Measuring Light Pollution with Fisheye Lens Imagery from A Moving Boat – A Proof of Concept

Abstract

Near all-sky imaging photometry was performed from a boat on the Gulf of Aqaba to measure the night sky brightness in a coastal environment. The boat was not anchored, and therefore drifted and rocked. The camera was mounted on a tripod without any inertia/motion stabilization. A commercial digital single lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400, with the exposure time varied between 0.5 s and 5 s. We find that despite movement of the vessel the measurements produce quantitatively comparable results apart from saturation effects. We discuss the potential and limitations of this method for mapping light pollution in marine and freshwater systems. This work represents the proof of concept that all-sky photometry with a commercial DSLR camera is a viable tool to determine light pollution in an ecological context from a moving boat.

How dark is a river? Artificial light at night in aquatic systems and the need for comprehensive night‐time light measurements

“…The directionality can be measured with cameras equipped with wide field optics, like fisheye lenses. Commercial DSLR cameras provide high‐resolution raw images in three spectral channels and Jechow, Kolláth, Lerner, et al () proved the applicability of such a system on a moving boat.…”

“…The directionality can be measured with cameras equipped with wide field optics, like fisheye lenses. Commercial DSLR cameras provide high-resolution raw images in three spectral channels and Jechow, Kolláth, Lerner, et al (2017a) proved the applicability of such a system on a moving boat. Figure 9a shows a sketch of the proposed platform setup using one hyperspectral sensor measuring spectral irradiance and three multispectral DSLR cameras with 180 fisheye lenses measuring the spectral radiance in three bands (RGB).…”

“…The camera measures the spatially resolved radiance over the whole hemisphere in three spectral bands in one image by a single measurement. The method is therefore quick, can provide many measurements per timeframe (Jechow, ; Jechow et al, ), is easily applicable during field work (Jechow et al, ; Jechow, Kolláth, Ribas, et al, ; Jechow, Kyba, & Hölker, ), and can help to extract the city emission function crucial for skyglow models (Kocifaj, Solano‐Lamphar, & Videen, ). Figure shows a false color luminance map acquired with this method at Pape Nature Reserve at the Baltic Sea (same location as Figure ).…”

“…They used a commercial DSLR camera with a fisheye lens to acquire all-sky and vertical plane hemispherical images and a small single-channel SQM photometer for long-term measurements. Jechow, Kolláth, Lerner, et al (2017a) later showed that the DSLR method can also be used from a moving boat, taking measurements in the Gulf of Eilat near some measurement spots of Tamir et al (2017). Ges, Bará, García-Gil, Zamorano, and Masana (2018) compared the predictions of the skyglow model by Falchi et al (2016) to SQM observations made during a transect with a boat from Barcelona, Spain, out to sea.…”

“…Thus, a measurement in the horizontal plane appears most straightforward. For larger water bodies and especially rivers, transects or multipoint measurements are recommended (Ges et al, 2018;Jechow, Kolláth, Lerner, et al, 2017a;Ludvigsen et al, 2018;Tamir et al, 2017). Single-point measurements on multiple water bodies like performed by Secondi et al (2017) are also reasonable especially in their context of small water bodies like ponds.…”