GPR* and Positioning Sensors Acquisition Interface


(*) GPR stands for Ground Penetrating Radar

The GPR operating interface was implemented using LabView on the onboard laptop. This programming tool allows the design and implementation of virtual interfaces to control instruments. For example, the GPR data acquisition and saving process are controlled from this interface.

Interface Structure

The interface structure is designed to save data of all present sensors. The data is gathered at the sensor rate and stored in a global variable. That global variable is written by all the sensor input interfaces, and read by the saving process. This guarantees that the most recent reading is stored. The saving rate of all the global variables is controlled by the GPR scan rate, which is the only synchronous input.  If any sensor is not working, that corresponding data will be all zeros.

Ground Penetrating Radar Interface

The GPR instrument itself has controls (knobs) that define variables as the maximum depth, the scan rate, three independent gain controls, and cut frequency for low and high pass filters.

The GPR interface is designed to control the analog data acquisition. It defines the instrument (A/D PMCIA board), the channel and the triggering method used. It also controls the scan rate and a time-out limit for trigger wait.

There are also two graphs windows. The upper one presents a amplitude vs. time graph of the analog signal received from the radar (each one called a trace). The time is related to the depth of the returned signal, according to the soil constant.

The second one presents a history of the traces, in a graph where the vertical axis is the time (related to the depth), the horizontal axis is a succession of the traces as being recorded (this usually related to the horizontal motion of the sled and the sensor antenna). The color of the graph is proportional to the amplitude of the signal. This graph is the usual visualization method for GPR data.

 

GPS interface

The GPS provides position and time information that is attached to each GPR trace. The GPS configuration includes two GPS receivers: one is mounted on the sled, the other is stationary. The difference gives an accurate vector between the two that is used to position the sled with respect to the station location (usually within a range of hundred meters).

The interface consist of three windows:

Position Window

The Position and Time window displays the position of the sled in longitude and latitude world coordinates and shows the estimated height above the sea level. Values for latitude and longitude are in degrees, minutes and seconds. Altitude is in meters.

Differential Vector Window

The differential window displays the position vector of the sled with respect to the fixed station. The values are in meters.
 

Status and Time Window

The status and time window will show the number of satellites being used for positioning, the GPS time (in milliseconds and weeks), and various flags that show the quality of the reception, and the current mode of the GPS system.
 

Inclinometer Interface

The inclinometer interface provides display for the angle readings. These angle reading could come from an inclinometer or an magnetic gyro compass. Both devices are connected serially to the computer. The displays show numerically and graphically the angles and the status of the serial connections with the sensor.
Back to Radar Experiment Results.

Robotic Search for Antarctic Meteorites 1998
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This document prepared by Michael Wagner.