THE SPECTRUM OF GPS MEASUREMENT ERRORS AND THE ACCURACY OF AIRBORNE GRAVITY MEASUREMENTS

Recent observations suggest that errors in GPS carrier phase observations at frequencies within the gravity passband of airborne gravity systems may be due mainly to multipath interference. Further, the power spectral density (PSD) of these errors has been found to fall off rapidly with increase in frequency throughout the anticipated gravity passband, in the manner of a red spectrum rather than a white (which remains constant). It is shown that this implies a much greater allowable error in GPS-derived altitude reference than would be the case if the PSD of altitude errors 1) was white, 2) had the same shape as that of typical aircraft vertical motion, or 3) was dominated by a sinusoidal wave located near the high frequency limit of the gravity passband. -from Authors