Bright Sky Background Research Articles

An Optical Daytime Astronomy Pathfinder for the Huntsman Telescope

Abstract Observing stars and satellites in optical wavelengths during the day (optical daytime astronomy) has begun a resurgence of interest. The recent dramatic dimming event of Betelgeuse has spurred interest in continuous monitoring of the brightest variable stars, even when an object is only visible during the day due to their proximity to the Sun. In addition, an exponential increase in the number of satellites being launched into low Earth orbit in recent years has driven an interest in optical daytime astronomy for the detection and monitoring of satellites in space situational awareness (SSA) networks. In this paper we explore the use of the Huntsman Telescope as an optical daytime astronomy facility, by conducting an exploratory survey using a pathfinder instrument. We find that an absolute photometric accuracy between 1 - 10% can be achieved during the day, with a detection limit of V band 4.6 mag at midday in sloan g‚ and r‚ wavelengths. In addition we characterise the daytime sky brightness, colour and observing conditions in order to achieve the most reliable and highest signal-to-noise observations within the limitations of the bright sky background. We undertake a 7 month survey of the brightness of Betelgeuse during the day and demonstrate that our results are in agreement with measurements from other observatories. Finally we present our preliminary results that demonstrate obtaining absolute photometric measurements of the International Space Station during the day.

NEW INFRARED CAMERA OF THE CAUCASIAN MOUNTAIN OBSERVATORY OF THE SAI MSU: DESIGN, MAIN PARAMETERS AND RST LIGHT

The paper presents a prototype of an infrared photometer, made by the SAI of MSU on the base of a commercial infrared module Gavin-615A. The operating spectral range of the photometer is 3-5 µm. Studies of the photometer detector have shown that its parameters correspond to those declared by the manufacturer. Nonlinearity of the detector does not exceed ∼ 5% in the whole range of signals, coe cients of correction--function were determined. Additionally, we determined the readout noise RN = 1200 ± 210 e, conversioncoe cient GAIN = 520 ± 9 e/ADU, the BIAS = 960.5 ± 2.2 ADU, and dark current ≈ (9.3 ± 1.1) · 106-e /s,which consists of the sum of the detector dark current and radiation of the entrance window of the detector◦module. The value of dark current was measured at the window temperature of 6 C. Observations werestarted with the photometer at the 2.5-m telescope of the Causasian Mountain Observatory of MSU, the rst results are given in the paper. The unvignetted eld of view is 30'' . In the M band under good atmosphericconditions, an image quality is close to di raction limit. Images of a star with magnitude L = 7.96 and M = 6.78 were obtained with exposure of 20 seconds and a SNR∼10 ratio. It is shown that at high image quality with SNR=3 and exposure of 20 seconds it is possible to observe stars up to L ∼9m and M ∼8m . The main module of the photometer was also used for measurements of the sky background brightness.

Rayleigh Doppler Lidar Technology Based on a Quadruple Dual-pass Fabry–Perot Interferometer

A novel Rayleigh Doppler lidar technology based on a quadruple dual-pass Fabry–Perot interferometer (FPI) that can accurately measure wind field, temperature and aerosol backscatter ratio from the troposphere to lower stratosphere is proposed. This study aims to analyse the detection principle of wind speed, temperature and aerosol backscatter ratio in detail and obtain their measurement error formulas. The structure of this type of lidar is studied and designed. The FPI consists of two edge channels FPI-1 and FPI-2, aerosol channel FPI-M and locking channel FPI-L. FPI-1, FPI-2 and FPI-M use a dual-pass optical path, whereas FPI-L uses a single-pass optical path. The parameters of FPI are optimised as follows: the free spectral spacing (FSR) is 12 GHz, the FWHM of FPI-1 and FPI-2 are both 2.2 GHz, the peak-to-peak interval of FPI-1 and FPI-2 is 5.8 GHz, the FWHM of FPI-M and FPI-L are both 1.2 GHz, the peak-to-peak interval of FPI-M and FPI-1 is 2.9 GHz and the peak-to-peak interval of FPI-L and FPI-1 is 2.3 GHz. Under simulated atmospheric conditions, for a daytime sky background brightness of 0.3 Wsr−1m−2nm−1 at 355 nm, using a laser with a pulse energy of 350 mJ and a repetition frequency of 50 Hz and a telescope with a 0.45-m aperture, with a vertical range resolution of 30 m at 0–10 km, 100 m at 10–20 km and 500 m at 20–35km, temporal resolution of 30 min, zenith angle of 0° for temperature and aerosol backscatter ratio detection and temporal resolution of 3 min and zenith angle of 30° for radial wind speed detection, the detection performance of the designed Rayleigh Doppler lidar is determined. The simulation results show that the measurement errors of aerosol backscatter ratio, temperature and radial wind speed of the lidar system in the daytime and night-time are less than 4.36 × 10−3 and 3.32 × 10−3 (excluding cirrus cloud area), 4.0 K and 3.0 K and 3.8 m/s and 1.9 m/s, respectively, from an altitude of 0.06 to 35km.

Atmospheric CW S-Lidars with Si/InGaAs Arrays: Potentialities in Real Environment

The article proposes a methodology for analyzing the performance of S-lidars (S comes from Scheimpflug) as a new class of environmental remote sensors operating under conditions of wide variability of optical weather and sky background brightness. The novelty of the problem statement, the methods used and the results obtained are determined by their application to laser sensing systems with unconventional design principles and the consequent need to revise the traditional ways of assessing their potential capabilities. The research method is based on a dimensionless-parametric approach, which allows comparing phenomena and systems of different scales and combining complementary characteristics and parameters. Effects of the dimensionless optical weather factor on lidar potential are shown being investigated under various environmental conditions, from the clear atmosphere through haze and mist to fog when probing in Vis/SWIR spectral bands and using Si/InGaAs detector arrays. It is shown exactly how and to what extent the significant differences in their spectral sensitivity and internal noise parameters are susceptible to the wide spectral and energy variability of the sky background brightness observed at very different angles to the Sun. A detailed analysis of the two most important influencing factors within the system, “S-Lidar instrument + Optical weather + External background source”, taking into account their wide variability, allowed us to describe their joint nonlinear influence and, thus, to anticipate the imposed limitations. The proposed dimensionless-parametric concept for predicting the potential capabilities of S-lidars with Si/InGaAs arrays is aimed at expanding applications of this rapidly developing class of remote sensors in a wide variety of environments.

Sky-brightness measurements inJ, H, andKs bands at DOME A with NISBM and early results

ABSTRACTThe radiance of sky brightness differs principally with wavelength passband. Atmospheric scattering of sunlight causes the radiation in the near-infrared band. The Antarctic is a singular area of the planet, marked by an unparalleled climate and geographical conditions, including the coldest temperatures and driest climate on Earth, which leads it to be the best candidate site for observing in infrared bands. At present, there are still no measurements of night-sky brightness at DOME A. We have developed the Near-Infrared Sky Brightness Monitor (NISBM) in the J, H, and Ks bands for measurements at DOME A. The instruments were installed at DOME A in 2019 and early results of NIR sky brightness from 2019 January–April have been obtained. The variation of sky background brightness with solar elevation and scanning angle is analysed. The zenith sky flux intensity for the early night at DOME A in the J band is in the 600–1100 μJy arcsec−2 range, that in the H band is between 1100 and 2600 μJy arcsec−2, and that in the Ks band is in the range ∼200–900 μJy arcsec−2. This result shows that the sky brightness in J and H bands is close to that of Ali in China and Mauna Kea in the USA. The sky brightness in the Ks band is much better than that in Ali, China and Mauna Kea, USA. This shows that, from our early results, DOME A is a good site for astronomical observation in the Ks band.

Application of the Gaussian modeling algorithm to a Shack-Hartmann wavefront sensor for daylight adaptive optics.

Daytime use of Shack-Hartmann wavefront sensor (SHWS)-based adaptive optics (AO) at a telescope is hindered by the fluctuating bright sky background. Therefore, we propose a Gaussian modeling centroid extraction algorithm that performs real-time daylight AO closed-loop corrections. The algorithm is executed in the process of modeling and updating each pixel of the consecutive SHWS images. The simulation results show that our method can provide a lower centroid estimation error (CEE) for bright sky background conditions. We also performed a field experiment on a 2 m ground-based telescope and achieved a daylight AO correction of 2.1 times diffraction limit for a star with a visual magnitude of 4.7 (HIP113116) when the elevation angle of the sun was 7.7°. This represents the first publicly reported daylight natural guide star AO correction result on a 2 m class telescope.

Wide Band Antenna with Ultra-smooth Spectral Characteristics

Understanding the evolution of Universe is, in the forefront of, the modern day observational cosmology. It requires precise and accurate measurement of cosmological signal, orders of magnitude weaker than the bright sky background. Detection of such a signal having distinct spectral signature, needs an antenna with frequency independent characteristics over more than an octave bandwidth. A spherical monopole antenna has been designed to operate in the frequency range 50-200 MHz with a spectral smoothness of about few parts in 104. The structure has been modeled and optimized using WIPL-D, to minimize spectral features arising out of abrupt reflections of surface currents and frequency dependent radiation patterns. A prototype has been built to validate the design. This paper presents the methodology adopted in the overall antenna design, experiences in its prototyping and simulation and the measurement results.

Infrared Observations of 2I/Borisov near Perihelion

Abstract As the first interstellar comet, 2I/Borisov provides a unique opportunity to study the surface composition of a comet from another stellar system, particularly whether it has water ice. In order to investigate the nature of 2I/Borisov, we conducted infrared observations close to perihelion. The water ice, if present, is expected to be revealed by absorption features at 1.5 and 2 micron. We therefore used FLAMINGOS-2 mounted on the Gemini south telescope, to carry out deep imaging on 2019 November 30 UT and spectroscopy on 2019 December 7 UT. At first glance, our imaging did not reveal an apparent coma or a cometary tail. This is due to the bright sky background and our short exposure times. Nevertheless we were able to put an upper limit of the size of the nucleus, as well as provide high-precision astrometry that can be used to investigate nongravitational acceleration in the future. Our infrared spectra showed a negative slope, contrary to the results by Yang et al. It is not unheard of for a comet to show a negative slope, and to progressively exhibit a spectrum with decreasing slope. Possible causes of the decreasing slope are an increase in water ice and/or decrease in dust size. Given the fact that our observations were carried out close to perihelion, it is likely that both factors contribute to the decreasing, negative slope of the infrared spectrum.

Image registration for daylight adaptive optics.

Daytime use of adaptive optics (AO) at large telescopes is hampered by shot noise from the bright sky background. Wave-front sensing may use a sodium laser guide star observed through a magneto-optical filter to suppress the background, but the laser beacon is not sensitive to overall image motion. To estimate that, laser-guided AO systems generally rely on light from the object itself, collected through the full aperture of the telescope. Daylight sets a lower limit to the brightness of an object that may be tracked at rates sufficient to overcome the image jitter. Below that limit, wave-front correction on the basis of the laser alone will yield an image that is approximately diffraction limited but that moves randomly. I describe an iterative registration algorithm that recovers high-resolution long-exposure images in this regime from a rapid series of short exposures with very low signal-to-noise ratio. The technique takes advantage of the fact that in the photon noise limit there is negligible penalty in taking short exposures, and also that once the images are recorded, it is not necessary, as in the case of an AO tracker loop, to estimate the image motion correctly and quickly on every cycle. The algorithm is likely to find application in space situational awareness, where high-resolution daytime imaging of artificial satellites is important.

Night Sky Background Brightness Estimation by the Example of the St. Petersburg City

Within the big city boundaries, artificial component of the sky glow increases every year. The main reasons are the expansion of the cities, the rapid growth of technical capabilities, inefficient lighting design without master-planning and lack of quality control of lighting projects. The data of astronomical observations confirm a significant brightness increasing in the lower atmosphere due to factors of terrestrial origin. The problem is mostly acute for observatories are located near major cities, which are struggling for the possibility of further research. Night sky background glow estimation is an actual direction for research in the modern world. The paper considers a model for calculating the sky brightness for the St. Petersburg city. According to the developed model observation position is located near the Pulkovo Observatory. The model is based on the Garstang’s method with use of Python programming language.

Performance Measurement of Photoelectric Detection and Target Tracking Algorithm

Abstract To solve the unstable problem of target tracking detection system, this paper proposes an improved mean-shift algorithm for object tracking, establishes object tracking processing model;provides the processing algorithm of object tracking. According to the principal of object tracking, papersets up sky background brightness calculation model in photoelectric tracking optical detection area and detection capability calculation model of space object, analyzes the effect of background illumination on the signal to noise ratio(SNR) of photoelectric tracking system, gives the change curve of detection capability based on the exposure time of CCD camera, SNR threshold of photoelectric detection system and dark current of photoelectric detection system. Through calculation and test , paperprovidesthe comparison results of the improved mean-shift and traditional mean-shift, verifies the correctness of the proposed algorithm and calculation models for photoelectric detection capability in target tracking detection system, the results show the improved mean-shiftobject tracking algorithm and detection capability calculation model are correct.

Deep searches for decametre-wavelength pulsed emission from radio-quiet gamma-ray pulsars

We report the results of (a) extensive follow-up observations of the gamma-ray pulsar J1732-3131 that has been recently detected at decameter wavelengths, and (b) deep searches for counterparts of 9 other radio-quiet gamma-ray pulsars at 34 MHz, using the Gauribidanur radio telescope. No periodic signal from J1732-3131 could be detected above a detection threshold of $8\sigma$, even with an effective integration time of more than 40 hours. However, the average profile obtained by combining data from several epochs, at a dispersion measure of 15.44 pc/cc, is found to be consistent with that from the earlier detection of this pulsar at a confidence level of 99.2 %. We present this consistency between the two profiles as an evidence that J1732-3131 is a faint radio pulsar with an average flux density of 200--400 mJy at 34 MHz. Detection sensitivity of our deep searches, despite the extremely bright sky background at such low frequencies, is generally comparable to that of higher frequency searches for these pulsars, when scaled using reasonable assumptions about the underlying pulsar spectrum. We provide details of our deep searches, and put stringent upper limits on the decameter wavelength flux densities of several radio-quiet gamma-ray pulsars.

CTA site characterization: a contribution on Sky Background Brightness

AbstractThe Cherenkov Telescope Array (CTA) is an international project for which more than 1000 scientists from 27 countries work together to install two observatories, one in the southern hemisphere and the other in the north, to study gamma-ray radiation. Argentina is a candidate site for one of the observatories, and to characterize proposed sites, one must study the sky background brightness. This critical point must be studied with care. Nearest cities can be a decisive factor in determining where to locate an observatory in our times.

An Automated Cirrus Cloud Detection Method for a Ground-Based Cloud Image

Abstract Cloud detection is a basic research for achieving cloud-cover state and other cloud characteristics. Because of the influence of sunlight, the brightness of sky background on the ground-based cloud image is usually nonuniform, which increases the difficulty for cirrus cloud detection, and few detection methods perform well for thin cirrus clouds. This paper presents an effective background estimation method to eliminate the influence of variable illumination conditions and proposes a background subtraction adaptive threshold method (BSAT) to detect cirrus clouds in visible images for the small field of view and mixed clear–cloud scenes. The BSAT algorithm consists of red-to-blue band operation, background subtraction, adaptive threshold selection, and binarization. The experimental results show that the BSAT algorithm is robust for all types of cirrus clouds, and the quantitative evaluation results demonstrate that the BSAT algorithm outperforms the fixed threshold (FT) and adaptive threshold (AT) methods in cirrus cloud detection.

Implementation of Models for Charge Transfer Inefficiency (CTI) in the Gaia Pixel-Level Data Simulator

The Gaia pixel-level data simulator GIBIS (Gaia Instrument and Basic Image Simulator, Babusiaux (2005)) provides detailed artificial data for all three instruments on-board the Gaia spacecraft. This data is used for the preparation of procedures required for the analysis of real Gaia data to come during the mission. Among the effects that strongly affect all Gaia data, that therefore have to be modelled with GIBIS, is charge transfer inefficiency (CTI). CTI, caused by radiation-induced microscopic defects in the CCD detectors, becomes manifest in a distortion of the line spread functions of observed objects, as well as in a loss of photo-generated charges inside the window allocated to each observed source. It affects the astrometric, photometric, and spectroscopic accuracy of the data. The CTI effects on a particular observation depend on observations done before, on CCD operations such as gate activity and charge injections, and on physical effects such as the sky background brightness and cosmic ray events in the detectors. In this paper, an approach for the simulation of CTI with GIBIS is presented and the influence of the sky background brightness and cosmic ray events of CTI is discussed in more detail.

∗A method of sky quality evaluation using wide field photometry : ZHOU Xu, CHEN Jian-sheng & JIANG Zhao-ji Beijing Astronomical Observatory, CAS, Beijing 100012

A statistical method based on wide field photometry is developed to give a quantitative evaluation of sky quality. The parameters used include the sky background brightness and transparency, the S/N and the limiting magnitude. Several tests have been used to check the reliability of the method. The paper shows that the method provides a real-time quantitative monitoring of the sky variation and so help optimize the usage of observing time of the BAO Schmidt CCD system.

Colliding Asteroids from Blind Directions

ABSTRACT: The Spaceguard Project proposes to set up a network of five ground‐based telescopes, each with an aperture of 2–3 m. With ground‐based telescopes, there is a blind celestial area surrounding the Sun (say, within 30 degrees), in which an asteroid approaching the Earth cannot be detected optically because of bright sky background. Our study shows that the number of close approaches of asteroids coming from this area to within a minimum distance of less than 0.01 AU of the Earth is more than 30% of the total.

Fabry–Perot CCD annular-summing spectroscopy: study and implementation for aeronomy applications

The technique of Fabry-Perot CCD annular-summing spectroscopy, with particular emphasis on applications in aeronomy, is discussed. Parameter choices for optimizing performance by the use of a standard format CCD array are detailed. Spectral calibration methods, techniques for determining the ring pattern center, and effects imposed by limited radial resolution caused by superpixel size, variable by on-chip binning, are demonstrated. The technique is carefully evaluated experimentally relative to the conventional scanning Fabry-Perot that uses a photomultiplier detector. We evaluate three extreme examples typical of aeronomical spectroscopy using calculated signal-to-noise ratios. Predicted sensitivity gains of 10-30 are typical. Of the cases considered, the largest savings in integration time are estimated for the day sky thermospheric O(1)D case, in which the bright sky background dominates the CCD read noise. For profile measurements of faint night sky emission lines, such as exospheric hydrogen Balmer-α, long integration times are required to achieve useful signal-to-noise ratios. In such cases, CCD read noise is largely overcome. Predictions of a factor of 10-15 savings in integration time for night sky Balmer-α observations are supported by field tests. Bright, isolated night sky lines such as thermospheric O(1)D require shorter integration times, and more modest gains dependent on signal level are predicted. For such cases it appears from estimate results that the Fabry-Perot CCD annular-summing technique with a conventional rectangular format may be outperformed by a factor of 2-5 by special CCD formats or by unusual optical coupling configurations that reduce the importance of read noise, based on the ideal transmission for any additional optics used in these configurations.

A procedure for the extraction of airglow features in the presence of strong background radiation

Ground‐based measurements of terrestrial airglow are useful for many applications in aeronomy. However, in the past observations have been limited to times and circumstances when the relatively weak airglow features are not overwhelmed by bright sky background emission due mainly to Rayleigh scattering of sunlight. In this paper we report a procedure which can be used to automatically extract weak airglow emissions in the presence of strong background radiation. The computer code developed for this purpose is user friendly and provides, in addition to retrieved airglow intensities, quantitative diagnostics which include estimates of error of measurement. The procedure is designed to allow rapid bulk processing of data which has not been possible previously.

On the Zeeman photometer observing upper atmospheric winds in the daytime

In order to observe the speeds and directions of upper atmospheric winds, the most precise and straightforward method is to take simultaneous photographs of the artificial luminescent clouds from several camera stations on the ground. This method, however, could not be applied to measure the wind in the daytime, because of a strong sky background for the optical observation of the artificial cloud. In order to overcome this difficulty a Zeeman photometer was developed which enable us to identify the artificial sodium cloud in the bright sky background.