SPECTRE service scheme

The SPECTRE service has been developed to provide several products from GPS measurement processing. The processing scheme is described below. The VTEC products are created daily in three steps.

SPECTRE processing scheme

1. GPS data acquistion

GPS data and satellite orbit data are downloaded daily from external FTP servers (IGS, EUREF, IGN...). The time samplings of these data are 30 seconds and 15 minutes respectively. Orbit data are resampled at 30 seconds to fit GPS data.

EUREF stations

Note that time delay between SPECTRE products availibility and day of products is about 3 days. The main reason is time delay between GPS data recording and GPS data availibility on FTP servers. This part represent 85% of the whole delay (GPS data availibility + GPS data processing).

2. TEC computation

GPS and orbit data are processed to compute the STEC at the SIPs (i.e. projections on the ground of the IPPs). Note that for GPS data availability reasons, a delay of 3 days in the product computations has been fixed: Products of day D are computed at day D+3. Below is an illustration of all the IPPs at a given instant (click on it to see the movie of the entire day, sampled every 5 minutes, 1.6 MB). Colors represent the GPS satellite identification number.

Piercing points

The estimated STEC data are first converted into VTEC data at the SIPs (see illustration below or click on it to see the movie of the entire day, sampled every 5 minutes, 1.8 MB).

VTEC at piercing points

3. TEC maps and biases estimations

Then they are interpolated on a regular grid to create VTEC distribution maps over Europe (see example below or click on it to download the full MPEG movie of the day, 1.6 MB). This is performed with a Kalman filter. IFB and TGD are also estimated and appended to the products created at the previous step.

VTEC maps

Finally, these data are filtered with low-pass filters to create 15 minute and 1 hour VTEC maps and the whole set of products is archived in a database.

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