The APEX Airborne Imaging Spectrometer
Jehle, Michael1; Hueni, Andreas1; Damm, Alexander1; D'Odorico, Petra1; Schaepman, Michael1; Meuleman, Koen2
1University of Zurich, SWITZERLAND; 2Vito, BELGIUM
The Airborne Prism EXperiment (APEX) is an instrument being developed by a joint Swiss-Belgian consortium composed of institutes (University of Zurich, Flemish Institute for Technological Research) and industries (RUAG, OIP, Netcetera) within the European Space Agency's (ESA) PRODEX programme. The imaging spectrometer measures the solar reflected radiance in the wavelength range from 380 nm to 2500 nm, using two spectrometer channels that share a common ground imaging optics. Depending on the flight altitude, the achieved resolution of 1000 spatial across track pixels covering a Field of View (FOV) of 28°, is approximately 1.75 m at 3500 m above ground level, with more than 330 reconfigurable spectral bands. What makes APEX a novel system is the inclusion of an In-Flight Characterization (IFC) facility allowing the characterization of radiometric, spectral, and geometric system properties, both in-flight and on-ground for the full Field-Of-View. The spectral calibration monitoring is achieved by means of an internally stabilized Quartz Tungsten Halogen (QTH) lamp and a filter wheel - equipped with a series of spectral filters - intercepting the light before it reaches the detector.
The instrument has been designed to provide high quality spectroscopic data for scientific applications, with special emphasis on topics related to the Earth System's spheres, and to simulate and support the development of future spaceborne remote sensing instruments.
APEX has passed ESA acceptance in December 2010 and is currently in its exploitation phase. Recent measurements in the calibration home base (CHB) and during extended flight campaigns within the last years show its ability for the derivation of higher level products and as a mission simulator. This paper outlines the activities performed during the APEX exploitation phase with a special focus on recent calibration improvements, new products and preliminary results of the latest measurement campaign.