Application Analysis of the Emergency Communication System in Weather Radar

According the work arrangements and requirements of carried satellite emergency communications, Fujian Meteorological Bureau establishes a satellite emergency communication system for radar stations to meet the needs of data transmission under the radar state of emergency. This paper introduces the main construction content, structure diagram, network diagram, drills and emergency communications procedures of the emergency communication system for the province’s meteorological radar satellite and provides the test emergency situation of the province’s meteorological radar-satellite data transmission. Satellite emergency communication system can basically meet the needs of emergency radar data transmission.


Introduction
With the progress of society and the improvement of people's living standards, higher and higher requirements have been put forward for the meteorological spirit of "accurate, timely, innovative and dedication" in the new era.Weather radar is an important means of disaster weather monitoring and early warning.
In various practices that detect the atmosphere on which humans depend, meteorological radars become disastrous weather with their high spatial and temporal resolution and timely and accurate remote sensing capabilities.In particular, it is an extremely effective tool for small and medium-scale severe weather monitoring and short-term forecasting [1].The communication network is the basis of modern meteorology.Natural disasters cause flooding and power outages, and heavily attack the terrestrial communication network.Communication is a key means to guarantee emergency operations, rescue and disaster relief.Satellite communication is one of the indispensable means of emergency communication and has received the attention of all countries [2].
At present, the data transmission of the meteorological radar system in our province uses the ground communication network dedicated line provided by the fixed network operator, although the cost is relatively low, but the transmission means is single.When an emergency occurs, such as the failure of the ground link, when the radar data is urgently needed, the data transmission cannot be guaranteed.According to the construction needs of meteorological services in Fujian Province, we propose to build a satellite emergency communication system for radar stations in the province, and propose a feasible, reliable and multi-mode link guarantee mechanism for data transmission between meteorological radar stations and provincial meteorological stations, solve the problem that the radar cloud image cannot be transmitted in the event of a sudden disaster, causing power and ground communication networks, thus ensuring the real-time transmission of radar data and ensuring the forecaster's trend and forecast of future weather.

Schematic Diagram of Satellite Communication Structure
The satellite communication system is mainly composed of a satellite transponder and a communication earth station (Figure 1).The communication satellite is a microwave relay station located in the air, and the communication system in the satellite is called a satellite transponder.Its main function is to receive low-noise amplification after receiving the signal from the ground, then perform power amplification, and then send it back to the ground.The communication earth station is composed of an antenna feeder device, a transmitting device, a receiving device, a communication device, and communication software, and is used for transmitting and receiving a carrier [3].

Vehicle Satellite Communication System
In recent years, a series of public emergencies such as floods and droughts, snowstorms, earthquakes, production and other environmental accidents have occurred frequently, improving the ability to prevent and handle public emergencies, and quickly constructing satellite communication networks at the scene of emergencies [4].It is an important guarantee for handling incidents quickly.
A single-box portable satellite station (hereinafter referred to as the product) can meet this demand.The product is highly maneuverable, flexible and off-road,

Main Content of Project Construction
Construction of satellite emergency communication system for radar stations in the province: Establish 8 satellite radar communication stations (including under construction) in the province; establish satellite central stations and portable satellite emergency communication vehicles in the provincial meteorological information center; and rent satellite links to meet emergency communication needs.
Each radar station and meteorological information center respectively set up a satellite ground station to communicate by satellite link (Figure 2).The data stream can be connected to the meteorological bureau through the satellite communication service provided by the operator.The central station and the radar station satellite terminal are directly connected to the local area network, and adopt the unified IP address of the whole province; the emergency vehicle is connected to the in-vehicle PC terminal to realize real-time data transmission.
Daily data transmission uses ground dedicated lines.The use of satellite links  disruption.The network uses VPN to establish a channel between the radar station and the weather station to ensure data security and bandwidth stability.

Functional Design of Satellite Emergency Communication System
The satellite emergency communication bandwidth resources are rich, up to 128 Kbps -2 Mbps, the disaster resistance is very strong (not subject to the ground environment), and the network is stable.At the same time, using satellites independently developed by China, satellite network security is strongly guaranteed.
The construction of the project includes: renting and sharing 512 M bandwidth satellite bandwidth (upgraded to 2 M if necessary to meet the requirements of real-time emergency communication).The existing satellite bandwidth is bidi-rectional transmission, and 512 K bandwidth is maintained at normal times to maintain connectivity.
1) The satellite communication line belongs to the emergency communication line.When the terrestrial network is interrupted, first power up the satellite communicator and router and check if the line connection is normal.
2) After the self-test of the satellite communication machine is completed, if it can be spelled out and the delay is normal, it indicates that the line switching is successful and data transmission can be performed.
3) Note: Remember not to open the satellite link and the ground link at the same time.The satellite link is used up and the satellite link must be disconnected after the ground link is restored.The disconnection method will power off the satellite communicator.

Satellite Communication Network Structure
The construction of the heaven and earth integrated multi-channel transmission platform (referred to as the Tiandi integrated platform) is a kind of intelligent device that integrates various communication means.It is characterized by support for satellite transmission links, users can freely switch back and forth between ordinary ground lines and satellite links, or can be controlled by a preset priority order and automatically switch.
The Tiandi integrated platform organically combines satellite communication and terrestrial network communication, and undergoes strict compatibility testing and stability testing to avoid various problems that users will encounter when building their own platforms.Take the Changle radar station in Figure 3 as an example.The network structure of other radar stations is the same, and the yellow line is the satellite link map.The red line is the daily ground link map (Figure 3).

Emergency Communication Drill Steps
The drill was conducted in accordance with the following steps (Figure 4).Step 2: Disconnect the fiber interface of the radar station ground communication link.At this time, the ground station router automatically switches the route  to the satellite channel to establish a satellite link connection with the provincial central station.
Step 3: Log in to the information center radar server address 10.140.X.X on the radar station intranet computer.If it can be connected and the delay is around 1300 ms, then the satellite link has been established.
Step 4: Use the portable station.When the ground communication link of the radar station is interrupted and the satellite ground station is unavailable, the emergency satellite communication portable station is enabled to realize the radar product data and the base data to the provincial information center data transmission.

Transmission Software
The satellite emergency communication data transmission software can use Fi-leZilla software [6].FileZilla is a fast, trusted FTP client and server-side open The satellite communication system related to emergency communication is classified into the fixed satellite service FSS (Fixed Satellite Service), the mobile satellite service MSS (Mobile Satellite Service), and the satellite short message communication.The currently used FSS is the VSAT satellite communication technology.Most of the VSAT satellite communications use the Earth's equatorial geosynchronous orbit (GEO, 35,786 km above the equator) communication satellites, mainly used in multimedia two-way communication systems, broadcast and television signal relay systems, etc., rarely used for personal communication.VSAT satellite communication is often a private network system with good security and catastrophic resistance, so it is always chosen as a means of emergency communication.There are many VSAT satellite communication technologies.From the perspective of network construction, they are mainly divided into three categories: point-to-point, mesh-shaped network, and star-shaped network.
is able to reach the forefront of the scene in time.The communication satellite and the satellite communication command vehicle are used to establish a sudden on-site information collection satellite communication network, and the communication link is constructed at the emergency scene and the event handling command center, and data, voice and video can be mutually communicated.The command center can understand the first-hand situation of the scene in real time, organize the resource transfer, and quickly dispose of it to achieve the goal of least loss[5].

Figure 1 .
Figure 1.Schematic diagram of satellite communication structure.

Step 1 :
Each radar station checks the status of the satellite communication machine.Usually, the communication machine is in the power-off state, and the satellite communication machine is powered on during the emergency.Observe that the two lights of the communication panel TX and RX are on, indicating that the communication machine is working normally.The network cable can also be used to connect to the computer and the communication machine, and log in to the communication machine to check the working status.But the computer IP and the communication machine should be set to the same network segment.

Figure 3 .
Figure 3. Radar station satellite communication network structure.
The satellite communication system of this project adopts a star topology Z. X. Zheng et al.As shown in the figure below, satellite ground stations, including indoor units and outdoor antennas, are established at each radar station, and a central station is established in the provincial center to realize data transmission via satellite.