INSAT UPLINKED AGROMET STATION--A SCIENTIFIC TOOL WITH A NETWORK OF AUTOMATED MICROMETEOROLOGICAL MEASUREMENTS FOR SOIL-CANOPY-ATMOSPHERE FEEDBACK STUDIES

摘要

The role of land surface in earth-atmosphere system is crucial to predict weather and future climate at meso (approx10 km) and micro (approx1 km) scales. Systematic measurements of Land Surface Processes (LSP) within boundary layer are extremely important to understand the vegetation-atmosphere feedback, to develop new parameterization schemes for Land Surface Models (LSM) and validation of satellite based estimates. Till now, India had no such network of regular micrometeorological observation system for recording, archiving and converting data into scientific usable format. A prototype model of 10 m tall micrometeorological tower known as Agro-Met Station (AMS) has been defined and designed for short canopies (maximum average height 3m) such as agriculture, grasslands, natural bush etc. This has sensors capable of measuring radiation, energy and soil water balance components continuously with a total of 26 quantities at half-an-hour interval. The data can be archived in and retrieved back from 16-channel datalogger alongwith station location and time stamping from in-built Global Positioning System (GPS). INSAT-uplinked AMS transmitter operates at a frequency of 402.75 MHz +- 200 KHz. This dessiminates in situ measured data every hour from any remote station installed in the footprint of INSAT / KALPANA-1 Satellite. The transmitter output is connected to crossed Yagi antenna through antenna port with antenna gain of 11.5 dBi with isotropic gain for both right-hand and left-hand polarization field. The data transmission rate is 4.8 kbps. Transmission format of AMS is programmed in such a way, that data can be transmitted in two bursts within one millisecond to accommodate a maximum of 26 measurement fields. The data are generally retransmitted through KALPANA-1 extended C-band transponder at 4.5 GHz frequency to earth which are received through antenna at earth station. This frequency is modulated at 2-3 times to reduce the frequencies and ultimately converted to rawdata, which were again converted to user-friendly data format. A 20 watt solar panel is used for charging the sealed maintenance free 12Volt /26AH Battery, which delivers typical peak power of 18 watts with full sunshine and acts as power source for AMS. A preliminary evaluation on functioning of prototype AMS has been carried out over four agricultural sites including C3 (rice, groundnut) and C4 (sorghum) crops over semi-arid climate in India. The seasonal variation of surface fluxes across the sites and crops have been well captured. The setting-up of network of such towers is in progress. This kind of in situ system with the aid of geostationary communication transponder is unique in the world and would help in systematic micrometeorological measurements for land surface studies also in other Asian countries within the satellite footprint.