Person:
Zamorano Calvo, Jaime

First Name

Jaime

Last Name

Zamorano Calvo

URI

https://hdl.handle.net/20.500.14352/74989

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de la Tierra y Astrofísica

Area

Astronomía y Astrofísica

Identifiers

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Now showing 1 - 8 of 8

Synthetic RGB photometry of bright stars: definition of the standard photometric system and UCM library of spectrophotometric spectra
(Monthly notices of The Royal Astronomical Society, 2021) Cardiel López, Nicolás; Zamorano Calvo, Jaime; Bará, Salvador; Sánchez de Miguel, Alejandro; Cabello González, Cristina; Gallego Maestro, Jesús; García, Lucía; González Fuentetaja, Rafael; Izquierdo Gómez, Jaime; Pascual Ramírez, Sergio; Robles, José; Sánchez Penim, Ainhoa; Tapia Ayuga, Carlos
Although the use of RGB photometry has exploded in the last decades due to the advent of high-quality and inexpensive digital cameras equipped with Bayer-like color filter systems, there is surprisingly no catalogue of bright stars that can be used for calibration purposes. Since due to their excessive brightness, accurate enough spectrophotometric measurements of bright stars typically cannot be performed with modern large telescopes, we have employed historical 13-color medium-narrow-band photometric data, gathered with quite reliable photomultipliers, to fit the spectrum of 1346 bright stars using stellar atmosphere models. This not only constitutes a useful compilation of bright spectrophotometric standards well spread in the celestial sphere, the UCM library of spectrophotometric spectra, but allows the generation of a catalogue of reference RGB magnitudes, with typical random uncertainties ∼ 0.01 mag. For that purpose, we have defined a new set of spectral sensitivity curves, computed as the median of 28 sets of empirical sensitivity curves from the literature, that can be used to establish a standard RGB photometric system. Conversions between RGB magnitudes computed with any of these sets of empirical RGB curves and those determined with the new standard photometric system are provided. Even though particular RGB measurements from single cameras are not expected to provide extremely accurate photometric data, the repeatability and multiplicity of observations will allow access to a large amount of exploitable data in many astronomical fields, such as the detailed monitoring of light pollution and its impact on the night sky brightness, or the study of meteors, solar system bodies, variable stars, and transient objects. In addition, the RGB magnitudes presented here make the sky an accessible and free laboratory for the calibration of the cameras themselves.
Colour remote sensing of the impact of artificial light at night (II): calibration of DSLR-based images from the International Space Station
(Remote sensing of environment, 2021) Sánchez de Miguel, Alejandro; Zamorano Calvo, Jaime; Aubé, Martin; Bennie, Jonathan; Gallego Maestro, Jesús; Ocaña González, Francisco; Pettit, Donald R.; Stefanov, William L.; Gaston, Kevin J.
Nighttime images taken with DSLR cameras from the International Space Station (ISS) can provide valuable information on the spatial and temporal variation of artificial nighttime lighting on Earth. In particular, this is the only source of historical and current visible multispectral data across the world (DMSP/OLS and SNPP/VIIRS- DNB data are panchromatic and multispectral in the infrared but not at visible wavelengths). The ISS images require substantial processing and proper calibration to exploit intensities and ratios from the RGB channels. Here we describe the different calibration steps, addressing in turn Decodification, Linearity correction (ISO dependent), Flat field/Vignetting, Spectral characterization of the channels, Astrometric calibration/georeferencing, Photometric calibration (stars)/Radiometric correction (settings correction - by exposure time, ISO, lens transmittance, etc) and Transmittance correction (window transmittance, atmospheric correction). We provide an example of the application of this processing method to an image of Spain.
RGB photometric calibration of 15 million Gaia stars
(Monthly notices of the Royal Astronomical Society, 2021) Cardiel López, Nicolás; Zamorano Calvo, Jaime; Bará, Salvador; Sánchez de Miguel, Alejandro; Cabello González, Cristina; Gallego Maestro, Jesús; García, Lucía; González, Rafael; Izquierdo Gómez, Jaime; Pascual Ramírez, Sergio; Sánchez Penim, Ainhoa; Tapia Ayuga, Carlos
Although the use of RGB photometry has exploded in the last decades due to the advent of high-quality and inexpensive digital cameras equipped with Bayer-like color filter systems, there is surprisingly no catalogue of bright stars that can be used for calibration purposes. Since due to their excessive brightness, accurate enough spectrophotometric measurements of bright stars typically cannot be performed with modern large telescopes, we have employed historical 13-color medium-narrow-band photometric data, gathered with quite reliable photomultipliers, to fit the spectrum of 1346 bright stars using stellar atmosphere models. This not only constitutes a useful compilation of bright spectrophotometric standards well spread in the celestial sphere, the UCM library of spectrophotometric spectra, but allows the generation of a catalogue of reference RGB magnitudes, with typical random uncertainties ∼ 0.01 mag. For that purpose, we have defined a new set of spectral sensitivity curves, computed as the median of 28 sets of empirical sensitivity curves from the literature, that can be used to establish a standard RGB photometric system. Conversions between RGB magnitudes computed with any of these sets of empirical RGB curves and those determined with the new standard photometric system are provided. Even though particular RGB measurements from single cameras are not expected to provide extremely accurate photometric data, the repeatability and multiplicity of observations will allow access to a large amount of exploitable data in many astronomical fields, such as the detailed monitoring of light pollution and its impact on the night sky brightness, or the study of meteors, solar system bodies, variable stars, and transient objects. In addition, the RGB magnitudes presented here make the sky an accessible and free laboratory for the calibration of the cameras themselves.
Mapping the melatonin suppression, star light and induced photosynthesis indices with the LANcube
(Remote Sensing, 2020) Aubé, Martin; Marseille, Charles; Farkouh, Amar; Dufour, Adam; Simoneau, Alexandre; Zamorano Calvo, Jaime; Roby, Johanne; Tapia Ayuga, Carlos
Increased exposure to artificial light at night can affect human health including disruption of melatonin production and circadian rhythms which can extend to increased risks of hormonal cancers and other serious diseases. In addition, multiple negative impacts on fauna and flora are well documented, and it is a matter of fact that artificial light at night is a nuisance for ground-based astronomy. These impacts are frequently linked to the colour of the light or more specifically to its spectral content. Artificial light at night is often mapped by using spaceborne sensors, but most of them are panchromatic and thus insensitive to the colour. In this paper, we suggest a method that allows high-resolution mapping of the artificial light at night by using ground-based measurements with the LANcube system. The newly developed device separates the light detected in four bands (Red, Green, Blue and Clear) and provides this information for six faces of a cube. We found relationships between the LANcube’s colour ratios and (1) the Melatonin Suppression Index, (2) the StarLight Index and (3) the Induced Photosynthesis Index. We show how such relationships combined with data acquisition from a LANcube positioned on the top of a car can be used to produce spectral indices maps of a whole city in a few hours.
Effects of the COVID-19 lockdown on urban light emissions: ground and satellite comparison
(Remote Sensing, 2021) Bustamante-Calabria, Máximo; Sánchez de Miguel, Alejandro; Martín-Ruiz, Susana; Ortiz, Jose-Luis; Vílchez, José M.; Pelegrina, Alicia; García, Antonio; Zamorano Calvo, Jaime; Bennie, Jonathan; Gaston, Kevin J.
'Lockdown' periods in response to COVID-19 have provided a unique opportunity to study the impacts of economic activity on environmental pollution (e.g., NO2, aerosols, noise, light). The effects on NO2 and aerosols have been very noticeable and readily demonstrated, but that on light pollution has proven challenging to determine. The main reason for this difficulty is that the primary source of nighttime satellite imagery of the earth is the SNPP-VIIRS/DNB instrument, which acquires data late at night after most human nocturnal activity has already occurred and much associated lighting has been turned off. Here, to analyze the effect of lockdown on urban light emissions, we use ground and satellite data for Granada, Spain, during the COVID-19 induced confinement of the city's population from 14 March until 31 May 2020. We find a clear decrease in light pollution due both to a decrease in light emissions from the city and to a decrease in anthropogenic aerosol content in the atmosphere which resulted in less light being scattered. A clear correlation between the abundance of PM10 particles and sky brightness is observed, such that the more polluted the atmosphere the brighter the urban night sky. An empirical expression is determined that relates PM10 particle abundance and sky brightness at three different wavelength bands.
The nature of the diffuse light near cities detected in nighttime satellite imagery
(Scientific reports, 2020) Sánchez de Miguel, Alejandro; Kyba, Christopher C. M.; Zamorano Calvo, Jaime; Gallego Maestro, Jesús; Gaston, Kevin J.
Difuse glow has been observed around brightly lit cities in nighttime satellite imagery since at least the frst publication of large scale maps in the late 1990s. In the literature, this has often been assumed to be an error related to the sensor, and referred to as “blooming”, presumably in relation to the efect that can occur when using a CCD to photograph a bright light source. Here we show that the efect seen on the DMSP/OLS, SNPP/VIIRS-DNB and ISS is not only instrumental, but in fact represents a real detection of light scattered by the atmosphere. Data from the Universidad Complutense Madrid sky brightness survey are compared to nighttime imagery from multiple sensors with difering spatial resolutions, and found to be strongly correlated. These results suggest that it should be possible for a future space-based imaging radiometer to monitor changes in the difuse artifcial skyglow of cities.
Evolution of brightness and color of the night sky in Madrid
(Remote Sensing, 2021) Robles, José; Zamorano Calvo, Jaime; Pascual Ramírez, Sergio; Sánchez de Miguel, Alejandro; Gallego Maestro, Jesús; Gaston, Kevin J.
Major schemes to replace other streetlight technologies with Light-Emitting Diode (LED) lamps are being undertaken across much of the world. This is predicted to have important consequences for nighttime sky brightness and color. Here, we report the results of a long-term study of these characteristics focused on the skies above Madrid. The sky brightness and color monitoring station at Universidad Complutense de Madrid (inside the city) collected Johnson B, V, and R sky brightness data, Sky Quality Meter (SQM), and Telescope Encoder Sky Sensor-WiFi (TESS-W) broadband photometry throughout the night, every night between 2010–2020. Our analysis includes a data filtering process that can be used with other similar sky brightness monitoring data. Major changes in sky brightness and color took place during 2015–2016, when a sizable fraction of the streetlamps in Madrid changed from High-Pressure Sodium (HPS) to LEDs. The sky brightness detected in the Johnson B band darkened by 14% from 2011 to 2015 and brightened by 32% from 2015 to 2019.
Magnitude to luminance conversions and visual brightness of the night sky
(Monthly notices of The Royal Astronomical Society, 2020) Bará, Salvador; Aubé, Martin; Barentine, John; Zamorano Calvo, Jaime
The visual brightness of the night sky is not a single-valued function of its brightness in other photometric bands, because the transformations between photometric systems depend on the spectral power distribution of the skyglow. We analyze the transformation between the night sky brightness in the Johnson-Cousins V band (mV, measured in magnitudes per square arcsecond, mpsas) and its visual luminance (L, in SI units cd m^(-2) ) for observers with photopic and scotopic adaptation, in terms of the spectral power distribution of the incident light. We calculate the zero-point luminances for a set of skyglow spectra recorded at different places in the world, including strongly light-polluted locations and sites with nearly pristine natural dark skies. The photopic skyglow luminance corresponding to m_(v)=0.00 mpsas is found to vary between 1.11-1.34 x 10^(5) cd m^(-2) if m_(v) is reported in the absolute (AB) magnitude scale, and between 1.18-1.43 x 10^(5) cd m^(-2) if a Vega scale for m_(v) is used instead. The photopic luminance for m_(v)=22.0 mpsas is correspondingly comprised between 176 and 213 µcd m^(-2) (AB), or 187 and 227 µcd m^(-2) (Vega). These constants tend to decrease for increasing correlated color temperatures (CCT). The photopic zero-point luminances are generally higher than the ones expected for blackbody radiation of comparable CCT. The scotopic-to-photopic luminance ratio (S/P) for our spectral dataset varies from 0.8 to 2.5. Under scotopic adaptation the dependence of the zero-point luminances with the CCT, and their values relative to blackbody radiation, are reversed with respect to photopic ones.