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ISS nocturnal images as a scienti c tool against Light Pollution: Flux calibration and colors

Authors:
Alejandro Sanchez de Miguel at Complutense University of Madrid
Alejandro Sanchez de Miguel
J. Zamorano
J. Zamorano
J. Zamorano
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Sergio Pascual at Complutense University of Madrid
Sergio Pascual
M. López Cayuela
M. López Cayuela
M. López Cayuela
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Abstract and Figures

The potential of the pictures of the Earth taken at night from the International Space Station (ISS) with a Nikon D3s digital camera to fight against light pollution is shown. We show that RAW pictures should be used to obtain fluxes. We have developed a method to perform absolute photometric calibration measuring fluxes of the stars recorded in the pictures and also calibrated sources at earth.
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ISS nocturnal images as a scientific tool against
Light Pollution: Flux calibration and colors
A. S´anchez de Miguel1, J. Zamorano1, S. Pascual1, M. L´opez Cayuela1,
F. Oca˜na1, P. Challupner1, J. G´omez Casta˜no1, A. Fern´andez-Renau2,
J.A. G´omez2, and E. de Miguel2
1Departamento de Astrof´ısica y CC. de la Atm´osfera, Universidad Complutense de Madrid
2Remote Sensing Laboratory, INTA
Abstract
The potential of the pictures of the Earth taken at night from the International Space
Station (ISS) with a Nikon D3s digital camera to fight against light pollution is shown. We
show that RAW pictures should be used to obtain fluxes. We have developed a method
to perform absolute photometric calibration measuring fluxes of the stars recorded in the
pictures and also calibrated sources at earth.
1 Light Pollution studies with images of the Earth at night
Light pollution (the introduction by humans, directly or indirectly, of artificial light into the
environment) is a major issue worldwide, especially in urban areas. It increases the sky glow
and prevents citizens from observing a dark starry sky. This is why astronomers are among
the worst affected by urban sky glow [1] and they were probably the first to fight against
light pollution. One of the key parameters to select a site to build an observatory is the night
sky brightness because some astronomical research could not be performed with the required
quality if the sky is not dark enough. Thus, it is not a surprise to find that the astronomical
observatories are located in remote areas far from light pollution sources and efforts are made
to prevent the increase of light pollution in the observatory surrounding areas.
The brightness of the night sky measured in some place is related to the amount of
light emitted to the sky in an extended area around. Artificial lighting is easily registered
from space. The main data input has been the images obtained with sensors onboard the US
Air Force Defense Meteorological Satellite Program (DMSP) Operational Linescan System
(OLS) developed to map human settlements.
Astronauts aboard the International Space Station (ISS) are publishing pictures of the
Earth taken from the space. These beautiful pictures are freely available and can be obtained
A. S´anchez de Miguel & J. Zamorano et al. 917
Figure 1: Typical spectra of two different lamps with RGB response of a Nikon camera.
Lamp spectra from http://www.ngdc.noaa.gov/dmsp/spectra.html.
from a repository maintained by NASA on Internet. A portion of the images is being taken
at night and some of them show a network of light of the big cities. This illumination comes
mainly from public lighting of the streets and buildings. The intensity in the picture is
related to the light being sent to the space and bright light reveals an excess or bad use of
lighting. These images speak by themselves and are very useful to draw public attention
of the problem. The intensity in the picture is related to the light being sent to the space
and bright light reveals an excess or bad use of lighting. The extension and intensity of this
emission put in evidence that light pollution is, besides a worry for astronomers, a global
problem that is damaging our environment.
2 Digital pictures from ISS versus DMSP-OLS satellite data
Radiance calibrated, single spectral band (0.47 −0.95 micron) DMSP-OLS satellite images
of the Earth have been used up to now. They provide full coverage of the Earth at night
using a photomultiplier detector with 10−5
−10−9(W cm−2sr−1micron−1). The spatial scale
ranges from 0.55 to 2.7 km/pixel [2]. Since the satellite mission main goal was to detect the
extend of human settlements, most urban areas are saturated. Pictures taken by astronauts
aboard the International Space Station (ISS) with a Nikon D3s digital camera could provide
better spatial resolution (in the range 1 m −1 km/pixel) and also RGB color information.
Since the detector is a linear CMOS, pictures can be calibrated in radiance.
The three RGB channel images obtained after splitting the RAW pictures is used to get
information on lighting type. Lamp type is defined by its spectrum (Fig. 1; [3]). The bluer
the lamp the most effective is scattering and the light pollution reaches far away. Althought
JPEG files could be used to get an idea of the lighting type, JPEG compression lost intensity
and color information. To perform any scientific study using pictures one should use the
RAW uncompressed images.
918 ISS nocturnal images as a scientific tool against Light Pollution
Figure 2: Spectrum of a typical High Pressure Sodium Lamp with the observed (black open
points) and expected (red dots) data from INTA-AHS hyperspectral camera superinposed.
The lamp type is unambigously identified with this airborne observation.
3 Absolute photometric calibration of nocturnal ISS pictures
A previous step before using the pictures to obtain fluxes emitted to the space is photometric
calibration. On the one hand we have performed absolute calibration using sources at Earth.
We have compared radiance calibrated images of Madrid at night taken with an airborne
spectral radiometer with the RAW file of a nocturnal image of Madrid obtained from ISS.
The selected area is lighted by isolated lamps of sodium (HPS) whose spectrum matched that
obtained with the hyperspectral data (see Fig. 2).
On the other hand we have calibrated using fluxes of standard stars (the astronomers
way) measured on a wide angle picture taken from ISS that contains also the Iberian peninsula
at night. Since the spectral response of the Gchannel of DSLR cameras is similar to the
astronomical Johnson Vband, we have plotted in Fig. 3 integrated star counts in G channel
versus tabulated fluxes of the stars in Johnson V. The calibration factor is obtained from
the tight linear relationship that we fit without the need of a color term.
We have shown that digital pictures from ISS can be calibrated using sources at Earth
and stars as calibrators. The RGB color information provides information on lighting type
but RAW files shold be used.
The calibrated nocturnal images of the Earth at night taken from ISS1will provide a
measure of light pollution both on radiance and color. Information on lighting efficiency will
be obtained when compared with energy consumption data and the type of lamps.
1The International Space Station (ISS) is a co-operative program between space agencies: National Aero-
nautics and Space Agency (NASA) from United States, the Russian Federal Space Agency (Roscosmos),
Canadian Space Agency (CSA), European Space Agency (ESA) and Japan Aerospace Exploration Agency
(JAXA) for the joint development, operation and utilization of a permanently inhabited Space Station in low
Earth orbit.
A. S´anchez de Miguel & J. Zamorano et al. 919
Figure 3: Stellar fluxes for the stars measured in the ISS picture (green Gchannel) versus
the Johnson Vband magnitude. The liear fit is so goog that no color term is needed.
Acknowledgments
We acknowledge the the Image Science and Analysis Laboratory NASA-Johnson Space Cen-
ter “The Gateway to Astronaut Photography of Earth” for providing the ISS original im-
ages.This research has been carried out in the Laboratorio de Investigacin Cient´ıfica Avanzada
(LICA) of the Moncloa Campus of International Excellence(CEI)(UCM-UPM). We acknowl-
edge support from the Spanish Programa Nacional de Astronom´ıa y Astrof´ısica under grant
AYA2009-10368. Partially funded by the Spanish MICINN under the Consolider-Ingenio
2010 Program grant CSD2006-00070: First Science with the GTC.
References
[1] Falchi, F. & Cinzano, P. 2000, MmSAI, 71, 139
[2] Elvidge, C.D., Baugh, K.E., et al. 1999, Remote Sensing of Environment 68, 977
[3] Elvidge, C.D. & Keith, D. 2010, Sensors 10, 3961
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... The cameras take images through the ISS windows, and this introduces an unknown attenuation factor. Radiance calibration of the camera/lens/window system could be obtained via stellar photometry [25,26]. The windows potentially set a limit on the best possible image resolution and prevent imaging when the Sun shines on the window. ...
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... The focal lengths of the Nikon DSLR cameras in this study were 180 mm and 400 mm, respectively. These sensors, mounted on a specially designed device to compensate for the movement of the ISS, can take multi-spectral images in visible wavelengths, making it capable of detecting ground features under faint illumination from space [39][40][41][42]. In addition, a Hasselblad L1D-20c camera was mounted on a DJI MAVIC2 Pro UAV, with a focal length of 35 mm. ...
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... Calibrated DSLR images from the ISS have been used for epidemiological studies (Garcia-Saenz et al., 2018), energy use and lighting technology studies (Kyba et al., 2015a,b), environmental impact studies (Pauwels et al., 2019) and ecological studies (Mazor et al., 2013). In some cases, researchers have used ISS images without using, or at least without explaining, a radiometric calibration; however, Sánchez de Miguel et al. (2013b) have developed a method to perform an absolute photometric calibration of ISS photos. Two companies currently provide calibration on demand of ISS images: www.noktosat.com ...
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... At larger nadir angles, the reflection of lights from the street surface begins to be screened by buildings. In some high-incident angle photographs from the International Space Station [30], the visibility of streets in one direction may nearly or completely disappear. In addition to causing variability in the radiance of a surface parcel, this effect also means that the sensitivity of satellite sensors to different sources of radiation (e.g., illuminated signs vs. parking lot lighting) depends on imaging angle. ...
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With the growing size and use of night light time series from the Visible Infrared Imaging Radiometer Suite Day/Night Band (DNB), it is important to understand the stability of the dataset. All satellites observe differences in pixel values during repeat observations. In the case of night light data, these changes can be due to both environmental effects and changes in light emission. Here we examine the stability of individual locations of particular large scale light sources (e.g., airports and prisons) in the monthly composites of DNB data from April 2012 to September 2017. The radiances for individual pixels of most large light emitters are approximately normally distributed, with a standard deviation of typically 15–20% of the mean. Greenhouses and flares, however, are not stable sources. We observe geospatial autocorrelation in the monthly variations for nearby sites, while the correlation for sites separated by large distances is small. This suggests that local factors contribute most to the variation in the pixel radiances and furthermore that averaging radiances over large areas will reduce the total variation. A better understanding of the causes of temporal variation would improve the sensitivity of DNB to lighting changes.
View
... At larger nadir angles, the reflection of lights from the street surface begins to be screened by buildings. In some high-incident angle photographs from the International Space Station [30], the visibility of streets in one direction may nearly or completely disappear. In addition to causing variability in the radiance of a surface parcel, this effect also means that the sensitivity of satellite sensors to different sources of radiation (e.g. ...
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Preprint
Full-text available
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With the growing size and use of night lights time series from the Visible Infrared Imaging Radiometer Suite Day/Night Band (DNB), it is important to understand the stability of the dataset. All satellites observe differences in pixel values during repeat observations. In the case of night lights data, these changes can be due to both environmental effects and changes in light emission. Here we examine the stability of individual locations of particular large scale light sources (e.g. airports, prisons) in the monthly composites of DNB data from April 2012 to September 2017. The radiances for individual pixels of most large light emitters are approximately normally distributed, with a standard deviation of typically 15-20% of the mean. We observe geospatial autocorrelation in the monthly variations for nearby sites, while the correlation for sites separated by large distances is small. This suggests that local factors contribute most to the variation in the pixel radiances, and furthermore that averaging radiances over large areas will reduce the total variation. A better understanding of the causes of temporal variation would improve the sensitivity of DNB to lighting changes.
View
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Image classification of night time images detected from the International Space Station
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Right now there are around 1.800.000 images at the Johnson Space Center database (The Gateway of the Astronauts) and around of 1.200.000 images came from the ISS (date 20/02/2014). Although, the classified images are a number much smaller and there no archive of georeferenced images. There is a project to classify the day time images (Image detective). But, the techniques that are used in this project are not use full for the classification of night time images. The reason is that the patterns on earth are not the same during the day and night. That’s why it’s need it other technique to classify night time images.
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  • Jan 1999
  • REMOTE SENS ENVIRON
  • 977
  • C D Elvidge
  • K E Baugh
Elvidge, C.D., Baugh, K.E., et al. 1999, Remote Sensing of Environment 68, 977
  • Jan 2010
  • SENSORS-BASEL
  • 3961
  • C D Elvidge
  • D Keith
Elvidge, C.D. & Keith, D. 2010, Sensors 10, 3961
  • Jan 2000
  • 139
  • F Falchi
  • P Cinzano
Falchi, F. & Cinzano, P. 2000, MmSAI, 71, 139