PMD Analysis Center 2013 Annual Report

This report summarizes the activities of the Politecnico diMilano (PMD) IVS Analysis Center during the year 2013 and outlines the planned aspects of work for 2014. The main focuses in 2013 were in the framework of the IAG WG 1.4.2 on Co-location on Earth and in Space for the determination of the Celestial Reference Frame. Studies carried out concern e.g. simulations for some European VLBI antennas performed to investigate if the VLBI phase referencing technique can be used for precise determination of GNSS state vectors. Furthermore, investigations into possible deformations introduced by the change to ICRF2 [1] were also made for the processing of 24- hour observational session

DBBC3: AntArr Project

Low frequency bands in a traditional VLBI networks suffer not only from RFI but also from the low efficiency of the radio telescopes. Dedicated arrays have to be used which have to maintain all the constraints of a VLBI station, e.g., phase stability. With this aim a project with an alternative application of the DBBC3 was set up and is presented, where a set of antennas operating at frequencies lower than 1 GHz are combined into an array. The individual antennas cover the broadband frequency range from 10 MHz to 1000 MHz

PMD IVS Analysis Center

The main activities carried out at the PMD (Politecnico di Milano DIIAR) IVS Analysis Center during 2012 are briefly higlighted, and future plans for 2013 are sketched out. We principally continued to process European VLBI sessions using different approaches to evaluate possible differences due to various processing choices. Then VLBI solutions were also compared to the GPS ones as well as the ones calculated at co-located sites. Concerning the observational aspect, several tests were performed to identify the most suitable method to achieve the highest possible accuracy in the determination of GNSS (GLOBAL NAVIGATION SATELLITE SYSTEM) satellite positions using the VLBI technique

Large Satellite Constellations and Their Potential Impact on VGOS Operations

Large LEO satellite constellations (or so-called Mega-constellations) will significantly change the view of the sky in some radio frequency bands. For VGOS telescopes it is important to understand the potential impact these constellations will have in their operations, what is the risk of its receivers going into non-linear behaviour and how much additional power would a telescope receive if observing in the same frequencies where satellites are transmitting. This work describes three of these new constellations (as they would look fully deployed) and summarizes the results of a particular study considering two VGOS telescopes (Onsala and Wettzell).Comment: 10 pages, 9 figure

How to register a VGOS radio telescope at ITU and why it is important

VGOS radio telescopes enable observations in the range of 2-14 GHz and are much more receptive for unwanted radio frequency interference. Some space-borne transmitters may cause detrimental radiation to VGOS receivers. The registration of new VGOS sites at ITU is important to obtain administrative protection. This may help to avoid direct illumination by strong radars, as well as provide protection in the dedicated RAS bands from lower-level interference that degrades system sensitivity. This article introduces the risk of damage and explains the registration procedur

Geodati e cluster analysis, dalle immagini in bianco e nero alle mappe 3D

Il termine “Geomatica” vent’anni fa non era comunemente utilizzato, o almeno non in maniera così estesa come ora. Non si parlava di “geodati”, ma eventualmente di dati “spatially distributed”, l’analisi spaziale era “analisi dati” e certamente non avremmo definito “spatial analysis tools” i programmi in Fortran 77 o 90 che scrivevamo ad hoc per implementare gli algoritmi di analisi dati, in base alle esigenze delle specifiche ricerche. Certamente l’aspetto della distribuzione spaziale delle informazioni era rilevante, ma non eravamo abituati a visualizzare i dati su cui lavoravamo con la stessa facilità, velocità e versatilità di rappresentazione alle quali gli strumenti GIS e i loro “tool” ci hanno abituato. Per toccare con mano, come se fosse una fotografia in “time-lapse”, l’evoluzione delle tecnologie nelle nostre discipline, abbiamo svolto un esercizio recuperando i file originali delle anomalie di gravità e delle quote ortometriche utilizzate per alcuni test di un software di cluster analysis realizzati durante il triennio 1995/98, e descritti nella Tesi di Dottorato (Tornatore, 1998). Gli stessi dati, importati in ambiente GIS dopo quasi vent’anni, ci hanno permesso di calcolare indici statistici con la ben nota immediatezza e di realizzare facilmente modelli digitali del terreno e delle anomalie di gravità per la zona studiata. In conclusione, una riflessione su quello che nelle informazioni spaziali “vediamo” più di allora (e su come lo “vediamo”) grazie ai GIS

Comparison of ITRF2014 station coordinate input time series of DORIS, VLBI and GNSS

In this paper station coordinate time series from three space geodesy techniques that have contributed to the realization of the International Terrestrial Reference Frame 2014 (ITRF2014) are compared. In particular the height component time series extracted from official combined intra-technique solutions submitted for ITRF2014 by DORIS, VLBI and GNSS Combination Centers have been investigated. The main goal of this study is to assess the level of agreement among these three space geodetic techniques. A novel analytic method, modeling time series as discrete-time Markov processes, is presented and applied to the compared time series. The analysis method has proven to be particularly suited to obtain quasi-cyclostationary residuals which are an important property to carry out a reliable harmonic analysis. We looked for common signatures among the three techniques. Frequencies and amplitudes of the detected signals have been reported along with their percentage of incidence. Our comparison shows that two of the estimated signals, having one-year and 14 days periods, are common to all the techniques. Different hypotheses on the nature of the signal having a period of 14 days are presented. As a final check we have compared the estimated velocities and their standard deviations (STD) for the sites that co-located the VLBI, GNSS and DORIS stations, obtaining a good agreement among the three techniques both in the horizontal (1.0 mm/yr mean STD) and in the vertical (0.7 mm/yr mean STD) component, although some sites show larger STDs, mainly due to lack of data, different data spans or noisy observations

Planning of an Experiment for VLBI Tracking of GNSS Satellites

As a preparation for future possible orbit determination of global navigation satellite system (GNSS) satellites by VLBI observations an initial three-station experiment was planned and performed in January 2009. The goal was to get first experience and to verify the feasibility of using the method for accurate satellite tracking. GNSS orbits related to a satellite constellation can be expressed in the Terrestrial Reference Frame. A comparison with orbit results that might be obtained by VLBI can give valuable information on how the GNSS reference frame and the VLBI reference frame are linked. We present GNSS transmitter specifications and experimental results of the observations of some GLONASS satellites together with evaluations for the expected signal strengths at telescopes. The satellite flux densities detected on the Earth s surface are very high. The narrow bandwidth of the GNSS signal partly compensates for potential problems at the receiving stations, and signal attenuation is necessary. Attempts to correlate recorded data have been performed with different software

Analysis of GPS, VLBI and DORIS input time series for ITRF2014

In this work we have compared the Up component time series reprocessed in view of the new ITRF2014. The solutions that we have considered are the combinations of individual submissions of the Operational Analysis Centers (ACs) as o- cial IVS, IGS and IDS products.We have modelled time series as discrete-time Marcov processes, we have detected and removed discontinuities from data time series and estimated trends (long term signals). A frequency analysis making research of residual periodic signals and identification of the common ones to all the three space geodetic techniques has been performed. Preliminary results on co-located sites are shown