Computing the deflection of the vertical for improving aerial surveys: A comparison between EGM2008 and ITALGEO05 estimates

Recent studies on the influence of the anomalous gravity field in GNSS/INS applications
have shown that neglecting the impact of the deflection of vertical in aerial surveys induces horizontal
and vertical errors in the measurement of an object that is part of the observed scene; these errors can
vary from a few tens of centimetres to over one meter. The works reported in the literature refer to
vertical deflection values based on global geopotential model estimates. In this paper we compared
this approach with the one based on local gravity data and collocation methods. In particular, denoted
by ξ and η, the two mutually-perpendicular components of the deflection of the vertical vector (in the
north and east directions, respectively), their values were computed by collocation in the framework
of the Remove-Compute-Restore technique, applied to the gravity database used for estimating the
ITALGEO05 geoid. Following this approach, these values have been computed at different altitudes
that are relevant in aerial surveys. The (ξ, η) values were then also estimated using the high degree
EGM2008 global geopotential model and compared with those obtained in the previous computation.
The analysis of the differences between the two estimates has shown that the (ξ, η) global geopotential
model estimate can be reliably used in aerial navigation applications that require the use of sensors
connected to a GNSS/INS system only above a given height (e.g., 3000 m in this paper) that must be
defined by simulations.