Description of the AVAPS Dropsonde Aircraft Data System

The aircraft data system is completely different, both in system software and hardware, from all previous dropsonde systems NCAR has developed. The most significant development in the hardware is the narrow-band 400 MHz telemetry receiver. The design requirements of the aircraft data system are:

• Operation by one person
• Receive and process data from four dropsondes simultaneously
• Simple Graphical User Interface (GUI)
• Continuously output real-time PTH and wind for each channel to the aircraft computer systems as the dropsondes are descending
• Operation on aircraft with or without aircraft data systems.

The most significant feature of the AVAPS data system is its ability to receive and process data from up to 8 sondes simultaneously, essential for obtaining a fine horizontal distribution of soundings. Launch procedures are simple enough to allow releases less than 20 seconds apart, if desired.
The aircraft hardware is typically composed of a computer, monitor, telemetry chassis, and launcher. The hardware is designed for installation into a standard 19-inch rack. The system also requires a GPS antenna mounted on the top of the aircraft and a UHF antenna, for receiving the dropsonde signal, mounted on the bottom of the aircraft. If available, an Ethernet connection to the main aircraft data system for flight level information is highly desirable.

Telemetry Chassis Subsystem

Each install of AVAPS requires a receiver telemetry system. The receiver telemetry system comprises some sensitive 400MHz radio frequency (RF) modules with some tunable decoding hardware.  All these components are integrated into a 3U (5.25") tall 19" rack that mounts into standard width computer racks.  The chassis is constructed of the following electrically identical removeable modules:

• One Power Supply Module: A single Power Supply module provides the DC voltage required for telemetry chassis operation.
• Telemetry Receiver Module: The Telemetry Receiver module is a narrow-band 400 MHz receiver used to receive and demodulate the telemetry data from the dropsonde. Depending on requirements, there can be up to 10 receivers in a chassis, where 8 can track sondes, one records engineering data for all of the deployed dropsondes, and the last is a potential spare.
• Dropsonde Interface Module: The dropsonde interface module provides the local interface required to prepare a dropsonde for launch. The dropsonde is connected to the module using a specialized interface cable. Through this interface, dropsondes are initialized prior to dropping.

Each of the above modules, with the exception of the power supply, contains a microprocessor and a communication interface. The computer controls all functions and receives data from each module through I/O cards and displays the status of each module. All of the hardware in the telemetry chassis is designed and built by NCAR.