Infrared Sky Research Articles

Processing of global solar irradiance and ground-based infrared sky images for solar nowcasting and intra-hour forecasting applications

Shadows from moving clouds in the troposphere impact the energy generated by photovoltaic systems. intra-hour solar forecast can be used to regulate solar energy dispatch. This investigation develops a data processing method for cloud dynamic feature extraction from raw sky images and Global Solar Irradiance (GSI) measurements that can be integrated into solar forecasting algorithms to reduce the operational supervision of hardware. Sky images and GSI measurements are acquired from a low-cost long-wave infrared radiometric camera and a pyranometer. This sky imager is mounted on a solar tracker that maintains the Sun in the center of sky images throughout the day. Multiple processing methods are proposed here that take advantage of a hybrid approach to approximate the optimal parameters of physical models using computationally inexpensive machine learning models. A signal processing method removes cyclostationary biases in high-resolution clear sky index values found when detrending GSI measurements using the clear sky GSI. Image processing methods are then used to remove the effects of atmospheric radiation and the Sun’s direct radiation from infrared sky images, plus the radiation effect emitted by debris on the sky imager’s germanium outdoor lens. The result is an adaptive solar forecasting algorithm that can reduce the operational cost of power grids with the high participation of solar energy in the generation mix.

Irradiance Nowcasting by Means of Deep-Learning Analysis of Infrared Images

This work proposes and evaluates a method for the nowcasting of solar irradiance variability in multiple time horizons, namely 5, 10, and 15 min ahead. The method is based on a Convolutional Neural Network structure that exploits infrared sky images acquired through an All-Sky Imager to estimate the range of possible values that the Clear-Sky Index will possibly assume over a selected forecast horizon. All data available, from the infrared images to the measurements of Global Horizontal Irradiance (necessary in order to compute Clear-Sky Index), are acquired at SolarTechLAB in Politecnico di Milano. The proposed method demonstrated a discrete performance level, with an accuracy peak for the 5 min time horizon, where about 65% of the available samples are attributed to the correct range of Clear-Sky Index values.

Infrared Scanning Cloud Monitor for the Indian Astronomical Observatory, Hanle

A large number of clear nights at a given location is one of the key prerequisites for establishing an astronomical observatory. This parameter needs to be reliably determined before the site location is finalized. For an already exiting observatory site, monitoring of clouds on real-time basis helps automating many observing procedures, thus optimizing the scientific returns from the facility. We have developed an infrared (IR) scanning cloud monitor which generates a local sky-map and provides reliable information about the changing sky conditions. Our device measures the IR sky brightness temperature using a circular array of thermopile sensors mounted on a rotating system. In this paper, we give a detailed description of the instrument hardware, laboratory and on-site calibration procedures and further tests carried out to check the reliability of the device. The cloud monitor has been in regular use since its installation at the Indian Astronomical Observation (IAO), Hanle, Ladakh in 2015 December. We also present the analysis of a year long sky data to demonstrate the usefulness of the device.

Planckintermediate results

Although infrared (IR) overall dust emission from clusters of galaxies has been statistically detected using data from the Infrared Astronomical Satellite (IRAS), it has not been possible to sample the spectral energy distribution (SED) of this emission over its peak, and thus to break the degeneracy between dust temperature and mass. By complementing the IRAS spectral coverage with Planck satellite data from 100 to 857 GHz, we provide new constraints on the IR spectrum of thermal dust emission in clusters of galaxies. We achieve this by using a stacking approach for a sample of several hundred objects from the Planck cluster sample; this procedure averages out fluctuations from the IR sky, allowing us to reach a significant detection of the faint cluster contribution. We also use the large frequency range probed by Planck, together with component-separation techniques, to remove the contamination from both cosmic microwave background anisotropies and the thermal Sunyaev-Zeldovich effect (tSZ) signal, which dominate below 353 GHz. By excluding dominant spurious signals or systematic effects, averaged detections are reported at frequencies between 353 and 5000 GHz. We confirm the presence of dust in clusters of galaxies at low and intermediate redshifts, yielding an SED with a shape similar to that of the Milky Way. Planck's beam does not allow us to investigate the detailed spatial distribution of this emission (e.g., whether it comes from intergalactic dust or simply the dust content of the cluster galaxies), but the radial distribution of the emission appears to follow that of the stacked SZ signal, and thus the extent of the clusters. The recovered SED allows us to constrain the dust mass responsible for the signal, as well as its temperature. We additionally explore the evolution of the IR emission as a function of cluster mass and redshift.

Scientific Goals of the Kunlun Infrared Sky Survey (KISS)

AbstractThe high Antarctic plateau provides exceptional conditions for infrared observations on account of the cold, dry and stable atmosphere above the ice surface. This paper describes the scientific goals behind the first program to examine the time-varying universe in the infrared from Antarctica — the Kunlun Infrared Sky Survey (KISS). This will employ a 50cm telescope to monitor the southern skies in the 2.4μmKdark window from China's Kunlun station at Dome A, on the summit of the Antarctic plateau, through the uninterrupted 4-month period of winter darkness. An earlier paper discussed optimisation of the Kdark filter for sensitivity (Li et al. 2016). This paper examines the scientific program for KISS. We calculate the sensitivity of the camera for the extrema of observing conditions that will be encountered. We present the parameters for sample surveys that could then be carried out for a range of cadences and sensitivities. We then discuss several science programs that could be conducted with these capabilities, involving star formation, brown dwarfs and hot Jupiters, exoplanets around M dwarfs, the terminal phases of stellar evolution, fast transients, embedded supernova searches, reverberation mapping of AGN, gamma ray bursts and the detection of the cosmic infrared background.

Optimising theKDark Filter for the Kunlun Infrared Sky Survey

AbstractThe Kunlun Infrared Sky Survey will be the first comprehensive exploration of the time varying Universe in the infrared. A key feature in optimising the scientific yield of this ambitious research programme is the choice of the survey passband. In particular, the survey aims to maximally exploit the unique thermal and atmospheric conditions pertaining to the high Antarctic site. By simulating the expected signal-to-noise for varying filter properties within the so-called ‘KDARK’ 2.4 μm window, filter performance can be tuned and best-case designs are given covering a range of conditions.

YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49.

We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color-color and color-magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ⩾7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

Active galactic nuclei and their role in galaxy evolution: The infrared perspective

The remarkable progress made in infrared (IR) astronomical instruments over the last 10–15 years has radically changed our vision of the extragalactic IR sky, and overall understanding of galaxy evolution. In particular, this has been the case for the study of active galactic nuclei (AGN), for which IR observations provide a wealth of complementary information that cannot be derived from data in other wavelength regimes. In this review, I summarize the unique contribution that IR astronomy has recently made to our understanding of AGN and their role in galaxy evolution, including both physical studies of AGN at IR wavelengths, and the search for AGN among IR galaxies in general. Finally, I identify and discuss key open issues that should be possible to address with forthcoming IR telescopes.

Nocturnal infrared clear sky temperatures correlated with screen temperatures and GPS-derived PWV in southern Australia

Infrared (IR) clear sky temperatures ( Tsky), screen level temperature ( T) and Precipitable Water Vapour (PWV) were collected for a period of 2 years from a coastal region of southern Australia. IR sky temperatures were derived from simple infrared detectors, which have been developed by the authors for inexpensive monitoring of cloud cover, while data for PWV were obtained from Global Positioning Satellite (GPS) transmissions. Meteorological data were obtained from the Australian Bureau of Meteorology. Based on these data, statistical regression analyses between nocturnal Tsky and the T and PWV (one variable fit) were conducted. Direct proportional relationships between Tsky and T and between Tsky and PWV were found. The one variable fit was further optimized by applying the multiple regression fit between Tsky and both T and PWV. The resulting multilinear model was essentially unbiased, with a correlation coefficient ( R 2) of 0.97, mean bias error (MBE) of −2.7 × 10 −5 °C, and root mean square error (RMSE) of about 1.6 °C. The performance of the multilinear model was tested against a 1-year independent data set. In this case, the predictability of the model was superior, with MBE and RMSE being 0.13 °C and 2.23 °C respectively. After correcting the daytime observations for the biases caused by solar heating of the detection system, the performance of this model in calculating the daytime measurements was tested and showed MBE and RMSE values of 1.3 °C and 2.5 °C, respectively. Additionally, twenty schemes from the literature were tested and assessed for predicting the measured sky temperature. The performances of these models were all different. Whereas most of them underestimated the measured sky temperatures, three of these models showed a reasonable prediction ability. Finally, the multilinear model was compared with the simulated sky temperatures obtained using MODTRAN software. Perfect agreements were found between the two temperatures.

Impact of the March 2009 dust event in Saudi Arabia on aerosol optical properties, meteorological parameters, sky temperature and emissivity

On 10th March 2009 a widespread and severe dust storm event that lasted several hours struck Riyadh, and represented one of the most intense dust storms experienced in Saudi Arabia in the last two decades. This short-lived storm caused widespread and heavy dust deposition, zero visibility and total airport shutdown, as well as extensive damage to buildings, vehicles, power poles and trees across the city of Riyadh. Changes in Meteorological parameters, aerosol optical depth (AOD), Angstrom exponent α, infrared (IR) sky temperature and atmospheric emissivity were investigated before, during, and after the storm. The analysis showed significant changes in all of the above parameters due to this event. Shortly after the storm arrived, air pressure rapidly increased by 4 hPa, temperature decreased by 6 °C, relative humidly increased from 10% to 30%, the wind direction became northerly and the wind speed increased to a maximum of 30 m s−1. AOD at 550 nm increased from 0.396 to 1.71. The Angstrom exponent α rapidly decreased from 0.192 to −0.078. The mean AOD at 550 nm on the day of the storm was 0.953 higher than during the previous clear day, while α was −0.049 in comparison with 0.323 during the previous day. Theoretical simulations using SMART software showed remarkable changes in both spectral and broadband solar radiation components. The global and direct radiation components decreased by 42% and 68%, respectively, and the diffuse components increased by 44% in comparison with the previous clear day. IR sky temperatures and sky emissivity increased by 24 °C and 0.3, respectively, 2 h after the arrival of the storm. The effect of aerosol loading by the storm on IR atmospheric emission was investigated using MODTRAN software. It was found that the effect of aerosols caused an increase of the atmospheric emission in the atmospheric window (8–14 μm) such that the window emissions resembled those of a blackbody and the atmospheric window was almost closed.

ON THE EXISTENCE OF A DISTANT SOLAR COMPANION AND ITS POSSIBLE EFFECTS ON THE OORT CLOUD AND THE OBSERVED COMET POPULATION

We analyze the possible existence and detection of a distant massive solar companion. Such an object?if it exists?should be very faint in the visible, so its direct detection might depend on current or future infrared sky surveys, like WISE. Alternatively, its presence could be uncovered through its perturbing effects on nearby objects such as, for instance, Oort Cloud comets (OCCs). We then estimate how putative solar companions of different masses and semimajor axes can perturb nearby OCCs causing an enhancement of the comet flux along the companion's path. We find that a companion of 5 Jupiter masses (MJ ) can produce a signature detectable with the current record of observed new comets, provided that the Oort Cloud contains a dense inner core of comets and that the distance of the perturber is smaller than ~2 ? 104 AU. A 1 MJ perturber can produce a signature detectable in the current record only if its distance were smaller than ~(2-3) ? 103 AU. The sample of discovered new comets is found to be two orders of magnitude too small to show a signature caused by a Neptune-mass companion at any distance above ~103 AU to a significant level. We also estimate that the Oort Cloud will withstand the steady perturbing effects by a massive solar companion over the solar system age, with only a minor erosion, unless the companion had a mass a few MJ , and were at a distance a few 103 AU.

Correcting Calibrated Infrared Sky Imagery for the Effect of an Infrared Window

AbstractA method is demonstrated for deriving a correction for the effects of an infrared window when used to weatherproof a radiometrically calibrated thermal infrared imager. The technique relies on initial calibration of two identical imagers without windows and subsequently operating the imagers side by side: one with a window and one without. An equation is presented that expresses the scene radiance in terms of through-window radiance and the transmittance, reflectance, and emissivity of the window. The window’s optical properties are determined as a function of angle over the imager’s field of view through a matrix inversion using images observed simultaneously with and without a window. The technique is applied to calibrated sky images from infrared cloud imager systems. Application of this window correction algorithm to data obtained months before or after the algorithm was derived leads to an improvement from 0.46 to 0.91 for the correlation coefficient between data obtained simultaneously from imagers with and without a window. Once the window correction has been determined, the windowed imager can operate independently and provide accurate measurements of sky radiance.

Design and development of a simple infrared monitor for cloud detection

We have developed simple single pixel thermopile infrared (IR) detectors for monitoring clouds for the purpose of atmospheric research and for cloud detection over astronomical and astrophysical observatories. Those detectors were developed with 3° and 90° fields of view (FOV) and have a broad spectral response extended from 5.5 μm to above 20 μm centered on a wavelength of 10 μm. This paper aims to give a detailed description of these detectors, and the methodology followed to construct and calibrate them. Results from observations with these detectors will be given. Simulations using MODTRAN software were carried out to examine the theoretical expectation of the measured IR sky temperatures by these detectors. Good agreements between the measured and simulated data were found.

A model of the 2-35 micron Point Source Infrared Sky

view Abstract Citations (66) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model of the 2-35 micron Point Source Infrared Sky Cohen, Martin Abstract The Point Source Infrared Sky Model of Wainscoat et al. (1992) is extended to make predictions for any filter lying wholly within the range 2.0 to 35.0 micron. The development of a library of complete 2-35 micron low-resolution spectra that represent the 87 categories of Galactic object and four types of extragalactic source implicit in the Model supports this extension. This library is based upon the 'spectral template' technique whereby existing spectral fragments for individual sources (from ground-based, airborne, and satellite-borne instruments) are combined into complete spectra. Templates provide a natural way to represent the complete spectral energy distributions of celestial sources for which only infrared photometry and/or partial spectroscopy are available. Consequently, templates bear upon the important general problem of establishing midinfrared calibration sources. The new model is validated by comparison with broadband K source counts. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116560 Bibcode: 1993AJ....105.1860C Keywords: Astronomical Catalogs; Infrared Astronomy; Infrared Filters; Infrared Photometry; Infrared Spectroscopy; Point Sources; Brightness; Extragalactic Radio Sources; Quasars; Astronomy; INFRARED: GENERAL full text sources ADS | data products SIMBAD (177) CDS (1)

A Model of the 8–25 μm Point Source Infrared Sky

We have constructed a detailed model for the infrared (IR) point source sky that comprises geometrically and physically realistic representations of the galactic disk, bulge, stellar halo, spiral arms (including the “local arm”), molecular ring, and the extragalactic sky. We represent each of the distinct galactic components by up to 87 types of galactic source, each fully characterized by scale heights, space densities, and absolute magnitudes at BVJHK, 12, and 25 μm, and a spectrum from the IRAS Low Resolution Spectrometer (LRS). Our model has been guided by a parallel Monte Carlo simulation of the Galaxy at 12 μm. The content of our galactic source table constitutes an excellent match to the 12 μm luminosity function in the simulation, as well as to the luminosity functions at V and K. We are able to predict differential and cumulative IR source counts for any bandpass lying fully within the IRAS LRS range (7.7–22.7 μm) as well as for the IRAS 12 and 25 μm bands. These source counts match the IRAS observations extremely well. The model can be used to predict the character of the point source sky expected for observations from future IR space experiments (e.g., ISO, SIRTF, LDR).

THE INFRARED SKY: A SURVEY OF SURVEYS

ABSTRACT A subjective review is given of the major milestones in infrared astronomy. Emphasis is placed on the survey efforts between 2 and 120 μm, the realm of the extrinsic photodetector. The historical developments in infrared astronomy and the pioneering, often marginally successful, survey attempts are put in the perspective of improving technology. Some discussion is given to the survey discoveries and how they have extended our knowledge of the infrared celestial background.

Radio-sounding data for the determination of the infra-red sky radiation

The infra-red sky radiation comes from the physical phenomenon of emission-transmission of the superposed atmospherical layers. It can be computed from the composition and state of each of them. The various models built in some laboratories are based on the distribution and characteristics of the absorption lines. They are used with standard atmospheric profiles of pressure, temperature and composition. H Here, radio-sounding measurements have replaced the latter profiles, giving an original way to link theory and observation. Ten years of data, consisting of pressure, temperature and mixing ratio atmospheric profiles for clear weather conditions were collected. The computed results are in good agreement, with pyrradiometer data. The insensitiveness to the site and to the season is shown. The day-night effect is also pointed out.

Dust effect on infrared sky radiation in Kuwait

Abstract Infrared (i.r.) sky radiation and weather data were collected over a period of more than 1 year in Kuwait. Based on this data, an i.r. sky radiance model was developed, using statistical regression analysis, relating band hemispherical sky emissivity to absolute humidity (or dew point) and suspended dust.

Errata: an Observational Study of the AFCRL Infrared Sky Survey. III. Further Searches for Afcrl/ AFGL Sources and an Evaluation of the Contents of the Mid-Infrared Sky

Errata: an Observational Study of the AFCRL Infrared Sky Survey. III. Further Searches for Afcrl/ AFGL Sources and an Evaluation of the Contents of the Mid-Infrared Sky

2 - 14 ΜM STELLAR SPECTROPHOTOMETRY III. AFCRL SKY SURVEY OBJECTS.

ABSTRACT Broad-band photometry and spectrophotometry with resolution xlx 0.015 over the wavelength range 2-14 m is presented for a sample of sources in the AFCRL Infrared Sky Survey. Some of the objects discovered in this survey are shown to be stars of the conventional spectral sequence surrounded by optically thick circumstellar dust shells. Others exhibit no evidence of classical cool stellar objects and may represent various transition stages of stellar evolution. Key words: infrared objects - spectrophotometry - cool stars - circumstellar dust