combination of the postprocessing technique with
LSM
refine-
ment and boresight-misalignment correction (Experiment D)
produced a point cloud with a final altimetric accuracy of 10
cm and a planimetric accuracy of 10.2 cm in
E
and 26.2 cm
in
N
, for a flight height of 35 m. These results are comparable
to those of other approaches applying online synchroniza-
tion with similar
ALS
systems and
UAV
flight height, such as
by Jaakkola
et al.
(2010), Wallace
et al.
(2012), and Torres and
Tommaselli (2018), as discussed under Postprocessing Syn-
chronization Results: The Estimation of Clock Differences and
LSM
Refinement.
Four experiments were performed to evaluate the impact of
boresight correction and
LSM
refinement, combined with the
proposed postprocessing synchronization technique. An im-
provement of 85% in the planimetry and 33% in the altimetry
of the point cloud generated was achieved with the combined
approach (synchronization by correlation refined by
LSM
and
boresight correction) compared to Experiment A, which ap-
plied only postprocessing synchronization by correlation.
Based on the results, this proposed combined approach can
be considered an alternative to obtain a lidar point cloud with
UAV
systems in which the devices are decoupled.
Acknowledgments
This study was financed in part by the Coordenação de Aper-
feiçoamento de Pessoal de Nível Superior (
CAPES
), Finance
Code 001 (Grants 1774533 and 1481339); the Fundação de
Amparo à Pesquisa do Estado de São Paulo (
FAPESP
; Grant
2013/50426-4); and the Conselho Nacional de Desenvolvim-
ento Científico e Tecnológico (
CNPQ
; Grant 155739/2018-2).
The authors would also like to acknowledge support from the
partner company, Sensormap Geotecnologia.
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