SDG/HDG from Antarctica
 

Anyone got any idea what the 'SDG/HDG' (and variants) are at the end of
the METAR's reported from this station, and others in the region.
Observations for AMUNDSEN-SCOTT SOUTH, New Zealand (NZSP)
NZSP 190551Z 22005KT 9999 IC FEW030 FEW060 M32/ A2861 RMK SLPNO
GRID22005KT SDG/HDG
NZSP 190550Z 22005KT 6666 IC FEW030 FEW060 A2861 RMK SLPNO GRID22005KT
SDG/HDG
NZSP 190050Z 27009KT 9999 -SG SCT010 BKN060 M29/ A2869 RMK SDG/HDG --
Martin Rowleymeteorology @ bracknellW:
http://homepage.ntlworld.com/booty.weather/metindex.htm