Remote sensing of night lights: a review and an outlook for the future

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordRemote sensing of night light emissions in the visible band offers a unique opportunity to directly observe human activity from space. This has allowed a host of applications including mapping urban areas, estimating population and GDP, monitoring disasters and conflicts. More recently, remotely sensed night lights data have found use in understanding the environmental impacts of light emissions (light pollution), including their impacts on human health. In this review, we outline the historical development of night-time optical sensors up to the current state of the art sensors, highlight various applications of night light data, discuss the special challenges associated with remote sensing of night lights with a focus on the limitations of current sensors, and provide an outlook for the future of remote sensing of night lights. While the paper mainly focuses on space borne remote sensing, ground based sensing of night-time brightness for studies on astronomical and ecological light pollution, as well as for calibration and validation of space borne data, are also discussed. Although the development of night light sensors lags behind day-time sensors, we demonstrate that the field is in a stage of rapid development. The worldwide transition to LED lights poses a particular challenge for remote sensing of night lights, and strongly highlights the need for a new generation of space borne night lights instruments. This work shows that future sensors are needed to monitor temporal changes during the night (for example from a geostationary platform or constellation of satellites), and to better understand the angular patterns of light emission (roughly analogous to the BRDF in daylight sensing). Perhaps most importantly, we make the case that higher spatial resolution and multispectral sensors covering the range from blue to NIR are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.European Union Horizon 2020Helmholtz AssociationNatural Environment Research Council (NERC)Chinese Academy of ScienceLeibniz AssociationIGB Leibniz Institut

Parameterisation of underwater light fields in the Arctic Ocean and associated impact on biological processes

Accurate characterisation of underwater light is an integral component in modelling the dynamics of marine ecosystems, particularly primary production and animal migration patterns. Existing methods of estimating light fields either rely on satellite data, in situ measurements or radiative transfer models that only operate when the sun is above the horizon. These methods are of limited use in Arctic waters, particular during Polar Night due to extended periods of extremely low light levels and prolonged periods when the sun remains below horizon. Estimating underwater light in the region is further hindered by the optical complexities introduced by widespread and seasonally varying snow and ice cover, and many current ecosystem models either simplify these under-ice light fields or excluding them entirely, potentially disregarding biologically significant light levels. This work presents a model of spectrally resolved underwater light that demonstrates the ability to simulate light levels over the full year into the period of Polar Night and is validated by in situ data. Downwelling spectral irradiance in the photosynthetically active radiation (PAR, 400 – 700nm) range is calculated in both open and ice-covered water columns and includes multiple reflection amplification effects of above surface irradiance between snow and cloud. Validation of downwelling broadband irradiance in open waters shows a mean absolute error of 20% of above surface irradiance to penetrate through thin ice ( 20% of total productivity. In open waters, calculations of primary production were found to be highly sensitive to the parameterisation of the diffuse attenuation coefficient of light. Comparing the results of various light field models designed for use in the Arctic showed a factor 12 difference in calculated water column productivity when using output irradiances to drive a model of primary production. Comparing modelled underwater spectral irradiance to the diel vertical migration (DVM) patterns of Arctic krill in early spring 2018 showed that the spectral distribution of light may act as a trigger mechanism for DVM. Results appear to indicate that although diurnal changes in the magnitude of downwelling irradiance largely drives bulk migration patterns, the population of krill also responded to changes in the ratio of green to blue light, driven by changes in lunar and solar elevations, preferring to occupy regions of the water column with a dominant blue colour of underwater light.Accurate characterisation of underwater light is an integral component in modelling the dynamics of marine ecosystems, particularly primary production and animal migration patterns. Existing methods of estimating light fields either rely on satellite data, in situ measurements or radiative transfer models that only operate when the sun is above the horizon. These methods are of limited use in Arctic waters, particular during Polar Night due to extended periods of extremely low light levels and prolonged periods when the sun remains below horizon. Estimating underwater light in the region is further hindered by the optical complexities introduced by widespread and seasonally varying snow and ice cover, and many current ecosystem models either simplify these under-ice light fields or excluding them entirely, potentially disregarding biologically significant light levels. This work presents a model of spectrally resolved underwater light that demonstrates the ability to simulate light levels over the full year into the period of Polar Night and is validated by in situ data. Downwelling spectral irradiance in the photosynthetically active radiation (PAR, 400 – 700nm) range is calculated in both open and ice-covered water columns and includes multiple reflection amplification effects of above surface irradiance between snow and cloud. Validation of downwelling broadband irradiance in open waters shows a mean absolute error of 20% of above surface irradiance to penetrate through thin ice ( 20% of total productivity. In open waters, calculations of primary production were found to be highly sensitive to the parameterisation of the diffuse attenuation coefficient of light. Comparing the results of various light field models designed for use in the Arctic showed a factor 12 difference in calculated water column productivity when using output irradiances to drive a model of primary production. Comparing modelled underwater spectral irradiance to the diel vertical migration (DVM) patterns of Arctic krill in early spring 2018 showed that the spectral distribution of light may act as a trigger mechanism for DVM. Results appear to indicate that although diurnal changes in the magnitude of downwelling irradiance largely drives bulk migration patterns, the population of krill also responded to changes in the ratio of green to blue light, driven by changes in lunar and solar elevations, preferring to occupy regions of the water column with a dominant blue colour of underwater light

CIRA annual report FY 2014/2015

Reporting period July 1, 2014-March 31, 2015