scholarly journals Prediction Model for Diffuser Induced Spectral Features in Imaging Spectrometers

2020 ◽  
Author(s):  
Florian Richter ◽  
Corneli Keim ◽  
Jérôme Caron ◽  
Jasper Krauser ◽  
Dennis Weise ◽  
...  
Keyword(s):  
Prediction Model ◽  
Measurement Technique ◽  
Entrance Slit ◽  
Wide Field ◽  
Spectral Features ◽  
Radiometric Calibration ◽  
Detector Plane ◽  
Detection Plane ◽  
Significant Intensity ◽  
Incoming Light

Abstract. Wide-field spectrometers for Earth Observation missions require inflight radiometric calibration, for which the sun can be used as a known reference. Therefor a diffuser is placed in front of the spectrometer in order to scatter the incoming light into the entrance slit and provide homogeneous illumination. The diffuser however, introduces interference patterns known as speckles into the system, yielding potentially significant intensity variations at the detector plane, called Spectral Features. There have been several approaches implemented to characterize the Spectral Features of a spectrometer, e.g. end-to-end measurements with representative instruments. Additionally, in previous publications a measurement technique was proposed, which is based on the acquisition of monochromatic speckles in the entrance slit following a numerical propagation through the disperser to the detection plane. Based on this measurement technique we present a standalone prediction model for the magnitude of Spectral Features in imaging spectrometers, requiring only few input parameters and therefor mitigating the need for expensive measurement campaigns.

scholarly journals Prediction model for diffuser-induced spectral features in imaging spectrometers

2021 ◽  
Vol 14 (2) ◽  
pp. 1561-1571
Author(s):  
Florian Richter ◽  
Corneli Keim ◽  
Jérôme Caron ◽  
Jasper Krauser ◽  
Dennis Weise ◽  
...  
Keyword(s):  
Prediction Model ◽  
Measurement Technique ◽  
Entrance Slit ◽  
Wide Field ◽  
Spectral Features ◽  
Radiometric Calibration ◽  
Detector Plane ◽  
Detection Plane ◽  
Significant Intensity ◽  
Incoming Light

Abstract. Wide-field spectrometers for Earth observation missions require in-flight radiometric calibration for which the Sun can be used as a known reference. Therefore, a diffuser is placed in front of the spectrometer in order to scatter the incoming light into the entrance slit and provide homogeneous illumination. The diffuser, however, introduces interference patterns known as speckles into the system, yielding potentially significant intensity variations at the detector plane, called spectral features. There have been several approaches implemented to characterize the spectral features of a spectrometer, e.g., end-to-end measurements with representative instruments. Additionally, in previous publications a measurement technique was proposed, which is based on the acquisition of monochromatic speckles in the entrance slit following a numerical propagation through the disperser to the detection plane. Based on this measurement technique, we present a stand-alone prediction model for the magnitude of spectral features in imaging spectrometers, requiring only few input parameters and, therefore, mitigating the need for expensive measurement campaigns.

scholarly journals New developments in aerosol measurements using stellar photometry

2019 ◽  
Vol 197 ◽  
pp. 02007 ◽  
Author(s):  
Jan Ebr ◽  
Jakub Juryšek ◽  
Michael Prouza ◽  
Jiří Blažek ◽  
Petr Trávníček ◽  
...  
Keyword(s):  
Absolute Calibration ◽  
Wide Field ◽  
Telescope Array ◽  
New Developments ◽  
Fast Determination ◽  
Stellar Photometry ◽  
Southern Site ◽  
Ccd Detectors ◽  
Incoming Light

The idea of using stellar photometry for atmospheric monitoring for optical experiments in highenergy astrophysics is seemingly straightforward, but reaching high precision of the order of 0.01 in the determination of the vertical aerosol optical depth (VAOD) has proven difficult. Wide-field photometry over a large span of altitudes allows a fast determination of VAOD independently of the absolute calibration of the system, while providing this calibration as a useful by-product. Using several years of data taken by the FRAM (F/(Ph)otometric Robotic Atmospheric Monitor) telescope at the Pierre Auger Observatory in Argentina and about a year of data taken by a similar instrument deployed at the planned future Southern site of the Cherenkov Telescope Array in Chile, we have developed methods to improve the precision of this measurement technique towards and possibly beyond the 0.01 mark. Detailed laboratory measurements of the response of the whole system to both the spectrum and intensity of incoming light have proven indispensable in this analysis as the usual assumption of linearity of the CCD detectors is not valid anymore for the conditions of the observations.

scholarly journals The silicon micro-strip detector plane for the LOFT/wide-field monitor

2012 ◽  
Author(s):  
A. Goldwurm ◽  
P. Ferrando ◽  
D. Götz ◽  
P. Laurent ◽  
F. Lebrun ◽  
...  
Keyword(s):  
Wide Field ◽  
Detector Plane ◽  
Strip Detector

Multisite High-frequency Radiometric Calibration of GF-1 Wide Field of View

2018 ◽  
Vol 47 (2) ◽  
pp. 228001
Author(s):  
韦玮 WEI Wei ◽  
张艳娜 ZHANG Yan-na ◽  
张孟 ZHANG Meng ◽  
赵春艳 ZHAO Chun-yan ◽  
李新 LI Xin ◽  
...  
Keyword(s):  
High Frequency ◽  
Field Of View ◽  
Wide Field ◽  
Radiometric Calibration ◽  
Wide Field Of View

High-frequency radiometric calibration for wide field-of-view sensor of GF-1 satellite

2014 ◽  
Vol 22 (7) ◽  
pp. 1707-1714 ◽  
Author(s):  
韩启金 HAN Qi-jin ◽  
傅俏燕 FU Qiao-yan ◽  
张学文 ZHANG Xue-wen ◽  
刘李 LIU Li
Keyword(s):  
High Frequency ◽  
Field Of View ◽  
Wide Field ◽  
Radiometric Calibration ◽  
Wide Field Of View

scholarly journals Probing the high-redshift universe with SPICA: Toward the epoch of reionisation and beyond

2018 ◽  
Vol 35 ◽  
Author(s):  
E. Egami ◽  
S. Gallerani ◽  
R. Schneider ◽  
A. Pallottini ◽  
L. Vallini ◽  
...  
Keyword(s):  
High Redshift ◽  
Far Infrared ◽  
Spectroscopic Studies ◽  
Wide Field ◽  
Spectral Features ◽  
Star Forming ◽  
Luminous Infrared Galaxies ◽  
Chemical Enrichment ◽  
Solid Compounds ◽  
High Redshift Universe

AbstractWith the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > 5 that are hyper-luminous in the infrared (μ LIR > 1013 L⊙, where μ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionisation and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA’s far-infrared spectrometer SAFARI, which will probe a spectral range (35–230 μm) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies at z = 5 − 10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the properties of the molecular gas. From a broader perspective, SAFARI offers the potential to open up a new frontier in the study of the early Universe, providing access to uniquely powerful spectral features for probing first-generation objects, such as the key cooling lines of low-metallicity or metal-free forming galaxies (fine-structure and H2 lines) and emission features of solid compounds freshly synthesised by Population III supernovae. Ultimately, SAFARI’s ability to explore the high-redshift Universe will be determined by the availability of sufficiently bright targets (whether intrinsically luminous or gravitationally lensed). With its launch expected around 2030, SPICA is ideally positioned to take full advantage of upcoming wide-field surveys such as LSST, SKA, Euclid, and WFIRST, which are likely to provide extraordinary targets for SAFARI.

scholarly journals On the detection of supermassive primordial stars – II. Blue supergiants

2019 ◽  
Vol 488 (3) ◽  
pp. 3995-4003 ◽  
Author(s):  
Marco Surace ◽  
Erik Zackrisson ◽  
Daniel J Whalen ◽  
Tilman Hartwig ◽  
S C O Glover ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Near Infrared ◽  
Detection Limits ◽  
Wide Field ◽  
Spectral Features ◽  
Field Surveys ◽  
Space Telescope ◽  
Surface Temperatures ◽  
James Webb Space Telescope ◽  
The Universe

ABSTRACT Supermassive primordial stars in hot, atomically cooling haloes at z ∼ 15–20 may have given birth to the first quasars in the Universe. Most simulations of these rapidly accreting stars suggest that they are red, cool hypergiants, but more recent models indicate that some may have been bluer and hotter, with surface temperatures of 20 000–40 000 K. These stars have spectral features that are quite distinct from those of cooler stars and may have different detection limits in the near-infrared today. Here, we present spectra and AB magnitudes for hot, blue supermassive primordial stars calculated with the tlusty and cloudy codes. We find that photometric detections of these stars by the James Webb Space Telescope will be limited to z ≲ 10–12, lower redshifts than those at which red stars can be found, because of quenching by their accretion envelopes. With moderate gravitational lensing, Euclid and the Wide-Field Infrared Space Telescope could detect blue supermassive stars out to similar redshifts in wide-field surveys.

Radiometric calibration of the Sea-viewing Wide-Field-of-View Sensor using ground-reference techniques

2000 ◽  
Author(s):  
Emily E. Whittington ◽  
Kurtis J. Thome ◽  
Robert A. Barnes ◽  
Kelly A. Canham
Keyword(s):  
Field Of View ◽  
Wide Field ◽  
Radiometric Calibration ◽  
Wide Field Of View

scholarly journals Aerial Multispectral Imagery for Plant Disease Detection; Radiometric Calibration Necessity Assessment

2019 ◽  
Author(s):  
Hosseinh Pourazar ◽  
Farhad Samadzadegan ◽  
Farzaneh Dadrass Javan
Keyword(s):  
Plant Disease ◽  
Vegetation Indices ◽  
T Test ◽  
The Other ◽  
Experimental Result ◽  
Disease Detection ◽  
Spectral Features ◽  
Radiometric Calibration ◽  
Spectral Bands ◽  
The Impact

In recent years, using multispectral cameras on UAVs has provided an opportunity to capture separate bands that offer the extraction of spectral features used for early detection of diseased plants. One of the main steps in disease detection is radiometric calibration that converts digital numbers to reflectance values commonly using white reference panels. This paper focused on the necessity of radiometric calibration to distinguish disease trees in orchards based on aerial multi-spectral images. For this purpose, two study sites with various climate conditions and tree species as well as different disease types were selected where multispectral images were taken using a multirotor UAV. The impact of radiometric correction on plant disease detection was assessed in two ways: 1) comparison of separability between the healthy and diseased classes using T-test and entropy distances; 2) radiometric calibration effect on the accuracy of classification. The experimental result showed the insignificant effect of radiometric calibration on separability criteria. Furthermore, based on T-test and entropy distances criteria, NIR and R spectral features made highest distances between healthy and Greening infected citrus trees, respectively, at the first study site while NDRE and BNDVI spectral features made highest distances between healthy and peach leaf curl infected trees, respectively, at the other study site. In the second strategy, the experimental result showed that radiometric calibration had no effect on the accuracy of classification. As a result, the overall accuracy and kappa values for both un-calibrated and calibrated orthomosaic classifications of the citrus orchard were 96.6% and 0.94%, respectively, using five spectral bands as well as DVI, NDRE, NDVI and GNDVI vegetation indices using a random forest classifier. The experimental results were also similar at the other study site. Therefore, the overall accuracy and kappa values for both the un-calibrated and calibrated orthomosaic classifications were 96.1%, 0.92, respectively, using five spectral bands as well as NDRE, BNDVI, GNDVI, DVI, and NDVI vegetation indices.

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