Citation
Abstract
This report formulates the tropospheric covariance for Very Long Baseline Interferometry (VLBI) delay observations. The formulation describes calculations and data handling in COVTRP.f, the tropospheric covariance principal routine in MODEST, the Deep Space Network (DSN) VLBI parameter MODel-and-ESTimation software. The formulation in this report is intended to be an aid to anyone attempting to understand and/or modify the code. Two applications of the tropospheric covariance are identified: 1) It facilitates the calculation of the VLBI parameter-estimate covariance induced by tropospheric fluctuations, and 2) it also enables optimizing the parameter-estimate errors. It is shown that the formulation of the tropospheric covariance involves two-dimensional integrals over the structure function of refractivity (called D ). By casting the arguments of D as quadratic χ χ forms and invoking a two-dimensional version of Gauss’s theorem, the double integrals are reduced to single-dimension, line integrals, realizing an order of magnitude improvement in computation time. It is further argued that errors of ≈10% arise in this formulation of the tropospheric delay covariance, and in the COVTRP.f code, due to a flat-Earth assumption for intermediate-length (≈500 km) baselines. Proposed simulations are described, which are aimed at evaluating use of the tropospheric covariance with various wind vectors and saturation scales, as well as the effects of Earth curvature.
Keywords
Details
- Volume
- 42-230
- Published
- August 15, 2022
- Pages
- 1–17
- File Size
- 670.5 KB