Borowiec Astrogeodynamic Observatory

We report a stability below 7 × 10(-17) of two independent optical lattice clocks operating with bosonic (88)Sr isotope. The value (429 228 066 418 008.3(1.9)(syst) (0.9)(stat) Hz) of the absolute frequency of the (1)S(0) - (3)P(0) transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures.

In Poland, an accurate two-way optical fibre time transfer (TWOTT) baseline of 420 km has been developed with a standard uncertainty of 112 ps. Meanwhile, the BIPM has been engaged in a pilot project to reduce the uncertainty of UTC GNSS time transfer calibrations from 5 ns to approximately 1.5 ns, for which it has developed a standard calibration scheme, named METODE, associated with an integrated portable GNSS calibration station. The TWOTT and the METODE respectively represent the world ' s most advanced time transfer method and calibration facility. In July 2013, the BIPM calibrator and the TWOTT self-calibrated optical fibre transceivers were set up side by side to compare their results. This is the first time that an operational TWOTT has been used in accurate time transfer and the first time that a GNSS calibration method has been validated with a technique accurate to 200 ps. As the two systems are completely independent and the latter is one order of magnitude more accurate than the first, this comparison allowed validation of the METODE and its uncertainty. It also confirmed that any bias in the TWOTT is at most 1 ns.

The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.

Absolute frequencies of unperturbed (12)C(16)O transitions from the near-infrared (3-0) band were measured with uncertainties five-fold lower than previously available data. The frequency axis of spectra was linked to the primary frequency standard. Three different cavity enhanced absorption and dispersion spectroscopic methods and various approaches to data analysis were used to estimate potential systematic instrumental errors. Except for a well established frequency-stabilized cavity ring-down spectroscopy, we applied the cavity mode-width spectroscopy and the one-dimensional cavity mode-dispersion spectroscopy for measurement of absorption and dispersion spectra, respectively. We demonstrated the highest quality of the dispersion line shape measured in optical spectroscopy so far. We obtained line positions of the Doppler-broadened R24 and R28 transitions with relative uncertainties at the level of 10(-10). The pressure shifting coefficients were measured and the influence of the line asymmetry on unperturbed line positions was analyzed. Our dispersion spectra are the first demonstration of molecular spectroscopy with both axes of the spectra directly linked to the primary frequency standard, which is particularly desirable for the future reference-grade measurements of molecular spectra.

Abstract The (TOPography EXperiment) TOPEX/Poseidon (T/P) altimetry mission operated for 13 years before the satellite was decommissioned in January 2006, becoming a large space debris object at an altitude of 1,340 km. Since the end of the mission, the interaction of T/P with the space environment has driven the satellite's spin dynamics. Satellite laser ranging (SLR) measurements collected from June 2014 to October 2016 allow for the satellite spin axis orientation to be determined with an accuracy of 1.7°. The spin axis coincides with the platform yaw axis (formerly pointing in the nadir direction) about which the body rotates in a counterclockwise direction. The combined photometric and SLR data collected over the 11 year time span indicates that T/P has continuously gained rotational energy at an average rate of 2.87 J/d and spins with a period of 10.73 s as of 19 October 2016. The satellite attitude model shows a variation of the cross‐sectional area in the Sun direction between 8.2 m2 and 34 m2. The direct solar radiation pressure is the main factor responsible for the spin‐up of the body, and the exerted photon force varies from 65 μN to 228 μN around the mean value of 138.6 μN. Including realistic surface force modeling in orbit propagation algorithms will improve the prediction accuracy, giving better conjunction warnings for scenarios like the recent close approach reported by the ILRS Space Debris Study Group—an approximate 400 m flyby between T/P and Jason‐2 on 20 June 2017.

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for the generation of coordinated universal time (UTC). About 20 timing laboratories around the world continuously operate TWSTFT using satellite time and ranging equipment (SATRE 19 ) modems for remote time and frequency comparisons in this context. The precision of the SATRE TWSTFT as observed today is limited by an apparent daily variation pattern (diurnal) in the TWSTFT results. The observed peak-to-peak variation have been found as high as 2 ns in some cases. Investigations into the origins of the diurnals have so far provided no complete understanding about the cause of the diurnals. One major contributor to the diurnals, however, could be related to properties of the receive part in the modem. In 2014 and 2015, it was demonstrated that bypassing the receive part and the use of software-defined radio (SDR) receivers in TWSTFT ground stations (SDR TWSTFT) instead could considerably reduce both the diurnals and the measurement noise. In 2016, the International Bureau of Weights and Measures (BIPM) and the Consultative Committee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilot study on the application of SDR receivers in the TWSTFT network for UTC computation. The first results of the pilot study were reported to the CCTF WG on TWSTFT annual meeting in May 2017, demonstrating that SDR TWSTFT shows superior performance compared to that of SATRE TWSTFT for practically all links between participating stations. In particular, for continental TWSTFT links, in which the strongest diurnals appear, the use of SDR TWSTFT results in a significant suppression of the diurnals by a factor of between two and three. For the very long inter-continental links, e.g. the Europe-to-USA links where the diurnals are less pronounced, SDR TWSTFT achieved a smaller but still significant gain of 30%. These findings are supported by an evaluation of some of the links with an alternate technique based on GPS signals (GPS IPPP) as reported in this paper. Stimulated by these results, the WG on TWSTFT prepared a recommendation for the 21st CCTF meeting, which proposed the introduction of SDR TWSTFT in UTC generation. With CCTF approval of the recommendation, a roadmap was developed for the implementation of SDR TWSTFT in UTC generation. In accordance with the roadmap, most of the stations that participated in the pilot study have updated the SDR TWSTFT settings to facilitate the use of SDR TWSTFT data in UTC generation. In addition, the BIPM conducted a final evaluation to validate the long-term stability of SDR TWSTFT links, made test runs using the BIPM standard software for the calculation of UTC, now including SDR TWSTFT data, and started to calculate SDR TWSTFT time links as backup from October 2017. The use of SDR TWSTFT in UTC generation will begin in 2018.

Hg system.

We report on the design, assembly, testing, and delivery of a series of new cesium fountain primary frequency standards built through commercial and scientific collaboration with international users. The new design, based on proven National Physical Laboratory solutions, improves reliability, simplicity of operation, and transportability. The complete system consists of a novel physics package, a specially developed optical package, and dedicated electronics for system control. We present results showing that despite their simplified and more compact design, the new fountains have state-of-the-art performance in terms of signal-to-noise ratio and robust long-term operation. With a sufficiently low-noise local oscillator, they are capable of reaching a short-term stability below 3 × 10-14(1 s) and have potential accuracy in the low 10-16range, similar to the best cesium fountains currently in operation. This cost-effective solution could be used to increase the availability of accurate frequency references and timescales and provide redundancy in critical locations.

The LARES (LAser RElativity Satellite) was built by the Italian Space Agency (ASI) and launched on 13 February 2012 by the European Space Agency. It is intended for studying the Lense-Thirring effect resulting from general relativity as well as for geodynamic studies and satellite geodesy. The satellite is observed by most ground laser stations. The task of this work is to determine the station coordinates and to assess the quality of their determination by comparison with the results from the LAGEOS-1 and LAGEOS-2 satellites. Observation results in the form of normal points (396,105 normal points in total) were downloaded from the EUROLAS Data Center for the period from 29 February 2012 to 31 December 2015. Seven-day orbital arcs were computed by the NASA GSFC GEODYN-II software, determining the coordinates of seventeen selected measuring stations. The average Root Mean Square (RMS) (15.1 mm) of the determined orbits is nearly the same as for LAGEOS (15.2 mm). The stability of the coordinates of each station (3DRMS) is from 9 mm to 46 mm (for LAGEOS, from 5 mm to 15 mm) with the uncertainty of determining the coordinates of 3-11 mm (LAGEOS 2-7 mm). The combined positioning for the LARES + LAGEOS-1 + LAGEOS-2 satellites allows for the stability of 5-18 mm with an uncertainty of 2-6 mm. For most stations, this solution is slightly better than the LAGEOS-only one.

We report the measurement of the photoionization cross sections of the $5{S}_{1/2}$ and $5{P}_{3/2}$ states of $^{87}\mathrm{Rb}$ in a two-species Hg and Rb magneto-optical trap (MOT) by the cooling laser for Hg. The photoionization cross sections of Rb in the $5{S}_{1/2}$ and $5{P}_{3/2}$ states at 253.7 nm are determined to be ${1}_{\ensuremath{-}1}^{+4.3}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$ and $4.63(30)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$, respectively. To measure the $5{S}_{1/2}$ and $5{P}_{3/2}$ state fractions in the MOT we detected the photoionization rate of the $5{P}_{3/2}$ state by an additional 401.5 nm laser. The photoionization cross section of Rb in the $5{P}_{3/2}$ state at 401.5 nm is determined to be $\text{1.18(10)}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$.

In the paper we present and briefly characterize the methods of remote synchronization of atomic clocks. Two groups of technical solution are presented, namely the methods employing satellites, especially GPS Common View and Two Way Satelite Time and Frequency Transfer and the group of systems, which employs the ground-base fiber optic networks. The unidirectional and bidirectional time/frequency transfer schemes are considered, and theirs main limitations are pointed out. Finally, the newly established atomic clock signals distribution network called Optime is presented. In a first step, the network was a simple link which primary objective was to connect two most important Time and Frequency laboratories in Poland - in Central Office of Measures (GUM, Warsaw) and in Astrogeodynamic Observatory (AOS) in Borowiec near Poznan. Recently, Optime has been expanded by adding three newly installed branches connecting GUM and Orange Synchronization Center and AOS with National Laboratory of Atomic, Molecular and Optical Physics in Torun. and Astronomic Center in Piwnice.

The Fidelity consortium is currently implementing and will operate the Galileo Time Service Prototype Facility (GTSPF) in order to deliver Coordinated Universal Time (UTC) services to the Galileo satellite system during its in-orbit validation phase (due to begin in 2008). A key element of this plan is to integrate the Galileo timing activities into the wider time and frequency community, including the Bureau International des Poids et Mesures (BIPM). The main function of the GTSPF is to provide parameters for steering Galileo System Time (GST), as realized at the Galileo Precise Timing Facility (PTF), to UTC (modulo 1 s). This will be achieved in a three step process. First, the GST (as realized in the Galileo PTF from an ensemble of atomic clocks (active H-masers, high performance Caesium standards) with dedicated measurement equipment and clock ensemble algorithm) is compared against the participating UTC(k) time scales by Two-Way Satellite Time and Frequency Transfer (TWSTFT) and GPS P3 techniques. These raw data are sent to the GTSPF for processing. The Fidelity consortium is responsible for the calibration of the time transfer equipment. Second, the GTSPF generates a prediction of the difference UTC -GST (modulo 1 s) by means of an intermediate composite clock obtained from an ensemble of atomic standards maintained in the PTFs and in the participating European National Metrology Institutes (NMIs), and using the data of UTC -UTC(k) as computed by the BIPM. The benefits of the composite clock include enhanced stability and integrated integrity monitoring. Third, the GTSPF sends daily steering parameters to the PTF to be used to align the physical realization of GST against UTC (modulo 1 s) as required by the Galileo system specifications. The specification and design phase of the implementation of the GTSPF was concluded in August 2006 with the successful completion of the Critical Design Review (CDR). This included the functional and physical design of the GTSPF and the verification of the uncertainty budget by means of extensive simulations. The design and functions of the GTSPF currently being implemented are detailed in this paper. The algorithm to be used for the prediction of UTC - GST is described. The time transfer link calibration activities under the responsibility of Fidelity are detailed. The PTF interactions with the GTSPF are described. A possible relationship between the GTSPF and EGNOS, the first step of European navigation satellite systems, is proposed. Finally, this paper gives a summary of the current status of the GTSPF implementation and the planned future activities of the Fidelity consortium.

Unlike GPS, the GLONASS P-code is broadly accessible. This paper discuss GLONASS capabilities and prospects in terms of precise time transfer. We have tested GLONASS common-view time transfer using the C/A- and P-code, over time links varying in length from about 800 km to 9200 km. The raw GPS and GLONASS data were collected using 3S navigation receivers, and were corrected using IGS precise orbit data and IGS ionosphere maps. It is proposed that GLONASS time links be calculated monthly, initially as backup links for TAI calculation, and later as possible official time links

The OPTIME project creates an ultra-precise time and frequency signals dissemination system based on telecommunication networks. End users obtain access to these signals without incurring huge costs for the purchase of their own atomic clocks, and receive the service related to laboratories generating international atomic time scales, to which any precise time must be referred. OPTIME dissemination system is based on three main elements: reference time and frequency laboratories, local time and frequency repositories and fiber optical network with specialized transmission equipment to transfers signals between laboratories, repositories and end users. This article describes OPTIME system with particular emphasis on a new 330 km long dissemination line between Space Research Centre PAS, Astrogeodynamic Observatory (AOS) at Borowiec and National Laboratory of Atomic, Molecular and Optical Physics (KL FAMO) at Torun.

The OPTIME project creates an ultra-precise time and frequency signals dissemination system based on telecommunication networks. End users obtain access to these signals without incurring huge costs for the purchase of their own atomic clocks, and receive the service related to laboratories generating international atomic time scales, to which any precise time must be referred. This document describes the final stage of OPTIME project - which developed a self-calibrating, high precision dissemination system for time and frequency reference signals based on optical fiber links and ELSTAB devices developed at AGH University.

This paper presents the results of an orbital analysis of satellite laser ranging data performed by the Borowiec SLR station (7811) in the period from July 1993 to December 2019, including the determination of the station positions and velocity. The analysis was performed using the GEODYN-II orbital program for the independent monthly orbital arcs from the results of the LAGEOS-1 and LAGEOS-2 satellites. Each arc was created from the results of the laser observations of a dozen or so selected stations, which were characterized by a large number of normal points and a good quality of observations. The geocentric and topocentric coordinates of the station were analyzed. Factors influencing the uncertainty of the measurements were determined: the number of the normal points, the dispersion of the normal points in relation to the orbits, and the long-term stability of the systematic deviations. The position leap at the end of 2002 and its interpretation in ITRF2014 were analyzed. The 3D stability of the determined positions throughout the period of study was equal to 12.7 mm, with the uncertainty of determination being at the level of 4.3 mm. A very high compliance of the computed velocity of the Borowiec SLR station (24.9 mm/year) with ITRF2014 (25.0 mm/year) was found.

The remote synchronization of a Very Long Baseline Interferometry (VLBI) station with a “virtual” atomic clock delivered via an optical fiber is described. The time and frequency signals are provided from UTC(AOS) laboratory located at a distance of 345 kilometers from the VLBI station. Evaluation of the remote synchronization carried out by Joint Institute for VLBI ERIC is presented. To our best knowledge, this is the first operational fiber-optic link synchronizing VLBI observations.

The OPTIME project creates a long range dissemination system for transfer ultraprecise time scale and the references frequency signals in telecommunication networks. The highest accuracy signal is available only on fiber optical networks, but other type of networks can be used to transfer of signals with lower accuracy to adapt it to the needs of different user groups. Article also describes experience gained during an over-a-year experiment of connection between Central Office of Measures (GUM) in Warsaw and the Astrogeodynamic Observatory (AOS) in Borowiec.

The paper expounds relevant results of some of the present author's experiments defining the strapdown IMU sensors' errors and their propagation into and within DGPS/IMU.In order to deal with this problem, the author conducted both the laboratory and field-based experiments.In the landborne laboratory the stand-alone Low-Cost IMU MotionPak MKII was verified in terms of the accelerometer bias, scale factor, gyroscope rotation parameters and internal temperature cross-correlations.The waterborne field-trials based on board dedicated research ships at the lake and at the busy small sea harbour were augmented by the landborne ones.These experiments conducted during the small, average, and high dynamics of movement provided comparative sole-GPS, stand-alone DGPS and integrated DGPS/IMU solution error analysis in terms of the accuracy and the smoothness of the solution.This error estimation was also carried on in the context of the purposely-erroneous incipient DGPS/IMU initialisation and alignment and further in the circumstances of on-flight alignment improvement in the absence of the signal outages.Moreover, the lake-waterborne tests conducted during extremely low dynamics of movement informed about the deterioration of the correctly initialised DGPS/IMU solution with reference to the stand-alone DGPS solution and sole-GPS solution.The above-mentioned field experiments have checked positively the DGPS/MKI research integrating software prepared during the Polish/German European Union Research Project and modified during the subsequent Project supported by the Polish Committee for Scientific Research.

Abstract We report a remote, intercontinental frequency comparison between 171Yb (NMIJ) and 88Sr (UMK) optical lattice clocks. The frequencies were compared via the Global Positioning System Precise Point Positioning technique over the period from 10 March 2020, 00:00 UTC until 15 March 2020, 00:00 UTC. The comparison of the optical clocks yields results with a relative frequency uncertainty of 6.3 × 10 − 15 .