RIEGL Laser Scanning Software

RiMTAfor Automated Resolution of Range Ambiguities••automatic resolution of range
ambiguity in time-of-flight
ranging••unlimited number of MTA zones

Acquiring data in laser scanning with high measurement rates over long ranges frequently results in range
ambiguities. Instruments with multiple-time-aroundcapability (MTA), include information in the acquired
data which the RiMTA software utilizes to resolve theseambiguities. Instead of requiring users to manuallyspecify the correct MTA zone for each data set or evensubset of data, RiMTA automatically calculates theMTA zone for each measurement.

••processes data acquiredwith RIEGL laser scanners withMTA-processing capabilities

In order to correctly determine the range to a target with a••smoothly integrated into theRIEGL data processing workflow

laser pulse intervals, it is necessary to correctly determine theLiDAR instrument using time-of-flight measurements with shortcorrelation of each received echo pulse to its causative
emitted laser pulse. At high pulse repetition rates (PRR)
and large target ranges this definite allocation becomesambiguous due to a limiting factor which may not be tweakedby engineer‘s skills: the speed of light.
Today’s RIEGL LiDAR instruments provide extremely highmeasurement rates as well as long measurement ranges. In such cases, target echoes received may notnecessarily

beassociatedwiththeimmediately

preceding laser pulse emitted (MTA-zone 1). Instead they
may be associated with any of the previous laser pulses emitted. Therefore it is necessary to correctly identify each pulse
echo with its correct originating laser emission. This is automatically done by RiMTA in a smootly integrated data proseccing
workflow.

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Ri Software

Data Sheet

RiMTA - For Automated Range Ambiguity Resolution in ALS
Figure 1 provides a visual demonstration of ALS (Airborne LaserScanning) data where each target echo has been calculated
utilizing four of the immediately previous laser pulses emitted. Thismeans that each single echo is represented by a measurement
range calculated in MTA zone 1, 2, 3 and 4 respectively. In reality
only one of the four realizations represents the true point cloudmodel of the scanned earth surface. The chosen example showsthat the scan data is correctly allocated to MTA zone 2, where theearth surface appears consistently flat. This result stands in contrast to the typical spatial characteristics of incorrectly calculated
ambiguous ranges in MTA zones 1, 3 and 4.
Unique techniques in high-speed signal processing and a novel
modulation scheme applied to the train of emitted laser pulses
Fig. 1

Profile of scan data processed in MTA zones
1 to 4 (data acquired by a RIEGL airbornelaser scanner)permit range measurements without any gaps at any distancewithin the instrument‘s maximum measurement range. The specific modulation scheme applied to the train of emitted laser

pulses avoids a total loss of data at the transitions between MTA-zones and retains range measurement at approximately half
the point density. The correct resolution of ambiguous echo ranges is accomplished using RiMTA in tandem with SDCImport andRiANALYZE for an optimized workflow that maintains fast processing speed for mass data production.

RiMTA - For Automated Range Ambiguity Resolution in TLS & MLS
TLS (Terrestrial Laser Scanning) and MLS (Mobile Laser Scanning), in
contrast to ALS, introduce an additional level of complexity in theresolution of such ranging ambiguities. It is possible that a single
laser pulse encounters multiple targets, e.g., in the near field andfar field, which results in multiple echoes in multiple MTA zones
from a single emitted pulse. Therefore, the resolution of theseambiguities has to be carried out strictly on an echo-to-echo basis and not simply on a laser shot basis. In a final automatic step,outliers are removed according to a confidence filtering testfor each resulting point.
For an optimized workflow in TLS, RiMTA is seamlessly integrated intoFig. 1

Profile of scan data physically present in
MTA zone 1 shown as manually processedin MTA zones 1-4

RiSCAN PRO, maintaining fast processing speeds for mass data production.
In MLS, the correct resolution of ambiguous echo ranges is accom-

plished using RiMTA in tandem with SDCImport and RiANALYZE to provide reliable data in mass data production.

RIEGL
Laser Measurement Systems GmbH
Riedenburgstraße 48
3580 Horn, Austria
Phone: +43 2982 4211
office@riegl.co.at | www.riegl.com

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Copyright RIEGL Laser Measurement Systems GmbH © 2019– All rights reserved.
Use of this data sheet other than for personal purposes requires RIEGL’s written consent.
This data sheet is compiled with care. However, errors cannot be fully excluded and alternations might be necessary.

Data Sheet, RiMTA, 2019-09-03