New OLCI orbit prediction files on FTP site

From 15 March 2018 users will have access to predicted Sentinel-3 orbit files, from March to December 2018, via an ftp site.

Wednesday, 14 March 2018

thumbnail-prediction-orbits

Sentinel-3 orbits

Sentinel-3 is a near-polar, sun-synchronous satellite (the surface is always illuminated at the same sun angle), characterised by a high inclination orbit (98. 65°), which corresponds to the angular distance of the orbital plane from the equator.

The orbit reference altitude is 814.5 km, and the orbit has a descending node equatorial crossing at 10:00 h Mean Local Solar time.

The orbit cycle of a satellite is when the satellite passes over the same geographical point on the ground — for Sentinel-3 satellite this cycle is 27 days (14+7/27 orbits per day, 385 orbits per cycle).

Accessing the data

The orbit prediction files can be accessed via our dedicated ftp website at:
ftp://ftp.eumetsat.int/pub/OPS/out/S-3_User_Data.

On the ftp site, there is a folder with the year, which contain 12 sub-folders, one for each month. In every sub-folder folder, there is a file for every day of the month.

The naming convention is: S3A_OS_yyymmdd_nnn (with nnn= Day of Year).

 
Figure 2
 
Figure 2: Orbit prediction: satellite track with time pass

File format

Files are provided in KML format, which can be opened using Google Earth. When displaying a KML single-day file in Google Earth, all the orbits swaths for that day are displayed in different colours, together with their satellite track. It is possible to plot the polygons of the reduced resolution swath and of the full resolution swath.

For every satellite track, there are different placeholders with the time of the satellite pass on that point (based on the reference orbit), see Figure 1 (top right, click to expand) and Figure 2.

When the file is open in Google Earth, a folder in the Places sidebar is displayed. Every single-day file contains one sub-folder for every orbit in that day (Figure 3), with the naming convention nnnnn-(mmm[pp]), with:

 
 
Figure 3: Files folder structure

nnnnn: absolute orbit number
mmm: relative orbit number
pp: cycle number.

Inside the folder there are different elements: the satellite track, the polygons displaying the Reduced Resolution swath (ERR) and the Full Resolution swath (EFR) with the frame numbers, and the placeholders with the satellite pass times.

For more information, contact our User Service Helpdesk.

 
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