"The countdown for the launch of IRNSS 1B commenced at 6.44 AM and it is continuing smoothly," ISRO sources said.
The launch of the satellite is scheduled at 5.14 PM on April 4 from Sriharikota spaceport.
The April 4 launch is the second of the seven satellites planned for Indian Regional Navigational Satellite System (IRNSS), whose applications include terrestrial and marine navigation, disaster management, vehicle tracking and fleet management.
IRNSS, being developed by India is designed to provide accurate position information service to users in the country as well as the region extending up to 1,500 km from its boundary, which is its primary service area.
The system is expected to provide a position accuracy of better than 20 metre in the primary service area.
IRNSS is similar to US' Global Positioning System (GPS), Russia's Glonass and Europe's Galileo. China and Japan too have similar systems named Beidou and Japanese Quasi Zenith Satellite System respectively, ISRO officials said.
ISRO had launched IRNSS 1-A, the first in the series, on July 1 last year onboard its workhorse Polar Satellite Launch Vehicle (PSLV) C-22.
ISRO officials further said that two more satellites for IRNSS would be launched before the end of this year and with four satellite in their positions, the IRNSS could start functioning. The remaining three would alone increase the system's efficiency.