Estimated ionospheric Group Delay for GPS Signal Residual range Error First order 16.2m 26.7m 0.0 Second Order: 1/f 3 ~1.6cm ~3.3cm ~-1.1cm Third Order: 1/f4 0.86mm 2.4 mm Calibrated llf term Based on a Thin Layer ~1-2mm ionospheric Model The phase advance can be obtained from the above table by multiplying each number by, -0.5 and -1/3 for the 1/f2,1/f and l/fterm, respectively wy Principles of the Global Positioning System 13 ionospheric Effect Removal by Using Dual Frequency Receivers ionosphere-free phase measurement Φ12=a1Φ1+a2 =p+T+a1N+a12N2+aE+a2E22=-2 f2-f2 similarly, ionosphere-free pseudorange can be obtained R2=R-2R2 The conditions applied are that sum of ionospheric effects on both frequencies multiplied by constants to be determined must be zero second condition is for example that sum of the constants is 1,or one constant is set to 1(verify!) Principles of the Global Positioning System 20054-1(147 Principles of the Global Positioning System 2005-4-1 13 L1 L2 Residual Range Error First Order: 1/f 2 16.2 m 26.7 m 0.0 Second Order: 1/f 3 ~ 1.6 cm ~ 3.3 cm ~ -1.1 cm Third Order: 1/f 4 ~ 0.86 mm ~ 2.4 mm ~ -0.66 mm Calibrated 1/f 3 Term Based on a Thin Layer Ionospheric Model ~ 1-2 mm The phase advance can be obtained from the above table by multiplying each number by -1, -0.5 and -1/3 for the 1/f 2, 1/f 3 and 1/f 4 term, respectively Estimated Ionospheric Group Delay for GPS Signal Principles of the Global Positioning System 2005-4-1 14 • ionosphere-free phase measurement Φ ΦΦ 12 1 1 2 2 1 1 1 2 2 2 11 2 2 , = + =++ + + + α α ρ αλ αλ αε αε TN N α α 1 1 2 1 2 2 2 2 2 2 1 2 2 2 = − = − − f f f f f f • similarly, ionosphere-free pseudorange can be obtained • The conditions applied are that sum of ionospheric effects on both frequencies multiplied by constants to be determined must be zero; second condition is for example that sum of the constants is 1, or one constant is set to 1 (verify!). 2 2 2 2 1 1,2 1 R f f R = R − Ionospheric Ionospheric Effect Removal by Effect Removal by Using Dual Frequency Receivers Using Dual Frequency Receivers