Abstract
Hyperspectral imagery has proven its potential in many research applications, especially in the field of environmental sciences. Currently, hyperspectral imaging is generally performed by satellite or aircraft platforms, but mini-UAV (Unmanned Aerial Vehicle) platforms (<20 kg) are now emerging. On such platforms, payload restrictions are critical, so sensors must be selected according to stringent specifications. This article presents the integration of a light pushbroom hyperspectral sensor onboard a multirotor UAV, which we have called Hyper-DRELIO (Hyperspectral DRone for Environmental and LIttoral Observations). This article depicts the system design: the UAV platform, the imaging module, the navigation module, and the interfacing between the different elements. Pushbroom sensors offer a better combination of spatial and spectral resolution than full-frame cameras. Nevertheless, data georectification has to be performed line by line, the quality of direct georeferencing being limited by mechanical stability, good timing accuracy, and the resolution and accuracy of the proprioceptive sensors. A georegistration procedure is proposed for geometrical pre-processing of hyperspectral data. The specifications of Hyper-DRELIO surveys are described through two examples of surveys above coastal or inland waters, with different flight altitudes. This system can collect hyperspectral data in VNIR (Visible and Near InfraRed) domain above small study sites (up to about 4 ha) with both high spatial resolution (<10 cm) and high spectral resolution (1.85 nm) and with georectification accuracy on the order of 1 to 2 m.
Highlights
Hyperspectral imagery offers a great potential for environmental research applications, on topics linked with the critical zone [1]:- bare continental surfaces: soil quality, geophysical and geochemical surface properties [2,3,4]; - vegetation: species distribution, ecosystems monitoring [5,6]; - coastal and inland waters: bathymetry, water quality, benthic habitats classification [7,8,9,10].Currently, hyperspectral imaging is mainly performed by satellite or aircraft platforms
For another flight at 100 m of altitude, which has been performed above Saint Aignan pond (Brittany, France), the georectification Root Mean Square Error (RMSE) computed on nine control points is about 1.9 m
Unmanned Aerial Vehicle (UAV) platforms equipped with hyperspectral sensors such as Hyper-DRELIO provide high spatial and high spectral resolution which would comparatively render full-frame sensor solutions, multispectral sensors, and/or lower spatial resolution systems less optimal
Summary
Hyperspectral imagery offers a great potential for environmental research applications, on topics linked with the critical zone [1]:- bare continental surfaces: soil quality, geophysical and geochemical surface properties [2,3,4]; - vegetation: species distribution, ecosystems monitoring [5,6]; - coastal and inland waters: bathymetry, water quality, benthic habitats classification [7,8,9,10].Currently, hyperspectral imaging is mainly performed by satellite or aircraft platforms. One can consider the helicopters, mainly equipped with a thermic engine and generally designed to support larger and heavier (>5 kg) payloads. This category includes very heavy-duty platforms, up to 100 kg. Helicopters can provide a higher scanning homogeneity than multi-rotor aircrafts for data collection in continuous forward flight [12], being less sensitive to wind gusts or side winds. They require specially trained operators and generate high frequency vibrations
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