From 9 to 13 December I participated in the AGU Fall Meeting 2013 presenting a poster of some interesting IGS work. As the IGS Infrastructure Committee Chairman I have coordinated an experiment together with the IGS Network Coordinator, the Reference Working Group, the Antenna Working Group, and the Analysis Center Coordinator. The experiment consisted on identifying the worse performing monument ties for co-located geodetic stations from ITRF08 involving a GNSS antenna covered with an uncalibrated radome.

Uncalibrated radomes introduce an unknown offset into the estimated station positions so via post-processing we have tried to estimate the radome effect in the tie between geodetic techniques. The stations analysed all have two or more geodetic techniques (GNSS, SLR or VLBI) and knowing the local ties precisely (measurements between reference points of each technique) is very important so that the processed solutions from each technique can be correctly fitted together to make the Terrestrial Reference Frame.

AGU13 Poster session

Nacho at the SAC IGS poster

You can get the poster clicking on the image below. The final conclusions are inconclusive for now. It is not possible to recover the radome effect from the global solutions we have generated and analysed. It is very likely that the radome effect is inside the station position time series noise. We will process the data in short baseline solutions in future developments and present the final results in the IGS Workshop 2014.

IGS IC poster at the AGU 2013

While at the AGU2013 I have also participated in the IGS Governing Board Meeting, the IGS Troposphere Working Group Meeting and the IGS Analysis Center Meeting. All the IGS different parts continue to work correctly and are advancing many issues forward.

Regards to all and Happy positioning!

Nacho

This entry is very late, sorry for that.

Let me share with you my two presentations at the IGS Workshop, 2010 held in Newcastle in 2010.

I gave a presentation on the overall state of the IGS Infrastructure up and down the Rinex data chain, considering both the challenges faced by the station operators, the data centers and the Analysis Centers.

Mon – Romero -minsize

The second talk was on the way to confront the infrastructure challenges in the next two years or so.

Tue – Romero – minsize

The workshop was a very well organised affair, we had very interesting sessions and dedicated meetings.

The IGS permanent GNSS stations are the backbone of the IGS as they provide the overwhelming bulk of the satellite observations used for the IGS products; orbits, clocks, station positions, TZD, etc. The station GNSS receivers record the measurements from the satellite constellations (GPS and GLONASS) as correctly as possible. This means following the IGS guidelines so as not to introduce unknown effects into the recorded observations. If measurements are not properly recorded by the receiver+antenna installation at each station the IGS Analysis Centers and other interested researchers will not be able to properly correct or compensate the effects and the data will be rendered useless in the estimation processes, or even worse the data will negatively affect the IGS products.

No matter how much care is taken into the installation of a permanent GNSS station it is possible that the data are biased due to local effects, either horizon blocks, reflective surfaces, uncontrolled radio-emitting sources, etc can affect the record measurements at the GNSS receiver making them less useful for the IGS.

One of the biggest concerns is the possible dependence of a station’s position calculation to the antenna’s near-field environment. If there are elements close to the antenna that disturb the signal reception then biased measurement can be recorded by the receiver. Since the antenna is a relatively small element compared to its surroundings it is possible to try to see the effect of the surroundings on the measurements by limiting how many of the measurements we actually use in any given calculation. By limiting the observations at low elevations we remove the measurements most likely to be affected by the surroundings.

Taking random days over all seasons during 2009 more than 325 are processed with fixed orbits . The runs go from 5 to 40 deg elevation cut-off angles. The height differences are calculated with respect to the 5 deg solution. It would be expected that the position solutions at a station not be affected too much by excluding low elevation data. Indeed this is correct for most of the stations, but some stations show very large differences when limiting the low elevation data the height estimate changes by decimeters sometimes! Here is the example of one of our (ESA/ESOC) stations MAS1, in Maspalomas, Gran Canaria. It can be seen by the red line that as the elevation cutoff is increased the station height estimate changes by up to 2 cm, and the error band increases of course as less data is used in the estimation.

This kind of processing is also helpful when the observation residuals are analyzed in azimuth and elevation. Taking all the residuals over each of the processed days in 2009 a “station fingerprint” (Huisman, et a., 2009) can be interpolated from the un-differenced residuals. In the case of MAS1 the station fingerprint shows the direction in which blocks and reflective surfaces are located, causing either a hole in the observations or significant negative/positive residuals.

These kind of investigations are important when evaluating the performance of a GNSS permanent station, and is the kind of in-depth analysis I have been doing as part of the IGS Infrastructure Committee.

Happy positioning
Ignacio Romero (Nacho of the IGS!)

I was honored by my IGS colleagues last year by being selected as the first IGS Infrastructure Committee Chairman. This is a great honor and I hope to be able to make the IC relevant and responsive within the IGS to all infrastructure issues. At the IC 13 IGS members are tasked with providing advice, analysis, in-depth comments, monitoring ideas, etc to the IGS Governing Board and Central Bureau (the executive arms of the IGS)

At the IC we are taking up very significant issues that have gone unaddressed for too long in the IGS in particular in terms of the IGS station network as it has grown beyond many’s expectations. The network is a collection of resources from many different organizations, which voluntarily have agreed to operate their permanent GNSS stations following the IGS standards and which provide the backbone of GNSS observations that go into the different IGS products: orbits, clocks, station positions, TZD, etc. The IGS network:

The IGS worldwide network of permanent GNSS stations have recently reached 420. The IC will be initially trying to understand the following: how many IGS are regularly missing from the Data Centers, how many stations have RINEX header inconsistencies with their published station logs, what RINEX data format version are IGS stations using, etc. Many of these basic issues are not being properly documented and tracked to see what the real performance of the network as a whole is.

The IC is particularly concerned with trying to understand the station and format issues so that they can be properly addressed. The main concern is that the IGS stations are able to provide access to the latest International Terrestrial Reference Frame by having stable position and velocity estimations for the stations, and by having stations with good data and with no jumps.

The IC will be making recommendations to the IGS GB and CB on the following issues: the raw navigation bit message, improved monitoring for stations, in-depth station performance analysis, RINEX format, RTCM streaming data format, etc.

I look forward to trying to make a positive impact in the IGS IC!
Ignacio Romero (Nacho of the IGS!)