Inside GNSS Media & Research

MAY-JUN 2018

Issue link: https://insidegnss.epubxp.com/i/987551

Contents of this Issue

Navigation

Page 34 of 67

www.insidegnss.com M A Y / J U N E 2 0 1 8 Inside GNSS 35 cial type of beacon designed to be activated in flight as soon as a dis- tress situation is detected • SGB (Second Generation Beacons) specially optimized for MEOSAR system and offering an improved performance (detection and inde- pendent loc a l i z at ion acc u rac y) compared to current beacons. SGB sta ndard w i l l cover a l l t y pes of Cospas-Sarsat beacons. ELT(DT): the Cospas-Sarsat ADT Solution In order to answer ICAO requirement of Annex 6 for ADT, Cospas-Sarsat has been working on a new beacon standard named ELT(DT). Compared to other types of beacons used in Cospas-Sarsat (EPIRB, ELT, PLB), ELT(DT) has been designed for a particular use case: being activated in flight upon a distress situ- ation. is use case involves additional constraints that were taken into account during the specification phase: • Based on BEA (Bureau Enquête et Analyse: French Office for Aeronau- tical Accidents Investigation) stud- ies, it appears that in many cases an aircraft will impact the surface within just a few minutes aer the detection of the distress situation. At impact, the beacon and/or the external antenna on the fuselage may be destroyed or the aircraft may sink underwater. In both cases, it is no longer possible to receive sig- nals from the beacon. It was then determined that the beacon has to transmit its signal as soon as a dis- tress situation is detected and until the crash, with a repetition rate high enough to get a sufficient detection probability at ground stations and to make sure that the last burst is not too early before the crash: ■ Transmission of the first burst 5 seconds aer reception of the trigger (manual or automatic) ■ A repetition rate of: • 5 seconds during the first 120 seconds aer activation • 10 seconds aer the first 120 seconds and before 300 sec- onds aer activation • 30 seconds aer 300 seconds aer activation • A special transmitted message was designed to indicate at least: ■ e trigger which activated the beacon (automatic trigger or manual trigger) ■ The encoded location from an integrated GNSS receiver Last but not least, one can note that the MEOSAR system is well suited to process ELT(DT) signals as it allows instantaneous detection and global coverage. MEO satellite visibility offers redundancy then allowing for a high detection rate of the signals. Moreover, if a signal is detected through a sufficient number of satellites, the ground station can compute an independent loca- tion associated with speed estimation. Finally, completed by an internationally well-known ground segment for the dis- tribution of the alerts between countries and geographical areas, Cospas-Sarsat offers an efficient solution to ADT. Another advantage of the Cospas- Sarsat solution is the possibility to com- bine the ELT(DT) function with a legacy ELT beacon which triggers on crash. Into a single device, it is then possible to answer to both ICAO requirements for ADT and for ELT with minimum evo- lutions on the aircra. e specification for this combined solution is currently refined in standardization bodies, in particular in terms of use of homing sig- nal and battery duration, but this would be a significant additional advantage of the solution. To comply with exist- ing environmental and test conditions (lightning, radiofrequency, altitude, pressure, shocks, vibration, fire, trans- Capability MEOSAR capabilities LEOSAR capabilities compared to MEOSAR GEOSAR capabilities compared to MEOSAR Worldwide coverage Yes Yes No (no polar coverage) Real-time continuous access Yes No. Latency up to several hours until satellite pass, and then potential latency until downlink Real-time continuous access on covered area, but with a less favorable link budget compared to MEOSAR Number of satellites simultaneously in visibility More than 10 satellites in visibility at anytime and anywhere. Most of the time no satellite in view, and in general only one satellite at a time (except for polar areas where multiple visibilities can occur). Only 1 or 2 satellites in view and therefore important impacts masking effects Independent localization of static or slow- moving beacons Yes, single burst localization possible Available from Doppler measurements, but only with multiple burst (at least 4) Not available Independent localization of fast- moving beacons Yes Not available Not available Processing of new generation of beacons (SGB) Upgrade of the ground stations necessary and planned Not available (on- board processing) Upgrade of the ground stations necessary and planned Figure 3: Assets of the MEOSAR system

Articles in this issue

Links on this page

view archives of Inside GNSS Media & Research - MAY-JUN 2018