“Impact  andMitigation  of  SpaceWeather  Effects  on  GNSS  Receiver  Performance”  	  V.	  SREEJA	  Nottingham  Geospatial  Institute,  University  of  Nottingham,  United  Kingdom  	  There	  is	  a	  growing	  reliance	  on	  Global	  Navigation	  Satellite	  Systems	  (GNSS)	  for	  mission-­‐critical	  high-­‐precision	   applications	   such	   as	   air/marine	   transport,	   autonomous	   vehicles/machinery	  control	  and	  in	  areas	  such	  as	  construction,	  agriculture	  and	  offshore	  operations.	  GNSS	  suffer	  from	   a	   number	   of	   known	   vulnerabilities.	   A	   potentially	   severe	   vulnerability	   is	   the	   effect	   of	  space	   weather	   on	   the	   GNSS	   satellites	   signals,	   a	   topic	   highlighted	   in	   the	   report	   “Extreme	  space	   weather:	   impacts	   on	   engineered	   systems	   and	   infrastructure”	   published	   by	   the	   Royal	  Academy	   of	   Engineering	   in	   February	   2013.	   Following	   a	   brief	   introduction,	   this	   lecture	   will	  present	   the	   significant	   results	   from	   our	   studies	   on	   the	   impact	   and	   mitigation	   of	   space	  weather	  effects	  on	  GNSS	  receiver	  performance	  along	  with	  the	  validation	  strategies,	  practical	  aspects	   as	   well	   as	   limitations	   in	   the	   use	   of	   tracking	   jitter	   maps	   for	   scintillation	   mitigation.	  
Space	  weather	  effects	  on	  the	  signals	  transmitted	  by	  GNSS,	  such	  as	  GPS	  (Global	  Positioning	  System)	  and	  GLONASS	  (Global	  Navigation	  Satellite	  System),	  include	  the	  effect	  of	  ionospheric	  perturbations	  and	  solar	  radio	  bursts.	  Intense	  solar	  radio	  bursts	  occurring	  in	  the	  L-­‐Band	  can	  impact	  the	  tracking	  performance	  of	  GNSS	  receivers	  located	  in	  the	  sunlit	  hemisphere	  of	  the	  Earth.	  Significant	  decrease	  in	  the	  GNSS	  signal	  carrier-­‐to-­‐noise	  ratio	  (C/N0)	  is	  observed,	  which	  can	  lead	  to	  the	  complete	  loss	  of	  lock	  on	  the	  satellite	  signals.	  High-­‐precision	  GPS	  positioning	  on	   the	   entire	   sunlit	   side	   can	   be	   partially	   disrupted	   during	   solar	   radio	   bursts.	   Hence,	   solar	  radio	   bursts	   are	   potential	   threats	   to	   safetycritical	   systems	   based	   on	   GNSS.	   Consequently	  monitoring	  these	  events	  is	  important	  for	  suitable	  warnings	  to	  be	  issued	  in	  support	  to	  related	  services	   and	   applications.	   On	   the	   other	   hand,	   the	   space	   weather	   effects	   leading	   to	  ionospheric	   perturbations	   on	   the	   GNSS	   signals	   are	   either	   due	   to	   dispersion	   or	   scintillation	  caused	  by	  plasma	  density	  irregularities.	  The	  occurrence	  of	  scintillation	  shows	  large	  variability	  with	   local	   time	   of	   the	   day,	   season,	   latitude,	   longitude,	   as	   well	   as	   solar	   and	   geomagnetic	  activity.	   Auroral	   and	   high	   latitude	   scintillation	   occurrences	   can	   be	   correlated	   with	   the	  changes	   in	   the	   solar	   and	   interplanetary	   conditions	   with	   a	   consequential	   impact	   on	   GNSS	  receiver	   tracking	   performance.	   An	   assessment	   of	   the	   GNSS	   receiver	   tracking	   performance	  under	  scintillation	  can	  be	  analysed	  through	  the	  construction	  of	  receiver	  Phase	  Locked	  Loop	  (PLL)	   tracking	   jitter	   maps.	   These	   maps	   can	   offer	   a	   potentially	   useful	   tool	   to	   provide	   users	  with	   the	   prevailing	   tracking	   conditions	   under	   scintillations	   over	   a	   certain	   area	   and	   also	   be	  used	   to	   help	   mitigate	   the	   effects	   of	   scintillation	   on	   GNSS	   positioning.	   This	   can	   be	   done	   in	  association	  with	  a	  strategy	  that	  involves	  using	  the	  tracking	  errors	  to	  improve	  the	  stochastic	  model	   of	   the	   observations	   in	   the	   position	   estimation.	   We	   will	   try	   to	   answer	   the	   related	  questions,	  comments	  and	  suggestions.