antarctica as part of major international projects with the US and Italian Antarctic Programmes: the Amundsen Sea Embayment, the Wilkes Subglacial Basin and the Gamburtsev Subglacial Mountains.

The Antarctica's Gamburtsev Province (AGAP) project was one of the most ambitious, challenging and adventurous 'deep field' Antarctic missions of the International Polar Year. The Gamburtsev subglacial mountains are thought to be the birthplace of the vast East Antarctic Ice Sheet that covers 10 million km2 of our planet greater than the area of the USA. Working for weeks at high altitude the science teams worked in some of the harshest conditions imaginable. Seven nations pooled their resources to support the project and the British team acquired almost 80,000 line kilometres of data the equivalent of two trips around the globe. During the AGAP project, the PXI chassis rugged design survived the harsh Antarctic environment overcoming the -30°C ambient temperatures and high vibration levels from the aircraft. With only a short weather window of three weeks, the team worked around the clock. The PXI-based measurement system performed flawlessly and eight terabytes of data were collected.

LabVIEW-Based Radar

LabVIEW was chosen because of its ability to integrate cutting edge electronics easily in to the radar system. An Alliance member was consulted to lay the programming foundations and this allowed us to quickly develop the radar and easily optimise the setup to achieve the best results. The radar system is comprised of an arbitrary waveform generation (AWG) card and configured using LabVIEW. A chirp waveform is generated by the AWG and then transmitted to the four antennas on the port wing via a four channel transmitter operating at 150MHz. Four aerials on the starboard wing of the aircraft receive the reflected radio waves from the ice surface, internal layers and the bed beneath the ice. A high gain stable RF amplifier amplifies the returned signal prior to digital signal processing. A software-radio design was implemented in the digital receiver board and a customised FPGA performed signal stacking and down conversion. All the required synchronise clocks are produced by an in-house developed card. Once the signal has been converted into the digital domain LabVIEW streams the data to hard drives and performs fast digital signal processing to produce a real time waterfall display and an analogue scope to show the surface, bed and some of the stronger internals.

Throughout the development stages and testing the benefits of LabVIEW became very apparent with ability to do high speed sampling and achieve a very good signal to noise meaning we can study locations beneath tick-ice. To date the radar has sounder through 4,560 metres of ice.

To cover the large dynamic range of the received echoes the flexible radar design transmits a sequence of pulses of different amplitudes and coding. On reception these are sorted and processed. The coherent system operates at a centre frequency of 150MHz and 12 MHz bandwidth, and is capable of either conventional or polarimetric operational data bandwidth of 20 Mbytes/sec gives an along-track sampling of 20cm allows SAR post-processing to give a spatial resolution of 1m. Depth resolution is governed by pulse type, period and bandwidth, with this system it is typically 8m. Data is stored on dual-redundant removable media. A 4.5 hour flight covers around 1,000 km and will generate around 150GB of data. Advanced radar post processing is carried out back at Cambridge on the Sun data servers to produce corrected, compensated, calibrated and georeferenced radar data.

Advantages of the NI Solution

LabVIEW has provided our engineers and scientist a programming environment that allowed software to be developed quickly and easily. Integration with existing and new scientific equipment is quick and effective. The support and expertise NI has provided has proved invaluable saving hours of testing and redesigns allowing the system to be ready at the seasons start.

Using the NI PXI and LabVIEW PASIN can be easily maintained and updated to the latest sampling techniques and CompactPCl boards to keep the radar platform current. The use of NI equipment and LabVIEW has extended beyond the airborne survey radar application and is used also for ground based radars, magnetic and GPS base stations, BAS's metrological airborne survey system, data conversion and other scientific instruments at BAS. The future introduction of FlexRIO will allow the development of the radar system to keep pace with the science requirements.

Author Information:
Carl Robinson
British Antarctic Survey
High Cross, Madingley Road
United Kingdom
Tel: +44 1223 221338

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