ALTERNATIVE METHODOLOGIES FOR BORESIGHT CALIBRATION OF GNSS/INS-ASSISTED PUSH-BROOM HYPERSPECTRAL SCANNERS ON UAV PLATFORMS
ZhouTian
2019
<p>Low-cost unmanned aerial
vehicles (UAVs) utilizing push-broom hyperspectral scanners are poised to
become a popular alternative to conventional remote sensing platforms such as
manned aircraft and satellites. In order to employ this emerging technology in
fields such as high-throughput phenotyping and precision agriculture, direct
georeferencing of hyperspectral data using onboard integrated global navigation
satellite systems (GNSS) and inertial navigation systems (INS) is required.
Directly deriving the scanner position and orientation requires the spatial and
rotational relationship between the coordinate systems of the GNSS/INS unit and
hyperspectral scanner to be evaluated. The spatial offset (lever arm) between
the scanner and GNSS/INS unit can be measured manually. However, the angular
relationship (boresight angles) between the scanner and GNSS/INS coordinate
systems, which is more critical for accurate generation of georeferenced
products, is difficult to establish. This research presents three alternative calibration
approaches to estimate the boresight angles relating hyperspectral push-broom
scanner and GNSS/INS coordinate systems. For reliable/practical estimation of
the boresight angles, the thesis starts with establishing the optimal/minimal
flight and control/tie point configuration through a bias impact analysis
starting from the point positioning equation. Then, an approximate calibration
procedure utilizing tie points in overlapping scenes is presented after making
some assumptions about the flight trajectory and topography of covered terrain.
Next, two rigorous approaches are introduced – one using Ground Control Points
(GCPs) and one using tie points. The approximate/rigorous approaches are based
on enforcing the collinearity and coplanarity of the light rays connecting the
perspective centers of the imaging scanner, object point, and the respective
image points. To evaluate the accuracy of the proposed approaches, estimated
boresight angles are used for ortho-rectification of six hyperspectral UAV
datasets acquired over an agricultural field. Qualitative and quantitative
evaluations of the results have shown significant improvement in the derived
orthophotos to a level equivalent to the Ground Sampling Distance (GSD) of the
used scanner (namely, 3-5 cm when flying at 60 m).</p>