Refraction Study Group (RSG) Activities

Below is of list of meetings, activities, decisions and actions:



The Study Group found that based on ray tracing comparisons, the Marini and Murray model shows significant errors (several cm) at 15 degrees, and that Gardner mapping functions modified with a new dispersion model showed considerably better results. The group intends to use some two-color data for verification and to examine the effects of horizontal refraction gradients. Results from their studies are accessible at:

For additional information see: IAG 1999 resolutions, FORTRAN subroutines of new mapping functions1 for laser wavelengths developed by Virgilio B. Mendes and his colleagues at the University of Lisboa, Portugal.

In reference [1] it was indicated that a persistent bias of 1 mm was evident in the Zenith Delay (ZD) formulation that is used with the Marini-Murray model. Recent developments in this area include the derivation of a new ZD formula, in accordance with the IAG 1999 standards, and fully compatible with the previously released mapping functions. In this paper [2], we derive the ZD model from revised equations for the computation of the refractive index of the atmosphere, valid for a wide spectrum of optical wavelengths. The total ZD predicted with these models was tested against ray tracing through radiosonde data from a full year of data, for 180 stations distributed worldwide, and showed sub-millimeter accuracy for wavelengths ranging from 0.355 µm to 1.064 µm. The FORTRAN routine is the routine that is currently implemented in NASA Goddard's GEODYN s/w package, release 0407p2.


1 Mendes, V. B., G. Prates, E. C. Pavlis, D. E. Pavlis, and R. B. Langley "Improved Mapping Functions for Atmospheric Refraction Correction in SLR" Geophysical Research Letters, Vol. 29, NO. 10, 1414,10.1029/2001GL014394, 2002.

2 Mendes, V.B., Pavlis, E.C., "High-accuracy zenith delay prediction at optical wavelengths", Geophysical Research Letters, Vol. 31, L14602, doi:10.1029/2004GL020308, 2004.