With the help of satellite remote sensing imagery, scientists at the Institute of Remote Sensing Applications (IRSA) re-examined the Pearl River recently. Study shows that the accurate length of this river is 2320 kilometers, with a drainage basin area of 446,768 square kilometers. Geographically the Pearl River is the third longest river of China, and the second largest in terms of annual flow capacity.

The study corrects the commonly-used data about the length and drainage basin area of this river. For example, in some literatures the data were reported to be 2214 kilometers and 453,700 square meters respectively.

The study verifies the 1980s record that the source of the Pearl River is originated from a cave on a high cliff in a deep valley, at  the foot of east side of Maxiong Mountain, Zhanyi County in Yunnan Province, which is located in southwest China. But ancient records  were inconsistent with this. Documented source investigation of this river can be traced back to late Ming Dynasty (1368-1644), while XU Xiake, a geographer who travelled throughout China for more than 30 years and documented his travels extensively, made two expeditions into Zhanyi County for examining its genuine source. XU’s discovery challenged official geographical records of Yuan Dynasty (1279-1368) and it is close to the records nowadays.

The investigation into Pearl River belongs to a grand project which was launched in 1999, designed to re-examine the sources and lengths of major rivers on the earth. LIU Shaochuang, a researcher at IRSA, is the initiator of this project.

This project was created  with the consideration that the length and source of one river is important basic geographical information. More than that, pinpointing the source is regarded as great geographic discovery. But in the old days the length and source of one river were so different in various textbooks, atlases and encyclopedias, that the reliable information about a river turns out to be a mystery due to inhospitable environment and technological limitations.

Combining the analysis of satellite remote sensing images with field investigation into the river source regions, by far LIU and his team have finished the investigation of 15 principal rivers of the world, pinpointing the accurate source locations and measuring the accurate lengths. These rivers include top ten rivers with length over or close to 5,000 km such as the Nile (7,088 km), Amazon (6,575 km), Yangtze（6,236 km），Mississippi (6,084 km), Yenisei (5,816 km), Yellow (5,778 km), Ob (5,525 km), Heilongjiang (5,498 km), Congo (5,118 km), and Lancang (4,909 km). The results may represent the most accurate and reliable lengths for the great rivers that are currently achievable.

Other rivers enlisted on their 2012 annual work schedule are four great rivers in Russia including the Volga, Lena, Don, and Dnieper.