Data Collection Platforms

Abstract

The National Data Buoy Office through AEL has developed environmental monitoring systems that are capable of supporting various national and international experiments to be performed during the next five years. The knowledge from these experiments is required for developing numerical models for long range weather prediction and for assessing the long-term effects of pollutants on the atmosphere.The Random Access Measurement System (RAMS) will be launched aboard the NIMBUS-F meteorological satellite, by NASA during the spring of 1975 and will carry an electronics and communication system to locate and receive signals from a large number of DCP's. The satellite data will then be transmitted to a ground station where it will be readily available to the scientific community, RAMS is so named because the system will locate and retrieve sensor information from numerous movable platforms in a randomly timed fashion.Platforms that are particularly suited for use with RAMS are those which require both location and data transmission support. These include drifting ocean buoys that a r e taking oceanic and meteorological measurements, small weather platforms on slowly drifting ice, balloon-wind stations, and other moving platforms obtaining scientific data.The DCP platform is comprised of two major functional subsystems: the digital logic and the transmitter. The digital system receives the sensor data, converts this data as necessary, places them along with fixed data into a proper format, and encodes the data for phase shift key transmission. The transmitter consists of a stable oscillator circuit, a multiplier-phase shift key circuit, and a power amplifier circuit.The oscillator subassembly generates a highly stable carrier frequency (50.15 MHz); the multiplier-phase shift key circuit increases the frequency by a factor of eight and phase modulates the referenced Oo carrier p 60O); an F W amplifier subassembly increases the power output to the specified level.The oscillator exhibits a 1 second, short-term stability of better than 1 part in lo9, and has a drift rate of less than f 4.2 Hz/15 minutes. The oscillator is designed to maintain f 2 ppm frequency tolerance and drift characteristics from -5°C to -45°C. Since location is predicated on doppler measurements based on successive frequency measurements, the DCP must have small short term oscillator drift rate performance. Narrowband matching networks are utilized to reject undesirable harmonics, thereby meeting the spurious product specification of -50 dB down within * 15 kHz of the carrier. The power amplifier subsystem is a conventional three stage, high gain (20 dB) efficient UHF amplifier. A minimum amount of tuning is required to obtain the required output power of 2.4 watts maximum.