Measuring Glacier Thickness in the Yukon with a Portable USB Digitizer

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"Using the USB-5133 digitizer and LabVIEW, we created an ice thickness acquisition and analysis system at a fraction of the cost of comparable commercial products typically used for these measurements."

- Laurent Mingo, Blue System Integration, Ltd.

The Challenge:
Characterizing glacier thickness using a cost-effective, portable data acquisition system.

The Solution:
Integrating the NI USB-5133 bus-powered digitizer with a small laptop computer running NI LabVIEW software to create a customizable and mobile data acquisition and analysis system.

Author(s):
Laurent Mingo - Blue System Integration, Ltd.

Characterizing the natural environment is a fundamental step toward understanding more about the world. Faced with increasing environmental challenges, it is critical to expand our knowledge of natural processes such as the water cycle and the greenhouse effect. With an understanding of glacier dynamics and their responses to climate change, we can increase our understanding of the earth, and scientists at Simon Fraser University in Vancouver, British Columbia, are studying glaciers in this context. Our group is working to model glacier dynamics and develop a reliable 3D representation of the glaciers they study. We typically produce 3D representations using a combination of high-precision global position system (GPS) surveying and glacier bed radar surveys. We used a portable system to measure ice thickness over an entire glacier to produce the necessary data to build a 3D representation of the glacier by integrating a portable and low-power hardware device capable of acquiring radar signals at 100 MS/s with existing radar equipment to measure radar echograms and determine ice thickness.

Digitizing Signals Using NI Hardware

The core of a typical ice thickness measurement system consists of a radar device with a transmitter and a receiver. At a given location, the radar emission antenna generates a recurring pulse that travels through the ice and a fraction of its energy is reflected back, traveling upward through the ice again. When the pulse is reflected back to the ice surface, a receiving antenna terminated with a BNC connector captures the signal.

After the signal reaches the antenna, we digitize it using the lightweight (250 g) NI USB-5133 digitizer. For this application, we use analog triggering to start an acquisition as soon as the pulse is detected. We use the large 4 MB per channel onboard memory of the USB-5133 digitizer to store returned waves with long travel times due to thick ice sheets and to acquire multiple returned waves for further processing. In this application, the target has the ability to measure through a few hundred meters of ice.

For the computer, we chose the ASUS Eee PC laptop because it is low-cost, reasonably rugged, and lightweight. To associate each radar echogram with the measurement location, we used a portable, waterproof GPS instrument  that was USB-based and included a virtual serial communication port driver.

Implementing Data Acquisition and Analysis Software

For acquisition and analysis, we developed the IceRadar application using LabVIEW software. We simplified the development of a powerful digitizer application by taking full advantage of the native NI-SCOPE drivers, which provided an intuitive programming interface to the digitizer hardware. To improve the signal-to-noise ratio, the application offers returned wave stacking, which allows averaging of radar signals in real time. We implement stacking by capturing successive echograms in sequence at the full 100 MS/s sample rate, according to the 512 Hz radar pulse frequency. In addition, we can select automated echogram capture, with or without stacking, to acquire the signal at a predefined time interval.

We integrated the GPS unit into the system using the standard serial device drivers in LabVIEW. We also implemented parsing of the National Marine Electronics Association (NMEA) messages of the GPS in the software.

In addition, we focused on data management for our application. We associated each measurement location with radar data, GPS data, a location name, and a timestamp; we also collect meta data to indicate some of the data quality. For instance, we save the GPS coordinates with both a fix quality factor and the number of satellites used for producing the coordinates, which indicates the level of confidence of the position. It would be cumbersome and difficult to manage a simple file saving scheme due to the incongruous nature of the data set. Using IceRadar, we implemented a hierarchical data format so that the application can interpret the structure and content of a file without any outside information. First, we store the data in a top-level object, called lines, which represents a given path on the glacier where point measurements were taken. Then we attach each point measurement within a line to a subgroup, called a location, which contains the related data: it groups the radar data set as an array and the GPS data set as a cluster. We save the meta data as the attributes of a data set and consolidate these objects into the hierarchical file system for access by the analysis routines of IceRadar, or by any compatible third-party API.

By implementing these simple analysis routines, researchers can scan through hundreds of radar data echograms, keeping track of where each one was acquired. We can perform post-acquisition ice thickness calculations and consolidate the data into the hierarchical file scheme. The entire data set can be maintained within a single file and is hierarchically organized for fast access to key information.

 Successful Development of a Customizable and Mobile System

Using the USB-5133 digitizer and LabVIEW, we created an ice thickness acquisition and analysis system at a fraction of the cost of comparable commercial products typically used for these measurements. This system meets the portability requirements and can be used on foot or skis. We can also adapt the same hardware and software approach for ground-penetrating radar measurements (GPRS). We plan to make improvements for the next field season and expect to boost the analysis capabilities of the system to further improve portability.

Author Information:
Laurent Mingo
Blue System Integration, Ltd.
Laurent.m@bluesystem.ca

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