183 
PRACTICAL APPLICATION OF MULTIPLE PULSE IN AIR (MPIA) LIDAR 
IN LARGE-AREA SURVEYS 
R. B. Roth 3, *, J. Thompson 6 
a Leica Geosystems, 13 Park Drive, Westford, MA 01886, USA - ron.roth@leicaus.com 
b Northwest Group, Suite 212, 5438 - 11 th Street NE, Calgary, Alberta, Canada T2E 7E9 - 
james.thompson@nwgeo.com 
Commission I, WG 1/2 
KEY WORDS: LIDAR, Surveying, Technology, Acquisition, Calibration, Accuracy, Project 
ABSTRACT: 
Multiple Pulses in Air Technology, or MPiA, is a new technology allowing airborne LIDAR systems to be used at higher pulse rates 
than previously possible. By allowing the airborne LIDAR system to fire a second laser pulse prior to receipt of the previous pulse’s 
reflection, the pulse rate at any given altitude can be effectively doubled. Getting past the limitations imposed by the speed of light 
and conventional single-pulse-in-air LIDAR technology allows the airborne LIDAR system to achieve the desired point density at 
twice the coverage rate or, conversely, for twice the point density to be achieved at conventional coverage rates. Though announced 
publicly in 2006, it was not until well into 2007 that commercially-available MPiA-equipped systems were fielded. The technology 
can now be considered “mainstream”, and is actively being used on a variety of airborne LIDAR data acquisition projects. This 
study will present an overview of MPiA technology in the context of a large area survey project in Alberta, Canada. In addition to 
the consideration of MPiA technology in this project, implications on other facets of project organization will be presented. Overall 
results will be given, proving the ability of MPiA-equipped systems to achieve a nominal 2:1 productivity increase over that of 
conventional systems 
1. INTRODUCTION 
1.1 Introduction to Multiple Pulses in Air (MPiA) 
Technology 
Multiple Pulses in Air Technology, or MPiA, is a new 
technology allowing airborne LIDAR systems to be used at 
higher pulse rates than previously possible. By allowing the 
airborne LIDAR system to fire a second laser pulse prior to 
receipt of the previous pulse’s reflection, the pulse rate at any 
given flying height can be effectively doubled. Getting past the 
limitations imposed by the speed of light and conventional 
single-pulse-in-air LIDAR technology allows the airborne 
LIDAR system to achieve the desired point density to be 
achieved at twice the conventional coverage rate or, conversely, 
for twice the point density to be achieved at conventional 
coverage rates. Though announced publicly in 2006, it was not 
until well into 2007 that commercially available MPiA- 
equipped systems were fielded. The technology can now be 
considered “mainstream”, and is actively being used on a 
variety of airborne LIDAR data acquisition projects. 
Although the application of MPiA technology at very low 
altitudes can be limited by maximum achievable laser pulse 
rates, the use of this technology at higher altitudes presents few 
limitations. This makes the use of MPiA technology 
particularly applicable to large area surveying. Large area 
surveying is typically done for a variety of applications, 
including national mapping programs and regional flood zone 
or coastal mapping. In these applications, it is important to 
achieve a significant level of detail, with post spacing in the 
region of 2 meters. Although this level of detail can be readily 
achieved with conventional LIDAR systems, the typical flying 
heights used (2000 - 3000 m AGL) would normally result in 
laser pulse rates that limit maximum coverage rates. MPiA 
technology allows coverage rates to be effectively doubled thus 
lowering the data acquisition (i.e., flying) costs. This can be an 
important factor in the economic viability of large area mapping 
projects. 
In addition to simply increasing the possible laser pulse rates of 
the LIDAR system, MPiA also allows the user other benefits. 
Since the aircraft can fly substantially higher, the effects of 
terrain height variation on swath width are minimized, thus 
requiring less side overlap to assure complete area coverage. In 
addition, a narrower Field of View (FoV) can be used, resulting 
in better forest floor penetration in areas covered by vegetation. 
Finally, the generally higher flying altitudes used result in a less 
turbulent, more comfortable flight and less flight crew fatigue. 
This is particularly important given the high “duty cycle” of 
flying crews on large-area missions. In the example shown, 
multiple long-duration (up to 7 hours) missions are possible 
each day. 
1.2 Operating Envelope of Single-Pulse versus MPiA 
Systems 
Figure 1 gives a comparison of the performance envelopes for 
a single-pulse versus MPiA versions of the ALS50-II. 
* Corresponding author.