MILIPOL Paris 2017
Improve the accuracy of geolocations based on publicly available orbits
It is well known that accurate satellite carriers geolocation needs accurate ephemeris data. In many cases, the geolocation operator has to turn to the satellite operator to get such informations with good quality, and very often because of regular satellite manovers !
In some cases, these orbits are not available. What solutions are available in such a case ?
NovaGrid has developed a method named "co-orbit estimation" that estimates a "coupled orbit" (coined as "co-orbit") of the selected satellites. This co-orbit is obtained via a subset of carriers of known location (called secondary references). This co-orbit allows one to perform accurate geolocations. The accuracy is about the same as the accuracy we would obtain using true operator ephemeris.
The following video illustrate this by showing two HyperTask missions:
- the first one is the co-orbit mission. This mission estimates the satellites co-orbits using one main reference carrier and two secondary reference carriers. This co-orbit is available through RPC requests to other missions,
- the second mission is a massive and automatic geolocation mission. It uses the orbits provided by the first mission.
Simulatenous Multi-Target Geolocation Without Reference
Currently, the geolocation process using TDOA and FDOA measurements requires a carriers which location is known (actually, a "Reference carrier") in order to compensate the satellites on board OL drift and accuracy.
There are situations, when the operator of a geolocation system has to deal with couple of satellite where no reference carrier is available. What are the solutions provided by modern geolocation systems in such a case ? Usually, the suggested solution is to perform two measurements (several hours are needed between each measure) and estimate the crossing point the 2 TDOA line of points (one LOP for each measurement). While this is a nice and intuitive idea, when one of the two satellites follows an inclined orbit, when the two satellites have stable positions, this method is actually not reliable. It provides a very poor geolocation accuracy (hundreds of km) for the following reasons:
- the TDOA LOPs offer very small angular variations during the day (typically 0.1 degres )
- the limited accuracy of both TDOA measurements and satellites ephemeris will displace the estimated TDOA LOP (typically along the longitude axis)
In order to solve this situation, NovaGrid has developped an original method called "Simultaneous Multi-target Geolocation Without Reference". It is relevant when accurate orbits are available for both the main and the mirror satellites. The procedure is as follows:
- select the satellites (and ephemeris) involved and the transponders of interest,
- select a range of of 5 to 15 targets to locate,
The video below shows HyperTask, performing this mission on a real case :
A new HyperSuite software module is available : HyperStream !
HyperStream provides numerous tools and views to manipulate and analyze unknown bit streams.
HyperStream enables the user to discover technical facts about the bitstream (error correcting codes, periodic patterns, known patterns, scramblers, ...), extract binary information segments, compare binary information streams or segments, compute statistical tests, ... and much more !
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