GISdevelopment.net ---> AARS ---> ACRS 1992 ---> Earth Environment Application of Airborne Remote Sensing Data Transmission System in Earth Environment Monitoring Shi Zehua, Zhang Zhaming, Sun Maohua The Research Center for Space Science and Application, Academia Sinica Beijing P.R. China Abstract There are many different data types in airborne remote sensing because what kind of sensor can be used depends on the environment, so a digital communication system must can be varied to suit these different data. This paper mainly introduces a down - link and monitoring system. The data rate of the down-link ranges from 1. 2 kbps to 6Mbps, so the down-link can meet the requirements of all our sensors now, and we can get the high quality images of the target on the monitor in headquarter on earth, the data may also be sent to a computer to be processed. This system may be used in monitoring floods by SAR, monitoring forest fires by MSS and monitoring the windstorms in desert by CCD scanner, etc. This system was successfully used in monitoring the Chinese vast flood in 1991, in the paper we will give some flood photographs taken from the monitor screen that time. In China, there are many disasters that may cause vast losses every year, such as floods, forest fires and earthquakes , etc. Floods is the main source of the losses. In 1991, a vast flood took place in about one half the aera of China Yangtze-king River, Songhua River, Dongting Lake, Taihu Lake,, etc. are all in the range where are the main economic and industrial center in disaster monitoring system. We designed and realized this system . The system has many sets in series, the first one is a analo FM system, the second one is a digital QPSK system, the frequency of the system may be 800MHz, 1500MHz and 2000MHz, now we are using C and K band. This paper mainly discusses the digital system. 1. System Scheme and Principle In order to monitor disasters, there must be a remote sensor and a data link system. There are many kinds of remote sensors, so the data collected by sensors is different in bit rate, data scheme, etc. In order to meet the need of the sensors, a system with variable bit rate must be realized, The system is composed of a down-link subsystem and a receiver earth station. Fig 1. is the block diagram of the down-link subsystem on aeroplane. Fig 1. Down-link Subsystem on Airplane the need of monitoring different disasters, we can use the most sensitive sensors in the gathering of the important data, the weather also plays a key role in the choice of sensors, In flood, SAR is very sensitive to the difference of water and land, it is a microwave sensor which can be used in all weather. In the case of forest fire, MSS is sensitive to infrared ray. In evaluation the output of the plants, MSS is also suitable, but cloud and rain may decrease its efficiency. The second is a data processing block and a modem, in the block, the image information is transformed to digital signals then to serial data ( fig.2 is the structure of the data ), then the data is sent to a modem and become QPSK signals, the data bit rate is 17.18Mb/s, IF is 70MHz, fig. 3 is the net-figure of modulated signal. Fig. 4 is the frequency spectrum of IF. Fig 2. Data Structure Fig 3. Net-fig of QPSK Fig 4. IF specturm of modem The third is a IF amplifier. It gives signals of sufficient power to the frequency convertor. It's a linear amplifier with bandwidth of 30MHz. Fig 5. is the output spectrum. Fig 5. Specturm of IF Amplifier The fourth is a frequency converter and a local oscillator with the frequency of 1576MHz, the output of the convertor is 1506MHz. The fifth is a power amplifier which is B-C kind amplifier and not a linear amplifier. It gives 25W power to an antenna on aeroplane. Fig. 6 is the antenna on aeroplane. Fig 6. Aeroplane Antenna Fig. 7 is the block diagram of the receiver station. The error rate of the system is less then 10E-5. Fig 7. Diagram of receiving station of down-link Block 1 is a low noise amplifier, Nf<1dB, the spectrum of its output is showed in fig. 8. Block 2 is a frequency converter to change frequency to 70MHz. Block 3 is a demodulator of QPSK signal, fig.9 is the eye-figure of the demodulator, block 4 and 5 is a D/A convertor and a monitor. Fig 8. Frequency Spectrum of Receiver Fig 9. Eye-fignature of demodulator 2. Application The system has been used many times in monitoring floods. In 1988, Huaihe river flood. In 1989 Jingjiang river flood. In 1991, Yangtze-king river vast flood in China. Fig. 10 is the photocopy of the sytem , the earth station is mobile. Using the system and satellite communication system, necessary flood information can be sent to the headquarter in a short time, so leaders can make decisions quickly. The information can be memoried in a computer and shown on a monitor Fig. II is some photographs taken on the monitor. 3. Conclusion This system is designed and improved through several in-site experiments, and now a complete technical system with high performance, high quality and great convenience of usage is available for practical application. It can be used in many cases.