Archive for 2010

Eumetsat Meteo Satellite Conference

Wednesday, September 22nd, 2010

I just attended the Eumetsat Meteo Satellite Conference in Cordoba, Spain at a beautiful location right by the Mezquita.

The event brings together many satellite Meteo researchers. As you know most Meteorological satellites carry on-board many different scientific instruments, and this conference brings together a very heterogeneous group of scientific people which as very informative and useful to put our GNSS engineering work into context.

I was sent to the conference to present the GSN poster. The GSN is a support service that i have been a part of since 2003 through initial study, conceptual design, implementation, launch, improvements and maintenance. It provides Eumetsat with support GPS products on a very strict time basis to process the Metop satellite GRAS radio occultation instrument. The poster can be seen below, Enjoy!

















It was a fun short trip and I am glad to be able to represent the GSN project in this international conference.

All the best!
Nacho

IGS Workshop 2010

Thursday, July 1st, 2010

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.

IGS Station Height Tests

Saturday, March 13th, 2010

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.

MAS1_09032

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.

mas1_MP_map

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!)

Monitoring the Sky for Astronomy with GPS

Saturday, February 6th, 2010

SAC has continued to support the IAC (Instituto Astrofisico de Canarias) by calculating the Precipitable Water Vapor (PWV) at the Observatorio Roque de los Muchachos (ORM) in La Palma. The island of La Palma is about 250 Km from Gran Canaria where SAC is based, both in the archipelago of the Canary Islands, Spain, of course, and both beautiful places!!

There is a public GPS station at the ORM established since 2001 by the IGN-E (Instituto Geográfico Nacional de España) , with the designation LPAL, as part of the coordinate system definition for the Canary Islands and as part of the regional EUREF project. The station’s historical data is available as part of the EUREF permanent network.

Using precise orbits from the IGS Final products the data from a network of stations including LPAL has been solved to extract the Tropospheric Zenith Delay (TZD) at the ORM every two hours for a period of 10 years from 2001 to the end of 2009. The TZD is used to calculate the PWV as described in the enclosed published paper and presentation which the IAC have produced with SAC’s help. I encourage you to download and read the paper below:

SPIE2009_PWV1

The IAC have concluded that the PWV time series produced by SAC for the ORM is correct by correlating with independent radiometer observations that had been undertaken at the ORM during several weeks in 2001 and 2002. The level of correlation of the GPS PWV data to the local radiometer measurements is around 93%, thus confirming the very high-quality of the calculations undertaken by SAC with the LPAL GPS data. As a ‘control’ location SAC included in the calculations also the permanent station MKEA in Mauna Kea, Hawaii, the site of many astronomical Observatories as the ORM is, and the correlation was also very high with independent measurements from Hawaii.

This has lead the IAC to be able to conclude that in terms of PWV content in the atmosphere (a very significant determinant of sky clarity for ground-based infrared astronomical observations), the ORM is of similar quality than Mauna Kea, a location some 1300 m higher in elevation, you can read the conclusions in the pdf above.

To finalise the PWV study of the ORM SAC and the IAC came together recently and made a short presentation to explain to the rest of the IAC what we have done in this study pf the PWV at the ORM. You can find the presentation below.

sample seminar

ORMPWVseminar_IR.pdf

Happy positioning!!
Ignacio Romero (Nacho of the IGS)

IGS Infrastructure Committee / Comité de Infraestructura del IGS

Saturday, January 9th, 2010

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!)