In March 1998, C. Wayne Wright Wright and Edward J. Walsh of NASA began development of a new Linux-based data system for the NASA Goddard Space Flight Center scanning radar altimeter (SRA). The goal was to significantly reduce system weight and volume and thereby to enable its installation on one of the NOAA hurricane hunter WP3D aircraft (see… photo) for the 1998 hurricane season. The purpose of the SRA is to measure hurricane directional wave spectra and storm surge. The data will eventually be used to help refine and improve hurricane models and improve forecasting and understanding.

Interrupt response time, crash-proofness, and freedom from “lock-ups” were key considerations influencing the selection of the operating system for the SRA. The resulting SRA data system is built on top of a Red Hat 4.2 system and Linux kernel 2.0.29. It occupies eight inches of vertical rack space, weighs about 40 lbs, runs totally from an internal 12-volt aircraft battery, and requires about 120 watts of total input power. The system includes a custom ISA board with several PIC microchips which perform dedicated functions for the radar. It also includes the entire radar IF (intermediate frequency) strip, detectors, and a 2ns/point waveform digitizer. No monitor or keyboard is directly connected to the SRA; instead, Linux laptops are used for all control and display. Those laptops run Red Hat 5.1 and 2.0 Linux.

Additionally, RT-Linux (Real-time Linux) is used to . . .

• Drive the waveform digitizer.
• Compute the centroid-based range measurement between the transmit and return pulses.
• Manage 96 automatic gain control loops.
• Correct for aircraft attitude and off-nadir angle.
• Deposit formatted data in a shared memory block from which a normal Linux program extracts it and records it to a disk file.

* Read NASA paper *

 
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