Optical design of a hyperspectral drone advanced camera for soil monitoring using an electro-optical liquid crystal technology

Abstract

In the context of environmental monitoring, it is very important to improve systems for the identification, assessment and management of environmental risks through the use and integration of analytical techniques combined with hyperspectral airborne sensing technologies. Remote-sensing applications are varied, but nevertheless an accurate mapping of the soil required the use of complex scientific instruments installed on airplanes or helicopters. The high integration of electronics, combined with the computing power of modern processors, allows the development of integrated and compact hyperspectral systems installed on drones.1 The drone era poses new challenges to optical devices design: they shall be light, compact and robust, easy to assemble and to control. This work explains the optical system design of HYDRACAM (HYperspectral DRone Advanced CAMera), an instrument devoted to hyperspectral imaging by using an electro-optical liquid crystal tunable filter combined with a commercial camera. The commercial ray tracing software Zemax/OpticStudio2 was used to perform the optical design. The main challenge was to manufacture a low cost optical device, containing the mass and the total length to suit a drone payload. A huge effort was made in order to combine strict constraints (such as the filter narrow entrance aperture and its acceptance angle) with ambitious optical performance requirements (high spatial resolution, large field of view). First, a description of the work done to find a trade-off between cost and opto-mechanical constraints is provided: the choice of the commercial objective, the choice of the custom lenses materials and shapes and some optical design original solutions are addressed. Then, the details of the optical performance analysis are discussed.