GPS, GNSS, and Space Weather

The technology of space based radio navigation is changing. GPS is no longer a system with two frequencies and two codes and soon GPS will not be alone. GPS is introducing a new civilian code at L2 and a new civilian signal at L5. Europe, Russia, and China are developing independent systems to complement and compete with GPS while India and Japan are developing local systems to enhance GPS performance in their regions. These developments lead to two questions. Can these new technologies lead to better measurements of space weather and are these new technologies more vulnerable or less vulnerable to space weather?

The introduction of new, non-encrypted, codes and new frequencies will enable better TEC measurements using phase but TEC measurements using pseudorange will depend on the chipping rates. The new L2C signal chips at 1.023 MHz, the same as the L1CA signal, while the new L5 signal chips at 10.23 MHz. Hence the advantages of determining TEC from two 10.23 MHz chipping rates will not be achieved. Tracking during scintillation will be improved. New pilot codes (dataless) on L2C and L5 will enable increased accumulation times and better signal-to-noise ratios for tracking during fades.

From the viewpoint of vulnerability to scintillation the new signals at L2 and L5 are all lower in frequency and have longer Fresnel lengths. Hence they should have deeper fades than the signals at L1. This is confirmed with preliminary measurements. A major question is will the fades be independent on different frequencies? The preliminary evidence for moderate scintillation is that the fades are not independent. Instead they occur simultaneously.

Both the advantages and disadvantages of the modernized GPS signals will be evaluated during the next solar maximum.