Reducing Variability and Removing Natural Light from Nighttime Satellite Imagery: A Case Study Using the VIIRS DNB.

Jacqueline Coesfeld,Helga U Kuechly,Christopher C M Kyba,Theres Kuester

doi:10.3390/s20113287

Abstract

Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application.

Highlights

Space-based observations of the visible light emissions of Earth at night are a useful indicator of human activity [1,2]
Away from these bright areas, variations in natural light make confident detection of artificial light more challenging, especially for sensors with large ground footprints. This poses a problem for monitoring changes in lighting at regional and national scales (e.g., [5,6]), because small but spatially correlated changes in natural light over large areas can outweigh the signal from lit areas, and most land typically consists of unlit areas, even in brightly lit countries
We present a method for correcting for natural light over large areas, in order to improve the sensitivity of the sensor to faint artificial light sources and changes in sum of lights at large spatial scales

Summary

Introduction

Space-based observations of the visible light emissions of Earth at night are a useful indicator of human activity [1,2]. Near brightly lit infrastructure and especially large cities, the signal of artificial light is much larger than the background natural light (reflected starlight and airglow [3,4]) Away from these bright areas, variations in natural light make confident detection of artificial light more challenging, especially for sensors with large ground footprints. This poses a problem for monitoring changes in lighting at regional and national scales (e.g., [5,6]), because small but spatially correlated changes in natural light over large areas can outweigh the signal from lit areas, and most land typically consists of unlit areas (e.g., agricultural lands, forests, lakes [7,8]), even in brightly lit countries. We focus on data from the Visible Infrared Imaging Radiometer Suite Day-Night Band (DNB), but in principle the method could be used for other night light observing sensors

Methods

Results

Discussion

Conclusion