Knowledge Bank

The influences of short wavelength features of the earth's gravity field (equivalent to 5° blocks) on satellite to satellite summed range rate data, have been studied using simulated data. It is found that the influence of a 5 mgal 5° anomaly is highly detectable at the Apollo/Soyuz altitude but barely detectable at Geos-3 altitude. It is not possible to determine the expected magnitude of the influence comparable to observation because of the present limitation of the Geodyn program used in the study; but it is known that (for Rev. 8 of Apollo/Soyuz satellite), the r. m. s. influence of the higher degree (19 to 30) coefficients is larger than the corresponding influence of lower degree (12 to 18) coefficients. In the practical evaluation of the influences, it is found that they are very sensitive to the changes in the initial orbital elements. Since these initial elements are at present not known to the accuracy of being held fixed, it is concluded that contrary to the view expressed in Hajela (1974), it is not feasible to recover gravity anomalies from satellite to satellite range rate observables while holding the initial orbital elements fixed at some apriori values. A feasible method must be capable of removing the contaminating influence of the initial orbital elements on the ultimate observables that will be used in anomaly recovery. One such method is to apply the least squares collocation to a set of quantities derived from filtered satellite to satellite range rates.