NOAA-15 orbit number roll-over

[Nigel Atkinson]

If you use NOAA-15 direct readout data, please read on.

You may have seen an announcement from NOAA entitled “NOAA-15 reaches 100,000 Revs on August 5, 2017 and will roll over in count to Rev “1””.

The day of rollover seems to depend on which orbital bulletins are being used. According to the TLE bulletins, which are normally used in AAPP, rollover will not occur until August 7th.

TLE bulletins only hold 5 digits of orbit number information. So once the roll-over has been made, and is reflected in the TLE bulletin, everything should work in AAPP. However, there could be a problem on the day of rollover, when the orbit number in the TLEs is below 99999.

If you do nothing, AAPP_RUN_NOAA will fail on that day when processing NOAA-15. We recommend that you modify AAPP/src/navigation/libtle/tle_satpos.F as follows. Find the line containing “orbnum = orbnum+1” and after it insert the following:

            if ( orbnum .ge. 100000) orbnum = 1

Then “make lib; cd ../bin; make bin”.

It you still have problems after the rollover, we suggest that you rename tle_noaa15.index file and let the tleing command create a new one.

Regards,

Nigel

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