Geopotential resonance in a Landsat orbit

Abstract

When the orbit of the Landsat I spacecraft was liberated to natural forces, the loss of observations to the remote sensing community was balanced by a modest gain for geodesy. The orbit’s long ground-track repeat period of eighteen days gives rise to a shallow resonance with fourteenth, twenty-eighth and forty-second order terms in the geopotential. A single continuous span of twenty-four days of Unified S-Band tracking data, collected at a single station in 1976, has been analyzed to define constraints on the dominant resonance terms of these orders and of fourteenth-order fringe resonance effects depending on the eccentricitye≈.002. Tracking observations from other stations collected during 1974 and 1975 gave essentially the same results, which provided error estimates for the lumped resonance coefficients. The application of the resonance model can considerably improve the definition and prediction of the Landsat 1 orbit. Direct numerical estimates of the influence coefficients in the resonance constraint equations were made to confirm the accuracy of analytical expressions which allow the equations to be applied to geopotential fields of arbitrarily high degree and order. Several recently derived gravity fields were tested against the Landsat resonance constraints and their comparative agreement is discussed.