262
April 2015
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
addition, the PRADD project is utilizing the aerial videos and
oblique still imagery captured using Camera 1 (wide angle
lens) to conduct participatory mapping with local communities
in Forecariah Prefecture to delineate mining and agricultural
zones. This will assist with the formalization of property rights,
thus reducing local-scale conflicts over land use.
I
dentified
C
hallenges
While we identified numerous benefits to using UAS technology
for collecting data at ASM sites, we also encountered several
challenges. First, if a UAS has never been flown before in the
country, as was the case in Guinea, there will likely be no set of
established protocols to follow to acquire approval. Therefore, it
was the team’s responsibility to identify a process for contacting
the appropriate authorities in Guinea to acquire permission
to fly the UAS. This involved receiving signed letters from the
Minister of Mines and Geology, the Minister of Transportation,
and consent from the ministers of Defense and the Interior.
Figure 7. A subset of a UAS image mosaic collected at the
Gberdeabon site (A) and a 10 cm resolution digital surface model
(DSM) of the same site in the Forecariah Prefecture of western
Guinea, derived from the UAS imagery using SfM techniques (B).
The DSM incorporates both vegetation and tree cover features as
well as ground elevation showing mining pits.
Figure 8. A three-dimensional
diagram of a DSM with a UAS
image overlay of a subset of
the Gberdeabon study
site in the Forecariah
Prefecture of
western
Guinea.
This relative ease of data collection also translates into
greater survey repeatability. ASM is a dynamic activity in
which mine sites change rapidly. The ability to frequently
collect imagery of sites will greatly improve our understanding
of ASM and how sites, and therefore production, evolve over
time. A goal of this project is to conduct repeat flights of the
sites within six months to acquire the data necessary to
perform a change detection analysis. Of further significance
is the ability to collect high-quality imagery under cloudy
conditions, due to the low operational flying altitudes of small
UAS. This is of particular value when working in tropical
climates. Other benefits include the small size of many UAS,
which makes transportation into the field easier, as well as
the vertical take-off and landing and hovering capabilities
of rotary-wing UAS, which improves operability in terrains
with dense vegetation and disturbed topography.
D
ata
A
nalysis
Analysis of the UAS data collected in Guinea is currently
underway. The nadir aerial images are being used to develop
10 cm resolution DEMs of each mine site. High-resolution
ortho-image mosaics are being developed from the nadir image
frames, the DEM data, and from field GPS control points.
Together, the ortho-images and DEMs will help us to model the
geomorphology of the terrain and enable us to better understand
and identify areas of diamond deposition in the region. Products
are being generated using both structure from motion (SfM)
and traditional photogrammetric software algorithms, so that
comparisons can be made to evaluate the costs and benefits
of data processing in each environment (Figures 7 and 8). In
“To our knowledge
this project
represents the
first time a UAS
has been used for
mapping ASM”.
