Archive for 2008

SAC helping the ESA/ESOC GPS Reprocessing

Saturday, November 29th, 2008

The IGS Reprocessing is a fantastic activity which I have highlighted before in this blog.

The IGS reprocessing involves recalculating all the GPS products (Station coordinate files, Satellite orbits, Station and Satellite clocks and Earth Rotation Parameters). Most of the IGS Analysis Centers are participating in this effort to take all the IGS GPS data from 1994 to 2008 and recalculating everything with the current state-of-the-art programs and techniques. This will produce more precise and continuous GPS products for the lifetime of the IGS. All the details can be found at the IGS Analysis Center Coordinator Website on Reprocessing.

At ESA/ESOC/OPS-GN (Navigation Support Office) we are one of the original IGS Analysis Centers so we wanted to participate in the Reprocessing. Unfortunately we had no spare processing capacity, and it was not clear what new machines should be bought to take on this challenge.

To help resolve this situation our company, SAC s.l., provided access to the ESA/ESOC Navigation support engineers an Intel Quad Core PC with Ubuntu 64bit, named SAC01. On this new machine we could start doing compilation tests, short runs, speed tests, data handling tests, etc. The machine was bought and configured by SAC s.l. in February 2008 and located in Las Palmas, Spain, at the professional housing services of a local Internet Service Provider (ISP). The machine was accessible via ssh and via FreeNX which allows for graphical display export easily to any other internet-able computer. The machine, SAC01, has installed the ESA/ESOC software Napeos POD software:

SAC01 Ubuntu QuadCore PC for POD ESA/ESOC Napeos POD SW on SAC01

SAC01: Ubuntu QuadCore PC for POD

By the end of 2008 we will have reprocessed and delivered to the IGS all the days from year 2000 to 2007, using 150 stations per day. This has involved downloading and checking about 200Gb of GNSS data from the CDDIS. The processing was executed in parallel, leaving one core free for Operating System processes, so that 3 days are run at once. This raises the temperature of the PC considerably but there is enough cooling power at the ISP to handle it!!

The reprocessing has involved 150 stations per day (green crosses), it has generally taken 50 minutes per day (red crosses) using 30/31 satellites (blue stars), summaries of four of the years are shown below:

2000-2003 reprocessing statistics

2000-2003 reprocessing statistics

Also noted are the total number of GNSS stations downloaded from the IGS (blue squares), and the stations rejected from the processing (pink squares).

At the start of 2009 the ESOC reprocessing results from SAC for 2000 to 2007 will have been checked, submitted and validated at the IGS making them the official ESA/ESOC contribution for those 8 years. The excellent results obtained finally convinced ESA/ESOC to buy two similar machines which will be used to produce the 1994-1999 reprocessing internally.

We are very happy at SAC s.l. to have supported ESA/ESOC in this innovative and successful way,

Ignacio Romero

Vapor de Agua sobre Observatorio Roque de los Muchachos (LPAL)

Saturday, September 27th, 2008

En SAC hemos estudiado los datos de la estación LPAL, La Palma, con el objetivo de caracterizar la cantidad de vapor de agua en la atmósfera cerca de los observatorios astronómicos. Este estudio ha sido realizado para el Centro GNSS de Canarias a partir de una pregunta del Instituto de Astrofísica de Canarias.

La estación GPS de LPAL pertenece a la red nacional de España que pertenece al Instituto Geográfico Nacional. La estación contribuye sus datos libremente a EUREF, lleva instalada desde Mayo del 2001 y funcionando correctamente.

La caracterización del vapor de agua en la atmósfera es posible usando el cálculo preciso con los datos de LPAL. Los datos (las distancias a los satélites GPS visibles en esos momentos) se procesan en pasos de 300 segundos. Se han tomado dos años de datos (2005-2007) y se han procesado sacando un valor de troposfera cada 2 horas durante los dos años procesados. De este valor de troposfera se ha restado el valor del retraso hidroestático asumiendo la presión atmosférica debido a la altura sobre el nivel del mar de LPAL y la época del año. El resultado de todos estos cálculos es la cantidad de vapor de agua en la atmósfera. El conocimiento de la cantidad de vapor de agua es fundamental para poder hacer observaciones astronómicas en la banda de infrarojos con garantias.

El estudio y sus resultados se lo puede bajar aquí; el-cielo-de-la-palma-gen-iac-stu-0001-sac

Espero que le sea de interés y no dude de contactarnos con cualquier duda o pregunta,


Ignacio Romero

What is EGNOS?

Saturday, August 23rd, 2008

I was asked this question at a job interview many years ago and I did not know the answer … I didn´t get the job, but I have no regrets! let me explain a bit …

The European Geostationary Navigation Overlay System (EGNOS) is an enhancement and extension of GNSS (GPS/GLONASS). It is the European SBAS (Satellite Based Augmentation System). The other SBAS systems are WAAS (Wide Area Augmentation System in the USA, MSAS in Japan, SNAS in China, etc. This fact sheet from ESA explains it all very well.


The fact that all the different systems from around the world work together is a testament to international cooperation/collaboration in this case through ICAO (International Civil Aviation Authority) so that the messages transmitted using the different SBAS systems can be interpreted by all the SBAS qualified GNSSS receivers.

The Overlay part of the system refers to the fact that EGNOS transmits from Geostationary orbit (36000 Km) on L1 (1575.42 MHz) a message with additional information to help GNSS users. This additional information helps users

The information transmitted by EGNOS is received similarly to the GPS and GLONASS navigation messages. The EGNOS message is used on-board the user receiver to provide integrity to the GNSS service (GPS/GLONASS). This integrity provides protection levels to the GNSS users against constellation problems and malfunctions and it can improve the positioning accuracy.

EGNOS is therefore considered the pre-cursor of Galileo “The European GNSS system”

Additional resources:

Salabert, F., “Interoperability, from Signals to Integrity”, GPS World, pp 10-12, Nov 2008.

IGS reprocessing, an exciting project!

Sunday, July 13th, 2008

After the IGS workshop which we recently concluded to great success, one of the most important and interesting activities for the near future is the reprocessing of all the historical IGS data using current state-of-the-art techniques.

Reprocessing of GPS data back to 1994 is a high-priority of the IGS since modern techniques can better estimate the IGS products of the past. The original products produced week to week continue to be the “gold standard” of GPS precision as they are store in Data Centers around the world. These products can be used by scientist, engineers and researchers as the best GPS orbit, clocks and ITRF values for their own research and post-processing. The reasons for the urgent need for reprocessing all of the IGS products are as follows:

  1. The IGS is now using absolute Antenna Phase Center calibrations for ground and space antennas (ANTEX), this has brought the IGS ITRF station position estimations closer to other techniques and reduced uncertainty. This jump introduced in GPS week 1400 (Nov, 2006) creates a discontinuity with the previous IGS products, which needs to be removed by reprocessing the older data with the new standards.
  2. The IGS product consistency and accuracy has improved over time as better processing methods and standards have been implemented at each of the Analysis Centers. This high-level of consistency and increased accuracy which now exists needs to be extended backwards in time for the benefit of all. With more precise past products better science can be produced by the users of the IGS products.
  3. The IGS has adopted many reference frame updates as the ITRF reference frame has been updated over time. This creates a set of products that is not continuous over time as each new ITRF realization introduces a new set of precise coordinates and velocities for the stations. The reprocessing will produce a consistent set of products using the latest ITRF05 reference frame.
  4. Data processing limitations of the past are removed. As computer speed and power has increased , it is now possible to include many more stations as available in the reprocessing of the IGS products. The inclusion of more data for the reprocessing allows for better products and for many more reference station coordinates to be estimated precisely.

The improvement of the IGS products over time can be best highlighted by the IGS Analysis Center Coordinator orbit quality plot:

IGS Final Orbits from each AC since the IGS start

IGS Final Orbits from each AC since the IGS start

The justification for the IGS reprocessing are therefore clear, and most of the IGS Analysis Centers have committed time and resources to contribute to this effort to reprocess the data for the time period between 01/1994 to 12/2007. The reprocessing efforts are being coordinated by the IGS ACC from this website which I encourage anyone interested to visit: ACC Reprocessing website.

The main output, apart from the much improved GPS products, will be the station positions to be used in the next realization of the International Terrestrial Reference Frame (ITRF).

Take care
Nacho Romero

The CGC Station Information System

Wednesday, June 18th, 2008

I am proud to present to you the CGC Station Information System, a web-based monitoring system that we have developed at my company for the CGC.

The system has a main page to show all the stations being mirrored at the CGC server. The data from all these stations are available through the CGC in Daily 30 sec files (1 sec hourly files to come soon!). The display shows each station in a world Map with its 4 character acronym and the current state of data being received (red/yellow/green). To the right there is a “Station Panel” where the status of each station can be monitored based on several different data quality criteria (% – percent of data above 10 deg in the file ; nepo – number of epochs in the data file ; MP1/2 multipath delay (in m) on the L1 and L2 frequencies)

CGC Stations Information System

All these African stations are considered CORS stations (Continuous Operating Reference Stations) and they would be part of the AFREF definition. But as the display clearly shows many have no data (grey icon) or the data has bad quality indicators (red icons). Others have long data gaps as passing the mouse over the station icons will reveal. It is essential for these stations to be useful to have long, continuous, high quality data records. Even if the data is not available in a timely manner due to poor communications recovering the data and “filling” the holes is very important so that Earth studies (geodetic, atmospheric, etc) can benefit from the data over the years. You can access the CGC Station Information System from this link:

CGC Stations Information System

At SAC s.l. we are available to make such displays for distributed networks of scientific instruments for any groups or organisation. We are still refining the CGC system and when it is complete I will write another entry explaining the improvements but at this time it is already very useful to track the daily data flows from the GNSS stations in our region.

I have available a User’s guide for the CGC Station Information System but it is in Spanish. Download it from here, and as soon as I have translated it into English I will post it here too:

CGC Station System – Manual de Uso

Take care
Nacho Romero

IGS Workshop 2008 Contents & Summary

Monday, June 9th, 2008

I intended to write a daily summary from the 2008 IGS Workshop which just closed. Unfortunately that was optimistic I was too busy to have the energy to write at the end of each day! Therefore I have written a document with my summary of each day, please download the document below and read at your perusal.

2008 IGS Workshop Summary

The workshop to me was very, very good. The location was wonderful, the Ritz at Miami Beach treated us very well. The organisation of the event by the NGS was very professional, helpful and involved in what was going on each day.

IGS Chairman (Dr Dow) addressing the participants 2008 IGS WS location (The Ritz)

It helps to have a limited IGS workshop. The IGS is not a big organisation so having these plenary meetings where we can all sit and listen to each other in technical matters is very important. We are also lucky to be able to have these meetings every 2 years since it gives us time to do some real work between workshops!!

The things that I want to pursue first coming from the workshop are:

  1. Incorporating the 2nd and 3rd order iono corrections to the GPS processing
  2. Correlating antenna monuments with problems in our ESA IGS processing
  3. Participating in the incipient IGS Infrastructure Committee
  4. Learning more about the albedo/infrared implementation to resolve the SLR residual issues in the GPS processing

I gave two presentations on the first few days of the workshop, one on the “Reprocessing Station Use” and the other on the “IGS network and the ESA processing”. Both presentations were well received they can be found in the IGS workshop website for download.

I also presented a poster at the IGS Workshop on the CGC activities which we are trying to promote to help GNSS activities in our region (Macaronesia and Western Africa):

CGC poster at the 2008 IGS WS

The poster was very well received. I was able to reinforce the contacts with several researchers and also to make new contacts with institutions that have GNSS stations in Africa. These stations I just discovered may become public with a little bit of help from the CGC or others that I will try to movilise. So I am optimistic!

Take care
Ignacio (Nacho) Romero

The IGS Workshop 2008

Monday, June 2nd, 2008

Today the IGS Workshop kick off in the beautiful Ritz-Carlton Hotel in South Beach, Florida.

The Workshop is a small, dedicated, single-session gathering of most of the IGS people involved on: station network management, product generation, and new activities (real-time, antenna calibrations, etc). This meeting takes place every 2 years and is organised by a different Analysis Centre each time, this time the National Geodetic Survey (NGS)

At this excellent website (Thanks Jim Ray!) you will find the details of the program for this week and most of the papers and posters that we will present here in the next few days, and it should be up much later for reference: IGS AC Workshop 2008 official website

The previous AC worshop was in 2006 organised in Darmstadt, Germany at the European Space Operations Centre (ESOC), where I work!, and it was also an excellent chance to discuss all the IGS issues. You can scan the program and access the content from this link: IGS AC Worshop 2006

I am involved in the reprocessing activities both as part of the official ESA submission and as part of some coordinating actions from the IGS. The Reprocesing will substitute all the official orbit, clock and coordinate products for the last 15 years from the IGS with a smooth set of products to help provide consistency and state-of-the-art quality to the entire historical set of products.

During this week I will be writting my impressions and conclusions here at the workshop. It will not be an exhaustive account .. only what strikes me as most interesting at the time.

Best regards,
Nacho Romero

Datos GNSS libres y abiertos de España

Wednesday, May 21st, 2008

Un gran problema de los datos GNSS en España es que la mayoria no son libres y abiertos. Depende mucho de la zona, de la idiosincracia de cada sitio y de la “novedad” de las instalaciones. Las regiones con mas tradiccion y capacidad tienden a dar accesso libre a sus datos, otros no. Creo que en mi entrada anterior está claro que todos tenemos que tener una “Politica de datos” y darlos libre y abiertamente lo antes posible sin cortapisas a todos los usuarios en igualdad de condiciones.

datos GNSS abiertos de España

Les incluyo el siguiente documento que me han hecho llegar sobre los datos GNSS abiertos en España. Me encontraba yo precisamente haciendo algo parecido por mi cuenta cuando un conocido me mando este ejemplar. Como creo que es un documento de valor para muchos lo pongo aqui publicamente para que todos nos podamos beneficiar.

Tambien debeis saber ya que el Centro GNSS Canarias pone a vuestra disposición datos abiertos de la zona de Canarias (Macaronesia, Peninsula iberica y Africa Occidental) para que los podais usar sin restricciones. Actualmente estoy añadiendo los datos de 1Hz disponibles en nuestra region en el servidor del CGC para vuestro uso.


Ignacio Romero Trujillo

Data Policy – Política de Datos

Saturday, April 26th, 2008

Política de Datos es la especificación clara y por escrito por la institución que instala una estación permanente GNSS para que los datos recabados sean de dominio público en algun momento. Especificando un tiempo determinado para acceder a los datos es fundamental para que los datos, que normalmente se han pagado por todos los contribuyentes, sean accessibles a todos en igualdad de condiciones.

Actualmente existen muchas estaciones GPS permanentes en Canarias y Africa que simplemente NUNCA ofrecen sus datos a la comunidad científico/técnica. Esto no es positivo para el avance de los estudios de nuestra región y sólo sirve para que varios organismos terminen duplicando esfuerzos con recursos limitados lo cual es un despilfarro.

Lo más importante para cualquier organización que instale un equipo permanente GNSS (GPS o GPS+GLONASS, etc), o cualquier otro equipo científico, es institutir una “Política de Datos” que sea pública y clara para que todos sepamos cuanto tenemos que esperar por esos datos (1 seg, 1 dia, 1 semana, 1 mes, 1 año), pero NUNCA es inaceptable. Esos datos serán beneficiosos para estudios y analisis a largo plazo y si nunca se hacen públicos corren el serio riesgo de perderse por olvido o error.

Una vez que se tenga una Política de Datos” hay que cumplirla! y dar los datos libremente a todos sin ningún tipo de traba ni cortapisas. Para esto lo mejor es publicarlos en servidores de datos globales y regionales como SIO, CDDIS, CGC, EUREF, etc, y anuncuar este echo en comunicaciones oficiales y en las webs pertinentes.

Si tiene cualquier duda al leer esto o le sugiere alguna idea adicional por favor contacteme y ayudenme a cambiar la forma de pensar de tantos investigadores que trabajan en nuestra region! Gracias.

Data Policy with respect to permanent GNSS installations is a very critical issue. I generally work in the IGS context which has an “open data policy” and also an “open product policy”.

It is easy to assume that since the IGS has 300+ permanent GNSS stations from dozens of organizations we have “won this battle” but nothing is further from the truth. In fact more data is hidden than open especially in areas with difficulties for permanent installations. We have recently discovered many GPS stations in the Canary Islands which never make their data public, the same is true for many stations in the African continent. This seems unacceptable and should change.

Considering that all these stations belong to public institutions which are paid with tax payer’s money this hidding of data seems incorrect. All organisations that decide to invest in GNSS stations should have a publicly available “Data Policy” so that after a certain amount of time the data is “opened” for free access to all. This could be 1 second, 1 hour, 1 week, 1 month, 1 year or whatever. What is reasonable is to have a Data Policy so that all the data is available “at some point” for long term scientific studies to all members of the scientific community in an open and uncomplicated download method (CDDIS, SIO, EUREF, CGC, etc).


Ignacio Romero

Estaciones GNSS en Canarias

Tuesday, March 25th, 2008

Recientemente desde SAC y el CGC hemos escrito un documento general sobre el posible desarrollo de la red de estaciones GNSS Canarias, por favor descargeselo y haganme llegar sus comentarios y opiniones:

Estaciones GPS Canarias 3.0

La idea fundamental del documento (white paper) es explicar los beneficios de tener una red de estaciones de financiación “mixta” … en otras palabras no todas las estaciones tienen que ser instaladas por el mismo organismo. Al contrario tiene mas sentido que cada organismo instale sus propias estaciones para satisfacer sus necesidades pero que todos compartan los datos como un bien público. Las estaciones públicas actuales en nuestro archipielago son las siguientes:

Estaciones GNSS Canarias

Como se puede ver solo dos islas tienen estaciones con datos públicos (Gran Canaria y La Palma) las estaciones son; MAS1 (de la Agencia Espacial Europea), GMAS (de la Agencia Espacial Japonesa), PLUZ (Instituto Español de Oceanografía), LPAL (Instituto Geográfrico Nacional) y todas distribuyen sus datos libremente. (Perdón por dejar fuera de la imagen a Lanzarote y Fuerteventura pero no tiene estaciones GNSS públicas abiertas) (Mas información sobre el estado actual de las estaciones regionales en el CGC)

Es muy posible que los datos de las estaciones se consideren “propiedad” de cada organismo pero esto en prespectiva es un error y desde SAC y el CGC queremos que cada organismo e institucion que financie una estacion GNSS vea que los datos derivados de esta instalación tendrán una cierta vida útil (minutos, dias, semanas, meses) dentro de su organizacion y una ciertya finalidad. Pero que pasado un tiempo los datos se pueden hacer públicos sin ningún problema. Estos datos pasan entonces a ser accesibles a todo el mundo y se pueden usar para importantes estudios científicos, de estabilidad regional, etc. Esta “politica de datos” es muy importante, cada organismo que instale estaciones tiene que definir su propia politica de datos y cuando sea posible los datos se puedan publicar en servidores públicos como el CGC, EUREF, IGS, etc.

Próximamente publicaremos en estas páginas las recomendaciones para una buena instalación GNSS, para que las estaciones puedan reportar los máximos beneficios posibles a todos sus usuarios.


Ignacio Romero