The use of Lagrangian platforms and of Autonomous Underwater Vehicles (AUVs) in oceanography has increased rapidly over the last decade along with the development of improved biological and chemical sensors. These vehicles provide new spatial and temporal scales for observational studies of the ocean. They offer a broad range of deployment and recovery capabilities that reduce the need of large research vessels. This is especially true for ice-covered Arctic ocean where surface navigation is only possible during the summer period. Moreover, safe underwater navigation in icy waters requires the capability of detecting sea ice on the surface (ice sheets). AUVs navigating in such conditions risk collisions, RF communication shadowing, and being trapped by ice keels. In this paper, an underwater sea-ice detection apparatus is described. The source is a polarized continuous wave (CW) diode-pumped solid-state laser (DPSS) module operating at 532 nm. The detector is composed of a polarizing beam splitter, which separates light of S and P polarization states and two photodetectors, one for each polarized component. Since sea-ice is a strong depolarizer, the ratio P/S is an indicator of the presence or absence of sea-ice. The system is capable of detecting sea-ice at a distance of 12m. This apparatus is designed to be used by free drifting profiling floats (e.g., Argo floats), buoyancy driven vehicles (e.g., sea gliders) and propeller-driven robots (e.g., Hugin class AUV).
The accuracy of calibration patterns, their fabrication, and their setup are some of the important challenges in a zoom-lens camera calibration process. We address these problems by using a cross-diffractive optical element, which generates a virtual, dense, and robust calibration grid. We show that a 33×33 calibration grid provides enough control points to fill the entire field of view for 10 to 20× zoom lenses. We show that the calibration of a zoom camera at infinity can be done using this method. A polynomial function has been used to model the variation of the intrinsic calibration parameters over the zoom range. The obtained calibration model has also been validated using a well-known target pattern.
We present an analysis of the degradation of the optical and electrical properties of high-power light-emitting diodes (LEDs) used for general lighting applications. The study was conducted by submitting the LEDs to different current and temperature stress conditions. Those conditions are based on typical operating conditions that can be encountered on LED-based luminaires for general lighting. LEDs were stressed under four different operating currents, and two of those were stressed at two junction temperatures, controlled with a thermoelectric cooler. Results described in this paper indicate that the lumen droop due to an increase in nonradiative recombination is correlated with the stress conditions in accordance with the literature. However, the LED samples showed a forward-voltage droop which seems to be independent of the stresses. For all the stress conditions, the LED forward voltages decreased by about 1% after 1000 h of stress time. A link between forward voltage and lumen output was made through LED efficiency. Also, the yellow peak/blue peak ratio was measured and showed an increase after 1000 to 1200 h. This is attributed to LED chip degradation. These observations suggest the use of both current and voltage control to optimize the use of LEDs in general lighting.
The instrument group of the Herzberg Institute of Astrophysics has been commissioned by the Gemini Observatory as one of the three competing organizations to conduct a conceptual design study for a new Gemini High-Resolution Optical Spectrograph (GHOS). This paper outlines the main features of the optical design, including the Cassegrain-mounted science input unit, the bench-mounted spectrograph and the fibre relay system. The predicted imaging performance and efficiency are presented with the design trade offs explored in the study.
SPIRou is a near-infrared, echelle spectropolarimeter/velocimeter under design for the 3.6m Canada-France-Hawaii
Telescope (CFHT) on Mauna Kea, Hawaii. The unique scientific capabilities and technical design features are described
in the accompanying (eight) papers at this conference. In this paper we focus on the lens design of the optical
spectrograph. The SPIROU spectrograph is a near infrared fiber fed double pass cross dispersed spectrograph. The
cryogenic spectrograph is connected with the Cassegrain unit by the two science fibers. It is also fed by the fiber coming
from the calibration box and RV reference module of the instrument. It includes 2 off-axis parabolas (1 in double pass),
an echelle grating, a train of cross disperser prisms (in double pass), a flat folding mirror, a refractive camera and a
detector. This paper describes the optical design of the spectrograph unit and estimates the performances. In particular,
the echelle grating options are discussed as the goal grating is not available from the market.
A multiplexed moderate resolution (R = 34,000) and a single object high resolution (R = 90,000) spectroscopic facility
for the entire 340 - 950nm wavelength region has been designed for Gemini. The result is a high throughput, versatile
instrument that will enable precision spectroscopy for decades to come. The extended wavelength coverage for these
relatively high spectral resolutions is achieved by use of an Echelle grating with VPH cross-dispersers and for the R =
90,000 mode utilization of an image slicer. The design incorporates a fast, efficient, reliable system for acquiring targets
over the7 arcmin field of Gemini. This paper outlines the science case development and requirements flow-down process
that leads to the configuration of the HIA instrument and describes the overall GHOS conceptual design. In addition, this
paper discusses design trades examined during the conceptual design study instrument group of the Herzberg Institute of
Astrophysics has been commissioned by the Gemini Observatory as one of the three competing organizations to conduct
a conceptual design study for a new Gemini High-Resolution Optical Spectrograph (GHOS). This paper outlines the
science case development and requirements flow-down process that leads to the configuration of the HIA instrument and
describes the overall GHOS conceptual design. In addition, this paper discusses design trades examined during the
conceptual design study.
This paper presents an overview of the PDR level mechanical and opto-mechanical design of the cryogenic spectrograph
unit of the nIR spectropolarimeter (SPIROU) proposed as a new-generation instrument for CFHT. The design is driven
by the need for high thermo-mechanical stability in terms of the radial velocity (RV) of 1 m/s during one night, with the
requirement for thermal stability set at 1 mK/24 hours. This paper describes stress-free design of the cryogenic optical
mounts, mechanical design of the custom-build cryostat, mechanical design of the optical bench, and thermal design for
1 mK thermal stability. The thermal budget was calculated using lumped-mass model thermal analysis, implemented in
Modelica multi-domain modeling language. Discussion of thermal control options to achieve 1 mK thermal stability is
The polarization state of light provides valuable information about scenes that cannot be obtained directly from intensity
or spectral images. Polarized light reflected from scenes has been found to be useful and can reveal contrasts that do not
appear in classical intensity images and find many applications in remote sensing, biomedical imaging, or industrial
control. Cost, size, and technological complexity of polarimetric imagers depend on the number of polarimetric
parameters they measure. In this context, a key issue is to evaluate the added value of each measured polarimetric
parameter in order to optimize the compromise between complexity and efficiency of these systems. In target detection
applications, the relevant criterion for quantifying the performance of an imaging configuration is contrast (or
discrimination ability). Analysis of the contrast and its optimization in polarimetric images have been investigated in the
radar and optics communities. We investigate in the paper how the polarisation imaging can be applied in automotive
vision based sensor. This study present various type of polarisation sensitive optical system. Detection of small and
low-contrast objects has been found to be improved with the help of this kind of optical system.
Almost every aspect concerning the design of modern panoramic lenses brings new challenges to optical designers.
Examples of these include ray tracing programs having problems finding the entrance pupil which is moving through the
field of view, production particularities due to the shape of the front lenses, ways of tolerancing these systems having
strong distortion, particular setups required for their characterization and calibration, and algorithms to properly analyze
and make use of the obtained images. To better understand these modern panoramic lenses, the Optical Engineering
Research Laboratory at Laval University has been doing research on them during the past few years. The most
significant results are being presented in this paper.
Controlled distortion, as in commercial panomorph lenses (Immervision), is used to image a specific part of the object
with more pixels than in a normal fisheye lens. This idea is even more useful when a zone of interest vary in time with
dynamically adjustable distortion as in a panoramic locally magnifying imager. Another axis of research is the use of
modern computational techniques such as wavefront coding in wide-angle imaging systems. The particularities of such
techniques when the field of view is large or with anamorphic imagers are considered. Presentation of a novel circular
test bench in our laboratories, required to calibrate and check the image quality of wide-angle imaging system, follows.
Another presented setup uses a laser and diffractive optical elements to compactly calibrate wide-angle lenses. Then, a
discussion of the uniqueness in tolerancing these lenses, especially the front elements due to the large ratio between lens
diameter and entrance pupil diameter, is included. Lastly, particularities with polarization imaging and experiments of
triangle orientation detection tests before and after unwrapping the distorted images are briefly discussed.
The triangle orientation discrimination (TOD) method is an emerging technique for the evaluation of electro-optical
(EO) systems. In this method, the test pattern is a non-periodic equilateral triangle in one of four different orientations
(apex up, down, left, or right), and the measurement procedure is a robust four-alternative forced-choice psychophysical
process. This leads to a time-consuming task. Consequently, software models have been developed to replace the
required human observers. These models base their decision on the orientation of the target using correlation between
observed data and the set of four differently oriented targets.
This study investigates for the first time how this method can be applied to highly distorted OE systems like hemispheric
imagers. These types of systems have inherent large distortion, but the distortion should not be considered as an
aberration but rather the result of the projection of a hemispheric field (3D) on a 2D sensor. The distortion deforms the
image of the targets and image processing is usually performed to remove distortion and straighten the field of view.
We present a comparison in accuracy and computational burden for the evaluation of EO system performance between
cases where tested images are pre-processed and correlated to unchanged triangle targets and where untouched
(distorted) images are correlated with position-wise distorted targets. This is a first evaluation of the application of the
TOD with the goal of obtaining an image quality criterion for panoramic imagers.
Panoramic imaging is of growing importance in many applications around the world spurred by the development of
digital imaging. Panoramic lens characteristics are unique and their careful characterization can be a challenge. For
example, the price to pay for a large field of view in this type of lens is high distortion in the image. For vision
applications like security or inspection, a precise knowledge of the distortion introduced by panoramic lenses is essential
to produce natural unwrapped views to the operator. Of special concern is the image quality which must be uniformed
over the entire field of view because all directions are equally important. In addition, two hemispheric images can also
be stitched together to create a complete spherical image. For these reasons, we have developed a dedicated setup to
study the distortion and the image quality produced by panoramic lenses. The test setup is made of a 75-cm radius
cylindrical structure with targets placed on it. Using referenced equally-spaced targets, we obtained the radial image
mapping curves for various azymuthal angles, allowing us to calculate the full-field resolution map. Also, transition
targets were used to find field-dependent spatial frequency where the MTF is 50%. We tested four different panoramic
lenses, two panomorph lenses and two fisheyes. For each lens, we discussed the experimental resolution and MTF
curves and compared some of those results to theoretical design data.