Three successive overhead snapshots by orbiting civilian satellites provide the best, unclassified, big-picture view to date of the more than two-month-old battle for one of Syria’s key cities. Since late July troops loyal to embattled Syrian president Bashar Al Assad have waged a relentless air and ground campaign against rebels in Aleppo, a city of two million near the border with Turkey.

In the satellite photos, a tank appears then disappears, leaving a ruined building in its wake. Scorch marks, craters and debris chart the progression of brutal urban fighting. Makeshift defensive positions proliferate as the assault escalates.

These details and more are visible in commercial satellite images dated Aug. 9 and 23. Researchers  at the American Association for the Advancement of Science, based in Washington, D.C., compared the August snapshots to each other and to an October 2011 Google Earth image in order to understand the scale and evolution of the fighting.

The images “largely corroborate on-the-ground reports of heavy artillery assaults by the Syrian army moving through neighborhoods,” Susan Wolfinbarger, an AAAS senior program associate, said in a statement.

AAAS’ satellite-based assessment of nearly 200 square kilometers of dense urban terrain belies the growing power of independent observers to monitor civil fighting — and the paucity of on-the-ground reporting in embattled Aleppo, 18 months into Syria’s bloody civil war, which has killed 17,000 people including nearly 12,000 non-combatants.

Of the civilian satellites AAAS had access to, DigitalGlobe’s Quickbird-2 was the first to photograph Aleppo on Aug. 9. GeoEye’s IKONOS satellite followed two weeks later.

The first pass spotted what appeared to be a heavy armored vehicle in the city’s Ard As Sabbagh district. “The vehicle was no longer present by Aug. 23, and most of a nearby building had been destroyed,” Wolfinbarger noted.

“In the northern district of Ayn At Tal, 84 makeshift structures appeared to have been burned in the parking lot of an industrial facility,” Wolfinbarger added. “Scorch marks also were visible on buildings and craters had appeared in the streets.”

Researchers counted 102 “intact fortifications” in Aleppo and 72 “locations where roadblocks had been dismantled during the timeframe of the study,” Wolfinbarger wrote.

Aleppo is not the first conflict zone to get the remote-sensing treatment. In 2007 AAAS used commercial satellite imagery to track human rights abuses in Burma. Three years later the association’s analysts helped assess, from above, the  earthquake devastation in Haiti. Actor George Clooney’s Satellite Sentinel Project has spied on repression in Sudan, eliciting laughable threats from dictator Omar Al Bashir.

And in July, civilian satellites spotted Al Assad’s fleet of drone aircraft.

However wide, the overhead view is far from perfect. “AAAS emphasized that its image analysis was limited by the high-population density of Aleppo … and shadows cast by many tall buildings,” Wolfinbarger wrote. “In the Salaheddine neighborhood, for instance, smoke could be seen above an urban area too tightly packed to reveal street-level changes.”

But a sometimes murky lens is better than no lens at all when it comes to Syria’s grinding civil war.