Archive for the 'Technique' Category

AGU2013 IGS Infrastructure Committee poster

Wednesday, December 11th, 2013

TELECAN project comes to a close

Friday, November 29th, 2013

IGS Station Height Tests

Saturday, March 13th, 2010

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.

At the EGU General Assembly 2009

Saturday, April 25th, 2009

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

Saturday, September 27th, 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

P1-C1 bias … and other Code biases

Saturday, March 15th, 2008

GGTO – an interesting correction

Thursday, November 8th, 2007

GPS Control Center updated!

Tuesday, October 16th, 2007