Wave propagation effect on differential image motion monitor measurements

2019 ◽  
Vol 488 (1) ◽  
pp. 1273-1281
Author(s):  
Victor Kornilov ◽  
Boris Safonov
Keyword(s):  
Wave Propagation ◽  
Spectral Band ◽  
Image Motion ◽  
Line Of Sight ◽  
Negative Bias ◽  
Vertical Profiles ◽  
Propagation Effect ◽  
Site Testing ◽  
Weighting Functions ◽  
Turbulent Layer

ABSTRACT The differential image motion monitor (DIMM) is widely used to measure the atmospheric optical turbulence (OT) integral over the line of sight. However, it is known that because of the wave propagation effect, the DIMM’s sensitivity falls with the distance to the turbulent layer and the variance of differential image motion is only approximately proportional to the OT integral. In this paper, we study this problem using the formalism of so-called weighting functions (WFs). We develop a method for calculating these WFs, including the case of the wide spectral band of detected radiation. The effect of underestimating the OT integral for different DIMM devices involved in previous site-testing campaigns is estimated using real measurements of OT vertical profiles. For instruments with small apertures (4–6 cm), the underestimation is ≈10 per cent, whereas for larger devices with apertures of 8–10 cm, the underestimation is less than 5 per cent, on average. This leads to a negative bias in seeing estimation of 7 and 3 per cent, respectively.

scholarly journals Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder

2018 ◽  
Author(s):  
Philippe Baron ◽  
Donal Murtagh ◽  
Patrick Eriksson ◽  
Jana Mendrok ◽  
Satoshi Ochiai ◽  
...  
Keyword(s):  
Simulation Study ◽  
Spectral Band ◽  
Chemical Species ◽  
Field Of View ◽  
Emission Lines ◽  
Horizontal Wind ◽  
Line Of Sight ◽  
Heterodyne Receiver ◽  
Vertical Field ◽  
Wind Measurements

Abstract. Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform launch planned near 2022. It is intended to fill the altitude gap between 30–70 km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10–90 km when current satellite missions are probably stopped. Line-of-sight winds are retrieved from the Doppler shift of the emission lines introduced by 5 the wind field. Observations will be performed with two antennas pointing toward the limb with perpendicular directions to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view of 5 km. The chosen spectral band near 655 GHz contains a dense group of strong O3 lines suitable for exploiting the small wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured including O3-isopotologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents the simulation study for assessing the measurement performances. The line-of-sight winds are retrieved between 30–90 km with the best sensitivity between 35–70 km where the precision (1-sigma) is 5–10 m s−1 for a single scan. Similar performances can be obtained during day and night conditions except in the lower mesosphere where the photo-dissociation of O3 in day-time reduces the sensitivity by 50 % near 70 km. Profiles of O3, H2O and temperature are retrieved with a high precision up to 50 km (

scholarly journals Line of Sight and Image Motion Compensation for Step and Stare Imaging System

2020 ◽  
Vol 10 (20) ◽  
pp. 7119
Author(s):  
Jihong Xiu ◽  
Pu Huang ◽  
Jun Li ◽  
Hongwen Zhang ◽  
Youyi Li
Keyword(s):  
High Resolution ◽  
Motion Compensation ◽  
Imaging System ◽  
Control Flow ◽  
Image Motion ◽  
Line Of Sight ◽  
Pointing Accuracy ◽  
High Resolution Images ◽  
Pointing Control ◽  
And Control

In recent years, applications such as marine search and rescue, border patrol, etc. require electro-optical equipment to have both high resolution and precise geographic positioning abilities. The step and stare working based on a composite control system is a preferred solution. This paper proposed a step and stare system composed of two single-axis fast steering mirrors and a two-axis gimbal. The fast steering mirrors (FSMs) realize image motion compensation and the gimbal completes pointing control. The working principle and the working mode of the system are described first. According to the imaging optical path, the algorithm and control flow of the line of sight (LOS) and image motion compensation are developed. The proposed method is verified through ground imaging and flight tests. Under the condition of flight, the pointing accuracy of the target can be controlled within 15 m. The proposed algorithm can achieve effective motion compensation and get high-resolution images. This achieves high resolution and accurate LOS simultaneously.

scholarly journals Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder

2018 ◽  
Vol 11 (7) ◽  
pp. 4545-4566 ◽  
Author(s):  
Philippe Baron ◽  
Donal Murtagh ◽  
Patrick Eriksson ◽  
Jana Mendrok ◽  
Satoshi Ochiai ◽  
...  
Keyword(s):  
Simulation Study ◽  
Spectral Band ◽  
Chemical Species ◽  
Horizontal Wind ◽  
Line Of Sight ◽  
Parameter Uncertainties ◽  
Wind Retrieval ◽  
Wind Measurements ◽  
Large Wind ◽  
Retrieval Bias

Abstract. Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform, with launch planned for around 2022. It is intended to fill the altitude gap between 30 and 70 km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10 and 90 km when current satellite missions will probably come to an end. Line-of-sight winds are retrieved from the Doppler shift of molecular emission lines introduced by the wind field. Observations will be performed with two antennas pointing toward the limb in perpendicular directions in order to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view (FOV) of 5 km. The chosen spectral band, near 655 GHz, contains a dense group of strong O3 lines suitable for exploiting the small amount of wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured, including O3 isotopologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents a simulation study that assesses measurement performance. The line-of-sight winds are retrieved between 30 and 90 km with the best sensitivity between 35 and 70 km, where the precision (1σ) is 5–10 m s−1 for a single scan. Similar performance can be obtained during day and night conditions except in the lower mesosphere, where the photo-dissociation of O3 in daytime reduces the sensitivity by 50 % near 70 km. Profiles of O3, H2O and temperature are retrieved with high precision up to 50 km ( < 1 %,  < 2 %, 1 K, respectively). Systematic errors due to uncertainties in spectroscopic parameters, in the radiometer sideband ratio and in the radiance calibration process are investigated. A large wind retrieval bias of 10–30 m s−1 between 30 and 40 km could be induced by the air-broadening parameter uncertainties of O3 lines. This highlights the need for good knowledge of these parameters and for studying methods to mitigate the retrieval bias.

Seasonal variation of ozone vertical profiles form ExoMars TGO and comparison to water

2021 ◽  
Author(s):  
Manish R. Patel ◽  
Graham Seller ◽  
Jonathon Mason ◽  
James Holmes ◽  
Megan Brown ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
High Altitude ◽  
Relative Abundance ◽  
High Latitude ◽  
Dust Storm ◽  
Trace Gas ◽  
Line Of Sight ◽  
Vertical Profiles ◽  
Elevated Ozone ◽  
Vertical Distributions

&lt;p&gt;The Ultraviolet and Visible Spectrometer (UVIS) channel [1] of the Nadir and Occultation for Mars Discovery (NOMAD) instrument [2] aboard the ExoMars Trace Gas Orbiter has been making observations of the vertical, latitudinal and seasonal distributions of ozone.&amp;#160; Here, we present ~1.5 Mars Years (MY) of vertical profiles of ozone, from &lt;em&gt;L&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt; = 163&amp;#176; in MY34 to &lt;em&gt;L&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt; = 320&amp;#176; in MY35.&amp;#160; This period includes the occurrence of the MY34 Global Dust Storm. The relative abundance of both ozone and water (from coincident NOMAD measurements) increases with decreasing altitude below ~40&amp;#160;km at perihelion and at aphelion, localised decreases in ozone abundance exist between 25-35&amp;#160;km coincident with the location of modelled peak water abundances. High latitude (&gt; &amp;#177; 55&amp;#176;), high altitude (40-55&amp;#160;km) equinoctial ozone enhancements are observed in both hemispheres (&lt;em&gt;L&lt;/em&gt;&lt;sub&gt;S&lt;/sub&gt; ~350&amp;#8209;40&amp;#176;).&amp;#160; Morning terminator observations show elevated ozone abundances with respect to evening observations, most likely attributed to diurnal photochemical partitioning along the line of sight between ozone and O. The ozone retrievals presented here provide the most complete global description of Mars ozone vertical distributions to date as a function of season and latitude&lt;/p&gt;

scholarly journals Measuring the electron temperatures of coronal mass ejections with future space-based multi-channel coronagraphs: a numerical test

2018 ◽  
Vol 619 ◽  
pp. A25 ◽  
Author(s):  
A. Bemporad ◽  
P. Pagano ◽  
S. Giordano
Keyword(s):  
Visible Light ◽  
Coronal Mass Ejections ◽  
Spectral Band ◽  
Synthetic Data ◽  
Diagnostic Techniques ◽  
Plasma Electron ◽  
Propagation Direction ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Plasma Diagnostic

Context. The determination from coronagraphic observations of physical parameters of the plasma embedded in coronal mass ejections (CMEs) is of crucial importance for our understanding of the origin and evolution of these phenomena. Aims. The aim of this work is to perform the first ever numerical simulations of a CME as it will be observed by future two-channel (visible light VL and UV Ly-α) coronagraphs, such as the Metis instrument on-board ESA-Solar Orbiter mission, or any other future coronagraphs with the same spectral band-passes. These simulations are then used to test and optimize the plasma diagnostic techniques to be applied to future observations of CMEs. Methods. The CME diagnostic techniques are tested here by analyzing synthetic coronagraphic observations. First, a numerical three-dimensional (3D) magnetohydrodynamic (MHD) simulation of a CME is performed, and the plasma parameters in the simulation are used to generate synthetic visible light (VL) and ultraviolet (UV) coronagraphic two-dimensional (2D) images of the eruption (i.e., integrated along the line-of-sight). Second, synthetic data are analyzed with different assumptions (as will be done with real data), to infer the kinematic properties of the CME (such as the extension along the line-of-sight of the emitting region, the expansion speed, and the CME propagation direction), as well as physical parameters of the CME plasma (the plasma electron density and temperature). A comparison between input parameters from the simulation and output parameters from the synthetic data analysis is then performed. Results. The inversion of VL polarized data allows to successfully determine the CME speed and 3D propagation direction (with the polarization ratio technique), as well as to derive information on the extension along the line-of-sight of the emitting plasma, a crucial parameter needed to convert the plasma electron column densities into number densities. These parameters are used to analyze UV Ly-α images and to estimate the CME plasma temperature, also taking into account Doppler dimming effect. Output plasma temperatures are in general underestimated, both in the CME body and core regions. By neglecting the UV Ly-α radiative excitation of H atoms, reliable temperatures can be more easily derived in the CME core (within ∼60%). On the other hand, we show that a determination of temperatures (within ∼20−30%) in the CME body requires 2D maps of CME radial speeds and Doppler dimming coefficients to be derived.

scholarly journals Preliminary daytime seeing monitoring at Dome A, Antarctica

2012 ◽  
Vol 8 (S288) ◽  
pp. 296-297
Author(s):  
Chong Pei ◽  
Zhengyangg Li ◽  
Hualin Chen ◽  
Xiangyan Yuan
Keyword(s):  
Large Scale ◽  
Angular Resolution ◽  
Image Motion ◽  
Future Research ◽  
High Angular Resolution ◽  
Optical Parameters ◽  
Site Testing ◽  
Dome A ◽  
Long Period ◽  
Better Than

AbstractSites on Antarctic plateau have unique atmospheric properties that make them better than any mid-latitude sites as observatory locations. From site testing measurements over 4 years on Dome A carried out by the Chinese Center for Antarctic Astronomy, we can reasonably predict that Dome A is as good as or even better than Dome C, which has been proved to be the best astronomical site by now, and suitable for high angular resolution observations. Seeing monitoring is necessary for planning large scale ground-based optical astronomical telescopes. In 2012, the 28th Chinese Antarctic Scientific Expedition carried out preliminary daytime seeing monitoring using a Differential Image Motion Monitor (DIMM) placed at a height of 3.5m. The median seeing was found to be 0.8″. This will be the foundation of future research that obtains comprehensive and long-period monitoring of the site's optical parameters.

scholarly journals Characterization of shock wave signatures at millimetre wavelengths from Bifrost simulations

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200185 ◽  
Author(s):  
Henrik Eklund ◽  
Sven Wedemeyer ◽  
Ben Snow ◽  
David B. Jess ◽  
Shahin Jafarzadeh ◽  
...  
Keyword(s):  
Shock Wave ◽  
Wave Propagation ◽  
Brightness Temperature ◽  
Spectral Band ◽  
Three Dimensional ◽  
Strong Shock ◽  
Shock Wave Propagation ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Brightness Temperatures

Observations at millimetre wavelengths provide a valuable tool to study the small-scale dynamics in the solar chromosphere. We evaluate the physical conditions of the atmosphere in the presence of a propagating shock wave and link that to the observable signatures in mm-wavelength radiation, providing valuable insights into the underlying physics of mm-wavelength observations. A realistic numerical simulation from the three-dimensional radiative magnetohydrodynamic code Bifrost is used to interpret changes in the atmosphere caused by shock wave propagation. High-cadence (1 s) time series of brightness temperature ( T b ) maps are calculated with the Advanced Radiative Transfer code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite sides of spectral band 6 of the Atacama Large Millimeter/submillimeter Array (ALMA). An example of shock wave propagation is presented. The brightness temperatures show a strong shock wave signature with large variation in formation height between approximately 0.7 and 1.4 Mm. The results demonstrate that millimetre brightness temperatures efficiently track upwardly propagating shock waves in the middle chromosphere. In addition, we show that the gradient of the brightness temperature between wavelengths within ALMA band 6 can potentially be used as a diagnostics tool in understanding the small-scale dynamics at the sampled layers. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals ASTROCLIMATIC STATISTICS AT THE SAYAN SOLAR OBSERVATORY

2020 ◽  
Vol 6 (1) ◽  
pp. 126-133
Author(s):  
Artem Shikhovtsev ◽  
Pavel Kovadlo ◽  
Aleksandr Kiselev
Keyword(s):  
Adaptive Optics ◽  
Solar Observatory ◽  
Line Of Sight ◽  
Solar Telescope ◽  
Vertical Profiles ◽  
Minimum Level ◽  
Optical Turbulence ◽  
Low Intensity ◽  
Spatial Features ◽  
Adaptive Optics System

The paper analyzes meteorological and optical characteristics of the atmosphere at the Sayan Solar Observatory (SSO) and the future 3 m Large Solar Telescope (LST-3). We examine spatial features of changes in astroclimatic characteristics for the Sayan Solar Observatory and Baikal Astrophysical Observatory (BAO). We have obtained a vertical profile of the structural characteristic of air refractive index fluctuations for a low intensity optical turbulence along the line of sight. This profile is an important result because it will allow us to adjust the adaptive optics system of LST-3 to the best astroclimatic conditions when the correction efficiency is maximal. In order to analyze vertical profiles of optical turbulence characteristics and to assess the contribution of individual atmospheric layers to the isoplanatic angle for a minimum level of total turbulence, we give recommendations for the design of multi-conjugated adaptive optics in general and for LST-3 in particular.

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