Herbert Jahn

A sensor-based approach to image quality

In the past 20 years a large effort has been made to characterize the image quality of remote sensing systems. The image quality can actually be measured only by the quality of the final product (e.g. object detection, classification). One option now is to use the National Image Interpretability Rating Scales (NIIRS), because NIIRS is related to object detection. From an engineering standpoint a task-based scale, like NIIRS is not well suited, because it cannot be derived from the fundamental sensor and scene behaviour. Therefore, the aim of this paper is to derive an image quality criterion, based on the physical characteristics of sensor and scene. To assess the image quality, we compare the output of the real sensor with the output of an ideal sensor based on a Local Mean Squared Error (LMSE). This criterion, we abbreviate in the following with YAIQC (Yet Another Image Quality Criteria)

Design and analysis of a small bispectral infrared push broom scanner for hot spot recognition

A small bispectral infrared detection (BIRD) push broom scanner for a small satellite emission is described, which is dedicated to the detection and analysis of high temperature events (HTE). Current operating and planned satellite sensors are not designed for high temperature event observation and therefore show some serious drawbacks such as saturation of the IR channels for target temperatures higher than 50 degrees Celsius, low spatial resolution in case of daily coverage, low coverage of spatially high resolving systems, or not adequate IR channels. The BIRD instrumentation is a first attempt to overcome these disadvantages. For this purpose two infrared line scanners (3.4 - 4.2 micrometer and 8.5 - 9.3 micrometer) are combined with a wide angle stereo scanner (WAOSS) in the visible. Because of the limited resources of a small satellite the design of all instruments is based on the usage of staring focal plane arrays. To observe HTE directly the covered sounding area should be as large as possible whereas at first glance the ground resolution of the sensor should be in order of some 10 m. These demands are in contradiction with the number of the infrared detector array elements currently available. For this reason methods of subpixel target detection and analysis have to be used. According to this concept a combination of the data from at least to radiometric high sensitive infrared sensor channels is used to compensate the lack of high ground resolution. Adding to the infrared cameras a suitable CCD-line scanner for a pre-classification with a higher ground resolution, a marked improvement can be achieved.

MERTIS: system theory and simulation

The deep-space ESA mission BepiColombo to planet Mercury will contain the advanced infrared remote sensing instrument MERTIS (MErcury Radiometer and Thermal infrared Imaging Spectrometer). The mission has the goal to explore the planets inner and surface structure and its environment. With MERTIS investigations of Mercurys surface layer within a spectral range of 7-14μm shall be conducted to specify and map Mercurys mineralogical composition with a spatial resolution of 500m. Due to the limited mass and power budget the used micro-bolometer detector array will only have a temperature-stabilization and will not be cooled. The theoretical description of the instrument is necessary to estimate the performance of the instrument especially the signal to noise ratio. For that purpose theoretical models are derived from system theory. For a better evaluation and understanding of the instrument performance simulations are performed to compute the passage of the radiation of a hypothetical mineralogical surface composition through the optical system, the influence of the inner instrument radiation and the conversion of the overall radiation into a detector voltage and digital output signal. The results of the simulation can support the optimization process of the instrument parameters and could also assist the analysis of gathered scientific data. The simulation tool can be used as well for performance estimations of MERTIS-like systems for future projects.

MERTIS - a highly integrated IR imaging spectrometer

With a background of several instrument developments in the past the German Aerospace Center in Berlin proposed for ESAs deep space mission BepiColombo an imaging spectrometer which meets the challenges of limited technical resources and a very special operational environment. An 80-channel push broom-type spectrometer has been drafted and it s development has been started under the name MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer). The instrument is dedicated to the mineralogy surface science and thermal characteristics studies of the innermost planet. It is based on modern un-cooled micro-bolometer technology and all-reflective optics design. The operation concept principle is characterised by intermediate scanning of the planet, deep space and black bodies as calibration targets. A miniaturised radiometer is included for low level temperature measurements. Altogether the system shall fit into a CD-package sized cube and weigh less than 3 kg. The paper will present the instrument architecture of MERTIS, its design status and will show the results of first components being built.

Advanced sensors for surveying and mapping

During the last years the department of Optical Information Systems of the German Aerospace Center (DLR) developed a considerable number of imaging sensor systems for a wide field of applications. Systems with a high geometric and radiometric resolution in dedicated spectral ranges of the electromagnetic spectrum were provided by developing and applying cutting edge technologies. Designed for photogrammetry and remote sensing, such systems play an important role for security and defence tasks. Complete system solutions were implemented considering theoretical framework, hardware design and deployment, overall system tests, calibration, sensor operation and data processing. Outstanding results were achieved with the airborne digital sensor ADS40 and the micro satellite BIRD and its infrared camera payload. Future activities will focus on intelligent cameras and sensor webs. The huge amount of data will force the issue of thematic multi-sensor data processing which is to be implemented in real time near the sensor. In dependence on well defined tasks, combinations of several sensors with special properties will be placed on spaceborne, airborne or terrestrial platforms. The paper gives an overview about finished and current projects and strategic goals.

Space-Borne Autonomous On-Board Recognition of High Temperature Events

Satellite fire detection and monitoring observations are currently in an experimental or preoperational phase and directed to the development and testing of fire detection and analysis algorithms.

Texture segmentation with a neural network

A neural method for gray value segmentation now is applied to texture segmentation. The parallel-sequential algorithm is based on recursive nonlinear feature smoothing in a 4- neighborhood. The smoothed feature values then can be segmented using an adaptive adjacency criterion which defines a special graph structure, called the Feature Similarity Graph. The segments are the connected components of that graph. The combination of results from the different image features is done in a hierarchical process starting, like in the human visual system with gray value segmentation. Besides segments with homogeneous gray value this process also provides texture elements which are the basis for the calculation of new image features. Then, first, the modulus of the gray value gradient is used as a new feature of the original image. The following segmentation basing on that feature provides regions which are homogeneous with respect to the mean gray value gradient. Furthermore, texel directions are calculated. That feature contains information on texture orientation of textured image regions. With these features the same neural segmentation method is able to separate not only regions with different mean gray values but also those with different textures.

New optical sensor systems for photogrammetry and remote sensing

Recent developments in the fields of detectors on one hand and a significant change of national and international political and commercial constraints on the other hand led to a large number of proposals for spaceborne sensor systems focusing on Earth observation in the last months. Due to the commercial availability of TDI lines and fast readable CCD-Chips new sensor concepts are feasible for high resolution sensor systems regarding geometry and radiometry und their data products. Systemic approaches are essential for the design of complex sensor systems for dedicated tasks. Starting with system theory optically, mechanical and electrical components are designed and deployed. Single modules and the entire system have to be calibrated using suitable procedures. The paper gives an overview about current activities at German Aerospace Center on the field of innovative sensor systems for photogrammetry and remote sensing.

System theoretical aspects for designing opto-electronic sensors for remote sensing

The design of passive optical sensor systems for remote sensing requires more or less complex theoretical investigations. Based on the user requirements which are characterized by data products all relevant physical effects influencing the generation of an image have to be considered and modeled. The goal is to build the whole chain of signal generation and transformation: from the source of light, through the atmosphere to the object to be observed, through the atmosphere again to the sensor system. These models can be applied for simulations which can be used for the optimization of sensor parameters and observation conditions and for the estimation of the potential performance of such a system. For this task, specific retrieval algorithms have to be considered closing the loop of developing camera systems. The paper contains classical approaches for a system design as a standard tool used in the Institute for Robotics and Mechatronics including methods for modeling the geometrical and radiometric relations and the description of camera hardware. The results of a complex investigation of the point spread function of camera systems is core topic of this paper.

Space instrument performance traceability for high resolution satellite systems

Technology changes in detector development and the significant improvement of manufacturing accuracy in combination with the permanent engineering research influences the spaceborne sensor systems, which are focused on Earth observation and remote sensing. Developments in focal plane technology, e.g. the combination of large TDI lines, intelligent synchronisation control, fast readable sensors and new focal plane and telescope concepts are the key developments for new remote sensing instruments. This class of instruments disposes of high spatial and radiometric resolution for the generation of data products for mapping and 3D GIS VR applications. Systemic approaches are essential for the design of complex sensor systems based on dedicated tasks. The system-theoretical description of the instrument inside and a simulated environment is the basic approach for the optimisation process of the optical, mechanical and electrical designs and assembly. Single modules and the entire system have to be calibrated and verified. The traceability of the performance-related parameters from the single sensor up to the flight readiness of the instrument forms the main focus inside such complex systems. In the future it will also be possible to prove the sensor performance on wafer level before assembly. This paper gives an overview about current technologies for performance measurements on sensor, focal plane assembly (FPA) and instrument level without the optical performance of the telescope. The paper proposes also a technology, which can be used for sensor performance measurements on wafer level.