GPR* and Positioning Sensors Acquisition
(*) 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.
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.
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:
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.
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
Robotic Search for Antarctic Meteorites 1998
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This document prepared by Michael