Aladdin's Magic Lamp: Developing Methods for Calibration and Geolocation Accuracy Assessment of the DMSP OLS

Nighttime satellite imagery from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) has a unique capability to observe nocturnal light emissions from sources including cities, wild fires, and gas flares. Data from the DMSP OLS is used in a wide range of studies including mapping urban areas, estimating informal economies, and estimating urban populations. Given the extensive and increasing list of applications a repeatable method for assessing geolocation accuracy, performing inter-calibration, and defining the minimum detectable brightness would be beneficial. An array of portable lights was designed and taken to multiple field sites known to have no other light sources. The lights were operated during nighttime overpasses by the DMSP OLS and observed in the imagery. A first estimate of the minimum detectable brightness is presented based on the field experiments conducted. An assessment of the geolocation accuracy was performed by measuring the distance between the GPS measured location of the lights and the observed location in the imagery. A systematic shift was observed and the mean distance was measured at 2.9km. A method for in situ radiance calibration of the DMSP OLS using a ground based light source as an active target is presented. The wattage of light used by the active target strongly correlates with the signal measured by the DMSP OLS. This approach can be used to enhance our ability to make inter-temporal and inter-satellite comparisons of DMSP OLS imagery. Exploring the possibility of establishing a permanent active target for the calibration of nocturnal imaging systems is recommended. The methods used to assess the minimum detectable brightness, assess the geolocation accuracy, and build inter-calibration models lay the ground work for assessing the energy expended on light emitted into the sky at night. An estimate of the total energy consumed to light the night sky globally is presented.

Disquieting Discretion: Race, Geography & the Colorado Death Penalty in the First Decade of the Twenty-First Century

This Article demonstrates through original statistical research that prosecutors in Colorado were more likely to seek the death penalty against minority defendants than against white defendants. Moreover, defendants in Colorado’s Eighteenth Judicial District were more likely to face a death prosecution than defendants elsewhere in the state. Our empirical analysis demonstrates that even when one controls for the differential rates at which different groups commit statutorily death-eligible murders, non-white defendants and defendants in the Eighteenth Judicial District were still more likely than others to face a death penalty prosecution. Even when the heinousness of the crime is accounted for, the race of the accused and the place of the crime are statistically significant predictors of whether prosecutors will seek the death penalty. We discuss the implications of this disparate impact on the constitutionality of Colorado’s death penalty regime, concluding that the Colorado statute does not meet the dictates of the Eighth Amendment to the Constitution.