Photo taken on March 29, 2017 shows a captive balloon floating in air at a testing ground in Liu'an, east China's Anhui Province. The captive balloon is an air platform carrying various devices, such as warning radar, video surveillance equipment, fog detection devices, communication relay devices and imaging equipment. The balloon is expected to play a role in precaution and detection, environmental surveillance, security and protection monitoring. (Xinhua/Guo Chen)
