PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required bright stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.
The Venus Emissivity Mapper (VEM) is the first flight instrument specially designed with a sole focus
on mapping the surface of Venus using the narrow atmospheric windows around 1μm. VEM will
provide a global map of surface composition as well as redox state of the surface, providing a
comprehensive picture of surface-atmosphere interaction on Venus. In addition, continuous observation
of the thermal emission of the Venus will provide tight constraints on current day volcanic activity.
These capabilities are complemented by measurements of atmospheric water vapor abundance as well as
cloud microphysics and dynamic. Atmospheric data will allow for the accurate correction of atmospheric
interference on the surface measurements and represent highly valuable science on their own. A mission
combining VEM with a high-resolution radar mapper such as the NASA VOX or the ESA EnVision
mission proposals in a low circular orbit will provide key insights in the divergent evolution of Venus.
Based on experience gained from using the VIRTIS instrument on Venus Express to observe the surface of Venus and the new high temperature laboratory experiments, we have developed the multispectral Venus Emissivity Mapper (VEM) to study the surface of Venus. VEM imposes minimal requirements on the spacecraft and mission design and can therefore be added to any future Venus mission. Ideally, the VEM instrument will be combined with a high-resolution radar mapper to provide accurate topographic information, as it will be the case for the NASA Discovery VERITAS mission or the ESA EnVision M5 proposal.
Geometrical sensor calibration is essential for space applications based on high accuracy optical measurements, in this case for the thermal infrared push-broom imaging spectrometer MERTIS. The goal is the determination of the interior sensor orientation. A conventional method is to measure the line of sight for a subset of pixels by single pixel illumination with collimated light. To adjust angles, which define the line of sight of a pixel, a manipulator construction is used.
A new method for geometrical sensor calibration is using Diffractive Optical Elements (DOE) in connection with laser beam equipment. Diffractive optical elements (DOE) are optical microstructures, which are used to split an incoming laser beam with a dedicated wavelength into a number of beams with well-known propagation directions. As the virtual sources of the diffracted beams are points at infinity, the resulting image is invariant against translation. This particular characteristic allows a complete geometrical sensor calibration with only one taken image avoiding complex adjustment procedures, resulting in a significant reduction of calibration effort.
We present a new method for geometrical calibration of a thermal infrared optical system, including an thermal infrared test optics and the MERTIS spectrometer bolometer detector. The fundamentals of this new approach for geometrical infrared optical systems calibration by applying diffractive optical elements and the test equipment are shown.
At the German Aerospace Center (DLR), within the department Optical Information Systems, investigations are
currently being performed on time delay and integration charge coupled devices, with respect to their applicability on
satellites for earth observing missions. This paper contains first results of dynamic measurements of point spread
function and modulation transfer function of a sensor with 9000 pixels and 64 time delay integration steps. The influence
of a mismatch between the line synchronisation frequency and satellite ground speed, as well as the effect of angle
misalignment between satellite flight direction and the orientation of the sensor itself onto point spread function, and
modulation transfer function was investigated. The performance of the test equipment will also be presented.
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.
Proc. SPIE. 6744, Sensors, Systems, and Next-Generation Satellites XI
KEYWORDS: Imaging systems, Sensors, Satellites, Remote sensing, Control systems, Charge-coupled devices, Microsoft Foundation Class Library, Modulation transfer functions, CCD image sensors, RGB color model
The department of Optical Information Systems (OS) at the Institute of Robotics and Mechatronics of the German Aerospace
Center (DLR) has more than 25 years experience with high-resolution imaging technology. The technology
changes in the development of detectors, as well as the significant change of the manufacturing accuracy in combination
with the engineering research define the next generation of spaceborne sensor systems focusing on Earth observation and
remote sensing. The combination of large TDI lines, intelligent synchronization control, fast-readable sensors and new
focal-plane concepts open the door to new remote-sensing instruments. This class of instruments is feasible for high-resolution
sensor systems regarding geometry and radiometry and their data products like 3D virtual reality. Systemic
approaches are essential for such designs of complex sensor systems for dedicated tasks. The system theory of the instrument
inside a simulated environment is the beginning of the optimization process for the optical, mechanical and
electrical designs. Single modules and the entire system have to be calibrated and verified. Suitable procedures must be
defined on component, module and system level for the assembly test and verification process. This kind of development
strategy allows the hardware-in-the-loop design. The paper gives an overview about the current activities at DLR in the
field of innovative sensor systems for photogrammetric and remote sensing purposes.
At the German Aerospace Center an airborne multi-wavelength differential absorption LIDAR for the measurement of
atmospheric water vapour is currently under development. This instrument will enable the retrieval of the complete
humidity profile from the surface up to the lowermost stratosphere with high vertical and horizontal resolution at a
systematic error below 5%. The LIDAR will work in the wavelength region around 935 nm at three different water
vapour absorption lines and one reference wavelength. A major sub-system of this instrument is a highly frequency
stabilized seed laser system for the optical parametrical oscillators which generate the narrowband high energy light
pulses. The development of the seed laser system includes the control software, the electronic control unit and the opto-mechanical
layout. The seed lasers are Peltier-cooled distributed feedback laser diodes with bandwidths of about
30 MHz, each one operating for 200 μs before switching to the next one. The required frequency stability is
± 30 MHz ≅ ± 10-4 nm under the rough environmental conditions aboard an aircraft. It is achieved by locking the laser
wavelength to a water vapour absorption line. The paper describes the opto-mechanical layout of the seed laser system,
the stabilization procedure and the results obtained with this equipment.
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.
Trace gases are components of the Earth's atmosphere influencing weather and climate significantly. They play an important role in atmosphere's chemistry. Ground-based and airborne Differential-Absorption-Lidar-Systems (DIAL) designed for atmospheric investigations are operated since 20 years. Based on the long-term experience in development and operation, the DLR Lidar group initiated a new airborne water vapour Lidar experiment which will perform its first test flight in 2006. Software simulation is one of the major tools for the development of such complex opto-electronic systems. It allows the optimization of system parameters and observation conditions, the development and test of data processing software and the estimation of the capabilities of the sensor system in terms of product quality. The paper describes the physical basics and the DLR DIAL concept. The simulations' end results are presented.
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.
The consistent end-to-end simulation of airborne and spaceborne remote sensing systems is an important task and sometimes the only way for the adaptation and optimization of a sensor and its observation conditions, the choice and test of algorithms for data processing, error estimation and the evaluation of the capabilities of the whole sensor system. The presented software simulator SENSOR (Software ENvironment for the Simulation of Optical Remote sensing systems) includes a full model of the sensor hardware, the observed scene, and the atmosphere in between. It allows the simulation of a wide range of optoelectronic systems for remote sensing. The simulator consists of three parts. The first part describes the geometrical relations between scene, sun, and the remote sensing system using a ray tracing algorithm. The second part of the simulation environment considers the radiometry. It calculates the at-sensor radiance using a pre-calculated multidimensional lookup-table taking the atmospheric influence on the radiation into account. Part three consists of an optical and an electronic sensor model for the generation of digital images. Using SENSOR for an optimization requires the additional application of task-specific data processing algorithms. The principle of the end-to-end-simulation approach is explained, all relevant concepts of SENSOR are discussed, and examples of its use are given. The verification of SENSOR is demonstrated.
12 An end-to-end simulation is a valuable tool for sensor system design, development, optimization, testing, and calibration. This contribution describes the radiometry module of the end-to-end simulation tool SENSOR. It features MODTRAN 4.0-based look up tables in conjunction with a cache-based multilinear interpolation algorithm to speed up radiometry calculations. It employs a linear reflectance parameterization to reduce look up table size, considers effects due to the topology of a digital elevation model (surface slope, sky view factor) and uses a reflectance class feature map to assign Lambertian and BRDF reflectance properties to the digital elevation model. The overall consistency of the radiometry part is demonstrated by good agreement between ATCOR 4-retrieved reflectance spectra of a simulated digital image cube and the original reflectance spectra used to simulate this image data cube.
12 During the past two years the company LH Systems and the German Aerospace Center (DLR) have developed the commercial airborne digital sensor ADS40 based on the three-line principle. By assembling additional CCD lines into the same focal plane, the sensor is capable of generating a number of color images. In the first part, the sensor system itself is introduced shortly. The main concept and the key features are described and an overview of the data processing scheme is given. After that, we will focus on the results of test flights. The emphasis is placed on the properties of the overall system including the sensor itself, platform, airplane, and inertial measurement unit. The effect of using staggered CCD lines is discussed. Flights over well known test areas are used to prove the accuracy of derived data products, DEMs, color images, and ortho-images. Differences in data processing methods are pointed out in comparison to sensor systems based on CCD matrices or film.
The consistent simulation of airborne and spaceborne hyperspectral data is an important task and sometimes the only way for the adaptation and optimization of a sensor and its observing conditions, the choice and test of algorithms for data processing, error estimations and the evaluation of the capabilities of the whole sensor system. The integration of three approaches is suggested for the data simulation of APEX (Airborne Prism Experiment): (1) a spectrally consistent approach (e.g. using AVIRIS data), (2) a geometrically consistent approach (e.g. using CASI data), and (3) an end-to- end simulation of the sensor system. In this paper, the last approach is discussed in detail. Such a technique should be used if there is no simple deterministic relation between input and output parameters. The simulation environment SENSOR (Software Environment for the Simulation of Optical Remote Sensing Systems) presented here includes a full model of the sensor system, the observed object and the atmosphere. The simulator consists of three parts. The first part describes the geometrical relations between object, sun, and sensor using a ray tracing algorithm. The second part of the simulation environment considers the radiometry. It calculates the at-sensor-radiance using a pre-calculated multidimensional lookup-table for the atmospheric boundary conditions and bi- directional reflectances. Part three consists of an optical and an electronic sensor model for the generation of digital images. Application-specific algorithms for data processing must be considered additionally. The benefit of using an end- to-end simulation approach is demonstrated, an example of a simulated APEX data cube is given, and preliminary steps of evaluation of SENSOR are carried out.