The Goldstone Solar System Radar CW Imaging System (CWIS) is the processing system described herein. It is a component of the Goldstone Solar System Radar (GSSR).

The Goldstone Solar System Radar (GSSR) is a telecommunication facility that uses the Deep Space Network (DSN) antennas and receivers to generate images of planets and asteroids. Data products are generated from low resolution delay-Doppler radar imaging of over-spread targets by coherent processing of random hop frequency sequences. The CW Imaging System (CWIS) is a high-speed data acquisition, storage, processing and display computer. Baseband CW radar return signals from DSN receivers are digitized at up to 10 MHz. A high capacity disk drive stores data during real-time acquisition. An 8 mm tape drive stores archived data. Parallel processing elements receive acquired data and execute display algorithms. A high resolution color console displays algorithm results. The storage device stores data as bandwidth permits. On-line mass data storage is provided. Data archival and retrieval operates concurrently with real-time computation and display activity. Hardware and software interfaces are provided for data acquisition, mass storage and information display.

This document defines the functional requirements of the Goldstone Solar System Radar CW Imaging System. Section 2 describes the CWIS functional requirements. Section 3 defines the software and hardware design standards.

The CWIS acquires baseband analog radar data from the GSSR receiver downconverter. The number of complex channels is set to 1, 2 or 4. Two channel operation may be configured as two channels in a single VMEbus processing chain or one channel per VMEbus processing chain. The CWIS also acquires the current receiving system parameters used for data calibration. Antenna pointing data, receiver noise temperature and transmitter power are acquired.

Radar information is received on up to four complex analog channels. Two complex channels each are acquired from two receiving stations. The CWIS digitizes a complex signal pair from two received polarizations from each receiving station, for a maximum of eight sampled analog signals. Table 1 shows the received signals. The received analog inphase and quadrature complex pairs are signals from right circular and left circular polarization antenna feeds. The CWIS must acquire and store two complex channels at a sample rate of 1 MHz each. The A/D converter maximum sample rate is 10 MHz. Data resolution is 12 bits. Signal sampling is simultaneous across the eight channels.

The CWIS records large amounts of data produced during GSSR experiments including raw complex voltage samples, averaged power and cross power data and baseline removed and averaged power data. A high-speed mass storage system is required to archive the large amount of data. A lower speed tape unit is required for off-loading acquired data. The storage system must accept data from all channels simultaneously at the specified sampling rate. The storage must have a standard SCSI interface to simplify future upgrades. Figure 1 shows the CWIS block diagram. The CWIS is configured with two hard drives and 8 mm data recorders, one each per VMEbus card cage. The hard drives are for real-time data storage. The tape drives are for data archiving, data reduction and transport. Standard data file formats such as the "Ostro" format are supported to allow easy data transfers.

The CWIS must acquire and store two complex channels at 1 MHz. One complex channel requires 3 MB/sec sustained storage at 1 MHz and 12 bits/sample. A large hard drive is required for maximum real-time data storage time. A 9 GB SCSI unit is currently available from Seagate. The ELITE 9 ST410800 drive has a Fast-Wide SCSI interface and a sustained transfer rate of 5.2 MB/sec for inner tracks and 7.6 MB/sec for outer tracks. The burst transfer rate is 20 MB/sec. The two channel 1 MHz storage requirement is met by allocating one complex channel per VMEbus processing unit. Each hard drive stores data from one complex channel at 3 MB/sec, leaving 1.2 MB/sec minimum for processed data and system parameters. The continuous recording time is 50 minutes.

The CWIS must off-load acquired and processed data to a high capacity removable storage unit. The 8 mm Exabyte cartridge tape subsystem has a 5 GB minimum capacity per tape and a 500 kB/sec sustained transfer rate. The unit has a SCSI interface. A hard drive with 9 GB of data takes 5 hours to archive and requires two 8 mm tapes.

The CWIS hardware provides data processing as required to produce real-time or near real-time data products. Images and plots are produced in real-time from acquired data and produced after acquisition from data previously stored on disk or tape.

Continuous complex FFTs are run on all active channels. The spectra are displayed directly if frequency hopping is disabled. Otherwise, the FFTs are converted to power and cross power products for use in hop state accumulation. The size of the FFT is user selected and ranges from 2⁶ to 2¹⁸.

Power and cross power products are generated from FFTs of the input data streams. The data is generated in real-time and accumulated into bins per the current hop state. The accumulated data is used to perform baseline noise removal.

The baseline noise floor is removed from the power and cross power products. For a given hop state sequence, the accumulated hop state power and cross power noise averages are subtracted from the hop state signal average to remove the noise floor. The spectrum is then divided by the averaged noise to generate an SNR corrected for the filter function of the analog downconvert chain. Multiple hop state sequences are averaged to generate the final baseline removal plots. The number of allowed hop states is 2, 4 or 8. The output is plotted as SNR versus frequency for each input data stream and cross power product. Corrections may be made for variations in antenna gain, receiver temperature and transmitted power, if real-time processing permits. Baseline removed SNR plots are delayed until sufficient spectra have been averaged to produce meaningful SNR statistics.

The CWIS is configured with 28 TMS320C40 digital signal processors and two 68040 supervisory processors. The 28 DSPs are configured as two 14 DSP processing chains. Figure 2 shows a dual complex channel CWIS DSP processing chain. Each processing chain has a dedicated VMEbus backplane. A 20 MB/sec serial DSP link or shared memory connects the two backplanes. One or more DSPs combine the two complex channels. Data from previous sessions is combined with real-time data to produce a new image when appropriate. Further performance requirements are met with the addition of hardware elements such as DSP modules. The hardware and software architecture must allow for modular expansion. The architecture may be reconfigured to address different radar targets.

Data stored on disk or tape from previous sessions may be retrieved and processed to produce new data products and images. Retrieved data may be combined with real-time data to produce a new real-time image. Data may be processed and stored for later use.

A high resolution color display console attached to the 68040 supervisory processor produces the final images for a data processing pass. A 256 gray level image or enhanced color image is available. The user selects an image or plot window from the control screen and the system updates the window in real-time.

FFTs of the input data streams is provided for display. FFT sizes are selected from 2⁶ to 2¹⁸. The system must display low resolution spectra from terrestrial planets and high resolution spectra from near earth asteroids.

The CWIS generates a hop frequency, baseline removal screen in real-time. Magnitude and phase plots for each hop state, input channel and cross power combination are displayed. SNR plots are produced for the input channels and the cross power data stream as the minimum summation criterion is met for the SNR division calculation.

The CWIS generates a "sonogram" plot of time versus frequency in real time. The sonogram is a gray scale image used to follow a drifting signal or detect polarization changes.

The CWIS generates a gray scale rasterized spectrum display to help locate an object in a wide spectrum. The spectrum is divided into n segments. Each segment is plotted as a line on a raster. Bright spots on the raster indicate peaks in the spectrum and a possible object of interest. The user may zoom in on a given bright area with the mouse to display an expanded plot. The spectrum is normalized to provide a full range gray scale image. The CWIS will automatically detect raster peaks in order of intensity and the user may zoom in as required.

The CWIS generates a gray scale or color enhanced image in real-time from real-time and stored data. The system combines data stored and processed during previous sessions with incoming data to generate images on the display console.

The user interface is intuitive and requires that only parameters meaningful to the experimenter need be set. Default values are shown as recommendations. Hardware configurations that limit the user input are checked for validity and changes are recommended. Invalid configurations are prohibited. A mouse driven user interface program configures, loads and controls the multiple processors. As the processing architectures are finalized, the user interface program is modified, providing pushbutton access to multiple acquisition and display configurations. The user interface runs on the 68040 supervisory processor. VxWORKS provides simultaneous control and display functions on a single terminal. The CWIS provides advanced features such as configuration changes during acquisition, display "zoom," and restarting an integration.

The CWIS is a turnkey system that initializes without operator intervention. The user interface and control software is provided on hard disk and self-starts on power-up.

The CWIS contains a DSN Time Code Translator (TCT) timekeeping interface. The interface provides precise, corrected time to the CWIS for data acquisition and time stamps. The time of the first sample is known to the accuracy of the station clock. Acquired data is stamped with the time and date. A 5 MHz or greater station clock is provided by the TCT for high accuracy timekeeping. One DSP is dedicated to providing programmable sample timing from the station reference. The sample clock drives the programmable A/D converters.

A real-time, multi-tasking operating system (OS) is required for resource management within the CWIS supervisory processor. VxWORKS is the real-time operating system. An interface is provided to load individual DSPs with code and to set the system configuration for a specific session.

A multi-tasking kernel is required for creation and coordination of tasks, memory management and I/O control. The kernel must support prioritized task scheduling and event-driven signaling. Inter-task communication requires mailboxes, queues, semaphores and memory management. A high level language interface is required.

The CWIS provides and external ethernet interface for data transfer and system control. Data and displays must be accessible from remote X-Windows terminals. Remote control is provided for operation and debug.

The CWIS provides a hardcopy printout of any data image. Color is required. Images are generated from real-time or stored data.

The development environment is a SUN SPARC computer networked to the VxWORKS target processors. Supervisory processor and DSP code is written on the SUN and transferred to the VxWORKS disk for loading and execution.

The CWIS uses dual VMEbus backplanes to process and transfer data between the system boards. The VMEbus provides 32 bits of address and 32 bits of data. A VSB backplane provides a second 32 bit data path. A minimum of 12 VMEbus slots is required. The bus must support multiple chained interrupts for real-time hardware control.

The power supply must be internal to the CWIS enclosure. It must be of sufficient capacity to drive all system boards while running at 50° C. The enclosure must mount in a 19 inch rack and contain an integral fan assembly. It must be rack mountable. 120 volt AC operation is required.

The CWIS architecture must be modular in design to allow for simple upgrade or expansion. It must use an industry standard, high-performance backplane with suitable plug-in cards.

The CWIS application program is written in the C language. Time critical routines and interrupt service routines (ISRs) are written in assembly language as needed to meet performance requirements. A real-time operating system kernel may be used to provide a modular, multi-tasking architecture. A re-entrant C interface library for the real-time kernel is required to access kernel services.