Three satellites launched by NASA from 2000 to 2002 are monitoring the levels of pollution on earth for the big cities across it.

The data sent by these satellites, namely MODISTerra, MODISAqua and MISR, is combined together to track the concentration of aerosol in the earth's atmosphere. The data is being collected for the 189 megacities across the world, including Mumbai, Tokyo and New York City.

Of the cities being tracked from space, as much as 58 cities have recorded population of more than 5 million, thereby leading to more industries, traffic and hence, denser smog in these.

Environmentalists are greatly depending on the data released by these satellites as they don't find the same collected by ground monitoring stations to be reliable. It is first method that provides standardized testing of levels of pollution, a statement from Tel Aviv University asserted.

Professor of Geophysics and Planetary science at the TAU, Pinhas Alpert said the data helps to provide exact figures of pollution for countries individually, which urges them to opt for environment friendly techniques.

"By merging the data from three imperfect sensors, their flaws are mostly counterbalanced. In cases where the three sensors show differing signs of pollution levels, more research is required", commented Alpert about the three satellites doing the task.