This paper presents an imaging spectrometer principle based on a novel prism-grating-prism (PGP) element as the dispersive component and advanced camera solutions for on-line applications. The PGP element uses a volume type holographic plane transmission grating made of dichromated gelatin (DCG). Currently, spectrographs have been realized for the 400 - 1050 nm region but the applicable spectral region of the PGP is 380 - 1800 nm. Spectral resolution is typically between 1.5 and 5 nm. The on-axis optical configuration and simple rugged tubular optomechanical construction of the spectrograph provide a good image quality and resistance to harsh environmental conditions. Spectrograph optics are designed to be interfaced to any standard CCD camera. Special camera structures and operating modes can be used for applications requiring on-line data interpretation and process control.
During the year 1992 a prototype airborne imaging spectrometer is developed in Finland. The instrument is in the first place developed for technology demonstration, performance verification and algorithm development. The first tests of the AISA (Airborne Imaging Spectrometer for different Applications) are performed during the end of 1992 and the beginning of 1993. This paper describes the instrument design concept and will list the first test results. The instrument has 288 spectral channels, a spatial resolution of 384 pixels across track and is through software flexible programmable. Targets during the development have been simplicity and robustness. Applications can be found in forestry, ecology, hydrology, geology, agriculture etc.