Modern IR cameras are increasingly equipped with built-in advanced (often non-linear) image and signal processing
algorithms (like fusion, super-resolution, dynamic range compression etc.) which can tremendously influence
performance characteristics. Traditional approaches to range performance modeling are of limited use for these types of
equipment. Several groups have tried to overcome this problem by producing a variety of imagery to assess the impact of
advanced signal and image processing. Mostly, this data was taken from classified targets and/ or using classified imager
and is thus not suitable for comparison studies between different groups from government, industry and universities. To
ameliorate this situation, NATO SET-140 has undertaken a systematic measurement campaign at the DGA technical
proving ground in Angers, France, to produce an openly distributable data set suitable for the assessment of fusion,
super-resolution, local contrast enhancement, dynamic range compression and image-based NUC algorithm
performance. The imagery was recorded for different target / background settings, camera and/or object movements and
temperature contrasts. MWIR, LWIR and Dual-band cameras were used for recording and were also thoroughly
characterized in the lab. We present a selection of the data set together with examples of their use in the assessment of
super-resolution and contrast enhancement algorithms.
The development and implementation of a computer model to simulate the impact of atmospheric turbulence on image
quality for a passive imaging system is presented. The presented model is an empirical one based upon the analysis of
imaging distortions in real image sequences recorded under different atmospheric conditions. Only horizontal views are
considered, which are typical for a ground to ground application.
The computer simulation uses pristine, single images (showing no turbulence effects) as input and produces image
sequences that are degraded by the specified turbulence. The implemented method can be applied for instance to the
images calculated by any existing imaging simulation tool of a passive camera in a post processing step. Imagers with
high frame rates can be simulated. The simulation results for a medium and a strong turbulent condition are compared to
field data collected by Germany during the NATO-RTG40 White Sands Missile Range field trials of November 2005.
An important feature of the presented simulation method is the consideration of the range information, which is the
viewing distance to an object, or in other words, the length of the optical propagation path. In contrast to the usual way
how turbulence is included into imaging simulations by assuming only a single viewing distance for all parts of a scene,
different range information for different image areas can be used in our simulation. Such spatially high resolved range
information can be for instance easily calculated for synthetic scenarios by computer graphics tools. Examples are
presented showing the advantages of the range dependent turbulence simulation.
The presented simulation method is fast in terms of computing time and well suited for real-time simulations using the
computing power of nowadays graphics processors.
Analytical range performance models like NVThermIP and TRM have proved very useful in the development,
procurement, and quality control of thermal imaging systems. The analytical approach, however, cannot produce images
usable for the visualization of expected capabilities of a planned system or suitable for observer experiments. In order to
overcome this limitation, a software package, pcSitoS, was developed at FGAN-FOM that implements most of the
features covered by the analytical modeling package TRM but is capable of producing simulated high-quality output
images for a given IR system. The simulation model is presented and examples of simulated imagery from both scanning
and staring thermal imaging systems are shown.
The development and implementation of a computer model to simulate the impact of atmospheric turbulence on image
quality is presented. The model is based on first- and second-order statistics of atmospheric turbulence. Necessary
simulation parameters were derived from data collected by Germany during the NATO-RTG40 White Sands Missile
Range field trials of November 2005. The data set consists of image sequences recorded with a high-speed TV camera.
Parameter values were derived by analyzing image sequences recorded at weak and strong turbulence conditions. The
procedures used to analyze the images and to extract simulation parameters are presented.
The FGAN-FOM computer model for turbulence simulation uses static images without turbulence as input and produces
image sequences that are degraded by the specified turbulence. Imagers with high frame rates can be simulated.
Examples are presented.
In order to further assess the accuracy of this heuristics-based and near real-time simulation of turbulence-degraded
image sequences, some test cases are compared against the results obtained by a full, physically based simulation of
radiation propagation through the turbulent atmosphere. Of special interest are the angle-of-arrival fluctuation statistics,
scintillation, and consequences for long exposure resolution.
The increasing use of IR pilot sight in helicopters calls for a reliable prediction of perception ranges for a variety of
objects, especially those needed for orientation and those posing as a potential hazard, like power poles, masts, isolated
trees etc. Since the visibility of objects in the IR depends mainly on the temperature differences between those objects
and a given background and only marginally on illumination, range prediction techniques used for the visual range or
light-amplified vision are only of very limited use. While range predictions based on the Johnson criterion do offer some
insight into expected ranges, the inherently nominal nature of distance estimates thus obtained hampers their use for an
actual field-deployable pre-flight consulting procedure. In order to overcome those limitations, long-term simultaneous
measurements of relevant objects and background temperatures and weather data were carried out and used for
temperature prediction from prevalent weather conditions. Together with a perception model derived from extensive
observer experiments based on synthetic images of the UH Tiger Pilot Sight Unit we developed a perception range
prediction package which is currently evaluated by the weather service of the Bundeswehr. We will present results from
the observer experiments together with the derived perception models. These are then compared to actual perception
ranges as obtained from flight experiments.
Hereby we present the idea of a new passive sensor intended to compensate atmospheric turbulence distortions
of object images. It is based on the applications of the already successful concept of adaptive optics. The
main application of this sensor will be the compensation of the trajectory jitter of flaring objects in the far
distance which will allow quicker identification and better tracking. The system consists of a wavefront sensor
and a deformable correcting mirror, both commercially available, keeping the overall costs and size in reasonable
limits. The research is divided into two main topics: the first is the characterization of the influence of the
atmospheric turbulence on the object image when the observer's line of sight is parallel to the ground. The
second is the development of the components and the software to achieve the required performances. First
progress have been made on determining the shape of the deformable mirror with good accuracy by means of a
modal reconstruction as well as in measuring the wave front distortions of a point-like source due to atmospheric
We present design considerations for a mobile adaptive optics (AO) system intended for ground-level or near ground-level applications in the near infrared spectral range. Starting from the expected atmospheric parameters we arrive at a preliminary system design. Since atmospheric conditions at ground level are considerably worse than those encountered for vertical AO systems, we conducted extensive end-to-end simulations of our system design for three anticipated scenarios in order to evaluate expected performance; these simulations concentrated on anisoplanacy and the effect of scintillations on wave-front control.
LINC-NIRVANA is an imaging interferometer for the Large Binocular Telescope (LBT) and will make use of multi-conjugated adaptive optics (MCAO) with two 349 actuators deformable mirrors (DM), two 672 actuator deformable secondary mirrors and a total of 4 wavefront sensors (WFS) by using 8 or 12 natural guide stars each. The goal of the MCAO is to increase sky coverage and achieve a medium Strehl-ratio over the 2 arcmin field of view. To test the concepts and prototypes, a laboratory setup of one MCAO arm is being built. We present the layout of the MCAO prototype, planned and accomplished tests, especially for the used Xinetics DMs, and a possible setup for a test on sky with an existing 8m class telescope.
On the way to the Extremely Large Telescopes (ELT) the Large Binocular
Telescope (LBT) is an intermediate step. The two 8.4m mirrors create a masked aperture of 23m. LINC-NIRVANA is an instrument taking advantage of this opportunity. It will get, by means of Multi-Conjugated Adaptive Optics (MCAO), a moderate Strehl Ratio over a 2 arcmin field of view, which is used for Fizeau (imaging) interferometry in J,H and K. Several MCAO concepts, which are
proposed for ELTs, will be proven with this instrument. Studies of sub-systems are done in the laboratory and the option to test them on sky are kept open. We will show the implementation of the MCAO concepts and control aspects of the instrument and present the road map to the final installation at LBT. Major milestones of LINC-NIRVANA, like preliminary design review or final design review are already done or in preparation. LINC-NIRVANA is one of the
few MCAO instruments in the world which will see first light and go into operation within the next years.
As advanced wavefront control components and systems are developed, they must be tested. This paper describes the methodology and hardware used in the laboratory at FGAN-FOM, The Research Institute for Optronics and Pattern Recognition in Germany, to evaluate components and systems to be used for wavefront control. The test bed described is unique in two ways: (1) it uses a Hamamatsu parallel aligned liquid crystal phase modulator as a pupil plane phase screen to generate degraded input wavefronts for testing the wavefront control systems, and (2) it may be used to evaluate a variety of wavefront sensor, corrector, and control elements without changing the layout or realigning the optical components that comprise the basic test bed. For example, once the test bed is assembled and aligned, a desired wavefront sensor, with its matching telecentric pupil-imaging lens pair, is simply inserted at the end of the beam train, aligned with the test bed output beam, calibrated, and tested. Similarly, a desired wavefront corrector is inserted at the appropriate pupil plane, aligned, and tested. The paper also presents typical test results.
LINC-NIRVANA is a Fizeau interferometer which will be built for the Large Binocular Telescope (LBT). The LBT exists of two 8.4m mirrors on one mounting with a distance of 22.8m between the outer edges of the two mirrors. The interferometric technique used in LINC-NIRVANA provides direct imaging with the resolution of a 23m telescope in one direction and 8.4m in the other. The instrument uses multi-conjugated adaptive optics (MCAO) to increase the sky coverage and achieve the diffraction limit in J, H, K over a moderate Field of View (2 arcmin in diameter). During the preliminary design phase the team faced several problems similar to those for an instrument at a 23m telescope. We will give an overview of the current design, explain problems related to 20m class telescopes and present solutions.
Adaptive optics systems that use a single guide star can only accomplish their best atmospheric correction over a small area. Layer oriented MCAO has been proposed for extremely large telescopes as a method to achieve adaptive optics correction over a larger field of view. Diolaiti et al have analyzed the stability and steady-state performance properties of layer oriented MCAO system with a number of (reasonable) simplifying assumptions: no loop delay; no mirror dynamics; continuous and position-independent control action; significantly faster adaptive optics loop than turbulence; and performance assessed by the static response of the closed loop system. This paper will use dynamic analyses to investigate the effects of these assumptions on the overall system performance and stability.
Layer Oriented represented in the last few years a new and promising aproach to solve the problems related to the limited field of view achieved by classical Adaptive Optics systems. It is basically a different approach to multi conjugate adaptive optics, in which pupil plane wavefront sensors (like the pyramid one) are conjugated to the same altitudes as the deformable mirrors. Each wavefront sensor is independently driving its conjugated deformable mirror thus simplifying strongly the complexity of the wavefront computers used to reconstruct the deformations and drive the mirror themselves, fact that can become very important in the case of extremely large telescopes where the complexity is a serious issue. The fact of using pupil plane wavefront sensors allow for optical co-addition of the light at the level of the detector thus increasing the SNR of the system and permitting the usage of faint stars, improving the efficiency of the wavefront sensor. Furthermore if coupled to the Pyramid wavefront sensor (because of its high sensitivity), this technique is actually peforming a very efficient usage of the light leading to the expectation that, even by using only natural guide stars, a good sky coverage can be achieved, above all in the case of giant telescopes. These are the main reasons for which in the last two years several projects decided to make MCAO systems based on the Layer Oriented technique. This is the case of MAD (an MCAO demonstrator that ESO is building with one wavefront sensing channel based on the Layer Oriented concept) and NIRVANA (an instrument for LBT). Few months ago we built and successfully tested a first prototype of a layer oriented wavefront sensor and experiments and demonstrations on the sky are foreseen even before the effective first light of the above mentioned instruments. The current situation of all these projects is presented, including the extensive laboratory testing and the on-going experiments on the sky.
We are currently working on four projects employing Multi Conjugate Adaptive Optics in a Layer-Oriented fashion. These ranges from experimental validations, to demonstration facility or full instrument to be offered to an astronomical community and involves telescopes in the range of 4m to 24m equivalent telescope aperture. The current status of these projects along with their brief description is here given.
We are currently investigating the possibilities for a high-contrast, adaptive optics assisted instrument to be placed as a 2nd-generation instrument on ESO's VLT. This instrument will consist of an 'extreme-ao' system capable of producing very high Strehl ratios, a contrast-enhancing device and two differential imaging detection systems. It will be designed to collect photons directly coming from the surface of substellar companions - ideally down to planetary masses - to bright, nearby stars and disentangle them from the stellar photons. We will present our current design study for such an instrument and
discuss the various ways to tell stellar from companion photons. These ways include the use of polarimetric and/or spectroscopic
information as well as making use of knowledge about photon statistics. Results of our latest simulations regarding the instrument will be presented and the expected performance discussed.
Derived from the simulated performance we will also give details
about the expected science impact of the planet finder. This will
comprise the chances of finding different types of exo-planets -
notably the dilemma of going for hot planets marginally separated
from their parent stars or cold, far-away plamnets delivering very
little radiation, the scientific return of such detections and
follow-up examinations, as well as other topics like star-formation,
debris disks, and planetary nebulae where a high-resolution,
high-contrast system will trigger new break-throughs.
We present the design of and recent results from the Large Binocular Telescope (LBT) facility SCIDAR. To our knowledge, this work will produce the first SCIDAR designed as a user instrument for routine seeing measurements in support of telescope operations. Using a commercial, off-the-shelf approach, we have minimized the resources required for system construction.
We present results of simultaneous measurements of atmospheric parameters using a SCIDAR instrument and the Calar Alto ALFA adaptive optics (AO) system. First results indicated that SCIDAR measurements can indeed be useful for selecting appropriate closed-loop settings of an AO system. We will further establish this assumption by presenting the fully reduced data sets showing the time series of the Fried parameter and the isoplanatic angle as obtained from the two instruments. The data was recorded under varying seeing conditions on a binary star and an open cluster. Additionally, we will point out possible applications of simultaneous SCIDAR measurements in AO observations and systems.
The Max-Planck institutes for astronomy and for extraterrestrial physics run a high order adaptive optics system with a laser guide star facility at the Calar Alto 3.5- m telescope in southern Spain. This system, called ALFA, saw first light in September 1996. Today, ALFA can compensate for atmospheric turbulences with natural guide stars as faint as 13.5th magnitude in R-band. ALFA recently succeeded in overcoming this limiting magnitude with the deployment of its laser guide star. This paper briefly reviews the ALFA project and its progress over the last 3 years. We further discuss the impact of sodium-layer laser guide stars on wavefront sensing and present results obtained with both kinds of guide stars.
The MPIA/MPE adaptive optics with a laser guide star system ALFA works excellent with natural guide stars up to 13th magnitude in R-band. Using fainter natural guide stars or the extended laser guide star, ALFA's performance does not entirely satisfy our expectations. We describe our efforts in optimizing the wavefront estimation process. Starting with a detailed system analysis, this paper will show how to construct a modal basis set which efficiently uses Shack- Hartmann measurements while keeping a certain number of low order modes close to analytical basis sets like Zernikes or Karhunen-Loeve functions. We will also introduce various phase estimators (least squares, weighted least squares, maximum a posteriori) and show how these can be applied to the ALFA AO. A first test done at the Calar Alto 3.5-m-telescope will be discussed.