WP1: Innovative instrumentation for dimensional metrology in geodesy
The aim of this work package is to develop different prototypes that will go beyond the state of the art for measuring long distances (up to 5 km) or for measuring intermediate distances and positions outdoors (up to 200 m). Several principles will be used to tackle the recurrent issue of air index limitation in optical long‑distance measurements. The instruments developed in this WP will be applied to achieve the objectives in WP2 and WP3.
The first task is dedicated to the realization of two prototypes of Absolute Distance Meters (ADMs) for long‑distance field measurements over up to 5 km which intrinsically compensate for the index of refraction. The first prototype called “Arpent” is intended as a compact instrument very close to a commercial version. The second prototype called “CombiYAG” has the ambition to be a reference instrument.
The second task is dedicated to the measurement of 3D positions outdoors by multilateration. Intermediate distances of up to 200 m typical for local tie networks will be targeted. The prototypes will consist of a base unit and several measurement heads connected by fibre optics. PTB will develop a system with air index compensation called “Absolute3D”. CNAM and IGN will develop a single-colour distributed telemeter (called “Distrimetre”). This will require additional equipment (developed e.g. in task 1.3) for air index compensation.
The third task is dedicated to the realization of four innovative thermometers using three technologies, for outdoors refractive index compensation. They will be based on different physical principles to derive the effective air temperature. VTT will use oxygen spectroscopy along the measurement path. INRIM will develop a field-capable free space acoustic thermometer (FSAT) which will be able to measure the air temperature by the speed of sound. Information on temperature gradients, essential to model beam bending e.g. at GGOS-CSs, will be tackled explicitly as well. For this, NPL will realize a field instrument based on acoustic thermometry, PTB will extend the Absolute3D prototype by a thermometer mode.
In the fourth task an alternative compensation method using conventional sensors will be pursued. It combines information on air index gradients between local atmospheric measurement points with local atmospheric air index measurement. This can be of great practical use when measuring large geodetic networks.