310
May 2016
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
Lidar Technology: Strength,
Weakness and User Expectations
Although linear lidar systems have proved to be the
backbone of the mapping industry when it comes to
digital terrain modeling, users always hoped for better
productivity. For today’s consumer, excitement about
new features and capabilities with any technology—not
just the smartphone—is short-lived. It exists only until
excitement wanes and a newer generation of technology is
welcomed. Geospatial mapping users are no different from
other consumers. With their continuous innovations, lidar
manufacturers have set the bar high as clients and users
demand consistent increases in productivity from lidar
systems.
Linear lidar is a great technology, but innovations may
be reaching the limit of that technology when it comes to
point cloud density. The new lidar technologies, Geiger
mode and single photon, offer the market an opportunity
to acquire point density of around 15 to 30 points per
square meter (Figures 3 & 4 are examples on the data
quality from both Geiger mode and single photon lidar).
This means better acquisition efficiency, allowing users to
fly higher and capture a wider swath. They fill a gap in the
market when it comes to wide-area dense lidar survey, i.e.
national coverage. However, the advantage of the new lidar
technology becomes less obvious when it comes to small
projects or projects that require a lower density point cloud.
In such conditions, linear lidar systems will perform close to
or as good as Geiger mode and single photon lidar.
Critics of the new lidar technologies have found some
weaknesses. They cite the absence of the intensity image,
the lack of waveform digitization, and the weak signal
(fewer photons) used by the system, which makes the
technologies susceptible to solar noise. The high quality of
the intensity image produced by the linear mode system
is based on the full waveform principle using the large
flux of photons. This is not the case with Geiger mode and
single photon lidar systems, as they use very few photons.
However, some manufacturers have found an alternative
to the intensity image by representing the signal strength
or magnitude through rationing the number of the source
and the back scattered photons. Based on my preliminary
observations, I found this alterative product—called
“reflective image”—to be of good quality. It is comparable
to the intensity image, if you are going to use it to collect
break lines for the hydro-flattening process. As for the
lack of waveform digitization capability associated with
the Geiger mode and single photon lidar, the market has
not shown much demand for this product. Very few users
from the mapping community, if any, have used the full
waveform offered by linear lidar systems meaningfully.
Therefore, I do not expect the absence of full waveform
digitization capability to hinder the adoption of the new
lidar technologies, considering all the other benefits it
offers. As for the weak signal and the solar noise, an
Figure 3. Sample point clouds from Geiger mode lidar with density of 32 pts./m2, size: about 240m x 155m (courtesy of Harris Co.).
