Monitoring the Sky for Astronomy with GPS
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:
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.
Ignacio Romero (Nacho of the IGS)