Satellite

GK-2A Test Week

@sam210723

• 3 min read
GK-2A Test Week

Between Monday 2nd and Friday 5th of July 2019 the KMA NMSC conducted testing of their new geostationary weather satellite GEO-KOMPSAT-2A (GK-2A). This post is a summary of the testing carried out during this period, as well as some observations regarding new data types and formats.

RF Carriers

Around 9:50 AM KST the COMS-1 L-Band transponder was switched off to make way for the GK-2A LRIT and HRIT carriers. Initially only a strong Command and Data Acquisition Station (CDAS) carrier containing raw sensor data from GK-2A was visible.

LRIT and HRIT carriers containing processed GK-2A data appeared later in the day. HRIT was running at the usual 3 Mbps (3 MSps QPSK), but the data rate of LRIT had increased to 256 kbps (512 kSps BPSK). This faster data rate is what COMS-1 LRIT used before it was reduced to 64 kbps (128 kSps BPSK) in late March.

GK-2A LRIT and HRIT carriers were present for the rest of the week until around 11:00 AM on Friday 5th when the L-Band transponder was switched off. A few minutes later the COMS-1 L-Band transponder was re-enabled, followed by LRIT and HRIT carriers.

Observations

Only minor protocol changes were seen during the testing period. Most notably, all sensor wavelengths were combined into a single virtual channel (VCID 0) rather than each wavelength having its own VCID.

VCID COMS-1 GK-2A Testing
0 Visible Full Disk (all channels)
1 Short-wave Infrared not used
2 Water Vapour not used
3 Infrared 1 not used
4 Infrared 2 Additional Data
5 Alpha-numeric Text Alpha-numeric Text
63 Fill / Idle Fill / Idle

The observation interval of Full Disk images was drastically reduced from 3 hours to 10 minutes, allowing smooth animations to be created. No other image types such as COMS-1 Enhanced Northern Hemisphere were seen during the testing period.

0:00
/
Full disk false colour animation (03/07/19)

All GK-2A test data was encrypted in the same way COMS-1 is, except using a different key. Thankfully this key was from the same key table used by COMS-1. See this blog post for a detailed look at the key table file and decryption process:

COMS-1 LRIT Key Decryption
Like NOAA’s series of GOES meteorological satellites, COMS-1 (128.2°E) operated by the Korea Meteorological Administration (KMA) has both LRIT and HRIT downlinks for disseminating real-time meteorological data. Unlike GOES, these downlinks are encrypted using single-layer DES and decryption keys are…
VKSDRsam210723

Normal COMS-1 operation has been restored and will continue to operate until GK-2A is officially brought online later this year.