The GPS Validation Project

1
The GPS Validation Project
The GPS validation project is a monitoring
service developed by the Danish Meteorological
Institute and TERMA. The basic objectives for
the project are the following

• Identify and describe Space Weather conditions
  which can adversely affect the quality and
  reliability of atmospheric profiling data
  acquired through GPS occultation measurements.
• Define characteristics indicative of poor GPS
  data quality resulting from adverse space weather
  effects.
• Devise algorithms to validate GPS data products
  in an operating near-real-time end-to-end chain
  for processing of GPS data from telemetry to
  application

2
The content of the service
GRAS SAF will deliver RO products based on data
from Metop.
Metop
GPS
The service monitors effects of space weather on
radio occul-tations. Data from CHAMP is used.
Difference in temperature is monitored.
3
User needs
Defined to monitor and identify the occurrence of
space weather effect on GPS radio occultation
measurements. The difference between the
retrieved temperature profile and ECMWF is
selected as a suited measure to use for this
identification.

• The temperature difference with respect to ECMWF
  in each height interval must reflect the same
  local time and each difference are obtained as an
  average difference in the given interval.
• Local time difference between occultations shall
  be less than 1 hour.
• An average difference wrt. ECMWF is derived for
  each height interval.
• Height intervals are defined as 10-15, 15-20,
  20-25, and 25-30 km.
• Each difference is shown as a function of UTC for
  the given occultation.

4
User satisfaction

• The primary user of GPS validation is the GRAS
  SAF project, delivering atmosphere profiles in
  NRT to (NWP) centers.
• The algorithms to identify and validate effects
  of space weather on radio occultations is the
  primary goal.
• The cost of an operational service at the current
  level (web page, no guarantee for NRT) is
  approx. 0.5 my/yr.
• With additional products such as electron density
  the service has a potential to be supported as a
  EUMETSAT activity

5
Prospects for improvements

• This service is designed to monitor the effects
  of space weather on atmosphere profiles derived
  from radio occultation measurements (currently
  based only on GPS).
• The radio occultation data can also be used to
  directly derive profiles of electron density.
  Monitoring of the ionosphere is a potential for
  improvement.
• Collaboration with other SDAs such as
  Scintillation Quickmaps, SPECTRE, and SWIPPA.
• The data sources will increase next year with
  both Metop setting and rising occultations and
  the COSMIC constellation of six satellites.
• The potential customers are satellite
  organisations such as EUMETSAT. However this
  involves making the service a co-operating part
  of EUMETSAT.