6533b858fe1ef96bd12b57ff

RESEARCH PRODUCT

Configurable bandwidth imaging spectrometer based on acousto-optic tunable filter

subject

description

This paper presents a new portable instrument called Autonomous Tunable Filtering System (ATFS), developed for highly customisable imaging spectrometry in the VIS-NIR range. The ATFS instrument consists of an Acousto-Optic Tunable Filter (AOTF), an optical system, a Radio Frequency (RF) driver based on a Direct Digital Synthesiser (DDS) and control software. The ATFS can be attached to a variety of high-performance monochrome cameras. The system works as a spectral bandpass filter whose wavelength can be selected between 400nm and 1000nm and whose bandwidth can be adjusted between 4nm and 50nm. The filter can be tuned electronically at a very high speed and accuracy, thanks to the DDS versatility. The control software synchronises the camera with the RF generation and implements a smart auto-exposure algorithm that maximises the dynamic range of the instrument for each band. The software can take a set of spectral images sequentially and save them in ENVI® multispectral format or as multiple TIFF images. The system has been validated using a reference point spectrometer. An optional acquisition procedure has been developed, based on the acquisition of dark and white Spectralon® reference images, in order to use the system in applications involving quantitative (reflectance) measurements. Procedures have been established in order to fully calibrate the instrument. The system has been demonstrated in a real world application, which uses the ATFS to map the leaf chlorophyll content from multispectral reflectance images.