IERS Standards

Abstract

Due to weather-related travel delays Dr. McCarthy was unable to present his scheduled paper. In his absence, however, Dr. K. Yokoyama, Chairman of the International Earth Rotation Service (IERS), reported on the status of the revision of the IERS Standards carried out by McCarthy who provided the following precis.These standards are meant to be used in the reduction of observations contributed to the IERS and by those who require IERS estimates of polar motion, Universal Time and nutation to establish the most precise celestial and terrestrial reference systems. The goal of the IERS is to publish the document, an update of the previous version (McCarthy, 1989), in the beginning of 1992.

On calculating the Earth's C21 and S21 gravity coefficients in the IERS terrestrial reference frame

“…The formulae used at present to calculate " g 21 si and " 21 si are insucient in precision to ensure the mean values of the coecients recommended by the current IERS Conventions (McCarthy 1996). The proposed correction to the IERS mean values for " g 21 and " 21 is more than an order of magnitude larger than the adopted cuto for amplitudes of the timedependent terms of these coecients.…”

“…The relevant error of Eq. (2) is 3 Â 10 À12 , which is far above, for example, the adopted cuto 10 À13 for tidal variations of " g 21 and " 21 also considered by the formulation for the coecients (McCarthy 1996). It should be noted that the algorithm for calculating " g 21 and " 21 has been greatly improved in recent years.…”

“…It should be noted that the algorithm for calculating " g 21 and " 21 has been greatly improved in recent years. For example, the previous IERS Standards (McCarthy 1992) considered just four terms due to ocean tides in these coecients, but the current IERS Conventions (McCarthy 1996) include 111 terms. The latter document also proposed taking account of the Earth's inelasticity (and respectively complex values for Love numbers) in precise calculations of the eects of the solid Earth tides and of the planet's rotational deformation due to polar motion on the gravity coecients of the second degree.…”

Estimating atmospheric pressure loading regression coefficients from GPS observations

“…First, the regional pressure anomaly for many sites of the network would not be based on pressure data in land areas, but in ocean areas, which might respond quite differently to the loading. Second, this two parameter approach is not any more proposed in the new Conventions 2003 (McCarthy andPetit 2003), nor is it discussed within the recently established IERS Special Bureau for Loading .…”

On the precession constant: Values and constraints on the dynamical ellipticity; link with Oppolzer terms and tilt-over-mode

“…al., 1995;Williams, 1994;, and on (c) VLBI (see the list of references in Williams, 1994 andMcCarthy andLuzum, 1995) have been used.…”