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4.2 Data collection
When the MIRA system is connected as explained in Chapter 3, the system can be powered on and
data acquisition can start.
Note!
The power cannot be turned ON before the MIRA option is securely connected to the ProEx
unit.
The data collection is configured in the MIRASoft software. More can be read in the MIRASoft
operating manual. As the configuration is ready, the measurement can start.
Note!
W
henever possible, it’s always recommended to average data, so called stacking. In spite of the
high performance of the MIRA systems, this averaging and the selected point distance puts some
limits on the maximum survey speed. Assuming 200 kHz repetition rate and 8 cm point distance and
350 samples, the maximal survey speeds are listed below, at different number of averaging (number
of stacks).
Number of
averages (stacks)
Resulting maximum
survey speed, km/h
1
75
2
37
4
19
8
9
It should also be noted that if the higher speeds are used, the demands on the positioning system
(total station or GPS) become higher as well. It must be able to reliably track the position of the
antenna array box, regardless of the survey speed.
Practically, the site conditions usually constitute the limit in survey speed. Surface roughness,
obstacles preventing straight lines, crossing traffic and other details usually limit the speed to below
20km/h.
Note!
No measurements are carried out before the antenna array moves forward, and the encoder
wheel send a signal to the ProEx unit to measure.
The array gathers data at every point interval specified in the MIRA Acquisition software and the
operator should keep an eye on the incoming data and positioning during the survey.
During data collection the following is good to consider:
-
The warm up time for the system before measurement is at least 10 minutes for a 1.3 GHz
array and shorter for 200 MHz and 400 MHz.
-
The antenna array box should be kept on the ground, or as close to the ground as possible.
-
Be aware of all system warning messages from the MIRASoft, as for instance quality of
positioning data, exceeded measurement speed etc. For more information see MIRASoft
operating manual
-
For every swath, each channel will be precisely positioned and it is up to the operator to
overlay the previous swath somewhat in order to completely cover the area. Excess overlap
will be taken care of automatically by the processing software during the binning process but
uncovered areas will produce artefacts in the resulting images. The processing software has
been designed to minimize these effects but nevertheless, a careful data collection procedure
is essential for the resulting image quality.
-
It is ok to stop the movement of the antenna array and make a break.
Note!
However if the
break is long make sure to turn of the antenna array, as it will otherwise continue to use
power. Traces will only be collected when the encoder wheel is moving.
-
If a measurement swath is wrongly made, stop it and re do it. In the rSlicer you decide which
files will be concluded in a certain project.
