SKA Site Characterisation and Array Configuration; Overview and Status WP2 2011 Rob Millenaar, SPDO

Site Characterisation

1. Intro SKA Site Characterisation/Selection

2. Request for Information 1. In situ measurements

– RFI environment – Tropospheric phase stability

2. Configurations

Oct 2011 2 RPM / WP2 2011

Site Characterisation/Selection

Site Characterisation has been driven by site selection processes • Information gathered during PrepSKA WP3 by

– Studies – Measurements – Enquiries

• Recently, the Request for Information (RfI) and the site’s responses have addressed a number of site characteristics

Oct 2011 3 RPM / WP2 2011

Request for Information

Science and Technical Selection Factors: 1. Plans and cost for providing basic infrastructure components 2. Plans and cost for providing electrical power 3. Plans and cost for data transport 4. Physical characteristics of the sites that will affect the system

design 5. Radio Frequency Interference (RFI) environment (current and

long-term) and Radio Quiet Zone Protection 6. Ionospheric and Tropospheric characteristics 7. Array science performance and associated figures of merit for

each Candidate Site

Oct 2011 4 RPM / WP2 2011

Request for Information

’Other’ Selection Factors: 1. Political, Socio-Economic and Financial 2. Customs and Excise 3. Legal 4. Security 5. Employment 6. Working and support environment

Oct 2011 5 RPM / WP2 2011

Request for Information

• Responses to the RfI from both candidates were received by 15-9

• Expert Panels and Consultants to review the information supplied and identify strengths and weaknesses for the candidates to host the SKA

• Some summary reports to be written by SPDO • Deliver reports to SSAC

Oct 2011 6 RPM / WP2 2011

Site Characterisation

Physical characteristics, at various part of configuration • Climate/weather

– Air temperature, min, max (average and absolute) – Rain – Humidity – Wind – Solar radiation – Cloud cover – Severe weather

• Lightning • Strong winds/hurricanes/cyclones • (Flash)flooding • Large dust storms • Hail

• Geotechnical – Sub-surface strata – Water table – Surface and sub-surface temperature and conductivity

Oct 2011 7 RPM / WP2 2011

SKA Site Environment

The environment directly affecting science performance: – RFI environment • Current -> measurements (SPDO, sites) -> expert panel

• Future (RQZ) -> response to RfI

• Legislation -> response to RfI

– Tropospheric stability -> measurements (SPDO) -> expert panel

– Ionospheric stability (scintillation, TIDs) report done

Oct 2011 8 RPM / WP2 2011

external consultant

-> expert panel

RFI Measurements

Purpose is to characterise the RFI environment at: • Core location, with high sensitivity to assess

the relative quietness of the sites. • Remote sites, with reduced sensitivity, to

assess the typical RFI environment outside the RQZ.

Results to be used in the site selection process and will inform instrumentation design.

Oct 2011 9 RPM / WP2 2011

RFI Measurements

Partners: • LN Receiver, control, infrastructure: SA • FFT Spectrometer, filter bank: Aus • Data processing and reporting software: Neth.

Oct 2011 10 RPM / WP2 2011

RX FB

NS

FS

R pol

az Proc

Ctrl

Rpt

RFI Measurements

Some details • 70-2000 MHz in 9 bands at ~30 kHz BW • ~6dBi logper antenna • Pointed to horizon, 4 azimuthal directions,

2 polarisations • Frequent calibrations

Oct 2011 11 RPM / WP2 2011

RFI Measurements

A set of measurement modes to test various aspects • Quick scan mode, to provide a medium sensitivity

overview in all directions and polarisations. • High sensitivity mode, same with long

integrations. • Rural mode, med sensitivity, at remote sites. • Max-hold mode, low sensitivity, medium time

resolution, done as variation of quick scan mode. Carried out at remote sites.

Oct 2011 12 RPM / WP2 2011

RFI @ Core

Oct 2011 13 RPM / WP2 2011

RFI @ Core

Oct 2011 14 RPM / WP2 2011

RFI campaign at core

• Campaign completed mid 2010 at both core sites • In some cases excessive signal levels have

produced spurious signals – Required exception handling in report generation

• In both countires sources of unavoidable RFI are prominent in the spectra: – Military satellite systems (VHF, FLTSATCOM) – Communications and nav satellite systems

(Globalstar, Iridium, GPS, Glonass) in L-band – Aircraft comms (VHF) and nav (UHF) systems

• These, along with terrestrial RFI, set minimum design requirements for RFI robustness. Oct 2011 15 RPM / WP2 2011

RFI campaign at remote sites

• Selection of 4 from 25 remote stations (>180 km)

• Measurements at the remote sites were delayed, because: – Initial design of remote station configuration

needed to be refined, because of • Investigations of availability of land • Impact of RFI: find ‘acceptably quiet’ locations

– 1. Maximum tolerable levels – 2. Consider transmitters, antenna patterns and antenna

height, transmitted power levels (national databases) – 3. Propagation attenuation (apply terrain information)

Oct 2011 16 RPM / WP2 2011

RFI campaign status

Status now: • Measurements at the core and remote sites

completed • Reports made and submitted to Expert Panel • Expert Panel’s report expected next week, to

be submitted to the external consultant reviewing current and future RF environment at the sites.

Oct 2011 17 RPM / WP2 2011

RFI Results

Site Selection is targeted to be completed by Feb/March 2012. Because this is a very sensitive matter it is not appropriate to show any RFI results from either candidate site now. Once released, the SKA community will have an excellent snapshot of the RFI environment at the core site and at representative remote sites in the selected country.

Oct 2011 18 RPM / WP2 2011

Tropospheric Turbulence

Investigating the stability of the troposphere was one of the PrepSKA WPs. On recommendation of the IEAC (2009) and SSEC the study of tropospheric turbulence was taken beyond investigating cloud coverage over the two candidate sites, and a measurement programme using a phase monitoring interferometer was started up.

Oct 2011 19 RPM / WP2 2011

Tropospheric Turbulence

Instrumentation • Principle: Interferometer pointing to

geostationary satellite and recording the (variations) in phase. Derive delay statistics.

• CfA/SMA-based system designed by JPL • Two systems at core sites, consisting of:

– Two antenna boxes (single baseline interferometer), with lnb, IF ampl, optical transducers

– Central rack, with LO generation, IF ampl, correlator, control computer

– LO and IF via analog fibre

• Remote readout of data via ssh, sftp. Oct 2011 20 RPM / WP2 2011

Tropospheric Turbulence

Instrumentation characteristics: • Baseline ~200m • Wideband correlator (200MHz) using

broadcasting transponders • Frequency ~12GHz • In AUS we use Optus D3 (156°E, lin) • In SA we use Eutelsat W7 (36°E, circ)

Oct 2011 21 RPM / WP2 2011

Tropospheric Turbulence

Oct 2011 22 RPM / WP2 2011

Tropospheric Turbulence

Oct 2011 23 RPM / WP2 2011

Tropospheric Turbulence

Standard data processing • Information stored:

– System Monitoring (voltages, LO lock, etc) – IF power levels – IQ data – Structure function data

• Example Plots: – Raw unwrapped phase – Correlated amplitude – Filtered phase – RMS delay – Cumulative distributions

Oct 2011 24 RPM / WP2 2011

Tropospheric Turbulence

Target programme • Measure for at least one full year, sampling all seasons, esp.

summer months. • Continue measuring after site selection However • Delayed installation activities at the sites • Difficulties in overcoming problems in the field Current status • One site has been measuring for 9 months • The other site since 4 months • Implies limited overlap in time, no summer months before site

selection reporting time • Report to be delivered to expert panel by end October

Oct 2011 25 RPM / WP2 2011

Tropo Results

Site Selection is targeted to be completed by end Feb 2012. Because this is a very sensitive matter it is not appropriate to show any tropospheric results from either candidate site now.

Oct 2011 26 RPM / WP2 2011

Array Configuration

• The questions in the RfI have been based on a Model for the full SKA (Phase 2)

• The Phase 1 configuration is a (small) subset of Phase 2

• Generic configurations have been designed for the purpose of – Exploring the parameter space/options/FoMs – Creating the Model

• Site-specific configurations were designed, starting from generic configuration, applying local constraints (masks). The responses to the RfI were based on these site-specific configurations.

Oct 2011 27 RPM / WP2 2011

Generic Configuration overview

Maximal Phase II: Full layout to 180km

Phase I: Central 40km by 40km

Science performance

• A number of array performance Figures of Merit have been devised

• Both site-specific P2 SKA configurations evaluated

• Report on these findings nearly completed.

Oct 2011 30 RPM / WP2 2011

Future Configurations Work

After site selection much more configurations design work is needed to address: • Tradeoffs cost/performance • Refine core configurations for dishes, AA low, AA mid (specifications

for number and size of AA stations needs to mature) • Further refine configurations w.r.t. terrain realities (‘mask’) • Detailed exploration of options for reticulation of power and fibre • Design the P1 configuration such that

– optimal configuration for the science – infrastructure/cost can be shared P1/P2 – P1 as a subset of P2 – expansion from P1 to P2 must be possible, cost effective and that

operations of P1 can continue while rolling out P2 – establish minimum infrastructure for P1, with P2 in mind – in relation to previous point: Explore P1 clumpy core options/performance

• Further refine locations of remote stations (P2) • Design (remote) station configuration

Oct 2011 31 RPM / WP2 2011