Entwicklung von Messmethoden in der Spektrophotometrie

Abstract

The Remote Sensing Technology Institute (IMF) of the German Aerospace Center (DLR) in Oberpfaffenhofen engages in hyperspectral remote sensing of the environment. Remote sensing provides data from bio-geophysical properties for large areas, which are used as input parameters for a multitude of bio-geophysical models, see [SC01]. As the quality of these models depends on the quality of the data, the instruments collecting the data have to be calibrated thoroughly. For this purpose, the IMF department Experimental Methods operates a calibration facility for optical spectrometers, the Calibration Home Base, see [GE01]. Hyperspectral sensors (such as the Airborne Prism Experiment [GE01]) operating in a wavelength range of 350nm to 2550nm are calibrated there. Some calibration methods use filters and diffuse reflectance samples (spectralons). Filters are used to calibrate detectors for hyperspectral airborne experiments and spectralons are a source for the white balancing of field spectroradiometers. It is desirable, that the qualities of the calibration samples are known as precisely as possible. To characterize these filters and spectralons, a new double beam spectrophotometer Lambda 1050 of Perkin Elmer Industries, which has not been used yet, is available as well as an older device from Varian. These spectrophotometers are able to measure reflection and transmission qualities of samples as a function of wavelength. For the calibration tasks, the spectrophotometers must be able to deliver precise and reproducible measurement results. Therefore, the properties of the new Lambda device must been studied and measurement methods must been established. During my work at DLR, I characterized the new Perkin Elmer Lambda 1050 spectrophotometer for transmission and reflection measurements and developed measurement methods yielding appropriate results. To accomplish these tasks, I used a set of ten filters and two spectralons, which were calibrated already by the national metrological institutes of the UK and the U.S. This information was very helpful for validating my methods and the assessment of uncertainties of the DLR measurements. The results of my work are presented on the following pages and the Perkin Elmer Lambda 1050 Spectrophotometer is now ready for use as calibration instrument for DLR tasks. The methods can be found in chapter 2. The measurements also revealed some common mistakes which are discussed at the beginning of the results section.