P.K. Jain, N. Neelakantan, and V.S. Hedge

Weather poses a danger in many parts of the world, and early warning measures are critical for preventing disasters in countries like India.1,2 Rapid communications is a key component in any weather-related warning system, since forecasts and warnings must reach the general public with as few delays as possible to be effective.3 Fortunately, a low-cost Disaster Warning Dissemination System (DWDs) conceived by the India Space Research Organization (ISRO) can reach the general public in local languages with early warnings of potential weather dangers. It employs satellite-based Direct-to-home (DTH) television broadcasts to disseminate information. ISRO is working with the Indian Meteorological Department (IMD) and Doordarshan, Prasar Bhartithe Indian's government's premier television broadcast providerto install and implement the system in 500 locations along coastal India and across the country, using the DTH bouquet of the Doordarshan to disseminate cyclone warnings.

The IMD is mainly responsible for providing advance warnings against natural hazards and developing appropriate dissemination systems. Its area Cyclone Warning Centers (ACWCs) generate special warning bulletins and transmit them every hour in local languages to affected areas.4 Realizing the immense potential of the INSAT system for warning purposes, ISRO and IMD jointly developed an INSAT-based Cyclone Warning System in the 1980s, employing specially designed receivers produced by the Indian industry using ISRO's technology. The receivers were deployed at 250 locations in vulnerable coastal regions during 1984-1985. Unfortunately, these analog receivers required S-band parabolic receive antennas about 12 ft. in diameter, vulnerable to the high wind loads associated with cyclones, and required frequency replacement.5

Over time, ISRO modified the designs and developed the Digital Cyclone Warning Dissemination system (DCWDs). This utilized the latest digital modulation techniques and error-correction codes, and reduced the diameter of the receive antenna to about 70 cm. The digital system offered new features, including automatic acknowledgment when warning messages were received, as well as an advanced Network Management System (NMS) to log events and store transmitted messages. 5 The digital receivers were deployed at 100 villages within Andhra Pradesh State. Because the S-band receivers were custom built, the cost was relatively high, at about 120,000 Rupees ($2,500 USD) each excluding antenna, RF, acknowledgement-transmitter system, and battery. an exclusive 3.8-m, 400-W hub at IMD in Chennai, India controls the receivers (Fig. 1).6

Recognizing the need to develop a low-cost disaster warning dissemination system that overcomes the limitations of the existing DCWDs system with a greater number of installations, ISRO conceived a means of sending disaster warnings by means of the satellite-based DTH bouquet, which is received by a large number of people across the country. a commercially available set-top box (STB), used for receiving the DTH signals, is modified to process addresses from the DTH transmit-hub for disseminating the disaster warnings to affected areas only. The current selling price of such a unit is only about 8000 rupees ($175 USD); with larger-volume production, this price can be further reduced.

The DTH-based DWDs can provide warning and relief information in case of earthquakes, floods, landslides, or other natural disasters. It operates at Ku-band frequencies with the disaster warning audio channel integrated into the free-to-air (FTA) DTH bouquet of the Doodarshan. When warnings are issued from any of the ACWCs, the DW-STB is forced to tune to the disaster channel. The original channel is restored once the warnings are delivered. The warning channel cannot be changed until the warning message has been delivered. Any specific DW-STB or group of DW-STBs or all DW-STBs in the network can be selected by the ACWC to deliver the warnings. Warnings are issued in the local language, and the system supports multiple region-based independent ACWCs for issuing warnings. Each DW-STB has built-in speakers so that warnings can be heard independent of a television set. All warnings are preceded by a long audible alarm to draw a listener's attention.

In its current configuration for disseminating cyclone warnings (Fig. 2), the system uses the DH hub at Doordarshan. The configuration includes three main components. The first component is a network of 1.8-m C-band very-small-aperture-terminal (VSAT) units as remote head-ends. These VSATs are installed in five different IMD area cyclone warning centers (ACWCs) across the country. The VSATs are connected to the Doordarshan DTH hub through the network's sixth VSAT. The VSATs are part of the ISRO's disaster management support (DMS) network. Each remote head-end can record audio warning files in local languages, which are transmitted to the DTH hub through the VSAT using file-transfer-protocol (FTP) capability. Warning files are stored in the disaster warning network management system (DW-NMS) at the DTH hub. Each remote head-end can also perform live transmission of an audio warning.

The second component is the existing DTH Doordarshan hub that operates at Ku-band on INSAT-4B and receives audio warnings from the remote head-ends of the VSAT network. The hub includes the DW-NMS, which can build, edit, and store a data base of DTH receivers in the network, along with their unique identification numbers or addresses and locations. DTH receivers are grouped by region so that when a particular group of receivers is selected on DW-NMS, a warning can be transmitted to all of the DTH receivers in that group for a cyclone-affected area. An operator at a remote head-end can record an audio warning and send it to the DWNMS at the DTH hub. An operator can also control the DW-NMS and select a target group of DTH receivers for receiving the warning message. The DW-NMS then packetizes the control data information (such as identification numbers for the target DTH receivers) and feeds it to the auxiliary data port of one of the MPEG-2 encoders for the DTH uplink chain at 19.2 kb/s through its RS-232C port. The selected audio file is sent to the audio port of the encoder. The same control and audio data is split and fed to all the carriers of the DTH bouquet. Finally, the encoded data is modulated and send to the RF front end for uplink to the satellite. Figure 3 shows how the audio warning data is integrated into the DTH bouquet.

The 1.2-m Ku-band DTH receivers deployed across the coastal areas for receiving audio warnings form the third component of the DTH system. These DTH receivers consist of commercially available STBs (DW-STBs) which are suitably modified to receive, parse, and decode the auxiliary data.

The DW-STB receives single-channel-per-carrier (SCPC)/multiple-channels-per-carrier (MCPC) L-band signals (950 to 2150 MHz) fed from the low-noise block frequency converter (LNBF) and sends baseband video and audio signals to a television set connected to the DW-STB. The DW-STB also contains an audio amplifier and speaker to play warnings without a television set. The DW-STB is fully compliant with DVB-S satellite specifications and can decode the system layer as per ISO/ IEC 13818-1, video streams as per MPEG2 (MP@ML) ISO/ IEC 13818-2, and audio streams per ISO/ IEC 13818-3. The DW-STB will additionally feature DVB-data decoding per EN 301 192 and parsing of received data for providing addressability features.

The DW-STB tunes to the data stream packet identification (PID) automatically as soon as it is tuned for video/audio service. If the data stream or warning is detected and the target address in the incoming data stream matches its own address, the DW-STB tunes to the audio channel and enables its built-in audio amplifier and speaker. Audio is played through the DW-STB speaker as well as a connected television's speakers. As soon as the stop-warning message is received by the DW-STB, it disables the built-in audio amplifier and speaker and retunes itself to return to the previous video/audio channel. At the same time, the DW-STB sends character data (the receiver ID) to the RS-232C port for the purpose of sending an acknowledgment to the remote head-end. When the data stream is not available or the data stream is available but the target address is not matched by its own address, the DW-STB operates normally and remains tuned to the existing FTA channel.

This newer system provides many advantages over the existing cyclone warning dissemination system. It uses commercially available DTH STBs with minor modifications to maintain low cost. The IMD's existing cyclone warning dissemination system requires dedicated hubs at each of the ACWCs in order to transmit the warnings. The new DTH-based DWDS uses the DTH hub of the Doordarshan. This system also supports multiple independent warning issuing centers, saving recurring expenditures on operations and maintenance of multiple hubs. The new system, using DVSTBs with built-in audio amplifiers and speaker, does not require a television set to alert a household of a warning.

The low power consumption of the DW-STB results in increased battery backup time and reduced battery requirements compared to existing DCWDS receivers. DTH receivers are designed for continuous operation with battery backup for 6 to 7 days. Because the new warning system uses commercially available components, such as the antenna feed and LNB, receivers can be maintained with locally available vendors, reducing the maintenance cost compared to existing DCWDS receivers which are sold and maintained by special (proprietary) vendors.

Finally, no additional bandwidth is needed by the new system, since the small audio warning files are inserted into the existing DTH bouquet along with the control data information, and fed as auxiliary data to the encoders at a rate of 19.2 kb/s. The existing DCWDS system uses dedicated bandwidth in C x S transponder of INSAT to transmit audio-warnings.

A pilot project was run to assess the robustness and performance of the DTH system before deploying it at a larger scale. Five receivers were installed at Chennai, Thiruvallur, Machillipatanam, Kolkota, and Bhubaneswar, and two remote head ends at Channai and Kolkota. The remote head-ends were connected to the DTH hub through the existing ISRO VSAT network. Regular test runs were carried out for four months by transmitting audio-warnings through the Doordarshan DTH hub.

The performance of the system was found satisfactory and additional featuressuch as end-to-end monitoring of the system using a specially designed monitor terminal, self-test capability in the DW-STB, and a stronger antenna foundation to withstand 300 mph windswere incorporated into the system before clearing the system for fullscale deployment. Figure 4 shows the receive 1.2-m antenna and DW-STB and remote head-end equipment used in the pilot project.

The DTH-based DWDS is another important application based on space technology developed by ISRO for the benefit of society. It has provided an optimum and low-cost solution for ensuring timely warnings about impending disaster in local languages to people and local administrators in affected areas. Use of commercially available, off-the-shelf components and simple, low-cost DTH technology has made this system very attractive and promising.

Although the system is currently being deployed for disseminating cyclone warnings, it can always be used in helping mitigation and disaster-management operations during other types of natural disasters, such as floods and landslides, as well as in many more yet-to-be-explored new government-sponsored or commercial applications, such as promoting new government programs and strategic communications to a selected audience.

References
1. Pradeep Sahni, Alka Dhameja, and Uma Medury, "Disaster Mitigation: Experiences and Reflections," PHI Learning Pvt. Ltd., 2001.
2. Harsh K. Gupta, Disaster Management, Universities Press (India) Pvt Ltd, Hyderabad, 2003.
3. Jochen Zschau and Andreas N. Kuppers, Early Warning Systems for Natural Disaster Reduction, Springer, New York, 2003.
4. http://www.imdmumbai.gov.in/scripts/detail. asp?releaseId=E0000CY8.
5. ISRO, "Satellite Communication in India: Perspective on Vision to Reality," Space Applications Centre, ISRO, Ahmedabad, 2011.
6. http:// www.imdchennai.gov.in/SatMet.htm.