CPI has extensive experience in ionosphere specification from dual frequency (L1 and L2) Global Positioning System (GPS) measurements (Reilly and Singh, Radio Sci., 39, 1671, 2004). We have devised a technique to combine both range and phase measurements to remove instrument-related variations, which are more prevalent in range measurements. Our standard methodology for ionosphere specification has been to solve for the effective sunspot number (SSNe) and simultaneously solve for biases using discrete inverse theory. We have developed software to compensate for ionospheric Faraday rotation effects for a passive microwave satellite (WindSat) in an operational mode (Singh and Bettenhausen, Radio Sci., 46, RS4008, 2011). We have extensive experience in data acquisition as well as knowledge about the sensitivities and characteristics of various GPS receivers. We have developed software for better precision position from GPS system with augmentation from either differential GPS correction or atmospherically corrected differential corrections (Singh and Reilly, Radio Sci., 41, 1671, 2006).
We also have extensive experience in ionospheric irregularities at equatorial (Singh and Szuszczewicz, J. Geophys. Res., 89, 2313, 1984) as well as high latitudes (Singh et al., J. Geophys. Res., 90, 6525, 1985). Our research has not only focused on occurrence statistics, but also the cause-effect relationships with underlying physics phenomenon. We have experience in tropospheric delay determination and comparison with measurements from different instruments. The International GNSS Service (IGS) regularly provides zenith total tropospheric delay for over 100 GPS stations from all around the globe. We have studied almost one year’s worth of such data to estimate indirect delays from the troposphere.
The effects of the ionosphere on GPS signals. GPS signal refraction is caused by ionospheric irregularities that produce variations in signal group delay and phase advance. Signal diffraction is caused by ionospheric scattering of signals resulting in radio waves reaching receivers via multiple paths thereby causing fluctuations in signal amplitude and phase. Both refractive and diffractive effects on GPS signals are referred to as scintillation.