OLCI S3A AND S3B ORBIT PREDICTION FILES ON FTP SITE

Predicted Sentinel-3A and Sentinel-3B orbit files for 2020 are being generated, and will be made available successively between now and end of January 2020.

Thursday, 19 December 2019

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, when the satellite passes over the same geographical point on the ground, is 27 days (14+7/27 orbits per day, 385 orbits per cycle).

The mission is composed of two satellites: Sentinel-3A and Sentinel-3B. Sentinel-3B's orbit is identical to Sentinel-3A's orbit, but flies +/-140° out of phase with Sentinel-3A.

Accessing the data

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

The orbit prediction files for Sentinel-3A and Sentinel-3B 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, for S3A and for S3B.

The naming convention is: S3A_OS_yyymmdd_nnn or S3B_OS_yyymmdd_nnn (with nnn= Day of Year).

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.

 
 
Figure 3: Files folder structure

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:

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

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

For more information, contact our User Service Helpdesk.

 
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