METimage is an advanced multispectral radiometer for weather and climate forecasting developed by Airbus Defence & Space under the auspices of the German Space Administration (DLR) for the EUMETSAT Polar System –Second Generation (EPS-SG). The instrument is equipped with a continuously rotating scan mirror with a 1.7s period followed by a static telescope. The scan mirror permits an extended Earth view of 108° per revolution and regular views to on-board calibration sources. A derotator assembly, which is half-speed synchronised with the scanner, is inserted in the optical beam after the telescope to compensate the image rotation in the focal plane. The derotator optical arrangement is a fivemirror concept that minimises the polarisation sensitivity. The derotator design is constrained by optical performance, mass and compactness, which led to the selection of a full silicon carbide (SiC) concept. This paper describes the preliminary design and verification approach of the derotator optics.
Noncontact optical measurement methods are essential tools in many industrial and research domains. A family of new noncontact optical measurement methods based on the polarization states splitting technique and monochromatic light projection as a way to overcome ambient lighting for in-situ measurement has been developed. Recent works on a birefringent element, a Savart plate, allow one to build a more flexible and robust interferometer. This interferometer is a multipurpose metrological device. On one hand the interferometer can be set in front of a charge-coupled device (CCD) camera. This optical measurement system is called a shearography interferometer and allows one to measure microdisplacements between two states of the studied object under coherent lighting. On the other hand, by producing and shifting multiple sinusoidal Young’s interference patterns with this interferometer, and using a CCD camera, it is possible to build a three-dimensional structured light profilometer.
AMOS SA has been awarded of the contract for the design, manufacturing, assembly, tests and on site installation
(Devasthal, Nainital in central Himalayan region) of the 3.6 m Indo-Belgian Devasthal Optical Telescope (IDOT).
The telescope has a Ritchey-Chrétien optical configuration with a Cassegrain focus equipped with one axial port and two
side ports. The meniscus primary mirror is active and is supported by pneumatic actuators. The mount is an Alt-Az type
with for the azimuth axis a 5 m diameter hydrostatic track.
The telescope was completely assembled and tested in AMOS workshop. This step is completed and successful. The
telescope is now ready for shipment to Nainital.
This paper describes the test campaign at sub-system and system level that has taken place to demonstrate that the
telescope satisfies the main system requirements. Besides of the functionality of the telescope, the units interacting with
the image quality or the tracking performance were plenty tested. Some selected tests directly connected to the
performance of the telescope are also looked specifically in this paper.
A profilometer which takes advantage of polarization states splitting technique and monochromatic light projection
method as a way to overcome ambient lighting for in-situ measurement is under development [1, 2]. Because of the
Savart plate which refracts two out of axis beams, the device suffers from aberrations (mostly coma and astigmatism).
These aberrations affect the quality of the sinusoidal fringe pattern. In fringe projection profilometry, the unwrapped
phase distribution map contains the sum of the object's shape-related phase and carrier-fringe-related phase. In order to
extract the 3D shape of the object, the carrier phase has to be removed [3, 4]. An easy way to remove both the fringe
carrier and the aberrations of the optical system is to measure the phases of the test object and to measure the phase of a
reference plane with the same set up and to subtract both phase maps. This time consuming technique is suitable for
laboratory but not for industry. We propose a method to numerically remove both the fringe carrier and the aberrations.
A first reference phase of a calibration plane is evaluated knowing the position of the different elements in the set up and
the orientation of the fringes. Then a fitting of the phase map by Zernike polynomials is computed [5]. As the
triangulation parameters are known during the calibration, the computation of Zernike coefficients has only to be made
once. The wavefront error can be adjusted by a scale factor which depends on the position of the test object.
Shearography is an interferometric technique suitable for detecting defects because they yield singular fringes and high phase values in wrapped and unwrapped phasemaps, respectively. We propose a methodology that leads to the defect size from unwrapped phasemap by extracting the size of the high phase values area. The area size is evaluated, thanks to a wavelet transform algorithm that enables the location of its borders. The performances of the methodology and of the algorithm have been tested by applying them on a defect where the size is known. An error less than 1.5% root mean square was reached. Our approach is independent of the shearing amount and of the phase profile, and it can be extended for other interferometric techniques.
Non-contact optical measurement methods are essential tools in many industrial and research domains. A family of new
non-contact optical measurement methods based on the polarization states splitting technique and monochromatic light
projection as a way to overcome ambient lighting for in-situ measurement has been developed1,2. Recent works3 on a
birefringent element, a Savart plate, allow to build a more flexible and robust interferometer. This interferometer is a
multipurpose metrological device. On one hand, the interferometer can be set in front of a CCD camera. This optical
measurement system is called a shearography interferometer and allows to measure micro displacement between two
states of the studied object under coherent lighting. On the other hand, by producing and shifting multiple sinusoidal
Young's interference patterns with this interferometer, and using a CCD camera, it is possible to build a 3D structured
light profilometer. After giving the behavior of the Savart plate, an overview of the two devices will be given as well as
their specifications and some applications.
We studied scars and wounds depths and surfaces thanks to our interferometric fringes projector 3D scanner1, 2. Color
information of a wound indicates its deterioration level. That's why the visual color restitution, as realistic as possible, is
a highly important parameter. Firstly our acquired 3D pictures were color mapped with an image recorded by a RGB
camera. The results were not efficient enough. In order to improve our technique and provide more precise information,
we add a spectral characterization to the set-up. Before adding the spectral information and a realistic color mapping to
the 3D measurements, we evaluate the performances of colorimetric measurements. The tests have been made on mice
with scars on their back.
Shearography is a growing optical technique in the field of non-destructive testing (NDT)[1],[2]. Hololab developed an
out of plane, in line and almost common path interferometer based on polarization states separation using a coated prism
for digital phase-shifting shearography[3]. This setup is efficient but does not allow varying the shearing direction that is
an important parameter for defects detection[1]and quantification[2].
To overcome this disadvantage, the coated prism is substituted by a Savart plate device that allows scanning several
shearing directions by rotating the device around the light propagation axis. The behaviour of the Savart plate as a
shearing device is experimentally analyzed to optimize its integration within the interferometer. Recorded phasemaps in
NDT for different shearing directions are presented.
An original experimental setup for shearography with metrological applications is presented. The simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM polarization modes with a coating and a thin glass plate placed on its face. The use of this shearing device enables an in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability and a low sensitivity to external disturbances. Moreover, the sensitivity of the interferometer can be easily adjusted for different applications by varying the shearing amount with glass plates of different thicknesses or by moving the shearing device between two lenses along the optical axis. The temporal phase-shifting method is applied through the use of a liquid crystal variable retarder.
Shearography is a recognized interferometric technique in non-destructive testing to detect defects. Defects are
detectable in wrapped phase maps because they are characterized in their neighborhood by singular fringes.
They are detectable in unwrapped phase maps, because they induce unexpected phase values. By analyzing
the length of unexpected phase values area in shearing direction, and by taking into consideration shearing
amount, defect size can be locally estimated. To examine this length, we propose to locally determine borders of
unexpected phase values region by analyzing wavelet transform of unwrapped phase map profiles. The borders
of defect area are found by examining the convergence at fine scales of lines of wavelet modulus maxima. To
have a physical interpretation of this convergence, second derivate of a Gaussian is employed as mother wavelet:
estimated borders of defect region are some maximal curvature points of unwrapped phase map profile. To finish,
we show that shearing amount does not affect estimated defect size with our methodology. So, shearography is
adapted to quantify defects in shearing direction. Currently, in any other direction, an ambiguity exists on the
position where the local estimation of defect width is performed. The methodoly cannot be employed.
An original experimental setup for shearography with metrological applications is presented herein. The
simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM
polarization modes with a coating and a thin glass plate attached on its face. The use of this shearing device enables an
in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability of the
interferometer and a low sensitivity to external disturbances. Moreover the sensitivity of the interferometer can be easily
adjusted for different applications. The temporal phase shifting method is applied through the use of a liquid crystal
variable retarder.
An original experimental setup for shearography with metrological applications is presented herein. The
simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM
polarization modes with a coating and a thin glass plate attached on its face. The temporal phase shifting method is
applied through the use of a liquid crystal variable retarder. The use of this shearing device enables an in-line and almostcommon
path configuration for the shearing interferometer, a path that leads to high stability of the interferometer and a
low sensitivity to external disturbances. In order to prove the efficiency and the accuracy of this speckle shearing
interferometer, the out-of-plane displacement derivative relative to the shearing interferometry direction of a centrally
loaded steel plate has been measured by the shearographic interferometer and then compared with the out-of-plane
displacement derivative computed from the displacement field provided by the finite element method. The results are in
good agreement.
The goal of this work is to develop a simple and systematic method to highlight the properties of filters for their application in temporal phase shifting interferometry. In this study, the effects of elementary filters (mean, gaussian and median masks) are analyzed. In order to compare those filters, correlation fringes were numerically synthesized and a Gaussian noise has been added. The advantages and the failures of each studied filtering mask have been enhanced thanks to the comparison of different profiles and fidelity functions. Finally, this study is applied to the filtering of a shearogram recorded in our laboratory.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.