INTELLIGENT INTERFACE: REMOTE SENSING THROUGH SATELLITES by N. GOLDIE, I. JOHNS and I. DURHAM SUMMARY MODAC (MOBILESAT Data Acquisition and Control) is a facility for the transfer of field data to a personal computer in the office, laboratory, or works depot. MODAC, comprising the INMARSAT-C terminal and Intelligent Interface connects directly to the data acquisition equipment currently used by water authorities and environmental agencies worldwide. This breakthrough in low cost remote monitoring technology is the brainchild of the CSIRO Division of Water Resources, part of the Institute of Natural Resources and Environment. Essentially, the new technology involves a marriage between existing data loggers or remote location sensors and the INMARSAT-C satellite communications system, by way of MODAC fntelligent Interface. CSIRO scientists in Canberra worked for two years to perfect what they call, familiarly, "I-squared". MODAC has attracted international interest. This Australian development is unique because it provides connection of INMARSAT-C satellite communications to existing equipment. INMARSAT-C has geostationary satellites over the Atlantic, the Pacific, and the Indian Oceans, so that a user can have access to data from remote sites anywhere in the world.
Nick Goldie is a Communications Officer for the CS/RO Division of Water Resources, Canberra Laboratory. The development of the MODAC Intelligent Interface has been the prime responsibility of Ian Johns, Manager, and Ivor Durham, Engineering Supervisor of the Instrumentation Research and Development Group. A conference/ workshop on MODAC systems was held in Canberra, 28-30 October.
I. Durham
I. Johns
N. Goldie
It was this which led to the development of MODAC Intelligent
REMOTE MONITORING
Interface.
INMARSAT started life as a London-based marine communications system involving 56 countries and the United Nations; more recently INMARSAT have extended their operations to land-based communications. Used with the latest INMARSATC transceivers, the MODAC Intelligent Interface has eliminated the need for an operator at remote sites. The high costs of land lines and radio telemetry systems, when used over great distances, meant that it was necessary for an expedition to go to the site, plug a computer into the data recorder, and so collect the information. Intelligent Interface takes the place of the operator, and send the data home, back to a personal computer by way of an X.25 pad or X.32 modem. The Australian water industry has made limited use of low cost satellite telemetry since 1978, originally via the French ARGOS Data Collection Service. Oceanographers and meteorologists have used ARGOS since the early 1970s, but there were some major limitations, notably the uplink-only capability, the maximum message bits per transmission being 256, and the gap time between passes which did not allow continuous real-time data recovery. The introduction of INMARSAT-C has also substantially cut costs in actual bits-per-dollar charges, as compared to the fixed cost per day charged by ARGOS (see Figure 1). AUSSAT Pty Ltd briefed the Instrument R & D Group of the CSIRO to design an interface to the INMARSAT-C satellite system, suitable for data acquisition and control. DOLLARS PER K/blt (APPROX. ONLY)
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THE FIRST INSTALLATION The first commercial installation of Intelligent Interface was at Weeli Wolli Creek, in the remote mineral-rich Pilbara region of Western Australia, which was commissioned cm January 31st, 1991. The site is a priority metering station for hydrographers working at Karratha. Seven sensors measure river levels, rainfall, temperature, humidity, solar radiation, and wind speed and direction . Information from the sensors is rec~rded every two hours. After six hours three sets of readings are automatically transmitted over INMARSAT's Pacific Ocean satellite to an electronic mailbox at the new Perth Land Station operated by INMARSAT's Australian signatory OTC. Hydrographers at Karratha use their PCs to dial the OTC mailbox to review or recover data using a software program called Hydsys, which recovers the data from OTC and processes it to a telemetry data base. According to Ian Tite of the Western Australian Water Authority, the system has worked well, with no loss of transmissions.
THE SYSTEM Components of the INMARSAT-C SCADA (supervisory command and data acquisition) system would typically include sensors, a data logger, Intelligent Interface, and the INMARSAT-C transceiver, together with a solar panel and battery (see Figures 2 and 3). Data is transmitted on L band (1.5-1.6 GHz) to the satellite, and on C band to the CES (Coastal Earth Station), and from there by landline to its destination. The system cycles through three modes of operation on a pre-set time interval. These modes are: 1. sleep
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MODAC INMARSAT-C SYSTEM SATELLITE~
(INMAASA~
~
AUSSAT
L¡Band/Bi-direcUonal\ C.
Band
T-,y
2
EARTH STATION
ol-"<11111'--'"" 0
15
BITS/DAY MAX> 1112
OFFICE OR
30
46
55
66
76
90
LATITUDE (+/- Degrees)
ARGOS 1041
2104
21111
40H
HU
11H
7111
LABORATORY
Landlone~D PC MOOEM
Fig. 1 -
Argos/ lnmarsat-C
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WATER October 1991
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