Geodetic instruments need to be periodically checked and calibrated in order to perform reliable and scientific measuring. Calibrations and conformity checking on geodetic instruments are carried out by the Geodetic Division 

Calibrations

Calibration of various leveling staff: invar, barcode staff or staff with the indication of centimeters. The calibration is carried out by a specific collimator and the measurements obtained are compared with the ones obtained by a Laser HP interferometer device with a precision of tenths of micron. The calibration provides the precision of the zero marker of the levelling staff.

• Couple of invar leveling staff measuring 2 m
• Couple of invar leveling staff measuring 3 m
• Small metal band with staff
• Bands and metric cables

Certificate of Conformity to the specifications of geodetic instruments’ manufacturer

Conformity of GPS devices (GPS receivers-with antenna)

A one-metre iron board baseline, whose length is measured by an interferometer, is used to carry out the checking operations. Two antennas, one for the instrument to be checked and the other for a high precision receiver, called “gold”, are fixed at the two ends of the board. Data are recorded in a two-hours static session by the two GPS devices, epochs between two measurements are of few seconds. Data are registered by medium multipath (inferior to 0.2 m) and the useful information has to be more than 90% in order to provide accurate measurements. Raw data are processed by Bernese software version 5.2 in order to calculate the baseline length. Accurate satellite ephemeris provided by IERS (International Earth-Rotation and Reference System Service) are used for the computation. The mean squared error (MSE) of the computation is reduced to few millimeters by applying procedures aiming to eliminate errors like watch offset, cycle-slip, tropospheric and ionospheric delays. Length resulting from the calculation is compared and corrected according to thermal expansion. The device is certified as conform to the declared performances when the differences between the two lengths in Nord, Est and Up directions are within the accuracy range that the manufacturer has declared.

Conformity of Theodolites and Total Station

Angular measurement control, both of azimuth and zenith angles is carried out by repeating the measurement using a special collimator. Azimuth measurements are repeated by rotating the device in four different positions. Distance control is carried out by a 30 m base measured by interferometer.

Conformity of Levels

Level control is carried out by simulating the measurement of a part of one km, between benchmarks, whose heights are known, and geometric leveling starting from the middle.

Certificate of Conformity of a GPS device with antenna

Certificate of Conformity of Total Station or Theodolites

Certificate of Conformity of Leveling instrument or digital/optic-mechanical Self-leveling instrument

Instruments for geodetic measuring

Calibrated staff for vertical shelf benchmarks measurements

Calibrated staff for vertical shelf benchmarks measurements, supplied in a wooden box

Spherical cap support for geometric leveling measurements

Spherical cap support for geometric leveling measurements, supplied in a wooden box