High-emissivity blackbodies are mandatory as calibration sources in infrared radiometers. Besides the requirements on the high spectral emissivity and low reflectance, constraints regarding energy consumption, installation space and mass must be considered during instrument design. Cavity radiators provide an outstanding spectral emissivity to the price of installation space and mass of the calibration source. Surface radiation sources are mainly limited by the spectral emissivity of the functional coating and the homogeneity of the temperature distribution. The effective emissivity of a “black” surface can be optimized, by structuring the substrate with the aim to enlarge the ratio of the surface to its projection. <p> </p>Based on the experiences of the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) calibration source MBB3, the results of the surface structuring on the effective emissivity are described analytically and compared to the experimental performance. Different geometries are analyzed and the production methods are discussed. The high-emissivity temperature calibration source features values of 0.99 for wavelength from 5 μm to 10 μm and emissivity larger than 0.95 for the spectral range from 10 μm to 40 μm.
The development of MERTIS, a miniaturized thermal infrared imaging spectrometer onboard of ESA's cornerstone mission BepiColombo to Mercury has been completed. Qualification of the design is followed by the calibration of the instrument showing up first results of the technology used. Based on subsequent viewing of different targets including on-board calibration sources the push-broom instrument will use a 2-dimensional bolometer detector to provide spatial and spectral information. Here repetition accuracy of pointing and spectral assignment is supported by the design of instrument components under the restriction of limited resources. Additionally a concept of verification after launch and cruise phase of the mission was developed. The article describes how this has been implemented and what the results under environment testing are.
The Airborne Digital Sensor (ADS) a development to fulfil photogrammetric and remote sensing requirements. The new digital sensor is not only a camera for pretty nice pictures. It will be the next - full digital - generation as a measurement device for airborne photogrammetry and remote sensing. The high accuracy design of the focal plane system under flight and environmental conditions (pressure and temperature) will be presented. The ADS project will be introduced as a design of a modular customized CCD line scanner concept. It will be discussed on the ADS version with 4 multispectral CCD lines and 3 panchromatic CCD lines. The presentation will gives an overview of all dependencies and design constrains on the ADS Focal Pate Module (FPM). The ADS optical system has to support both photogrammetric accuracy and the requirement on the SNR for remote sensing applications. The principle to achieve good color pixel matching is described in relation to the customized CCD- and FPM- design. After a short description of the technical design and performances, some application examples are shown to demonstrate the main features of digital sensor: high accuracy, wide angle, high radiometric dynamics, high signal-to-noise-ratio, in-track stereo capability, multispectral capability.
The spectral-photometric IR camera SPICA is proposed as one of the German science instruments of the Stratospheric Observatory for IR Astronomy (SOFIA). It will cover a wavelength range of 20-220 micrometers with three large area detector arrays. With the 2.5 m SOFIA telescope, SPICA will provide unprecedented diffraction limited spatial resolution in the far-IR. In addition, low resolution 3D-imaging spectroscopy is planned. While the silicon array will be commercially available, the germanium arrays are being developed, including their cryogenic multiplexers. The overall instrument concept, its camera optics and the status of the detector development will be presented. The instrument is being developed by the DLR Institute of Space Sensor Technology in Berlin with support of several German and US partners.
The Stratospheric Observatory for Infrared Astronomy, SOFIA, is a joint US and German project and will start observations from altitudes up to 45,000 ft in late 2001. The 2.5 m telescope is being developed in Germany while the 747- aircraft modifications and preparation of the observatory's operations center is done by a US consortium. Several research institutions and universities of both countries have started to develop science instruments. The DLR Institute of Space Sensor Technology in Berlin plans on a spectral-photometric camera working in the 20 to 220 micrometers wavelength range, using doped silicon and germanium extrinsic photoconductors in large, 2D arrays: silicon blocked-impurity band detectors, Ge:Ga and stressed Ge:Ga. While the silicon array will be commercially available, the germanium arrays have to be developed, including their cryogenic multiplexers. Partner institutions in Germany and the US will support the development of the instrument and its observations.