Presentation on theme: "DBCP Workshop, Chennai October 2004 David Meldrum and Duncan Mercer Scottish Association for Marine Science www.sams.ac.uk Further refinements in the use."— Presentation transcript:
DBCP Workshop, Chennai October 2004 David Meldrum and Duncan Mercer Scottish Association for Marine Science www.sams.ac.uk Further refinements in the use of Iridium for polar applications
DBCP Workshop, Chennai October 2004 Satcom systems available to buoy operators Inmarsat D+PagerGEO< 1 kbyte/day GOES, MeteosatMessagingGEO< 5 kbyte/day ArgosMessagingLEO< 5 kbyte/day AprizeSatMessagingLEO?? Inmarsat CMessagingGEO< 10 kbyte/day OrbcommMessagingLEO< 50 kbyte/day IridiumVoiceBig LEO1 Mbyte/hr
DBCP Workshop, Chennai October 2004 Features of Iridium 66+ satellites in low earth orbit Designed for voice communications Real-time: inter-satellite comms 2-way True global Compact antenna Future more or less assured Detested by Argos
DBCP Workshop, Chennai October 2004 Iridium constellation
Iridium in the GreenIce project Climate change – is the Arctic ice thinning? Average ice thickness difficult to measure Nagurny theory: spectrum of swell waves penetrating ice is a function of area averaged thickness Small waves (λ = 1500m, 4mm pk-to-pk) Need to resolve 1 radian tilt (strain 4x10 -8 ) 75kbyte/day of spectral and other data Latest deployments spring/summer 2004 Met data on GTS via Metocean SVP-Bs and Argos
DBCP Workshop, Chennai October 2004 Iridium – modes of access Dial-up over voice circuit Modem to modem ~300bytes/s ~$1/min connect time A bit flaky – unexplained call drops Short Burst Data (SBD) E-mail service Mobile originated packet transfer ~2 kbyte max packet size ~$1/kbyte More or less bomb-proof Short Message Service Can be used to wake mobile up for SBD xfer Direct Internet Various flavours….
DBCP Workshop, Chennai October 2004 Short Burst Data Pathways Simple AT commands IRIDIUM NETWORK INTERNET SENSOR USER MODEM TX Buffer RX Buffer +SBDWB +SBDRB +SBDI Data@SBD.Iridium.com Iridium@sams.ac.uk
DBCP Workshop, Chennai October 2004 Example e-mail received by user (MO message) From: Sent: Tue, 23 Sep 2003 22:02:24 Subject: SBD Msg From Unit: 300090807080903 MOMSN:152 MTMSN:0 Session Status: TRANSFER OK Message Size (bytes): 1960 Unit Location: Lat = 56.457321 Long = -5.458788 CEPradius = 2 Message is attached.
DBCP Workshop, Chennai October 2004 seconds SBD Delivery Latency
SBD vs Dial Up SBD easy to implement….SBD easy to implement…. Cost penalty?Cost penalty?
DBCP Workshop, Chennai October 2004 SBD vs Dial Up SBD easy to implement….SBD easy to implement…. Cost penalty?Cost penalty? $115k for 6 months!$115k for 6 months!
DBCP Workshop, Chennai October 2004 Revisit dial-up! Charged at 1$/min, 10¢/kbyte or better Identify cause of call drops Modify ZMODEM protocol Create outbound file queue to deal with remaining call drops Establish dedicated modem and server Array of 5 platforms has run without problem since May
History repeats itself… Early problems for the Argos user Why buy Argos? Argos promises to meet user need The system works! How does it work? Will it do a new task? Suck it and see The system doesn’t work… God Only Knows (GOK) Satellite Operator Only Knows (SOOK) Whom do you contact? The system costs more than you can afford… Tariff and invoices incomprehensible
DBCP Workshop, Chennai October 2004 One solution – maybe for Iridium too? DBCP Technical Co-ordinator (1987) Based at Argos Toulouse Access to all elements of chain, incl GTS Access to Argos technical team JTA negotiations Discounted price for global bulk purchase Tariff and invoices still incomprehensible System still costs more than you can afford At least the mess is partly of our own making….