An electro holography using reflective LCD for enlarging visual field and viewing zone with the Fourier transform optical system in CGH

2010 ◽  
Author(s):  
Atsushi Kato ◽  
Yuji Sakamoto
Keyword(s):  
Fourier Transform ◽  
Visual Field ◽  
Optical System ◽  
The Fourier Transform

Balloon-borne GLORIA hyperspectral Limb and Nadir imager in the LWIR

2021 ◽  
Author(s):  
Erik Kretschmer ◽  
Felix Friedl-Vallon ◽  
Thomas Gulde ◽  
Michael Höpfner ◽  
Sören Johansson ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Optical System ◽  
Late Summer ◽  
High Spectral Resolution ◽  
Fourier Transform Spectrometer ◽  
System Improvement ◽  
The Fourier Transform ◽  
Temperature Retrieval ◽  
Long Wave Infrared ◽  
Better Than

<p>The GLORIA-B (Gimballed Limb Observer for Radiance Imaging of the Atmosphere - Balloon) instrument is an adaptation of the very successful GLORIA-AB imaging Fourier transform spectrometer (iFTS) flown on the research aircrafts HALO and M55 Geophysica. The high spectral resolution in the LWIR (Long Wave Infrared) allows for the retrieval of temperature and of a broad range of atmospheric trace gases, with the goal to retrieve O<sub>3</sub>, H<sub>2</sub>O, HNO<sub>3</sub>, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCOOH, CCl<sub>4</sub>, PAN, ClONO<sub>2</sub>, CFC-11, CFC-12, SF<sub>6</sub>, OCS, NH<sub>3</sub>, HCN, BrONO<sub>2</sub>, HO<sub>2</sub>NO<sub>2</sub>, N<sub>2</sub>O<sub>5</sub> and NO<sub>2</sub>. The radiometric sensitivity of the Balloon instrument is further increased in comparison with the GLORIA-AB instrument by having two detector channels on the same focal plane array, while keeping the same concept of a cooled optical system. This system improvement was achieved with minimal adaptation of the existing optical system.</p><p>The high spatial and temporal resolution of the instrument is ensured by the imaging capability of the Fourier transform spectrometer while stabilizing the line-of-sight in elevation with the instrument and in azimuth with the balloon gondola. In a single measurement lasting 13 seconds, the atmosphere can be sounded from mid-troposphere up to flight altitude, typically 30 km, with a vertical resolution always better than 1 km for most retrieved species; a spatial resolution up to 0.3 km can be achieved in favourable conditions. Temperature retrieval precision between 0.1 and 0.2 K is expected. A spectral sampling up to 0.0625 cm<sup>-1</sup> can be achieved.</p><p>The first flight of GLORIA-B shall take place during the late-summer polar jet turn-around at Kiruna/ESRANGE. This flight is organised in the frame of the HEMERA project and was scheduled for summer 2020, but was ultimately postponed to summer 2021. Beyond qualification of the first balloon-borne iFTS, the scientific goals of the flight are, among others, the quantification of the stratospheric bromine budget and its diurnal evolution by measuring vertical profiles of BrONO<sub>2 </sub>in combination with BrO observations by the DOAS instrument of University Heidelberg on the same platform.</p>

On the assessment of optical images

1955 ◽  
Vol 247 (931) ◽  
pp. 369-407 ◽  
Keyword(s):  
Fourier Transform ◽  
Optical System ◽  
Optical Image ◽  
Surface Element ◽  
Linear Filter ◽  
Optical Images ◽  
First Case ◽  
Spread Function ◽  
The Fourier Transform ◽  
Transmission Factors

In the formation of an optical image, each surface element of the object gives rise to a more or less blurred distribution in the image surface, of total brightness proportional to that of the object element. The image is the sum of these distributions in the appropriate sense: when the object is coherently lit, the image is built up by adding their complex amplitudes; when the object elements are regarded as incoherent it is the intensities which are added. In both cases the image can be expressed as the convolution of the object with a spread function which characterizes the optical system. In systems for which the spread function does not change appreciably from one part of the field to another, the Fourier transform of the image is obtained to a sufficient approximation on multiplying the Fourier transform of the object with that of the spread function. More generally, this holds for any part of the field of a non-isoplanatic system over which the changes in the form of the spread function are small enough to be disregarded; we call such an area an ‘isoplanatism-patch’. Working over such an area, an optical system can be regarded as a linear filter in which the Fourier components of the object reappear in the image multiplied by ‘transmission factors’. These factors, first considered by Duffieux, depend on the aperture and aberrations of the system, and in §2 they are evaluated in terms of an ikonal function. The qualities required of an optical image are so varied that an assessment valid over the whole range of practical applications seems out of the question. Two extreme cases are considered in the present paper. In the first of these it is assumed that the aim of an optical design is to produce an image which is directly similar to the object. This is appropriate when no process of image interpretation or reconstruction is envisaged. In the second case, the aim is to produce an image containing the greatest possible amount of information about the object, without regard to the complexity of the interpretation processes which may be needed to extract it. For the first case, a criterion of image fidelity is proposed in §2.4 which gives a numerical measure of the resemblance of image to object in terms of the transmission factors of the optical system. In the second case, assessment is based on the information content of the image in Shannon’s sense. This depends not only on the transmission factors of the system but also on the statistical properties of the presumed object set and of the unpredictable fluctuations which necessarily disturb observation; the analysis is carried through in §3. In §4 the assessment of optical images is discussed in terms of these two criteria.

scholarly journals CGH calculation with the ray tracing method for the Fourier transform optical system

2013 ◽  
Vol 21 (26) ◽  
pp. 32019 ◽  
Author(s):  
Tsubasa Ichikawa ◽  
Takuo Yoneyama ◽  
Yuji Sakamoto
Keyword(s):  
Fourier Transform ◽  
Ray Tracing ◽  
Optical System ◽  
Ray Tracing Method ◽  
The Fourier Transform ◽  
Tracing Method

scholarly journals Strain Sensitivity Enhancement of Broadband Ultrasonic Signals in Plates Using Spectral Phase Filtering

2021 ◽  
Vol 11 (6) ◽  
pp. 2582
Author(s):  
Lucas M. Martinho ◽  
Alan C. Kubrusly ◽  
Nicolás Pérez ◽  
Jean Pierre von der Weid
Keyword(s):  
Fourier Transform ◽  
Guided Waves ◽  
Strain Level ◽  
Energy Concentration ◽  
Short Time Fourier Transform ◽  
Time Frequency ◽  
Frequency Representation ◽  
The Fourier Transform ◽  
Short Time ◽  
Sensitivity Gain

The focused signal obtained by the time-reversal or the cross-correlation techniques of ultrasonic guided waves in plates changes when the medium is subject to strain, which can be used to monitor the medium strain level. In this paper, the sensitivity to strain of cross-correlated signals is enhanced by a post-processing filtering procedure aiming to preserve only strain-sensitive spectrum components. Two different strategies were adopted, based on the phase of either the Fourier transform or the short-time Fourier transform. Both use prior knowledge of the system impulse response at some strain level. The technique was evaluated in an aluminum plate, effectively providing up to twice higher sensitivity to strain. The sensitivity increase depends on a phase threshold parameter used in the filtering process. Its performance was assessed based on the sensitivity gain, the loss of energy concentration capability, and the value of the foreknown strain. Signals synthesized with the time–frequency representation, through the short-time Fourier transform, provided a better tradeoff between sensitivity gain and loss of energy concentration.

Determination of starch crystallinity with the Fourier-transform terahertz spectrometer

2021 ◽  
Vol 262 ◽  
pp. 117928
Author(s):  
Shusaku Nakajima ◽  
Shuhei Horiuchi ◽  
Akifumi Ikehata ◽  
Yuichi Ogawa
Keyword(s):  
Fourier Transform ◽  
The Fourier Transform ◽  
Starch Crystallinity
Sign in / Sign up

Export Citation Format

Share Document