They found that light output at night decreased across the board. And the pattern of decreases fit the pattern of ethnic cleaning already documented by earlier researchers.
The full article is here. I can not help but say "Amen" to their opening sentence:
Geographers and social scientists find it increasingly difficult to intervene in debates about vital matters of public interest, such as the Iraq war, because of the ideological polarization and lack of respect for empirical analysis that have afflicted US politics in recent years.
The key results:
In other words, the period of the surge coincides with a decline in the nighttime light of the city after an increase following the invasion and before the onset of the surge [...] This was not just temporary, and thus cannot be put down to military operations disrupting supplies, because the end date of 16 December 2007 is well after the most intensive military sweeps in the city.
pattern of [lightning intensity] declines correlates closely with the map of ethno-sectarian violence and neighborhood ethnic cleansing
They clinch their argument with this comparison of illumination changes in other Iraqi cities that experienced neither military surge nor ethnic cleansing:
Over the same period, there was no significant decline in nighttime light imagery in four other large cities in Iraq (table 3). Most importantly, during the period of the surge, Mosul, Tikrit, and Karbala all had significant increases in nighttime lights between March 2006 and December 2007.
So what role did the surge play?
I would imagine that it was not just the walls we built to wall off ethnically-cleansed neighborhoods, it was also our paying the bad guys to stop shooting at us.Our primary conclusion must be that to the extent that the so-called surge is involved at all in what has happened, it has helped to seal off neighborhoods from one another once they have become ethnically homogenized.