Introduction

The radar receiver (Rx) is fully controlled via the instrument's software interface. Once launched the application has several functionality clusters grouped into tabs:

• Hardware settings
• User inputs
• DataView 1D
• DataView 2D
• Power Management

Power Management Tab

Battery check is one of the tasks the radar system's operator must do regularly during a survey. The goal is to minimize the chances of the system losing power abruptly if the battery runs out, and if so preventing an orderly shutdown of the software system. In this case, there would be a risk of data corruption, potentially compromising hours of surveying. Even though this risk is small, it is not negligible and power status must be well managed to avoid an unintentional power brownout.

• Knowledge of the battery type/chemistry will determine what Shutdown Level (V) to prescribe. This voltage level will be used as the threshold at which the system will automatically turn off.
• The Shutdown Level (V) is set such that the system has enouhg time to shutdown gracefully (about 1 min).
• The Check Period is the number of minutes between each check.
• The GUI_VBattFactor is a coefficient that allows to tune the software voltage reading to the analog indicator...
• ...the analog indicator is on the main panel of the EPU and is easy to monitor, with readouts operating as soon as a battery is connected to the system.

• The Enable Data Backup is another built-in protection against potential data loss in the case of power brownout. A double backup scheme is implemented by saving a first copy of the current data file while the system is acquiring data. Then when it is time for an update, a new backup is created before deleting the original backup. This way there is always one backup available and not being open by any application, so free of data corruption risk.

Hardware Setup Tab

The Hardware Settings tab contains the most complex group of parameters. However, once familiar with its settings, there is only few adjustments to make. In versions >= 5.0, Theoritical Depth Horizon and Equivalent Resolution group and the Theoritical Signal Resolution (microV) group were added.

Time Related Settings (relating to ice-depth)

• Ice depth horizon and Sample Rate, Record Length pair: Sample Rate in megasamples/sec and Record Lengths in samples define the ice-depth horizon in meters at which the EPU will collect data. This can also be expressed as the duration (microseconds) that the EPU will acquire data once a trigger is detected. This duration relates to the two-way travel time (TWTT) of the radar pulse.
• During this time, the radar pulse travels from the transmitter's antennas, into the ice, reflects off a target (the bed or other significant reflecting horizon). Part of this reflected signal is then captured by the receiver antenna and into the EPU providing a time varying voltage. Time and distance are linked by the electromagnetic (EM) wave speed in ice, typically given as 0.168m/ns, roughly half the speed of light in a vacuum or air.

• This is expressed in the Theoritical Depth Horizon and Equivalent Resolution indicators group:

  • For instance: a sampling rate of 250 MS/s and record length of 1000 samples is equivalent to ~ 4 microsec of TWTT.
  • At the speed of EM wave in the ice of 0.168 m/ns , or 168 m/microsec, this corresponds to ~ 168*4 = 672 m two-way travel distance.
  • Now considering the EM pulse covers twice the distance equivalent to the ice thickness (to and from the reflector), we obtain an actual depth of 672/2 = 336 m.
  • If we consider the separation between transmitter and receiver, and assume the direct wave (air wave) travels at the speed of light between them, the actual TWTT becomes ~ 3.8 microsec, and horizon depth ~ 320m

• The Ref(%) setting indicates at which percentage of the entire width of the time window, the trigger event is positioned. In the example shown below, the direct wave starts at about 0.2 microsec from the start of the horizontal scale, while the full scale is 2.2+0.2 = 2.4 microsec, so the Ref setting was at 0.2/2.4~ 8% .

• Typically this setting would be set at 5 or 10% and allows for a full view of the direct wave

Time Related Settings - Newer Models

In software version > 5.0, the instrument's digitizing board offers faster sampling rate(s) and better resolution (up to 16 bit). The allowed combination of Sampling Rate and Resolution (ie, the number of bits) is mostly taken care of by the software. It is nonetheless important to know what they are.

• IceRadar versions up to 4.x

Bandwidth	Max Sampling Rate	Resolution	Smaller inpur Range
100 MHz	250 MS/s	12 bit	+/- 50 mV

• IceRadar versions 5.x

Bandwidth	Max Sampling Rate	Resolution	Smaller input Range
200 MHz	1 GS/s	8 bit	+/- 10 mV
200 MHz	500 MS/s	12 bit	+/- 20 mV
200 MHz	250 MS/s	12 bit	+/- 20 mV
200 MHz	125 MS/s	15 bit	+/- 50 mV
200 MHz	125 MS/s	12 bit	+/- 20 mV
200 MHz	62.5 MS/s	16 bit	+/- 50 mV

Signal Amplitude Settings (signal strength, and amplitude resolution)

This setting defines the bipolar amplitude range (i.e +/- 50mV) the input electronics is set at. All the digitization capabilities of the instrument will be spread over the range span (i.e 100mV span in this case). In this illustration, part of the radar signal greater than 50mV will be clipped. Increasing the input range will allow a wider span of the input signal to be digitized, at the cost of a diminished (less accurate) vertical resolution.

• 2^n levels, with n = number of bits
• Relates to voltage amplitude of radar signal

More readings:

• Acquiring an Analog Signal : including topics such as bandwidth, amplitude error, rise time, sample rate, the Nyquist Sampling Theorem, aliasing, and resolution.

• Triggering

Trigger Settings

A trigger is an external stimulus that initiates one or more instrument functions. Generally speaking, trigger stimuli include digital edges, software functions, and analog levels. The proper trigger can be derived from attributes of the signal to be acquired, such as the magnitute and slope of the signal. In the current version of the software options are either Edge or Immediate (no trigger). An edge trigger occurs when a signal crosses a user-selectable threshold defined in mV

More refinement can be obtained if you can specify the slope as either positive (on the rising edge) or negative (on the falling edge). The following figure shows edge triggering with different slope selections

User Inputs Tab

Under this tab the user can input the Wave Parameters, notably the wave velocity in air, the wave velocity in ice, and the antenna spacing settings.

As a guideline here is the distance used between transmitter and receiver when used in-line (one behind the other)

Center Freq.	Arm Length	Separation
5 MHz	8.4 m	~ 30-35 m
10 Mhz	4.2 m	~ 15 m
30 MHz	1.4 m	~ 5 m
40 MHz	1.1 m	~ 4 m
50 MHz	0.8 m	~ 3.5 m

...more details about this are found in the Rx-Tx separtion section.

This tab is also used to set the file where data will be stored. Next, the user can select two volumes or hard drives present on the system to check their size comparatively to the data file. It is recommended to regularly check the solid state drive capacity. Finally, this window also provides the user with the full GPS reading parsed from the $GGA NMEA message.

DataView 1D Tab

When not acquiring, the Acquire box is grey, and the data save control is set to No Data Saved in red.

Complete "Acquire" settings must show the following:

• Auto-Save : Green
• Enabled GPS: Green
  • also verifying the GPS gets a fix (green LED),
  • and the GPS Message is ok (green LED).
• Acquire : Green

The Auto-Save (s) setting indicate the rate at which a new location data save will be run.

DataView 2D Tab

Data Saving

IceRadar uses a hierarchical data format to store information (HDF5).

• Data are first grouped into a top level object, called a Line that represents a logical grouping of measurement locations on the terrain.
• For each physical location, a subgroup object called a Location is defined.
• In turns, the Location object contains datasets grouped into a datacapture object, linking together the radar data, the GPS data, and the computed depth data.
• All these objects can have Attributes (Meta data) associated to them.

The resulting dataset for Line_0 at Location_0 is :

• ../location_0/datacapture_0/echogram_0

All the data is consolidated into the hierarchical file system, and can be accessed by the analysis routines. IceRadarAnalyzer is such a routine, however many development environments and languages like Matlab, Python, etc... have HDF5 libraries available.

Backing up the System

To back up the IceRadar system and OS the following procedure is suggested:

• One option is to create a full image of the SSD that can then be restored later if needed
• To back-up IceRadar executables:
  • Navigate to the location of the exe file
  • backup to an external drive the entire folder containing the application
  • to restore: copy the backed up copy into any location and create a shortcut to the exe application. These applications require NI LabVIEW Runtime engine 2011 and NI-VISA 5.4.0 that can be downloaded from www.ni.com.

Note that the IceRadar software is provided as a licensed system for 1x radar system and as such cannot be copied to other computers.