COSMIC & GNSS
Common-Volume Observations
Brian Breitsch
Geometry
Method
Diurnal results
Long-term results
Future work
Assumptions
- model signal propagation paths as straight line segments
- use SGP4 orbit calculation model with NORAD TLE
- accuracy generally much better than 3km
SGP4 =
"Simplified General Perturbation Model"
version 4
Geometry
common observation volume
impact parameter
region of interest (ROI)
COSMIC satellites
- 72 degree inclination
- 780km (ish) altitude
Effects of Satellite Motion on ROI
max vertical ROI movement
exercise
Effects of Satellite Motion on ROI
max horizontal ROI movement
exercise
3D Line Intersection
3D "intersection"
3D Line Intersection
3D "intersection"
Line-Segment Intersection
line-segment intersect
line intersect
This case is useful when the common-volume ROI is close to the COSMIC satellite.
Common volume observation metric
We want a sense of how much "common-volume activity" is going on at a time...
line segment proximity
intersection point of interest (POI)
Total Number of Geometries
1 receiver
6 COSMIC satellites
32 GPS satellites
(but most of them we don't care about...)
possible common-volume geometries
at every moment
Mask/Filters
- GPS 1 (for RX) elevation > threshold (5 degrees)
- GPS 2 (for LEO) elevation > threshold (-20 degrees from LEO)
"We don't count geometries with line segments through the Earth!"
- proximity < threshold (1500km)
- POI-to-receiver distance < threshold (3000km)
"We don't count geometries that are not common or are too far out in space!"
Histogram
- bin total # of valid common-volume geometries according to proximity metric
bin cutoffs
Common volume observation
correlation with COSMIC elevation
CDAAC Data:
- podPhs (15-30min)
- occultation and pre-occultation phase observables
- LEO/GPS ECF coordinates
- podTec (15-30min)
- calibrated TEC
- LEO/GPS DCB values
- LEO/GPS ECF coordinates
- ionObs, opnGps, goxBin (always)
- ionosphere observations, open GPS format, GOX Binary format
- phase observables, some for > 0 GPS elevation angle
we'll just use this
Common volume observation
Common volume observation
Peru
Alaska
Note: there is a lot of "missing" data, partially due to the fact that COSMIC 2 and 3 have essentially been out of commission since 2009.
Common volume observation
Peru
Alaska
"Event" detection
- look at single COSMIC satellite
- check against proximity threshold
- i.e. 2 common-volumes at < 100km proximity
- event window threshold to combine "short" events
"Event" detection
Peru
Alaska
Conclusions
- definitely more common-volume observations (and occultations) at high latitude
- nicer/more periodic common-volume at high latitude
Future Work
(future as in...tonight...)
- extract long-term event results
- periodicity of high-latitude
- dominant azimuthal angle of ROI
- CDAAC data availability statistics
References
- SGP4:
- http://utias-sfl.net/wp-content/uploads/SSC09-X-7.pdf
- http://elib.dlr.de/87081/1/5a_P6_aida.pdf
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By Brian Breitsch
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- 597