WP2: Evaluation of design performance goals

February 12, 2010
This Work Package of the EISCAT_3D Design Study was dedicated to surveying the users’ requirements for the performance of the new radar, and synthesising these into a specification document.

The specifications, for which the EISCAT_3D project should aim, can be summarised as follows:

EISCAT 3D_Radar System Design Baseline

System configuration

• A central transmitting/receiving core, located at, or close to, the present EISCAT Tromsø radar site at Ramfjordmoen, Norway
• At least two receiving facilities for 3D measurements in the ionospheric F1, F2 and topside regions, located at ground distances of about 220-280 km roughly south and east of the transmitting facility, respectively
• At least two receiving facilities for 3D measurements in the ionospheric D and E regions, located at ground distances of about 90-120 km roughly south and east of the transmitting facility, respectively
• Data storage and communication systems located at, or close to, each facility

Operational characteristics

• The system designed for essentially unattended, continuous operation
• System control, monitoring, and data access to take place over the Internet
• Data access over the DataGrid available, once the Grid is extended to the deployment area
• Built-in test equipment (BITE) and test software
• Relative time between sites will be maintained to better than 100 ns
• A formal experiment scheduling system to allow scheduling protocols and experiment files to be uploaded and tested well in advance of the scheduled execution times, and executed automatically
• An override facility to enable experiments to be initiated by overriding the nominal schedule, either manually or automatically, in response to certain criteria being satisfied

Facilities at the central transmitting/receiving core

• A phased-array transmit/receive (TX/RX) system with at least one antenna
• RF signal generation equipment and RF power amplifiers
• A transmit/receive switching system
• Beam-steering systems for transmission and reception
• Several (four to ten) outlier, receive-only phased-array antennas for in-beam interferometry
• An incoherent-scatter receiver subsystem
• An interferometry receiver subsystem
• Time and frequency synchronisation equipment
• Digital signal processing equipment
• Built-in test equipment (BITE)

Facilities at each receiving site

• A phased-array antenna with its associated receivers
• At least five beam-formers
• Time and frequency synchronisation equipment
• Digital signal processing equipment
• Built-in test equipment (BITE)

Spatial resolution

• Resolution along the transmitted beam direction(s) better than 100 m at any altitude
• Horizontal –3 dB resolution at 100 km altitude better than 150 m

Radar field-of-view (FOV)

• Beam generated by the central core transmit/receive antenna array steerable out to a
  maximum zenith angle of about 40° in all azimuth directions
• The antenna arrays at the 3D receiving facilities arranged to permit tri-static observations to be made throughout the central core FOV at all altitudes up to 800 km

Beam steering

• Possibility to steer the beam from the central core transmit/receive antenna array into any one of more than 12,000 discrete pointing directions, regularly distributed over its FOV and separated by on average 0.625° in each of two orthogonal planes
• Beam steering system operational on timescales shorter than 500 ?s

Multi-beam 3D receiving

• Each receive-only phased array to be equipped with at least five beam-formers
• Possibility to steer each beam into any one of more than 12,000 discrete pointing directions, regularly distributed over the array FOV and separated by on average 0.625° in each of two orthogonal planes
• Beam steering systems operational on timescales shorter than 500 ?s timescale, synchronised with the central core beam steering
• 3D coverage provided by the D/E region receiving sites over the central core FOV from the bottom of the mesosphere out to a maximum altitude of approximately 250–300 km
• 3D coverage provided by the F/topside region receiving sites receiving sites over the range 200-800 km

Automatic/adaptive beam pointing calibration

• Software for automatic beam pointing calibration using celestial sources installed at each receive-only phased array
• Pointing corrections continually computed from the measured data and fed back into the beam-former control system

Transmitter parameters

• Centre frequency: between 220 – 250 MHz, subject to allocation
• Peak output power: ?2 MW
• Instantaneous –1 dB power bandwidth: ?5 MHz
• Pulse length: 0.5–2000 ?s
• Pulse repetition frequency: 0–3000 Hz
• Modulation: Arbitrary waveforms, limited only by power bandwidth

Receiver parameters

• Centre frequency: matching the transmitter centre frequency
• Instantaneous bandwidth: ±15 MHz
• Overall noise temperature: ?50 K referenced to input terminals
• Spurious-free dynamic range ?70 dB

Sensor performance in incoherent scatter mode

• Parameters of the different subsystems chosen so that the radar will generate estimates of incoherently scattered signal power with statistical accuracies of better than 10 % in the integration times specified in the Performance Specification Document

Sensor performance in in-beam interferometer mode

• 2D resolution of better than 20 m at 100 km altitude in interferometer mode.
• The interferometry receiver subsystem together with the main TX/RX antenna and the outlier receiving antenna arrays arranged to provide samples of the target visibility function on about 150 different baselines with lengths ranging from about six wavelengths (?) to more than 750?

Summary of Data Products

Standard data products from the 3D system at each of the following levels

• Beam-formed data stored in ring buffer of relatively long duration (hours to days) in a manner which allows for users to access and copy selected intervals
• At least one set of time-integrated correlated data from each set of beamformed data calculated, and permanently stored in a Grid/Web accessible master archive
• At least one, and possibly several, analysed data sets permanently stored corresponding to each set of correlated data. These should be usable for quick-look applications and statistical studies
• Use of primary data products to derive routine value-added parameters (such as velocities, conductivities, currents, and heating rates) to be available together with the analysed data sets

Additional data products also available from some (but not necessarily all) experiments using the EISCAT 3D radars

• Data on the properties of measured spectra (both ion-line and plasma line) comprising spectral power, numbers and locations of spectral peaks, asymmetries, spectral moments, and so on
• Data produced by interferometry applications (cross-phase, coherence and reconstructed visibility functions) stored in a ring buffer of sufficient duration

EISCAT_3D Data Storage, Access and Visualisation Baseline

Data Storage

• File-based and relational storage philosophies for data storage
• Storage systems to provide secure access for users and automated, secure remote backup, be Grid-compatible, and allow easy association between data and metadata
• Data Access
• Standard access applies to the majority of users, who wish to access the archived correlated and analysed data sets that EISCAT will store permanently, together with the appropriate metadata – accessible via the Web and ultimately via the Grid
• High-volume data access designed for interferometry data, beam-formed data and correlated data stored in medium term “ring buffer” storage at the pulse-to-pulse time resolution level

Access to data may be regulated according to “rules of the road” similar to those presently applied by the EISCAT Scientific Association.

Data Visualisation

• Sample-level data
  “Level meters” and similar utilities implemented; enabling the operator to probe the data flow rates the various antenna elements, to verify that the array is operating correctly
• Beam-formed data
  An approach similar to that used for the sample-level data implemented to enable scientists and operators to assess whether a particular beam-former is operating correctly and whether all of the input data streams from the antenna array are present
• Correlated data
  A capability provided to display data from multiple beams simultaneously, and to show detailed data from particular beams on request. The software will have the capacity to display data in the frequency domain (both ion line and plasma lines) and to show time histories of raw data
• System Status Information
  A user-friendly interface to provide operators and science users with various kinds of system information (transmitter power, system temperature, measurements of signal phase etc.) together with other “status” information required to establish that the various elements of system hardware are working correctly together.
  A fault-diagnostic and corrective capability built into the interface.
• Analysed data
  A set of tools displaying the results of the initial analysis of each correlated data set, in a format suitable for verifying the correct operation of the system. Links between the visualisation utilities for correlated data, the analysed data, and system monitoring data to enable the presence of a fault in any one part of the system to be easily recognised elsewhere and its causes and consequences determined

The main work in this Work Package was performed by EISCAT Scientific Association.