A network as shown in Fig. 6.2 of Digital Ionosonde Systems (Delhi & Bhopal), dual frequency GPS receivers (Delhi, Trivandrum) and NWRA Tomographic Receivers (Delhi and Bhopal) for having extensive measurements of foF2, hmF2, TEC and VHF, UHF & L-band Scintillation for developing Ionospheric models has been established. The GPS receivers are for TEC and L-band Scintillation monitoring, Tomographic Receivers for 150 and 400 MHz scintillation, latitudinal TEC profile for producing Tomographic Images and Digital ionosonde for continuous monitoring of different ionospheric layers etc. The main objective of all these is to produce near real time forecasting of TEC, foF2, Scintillation etc for various applications. Details of above NPL network are given below:

In addition to Delhi Ionosonde, which is operational since July 2000, one more Digital Ionodonde System (KEL IPS-71) was installed at Bhopal, near the equatorial ionization anomaly crest, in October 2006. As compared to old Ionosonde systems (IPS-41) operational in the country (Trivandrum, Waltair and Ahmedabad), these are the most modern and fully automated which give a variety of information, which were not possible with older models. These operate in the vertical as well as in oblique incidence mode and provide HF spectrum surveillance, amplitude and Doppler Ionograms and 24 hour summaries of Ionograms. Apart from information on ionospheric layer parameters, information on Doppler shifts, True height versus Electron Density, Ionospheric Irregularities (Spread F and Sporadic E) are also available on this system. Photograph of IPS-71 Digital Ionosonde System along with the types of Ionograms obtained, is shown in Fig. 6.3.

Two dual frequency GPS receivers - one at NPL New Delhi and other one at Equatorial location, Thumba, in collaboration with Space Physical Laboratory (ISRO), Trivandrum, providing TEC and L-band scintillation data has been installed.

In order to strengthen the ongoing CRABEX program, two NWRA ITS20S COHERENT RECEIVERS, one system is installed in NPL and operated by NPL and other one is installed at ISRO master control facility at Bhopal which is operated by SPL. These two (along with the one of SPL which is installed at Thumba) are most advanced systems replacing the earlier Indian systems installed by SPL under CRABEX program.