Adaptive optics (AO) techniques like laser tomography adaptive optics (LTAO) and multi-conjugated adaptive optics (MCAO) are becoming more and more used in the development of instrumentation for the existing 8-m class telescopes and future extremely large telescopes (ELT). Achieving the required level of AO correction over wide field of view requires the knowledge of the turbulence strength vs the altitude, first during the design phase of the instruments to ensure they match the needed performances, and then during the on-sky operation to optimize the AO control according to the atmospheric conditions. Obtaining reliable measurements of the turbulence in three dimensions is thus of high importance, today and in the future. The Paranal Observatory gives access to three atmosphere profilers and one atmosphere monitor on one single site. The possibility to obtain simultaneous data on independent systems is a great opportunity to compare their results and evaluate the advantages of each method. We present the results of statistical analysis of data coming from these systems, obtained in different periods and with various atmosphere conditions. From this analysis, we can draw conclusions on conditions needed for a useful comparison of the profilers and show the possible needed attempt to be made on aligning their assumptions and thus the provided parameters.
The ESO’s adaptive optics facility (AOF) is ending its commissioning at Paranal (Chile). It feeds two second-generation instruments of the VLT-UT4 telescope, HAWK-I and MUSE, with turbulence corrected wavefronts through the GALACSI and GRAAL modules. The main features of the AOF are its deformable secondary mirror with 1170 actuators and a laser asterism of 4 artificial stars that probe the atmosphere via four high-resolution Shack-Hartmann wavefront sensors (WFS), each with 40x40 subapertures. The system provides ground layer adaptive optics (GLAO) and laser tomography adaptive optics (LTAO) capabilities. In order to support the commissioning phases of the project, and later optimize and diagnose the operation of the system, a turbulence profiler has been developed and installed in SPARTA, the AOF real time controller (RTC). The profiler estimates two key turbulence parameters: the Cn2(h) and the outer scale (L0(h)) profiles and no limit on the number of the estimated layers exists, but for eight layers, the method takes about 2 minutes to yield a full characterization of the atmosphere. The maximum line of sight distance that the profiler can probed the atmosphere depends on the star separation defined for each operation mode: 3km for GRAAL; 14 km for GALACSI wide field and over 35km for GALACS narrow field mode. The remaining turbulence above these maxima (unseen turbulence from the undetected layers) are essential in the GRAAL mode and it is reliably estimated thanks to a novel method to determine the noise in the WFSs, which is mandatory for estimating this upper segment of the turbulence. The technique is also useful to alert about operational problems such as dome seeing and mis-registrations. The method is currently installed in the SPARTA RTC, providing continuous online estimations for the GALACSI (narrow and wide field modes), and for GRAAL mode. Results for several nights comprising hundreds of profiles show very good agreement with other independent measurements.
The long commissioning of the Adaptive Optics Facility (AOF) project has been completed shortly after this conference, providing AO correction to two Very Large Telescope (VLT) foci supported by an adaptive secondary mirror and four laser guide stars. Four AO modes are delivered: a Single Conjugate AO (SCAO) system for commissioning purpose, wide field and medium field Ground Layer AO (GLAO) for seeing improvement and narrow field Laser Tomography AO (LTAO) for ultimate performance. This paper intends to describe the implemented AO baseline and to highlight the most relevant results and lessons learned. In particular, it will address the control and reconstruction strategy, the wavefront sensing baseline and the online telemetry used to optimize the system online, estimate the turbulence profile and calibrate the misregistrations. Focusing on the LTAO mode, we will describe the tomography optimization, by exploring the reconstruction parameter space. Finally, on sky performance results will be presented both in terms of strehl ratio and limiting magnitude.
Mechanical vibrations affect the performance in modern adaptive optics systems. These structural vibrations induce aberration mainly in tip-tilt modes that reduce the accuracy of the astronomical instrument. Therefore, control actions need to be taken. With this purpose we present a laboratory demonstration of vibration rejection of tip-tilt modes using closed-loop control, inducing vibration on the test bench via an eccentric motor with controllable frequency, in order to simulate the structural vibrations mentioned above. We measure the laser vibration and its tip-tilt aberration using a camera and a Shack Hartmann Wave Front Sensor. The control action is carried out by a Fast Steering Mirror (FSM).
Wide Field Adaptive Optics (WFAO) systems represent the more sophisticated AO systems available today at large telescopes. One critical aspect for these WFAO systems in order to deliver an optimised performance is the knowledge of the vertical spatiotemporal distribution of the CN2 and the wind speed. Previous studies (Cortes et al., 2012) already proved the ability of GeMS (the Gemini Multi-Conjugated AO system) in retrieving CN2 and wind vertical stratification using the telemetry data. To assess the reliability of the GeMS wind speed estimates a preliminary study (Neichel et al., 2014) compared wind speed retrieved from GeMS with that obtained with the atmospherical model Meso-Nh on a small sample of nights providing promising results. The latter technique is very reliable for the wind speed vertical stratification. The model outputs gave, indeed, an excellent agreement with a large sample of radiosoundings (∼ 50) both in statistical terms and on individual flights (Masciadri et al., 2013). Such a tool can therefore be used as a valuable reference in this exercise of cross calibrating GeMS on-sky wind estimates with model predictions. The main results of Neichel et al. (2014) analysis showed that, on a great number of cases, GeMS could reconstruct very good wind speed estimates. At the same time it has been put in evidence, on a number of cases, not negligible discrepancies from the atmospherical model. However we observed that these discrepancies strongly decreased or even disappear if GeMS data reduction is done with the a priori knowledge of the wind speed stratification provided by the model Meso-Nh. Basically the a priori knowledge helped the data reduction of GeMS acquisitions. In this contribution we achieved a two-fold results: (1) we extended analysis on a much richer statistical sample (∼ 43 nights), we confirmed the preliminary results and we found an even better correlation between GeMS observations and the atmospherical model with basically no cases of not-negligible uncertainties; (2) we evaluate the possibility to use, as an input for GeMS, the Meso-Nh estimates of the wind speed stratification in an operational configuration. Under this configuration these estimates can be provided many hours in advanced with respect to the observations and with a very high temporal frequency (order of 2 minutes or less). Such a system would have a set of advantages: (a) to implement inside GeMS a total temporal and spatial coverage of the wind speed over ∼ 20 km and all along the night not only in real-time but in advance of a few hours, (b) to improve the detection of the CN2 vertical stratification from GeMS because a good wind speed estimation would improve the quality of the cross-correlation peaks detection, (c) the possibility to bypass the complex (and not necessarily reliable) procedures necessary to automatise the wind speed estimate of GeMS due to the relatively low vertical resolution of the system. Such a study can obviously be considered as a demonstrator for multiple operational AO and WFAO systems (AOF, LINC-NIRVANA, RAVEN, ...) of present top-class telescopes and for the forthcoming generation. It might have, therefore, an interest for the AO community well beyond the improvement of GeMS performance.
Prior statistical knowledge of the turbulence such as turbulence strength, layer altitudes and the outer scale is essential for atmospheric tomography in adaptive-optics (AO). These atmospheric parameters can be estimated from measurements of multiple Shack-Hartmann wave-front sensors (SH-WFSs) by the SLOpe Detection And Ranging (SLODAR). In this paper, we present the statistics of the vertical CN2 and the outer scale L0 at Maunakea in Hawaii estimated from 60 hours telemetry data in total from multiple SH-WFSs of RAVEN, which is an on-sky multi-object AO demonstrator tested on the Subaru telescope. The mean seeing during the RAVEN on-sky observations is 0.475 arcsec, and 55% turbulence is below 1.5 km. The vertical profile of CN2 from the RAVEN SLODAR is consistent with the profiles from CFHT DIMM and MASS, and TMT site characterization.
Estimating the outer scale profile, L0(h) in the context of current very large and future extremely large telescopes is crucial, as it impacts the on-line estimation of turbulence parameters (Cn2(h), r0, θ0 and τ0) and the performance of Wide Field Adaptive Optics (WFAO) systems. We describe an on-line technique that estimates L0(h) using AO loop data available at the facility instruments. It constructs the cross-correlation functions of the slopes of two or more wavefront sensors, which are fitted to linear combinations of theoretical responses for individual layers with different altitudes and outer scale values.
We analyze some restrictions found in the estimation process, which are general to any measurement technique. The insensitivity of the instrument to large values of outer scale is one of them, as the telescope becomes blind to outer scales larger than its diameter. Another problem is the contradiction between the length of data and the stationarity assumption of the turbulence (turbulence parameters may change during the data acquisition time).
Our method effectively deals with problems such as noise estimation, asymmetric correlation functions and wavefront propagation effects. It is shown that the latter cannot be neglected in high resolution AO systems or strong turbulence at high altitudes. The method is applied to the Gemini South MCAO system (GeMS) that comprises five wavefront sensors and two DMs. Statistical values of L0(h) at Cerro Pachón from data acquired with GeMS during three years are shown, where some interesting resemblance to other independent results in the literature are shown.
We report the study and analysis of different methods to generate arbitrary patterns of sodium laser guide stars asterisms starting from a single laser beam by using continuous face-sheet deformable mirrors. Two laser beam shaping procedures based on iterative Fourier transform algorithms have been explored. Numerical simulations with realistic parameters have been carried out to highlight the requirements on the phase retrieval algorithm and on the deformable mirrors employed.
We describe a novel technique atmospheric turbulence monitoring called FASS (full aperture seeing sensor) based on a low noise CCD detector. The method uses a Fourier processing approach that estimates the spatial frequency distribution of the scintillation images. This frequency approach samples the propagated images along pupil rings, making the frequency transformation circular, avoiding distortions due to the finite nature of the data. It is shown that aspects such as detector exposure time, opto-mechanical stability, detailed modelling of propagation, noise and star chromaticity, must be carefully addressed during the design and calibration stages.
Although only ground conjugation results are presented in this article, the technique is expected to operate in the generalized mode guaranteeing sufficiently large speckles (larger than the detector pixels). Pixel gains and offsets are effectively corrected, so they don’t significantly influence the accuracy of the profile estimation. Temporal correlations are also shown to provide complementary information not only on the layer wind velocity, but a coarse estimation of their altitude.
Factors limiting the accuracy of the method, such as chromaticity, turbulence strength, exposure time and vibrations are discussed. The method provides excellent performance in simulations and encouraging preliminary results from on-sky images acquired and Paranal, Chile. Comparison to coetaneous profiles estimated with the Durham Stereo-SCIDAR instrument (DSS) are analysed.
SPHERE is the VLT second generation planet hunter instrument. Installed since May 2014 on UT3, the system has been commissioned and verified for more than one year now and routinely delivers unprecedented images of star surroundings, exoplanets and dust disks. The exceptional performance required for this kind of observation makes the appointment: a repeatable Strehl Ratio of 90% in H band, a rough contrast level of email@example.com arcsec, and reaches 10-6 at the same separation after differential imaging (SDI, ADI). The instrument also presents high contrast levels in the visible and an unprecedented 17mas diffraction-limited resolution at 0.65 microns wavelength. SAXO is the SPHERE XAO system, allowing the system to reach its final detectivity. Its high performance and therefore highly sensitive capacities turns a new eye on telescope environment. Even if XAO performance are reached as expected, some unexpected limitations are here described and a first work around is proposed and discussed. Spatial limitation: wave-front aberrations have been identified, deviating from kolmogorov statistics, and therefore not easily seen and compensated for by the XAO system. The impact of this limitations results in a degraded performance in some particular low wind conditions. Solutions are developed and tested on sky to propose a new operation procedure reducing this limitation. Temporal limitation: high amplitude vibrations on the low order modes have been issued, due to telescope environment and XAO behaviour. Again, a solution is developed and an assessment of its performance is dressed. The potential application of these solutions to E-ELT is proposed.
The knowledge of the atmospheric turbulence profile directly above the telescope using the telemetry from wide-field
Adaptive Optics (AO) measurements can be extremely useful for the optimization of the correction in the new
generation of AO systems. For this purpose, two techniques have been recently implemented at the Gemini South
MCAO System (GeMS); both based on the SLODAR method. The first technique uses a matrix inversion approach of
the slopes covariance matrices and the second deconvolves the cross-correlation functions between all combinations of
slopes using the auto-correlation responses.
The deconvolution approach has proved to be more reliable that the one based on matrices inversion, so we use it for
estimating the profiles from on-sky telemetry gathered over three years (2012 - 2014), obtaining statistical parameters of
the turbulence at Cerro Pachón. These results are summarized in this article.
Particular attention is paid to the occurrence of turbulence in the dome of the Gemini South telescope.
The Adaptive Optics Facility (AOF) is a project that aims to transform the VLT UT4 into an adaptive telescope and
therefore to provide all its science instruments with turbulence corrected wavefronts. When used in its wide-field modes,
the AOF will allow to get a real time estimate of the turbulence distribution in the atmosphere, allowing an optimization
of the system correction. The so-called Wind Profiler (or Fourier Deconvolution) algorithm has been adapted to the AOF
configuration and validated through extensive tests. We show how it behaves under different modes and under typical
Paranal seeing conditions.
Multiple sodium laser beacons are a crucial development in multi-conjugate adaptive optics systems that offers wide-field diffraction limited adaptive optics correction to the astronomical community. This correction is strongly dependent on the laser beam power and quality, so a beam shaping concept is currently being developed to speed-up calibration and alignment of the laser before every run. A method previously reported, has now been implemented on a laboratory bench using MEMS deformable mirrors. Necessary calibration and characterization of the deformable mirrors are described and the results for experimental amplitude correction are presented.
The Gemini Planet Imager (GPI) entered on-sky commissioning and had its first-light at the Gemini South (GS) telescope in November 2013. GPI is an extreme adaptive optics (XAO), high-contrast imager and integral-field spectrograph dedicated to the direct detection of hot exo-planets down to a Jupiter mass. The performance of the apodized pupil Lyot coronagraph depends critically upon the residual wavefront error (design goal of 60nmRMS with <5 mas RMS tip/tilt), and therefore is most sensitive to vibration (internal or external) of Gemini's instrument suite. Excess vibration can be mitigated by a variety of methods such as passive or active dampening at the instrument or telescope structure or Kalman filtering of specific frequencies with the AO control loop. Understanding the sources, magnitudes and impact of vibration is key to mitigation. This paper gives an overview of related investigations based on instrument data (GPI AO module) as well as external data from accelerometer sensors placed at different locations on the GS telescope structure. We report the status of related mitigation efforts, and present corresponding results.
The advent of a new generation of Adaptive Optics systems called Wide Field AO (WFAO) mark the beginning of a new era. By using multiple Guide Stars (GSs), either Laser Guide Stars (LGSs) or Natural Guide Stars (NGSs), WFAO significantly increases the field of view of the AO-corrected images, and the fraction of the sky that can benefit from such correction. Different typologies of WFAO have been studied over the past years. They all require multiple GSs to perform a tomographic analysis of the atmospheric turbulence. One of the fundamental aspects of the new WFAO systems is the knowledge of the spatio-temporal distribution of the turbulence above the telescope. One way to get to this information is to use the telemetry data provided by the WFAO system itself. Indeed, it has been demonstrated that WFAO systems allows one to derive the C2 N and wind profile in the main turbulence layers (see e.g. Cortes et al. 20121). This method has the evident advantage to provide information on the turbulence stratification that effectively affects the AO system, property more difficultly respected by independently vertical profilers. In this paper, we compare the wind speeds profiles of GeMS with those predicted by a non-hydrostatical mesoscale atmospherical model (Meso-NH). It has been proved (Masciadri et al., 20132), indeed, that this model is able to provide reliable wind speed profiles on the whole troposphere and stratosphere (up to 20-25 km) above top-level astronomical sites. Correlation with measurements revealed to be very satisfactory when the model performances are analyzed from a statistical point of view as well on individual nights. Such a system appears therefore as an interesting reference to be used to quantify the GeMS wind speed profiles reliability.
PSF reconstruction (PSF-R) for AO systems was pioneered by J.P. Veran in 1997  and was successfully demonstrated at CFHT/PUEO. A recent example was presented in the case for the Keck telescope in 2012 . Nevertheless, it has been a constant struggle since to implement these technique as observatory standard. APETy (A PSF Estimation Tool for Yorick) has been developed since 2009 and applied for PSF reconstruction for the Near Infrared Coronograph Imager (NICI) at the Gemini South Observatory based on a 85 element curvature AO system. Using on-sky wavefront sensor data, we estimate the seeing (r0) from deformable mirror commands and reconstruct diffraction limited images (52 mas resolution) with an accuracy of approximately 90% when compared to the science images. APETy is publically available via GitHub (https://github.com/dgratadour/APETy) and can be adapted to other systems. APETy development includes the PSF-R variation proposed by Gendron  which proved to be almost 4 times faster than the original approach.
We present on-sky results obtained with Carmen, an artificial neural network tomographic reconstructor. It was tested during two nights in July 2013 on Canary, an AO demonstrator on the William Hershel Telescope. Carmen is trained during the day on the Canary calibration bench. This training regime ensures that Carmen is entirely flexible in terms of atmospheric turbulence profile, negating any need to re-optimise the reconstructor in changing atmospheric conditions. Carmen was run in short bursts, interlaced with an optimised Learn and Apply reconstructor. We found the performance of Carmen to be approximately 5% lower than that of Learn and Apply.
Two algorithms were recently studied for C2n profiling from wide-field Adaptive Optics (AO) measurements on GeMS (Gemini Multi-Conjugate AO system). They both rely on the Slope Detection and Ranging (SLODAR) approach, using spatial covariances of the measurements issued from various wavefront sensors. The first algorithm estimates the C2n profile by applying the truncated least-squares inverse of a matrix modeling the response of slopes covariances to various turbulent layer heights. In the second method, the profile is estimated by deconvolution of these spatial cross-covariances of slopes. We compare these methods in the new configuration of ESO Adaptive Optics Facility (AOF), a high-order multiple laser system under integration. For this, we use measurements simulated by the AO cluster of ESO. The impact of the measurement noise and of the outer scale of the atmospheric turbulence is analyzed. The important influence of the outer scale on the results leads to the development of a new step for outer scale fitting included in each algorithm. This increases the reliability and robustness of the turbulence strength and profile estimations.
Reduction of tip and tilt vibrations at the Gemini South MCAO System (GeMS) is addressed in this paper. A frequency
framework for the synthesis of controllers is described, with particular emphasis on the search for better closed-loop
performances by minimizing a H2 norm of the tilt residuals. Previous results have shown that modeling the turbulence
via identification tools using standard AR or Laplace representations can lead to non-optimal solutions, resulting in
excessive rejection of certain frequencies or an unbalanced residual spectrum due to poor modeling of vibrations. In this
novel approach we reconstruct the open loop slopes (pseudo-open-loop) from on-sky data and then perform a fine tuning
of the controller by finding the parameters that minimize the variance of residuals during a sequence of closed-loop runs
with increasing controller complexity. Although the method is not optimal, it effectively rejects the main vibrations in
the loop and it also improves the overall performance of the system. The method is compared to two standard integrators:
one with fixed gain and the other with optimized integral gain. Results show substantial improvements of this new
method when compared to the classical integrator.
We present in this paper an analysis of several tip-tilt on-sky data registered on adaptive optics systems installed on different telescopes (Gemini South, William Herschel Telescope, Large Binocular Telescope, Very Large Tele scope, Subaru). Vibration peaks can be detected, and it is shown that their presence and location may vary, and that their origin is not always easy to determine. Mechanical solution that have been realized to mitigate vibrations are presented. Nevertheless, residual vibrations may still affect the instruments' performance, ranging from narrow high frequency vibration peaks to wide low frequency windshake-type perturbations. Power Spectral Densities (PSDs) of on-sky data are presented to evidence these features. When possible, indications are given regarding the gain in performance that could be achieved with adequate controllers accounting for vibration mitigation. Two examples of controller identification and design illustrate their ability to compensate for various types of disturbances (turbulence, windshake, vibration peaks, ...),showing a significant gain in performance.
The atmospheric optical turbulence profile, the strength of the turbulence as a function of altitude above the ground, can
be used to determine the seeing statistics of a particular site. This information is useful for optimizing the tomographic
process in Adaptive Optics systems and for characterizing the performance. In this paper, we describe a method to
estimate the atmospheric turbulence profile based on the telemetry data coming out of GeMS, a Multi Conjugated
Adaptive Optics (MCAO) instrument installed on the Gemini South telescope. The method is based on the SLODAR
technique (SLOpe Detection and Ranging), where the wavefront slopes from two stars angularly separated on the sky are
measured, and their cross-correlation is used to retrieve the atmospheric optical profile. We have modified the classical
SLODAR method and adapted it for the closed loop, multiple laser guide stars case. In this paper we present our method,
validation of it in simulation, and its application for on-sky data.
The vast majority of large telescopes are now equipped with Adaptive Optics (AO) systems, and many use lasers to
create artificial stars (laser guide stars, LGS). Despite the significant advances in the use of LGS for AO, some problems
persist during the operations. In particular, achieving a satisfactory performance in terms of on-sky laser power and beam
quality usually requires frequent and complex alignments of the laser system, beam transfer optics and launch telescope.
To provide easier calibrations and faster pre-setting of the LGS facility during routine operations, we propose the
introduction of active elements (deformable mirrors) in the laser beam before it is propagated to the sky. The paper
studies an AO configuration with two deformable mirrors to correct for quasi-static and dynamic aberrations. The
problem of determining the correction phases to apply to the deformable mirrors is particularly challenging due to the
highly nonlinear problem and the possible appearance of branch points. We propose an iterative method based on a
phase retrieval algorithm that uses a weighted least squares unwrapper to avoid branch points. Simulations are performed
aiming to a future implementation in the Gemini Multi-conjugate-adaptive-optics System (GeMS). Results show that the
technique is accurate and robust, with a reasonable convergence speed.
Multi-object adaptive optics requires a tomographic reconstructor to compute the AO correction for scientific targets
within the field, using measurements of incoming turbulence from guide stars angularly separated from the science
targets. We have developed a reconstructor using an artificial neural network, which is trained in simulation only.
We obtained similar or better results than current reconstructors, such as least-squares and Learn and Apply, in
simulation and also tested the new technique in the laboratory. The method is robust and can cope well with
variations in the atmospheric conditions. We present the technique, our latest results and plans for a full MOAO experiment.
Open-loop adaptive optics is a technique in which the turbulent wavefront is measured before it hits the deformable
mirror for correction; therefore the correct control of the mirror in open-loop is key in achieving the expected level of
correction. In this paper, we present non-parametric estimation techniques to model deformable mirrors working in
open-loop. We have results with mirrors characterized by non-linear behavior: a Xinetics electrostrictive mirror and a
Boston Micromachines MEMS mirror. The inputs for these models are the wavefront corrections to apply to the mirror
and the outputs are the set of voltages to shape the mirror. We have performed experiments on both mirrors, achieving
Go-To errors relative to peak-to-peak wavefront excursion in the order of 1 % RMS for the Xinetics mirror and 3 %
RMS for the Boston mirror . These techniques are trained with interferometric data from the mirror under control;
therefore they do not depend on the physical parameters of the device.
The CANARY on-sky MOAO demonstrator is being integrated in the laboratory and a status update about its
various components is presented here. We also discuss the alignment and calibration procedures used to improve
system performance and overall stability. CANARY will be commissioned at the William Herschel Telescope at
the end of September 2010.
We present a new approach for the control of a deformable mirror (DM), part of a Multi Object Adaptive Optics (MOAO) on-sky demonstrator. The control is based on H∞ synthesis methods, achieving better performance than classical Proportional-Integral methods, while offering other appealing advantages such as an optimized design based on the temporal spectra of the wavefront and vibration rejection capabilities. We describe laboratory results obtained with a 97 actuator Xinetics DM, using a high-resolution Shack-Hartmann wavefront sensor for measuring DM surface. A
connection between the turbulence dynamics represented in a Zernike basis and the controller requirements is studied, showing that the controller parameters and structure can be easily optimized for each Zernike mode according to their particular temporal spectra.
A Deformable Mirror Controller (DMC) has been devised to overcome the open-loop nature of Multi Object Adaptive
Optics (MOAO), in particular for AO systems with update rates of 1 ms or less. The system is based on a figure sensor,
which uses a monochromatic illumination source and a Shack-Hartmann (SH) wavefront sensor (WFS) to obtain a fine
sampling of DM's 3D surface. The sensor's beam is optically separated from the science path in order to not interfere
with science observations. The DMC incorporates a real-time controller in charge of driving the DM. This controller
runs in a dedicated Field-Programmable-Gate-Array (FPGA) based processor to keep up with stringent speed
requirements. The DMC is being tested in the laboratory and is part of CANARY, an MOAO on-sky demonstrator to be
installed at the William Hershel Telescope.
We present a novel technique for the design of DM controllers in high spatial resolution adaptive optics systems, operating in open-loop. It consists of a Shack-Hartmann (SH) figure sensor and multiple overlapping MIMO controllers based on the H∞ synthesis method. The controller synthesis can be carried out periodically using a linearized representation of a continuously adjusted model that accounts for varying physical or ambient conditions and incorporates the spatial geometry of the SH. The figure sensor uses a bright reference source and a fast CMOS detector
to sample the DM surface sequentially with an optical arrangement that does not interfere with the main corrected beam.
Taking full advantage of such robust techniques, the controller can successfully handle the dynamics and non-linearity of
the DM, allowing one to decouple, from the main AO control loop standpoint, the turbulence estimation errors from
those originating in the DM servo-loop. It can also implement noise and vibration rejection without compromising the
loop stability, pushing the control bandwidth to the physical limits imposed by hardware and software components. By
splitting the control function into several overlapping controllers, implementation complexity is reduced and continuous
updating of the controller can be easily achieved. Simulations show its ability to successfully control the DM shape, in
spite of partial and non-simultaneous sampling of the SH figure sensor due to detector speed limitations.
This paper describes the application of the Extended Kalman Filter to the estimation of range and bearing biases in marine radars using data from hydrographic charts and radar scans. By defining at least two correspondence points from radar video and electronic charts, the technique provides a rapid and accurate calibration in range and bearing, giving also estimates for the own ship speed, heading and geographical position (latitude and longitude). The method is tested with real data from radar scan images and electronic charts displayed on a navigation console installed on a patrol boat. The technique does not require GPS nor speed information from the ship log unit, however it is shown that their inclusion can improve the estimation.
This paper describes a new method for object movement estimation using sequences of images taken from a monocular camera. The method integrates a Kalman filter to estimate the three dimensional parameters of the optical system and a lineal projective model to determine 3D point coordinates projected on the retinal plane. The method works with at least three distinctive points in the image, and they are updated using correlation methods. The result is an estimation of the rotation and translation parameters between successive images within the sequence and yield to the 3D coordinates of the points selected for correspondence. The method is tested with synthetic images to evaluate its accuracy and later an interesting application in autonomous navigation is presented.
The AGC of a conical scan tracking radar IF amplifier is designed using Hx synthesis. It is shown that this technique is particularly suited for this problem because of its loop shaping capabilities and because it can tackle particular frequencies effectively, providing a correct balance among closed loop stability, fast responses to echo changes and rejection of frequencies other than the echo modulation. Two controllers are implemented and compared to a standard controller, showing significant improvement in system tracking.