BDT Radio – 1a – CMV 2009/09/01

Basic Detection Techniques

Radio Detection TechniquesMarco de Vos, ASTRONdevos@astron.nl / 0521 595247

Literature: Selected chapters from

Krauss, Radio Astronomy, 2nd edition, 1986, Cygnus-Quasar Books, Ohio, ISBN 1-882484-00-2Perley et al., Synthesis Imaging in Radio Astronomy, 1994, BookCrafters, ISBN 0-937707-23-6

Selected LOFAR and APERTIF documentsLecture slides

BDT Radio – 1a – CMV 2009/09/01

Overview

1a (2009/09/01): IntroductionMeasurement properties, EM radiation, wavelength regimes, coherent & incoherent detection, caveats in interpretation. Historical example: detection of 21cm lineTour d’horizon, system perspective

1b (2009/09/04): Single pixel feedsTheory: basic properties, sky noise, system noise, Aeff/Tsys, receiver systems, mixing, filteringCase study: the LOFAR Low Band Antenna

2a (2009/10/06): Array antennasTheory: aperture arrays & phased array feeds, beamforming, tile calibration, …Case study: the DIGESTIF Phased Array Feed

Experiment (2009/10/08 TBC)Measurements with DIGESTIF (in Dwingeloo)

2b (2009/10/09): Synthesis arraysTheory: aperture synthesis, van Cittert-Zernike relation, propagation of instrumental effects, …Concluding case studies: WSRT MFFE, EVLA, LOFAR HBA

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

Measurement process

Atmospheric effects Imaging system Instrumentation

Conditioning of radiation before detectionSpectroscopes, photometers, phase modulators, …

DetectorsFrom photon/free space wave to …

Digital signal processingReal-time conditioning of detected data

Calibration & ModellingDetermining and removing instrumental signaturesDeriving physical quantities from measurementsAssessing significance by comparison with predictions

BDT Radio – 1a – CMV 2009/09/01

Observables

Neutrinos

Matter (cosmic rays, meteorites, moon rocks)

Gravitational waves (<=c)

EM wavesDirectionality (RA, dec, spatial resolution)

Time (timing accuracy, time resolution)

Frequency (spectral resolution)

Flux (total intensity, polarization properties)

BDT Radio – 1a – CMV 2009/09/01

Neutrino’s

Super-Kamiokande Neutrino Detector water tank showing the thousands of photon

detectors each about the size of a beach ball

Sudbury Neutrino Observatory

BDT Radio – 1a – CMV 2009/09/01

Gravitational waves

Gravitational wave causes optical path differences. A Michelson interferometer is used to detect the phase differences thus induced.

Indirect measurement through pulsar observations?

BDT Radio – 1a – CMV 2009/09/01

EM waves

Directionality (RA, dec, spatial resolution)

Time (timing accuracy, time resolution)

Frequency (spectral resolution)

Flux (total intensity, polarization properties)

),,,,( mltf

V

U

Q

I

BDT Radio – 1a – CMV 2009/09/01

Energy levels

BDT Radio – 1a – CMV 2009/09/01

Different wavelengths, different properties

BDT Radio – 1a – CMV 2009/09/01

Windows of opportunity

BDT Radio – 1a – CMV 2009/09/01

Photon detectors

Respond to individual photons:Bio/chemical: eye, photographic plateElectrical: CCD (photo excitation), photomultipliers (photo emission)X-ray/gamma-ray detectors: scintillators, …

Phase not preserved!!!Incoherent detectionOften integrating (e.g. CCD)

Inherently broadbandNeed instrumentation to get spectral resolution/accuracySensitive above threshold energy

BDT Radio – 1a – CMV 2009/09/01

ESO VLT Hawk I CCD

BDT Radio – 1a – CMV 2009/09/01

Energy detectors

Absorb energyBolometer: temperature rises with total EM energy deposited

“Read-out” by measuring electrical properties change with temperature

Used in FIR en sub-mm

Phase not preserved!!!Incoherent detection

Inherently broadband with slow responseNeed instrumentation to get spectral resolution/accuracy

No threshold energy

BDT Radio – 1a – CMV 2009/09/01

SCUBA bolometer

BDT Radio – 1a – CMV 2009/09/01

Coherent detectors

Responds to electric field ampl. of incident EM wavesActive dipole antennaDish + feed horn + LNARequires full receiver chain, up to A/D conversionRadiomm (turnoverpoint @ 300K)IR (downconversion by mixing with laser LOs)

Phase is preserved

Separation of polarizations

Typically narrow bandBut tunable, and with high spectral resolutionFor higher frequencies: needs frequency conversion schemes

BDT Radio – 1a – CMV 2009/09/01

Horn antennas

BDT Radio – 1a – CMV 2009/09/01

Wire antennas, vivaldi

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

“Unique selling points” of radio astronomy

Technical:Radio astronomy works at the diffraction limit (/D)It usually works at ‘thermal noise’ limit (after ‘selfcalibration’ in interferometry) Imaging on very wide angular resolution scales (degrees to ~100 arcsec) Extremely energy sensitive (due to large collecting area and low photon energy)Very wide frequency range (~5 decades; protected windows ! RFI important)Very high spectral resolution (<< 1 km/s) achievable due to digital techniquesVery high time resolution (< 1 nanoseconds) achievable Good dynamic range for spatial, temporal and spectral emission

Astrophysical:Most important source of information on cosmic magnetic fields No absorption by dust => unobscured view of UniverseInformation on very hot (relativistic component, synchrotron radiation) Diagnostics on very cold - atomic and molecular - gas

BDT Radio – 1a – CMV 2009/09/01

Early days of radio astronomy

1932 Discovery of cosmic radio waves (Karl Jansky)

Galactic centre

v=25MHz; dv=26kHz

BDT Radio – 1a – CMV 2009/09/01

The first radio astronomer (Grote Reber, USA)

Built the first radio telescope

"Good" angular resolution

Good visibility of the sky

Detected Milky Way, Sun, other radio sources

(ca. 1939-1947).

Published his results in astronomy journals.

Multi-frequency observations 160 & 480 MHz

BDT Radio – 1a – CMV 2009/09/01

Radio Spectral-lines

Predicted by van der Hulst (1944):discrete 1420 MHz (21 cm) emission from neutral Hydrogen (HI).

Detected by Ewen & Purcell (1951)

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

1956 1971

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

Connecting Europe …

BDT Radio – 1a – CMV 2009/09/01

Giant radio telescopes of the world

1957 76m Jodrell Bank, UK

~1970 64-70m Parkes, Australia

~1970 100m Effelsberg, Germany

~1970 300m Arecibo, Puerto Rico

~2000 100m GreenBank Telescope (GBT), USA

BDT Radio – 1a – CMV 2009/09/01

EVLA

27 x 25m dish

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

Grote vragen

Voor de antwoorden is een grote telescoop nodig

De Square Kilometre Array

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

A systems perspective

S c ien c e Ap p lic a tio n sD o c u m en t

S c ien c e Us erR eq u ir em en ts

D o c u m en t

S y s tem R eq u ir em en tS p ec if ic a tio n

S y s tem Arc h itec tu r a lD es ig n D o c u m en t

S u b s y s temR eq u ir em en tS p ec if ic a tio n

S u b s y s temAr c h itec tu r a l

D es ig n D o c u m en t

Sp ec ify

C omp liance

O p er a tio n sP lan

I n ter f ac e C o n tr o lD o c u m en t

An aly s isR ep o r ts

P r o to ty p ed es ig n s

R ef er en c ed o c u m en ts

Bac k g r o u n dd o c u m en ts

S c ien c ec o n s o r tiu m

S y s tem D es ig n& E n g in eer in g

S D E /w o r k -p ac k ag es

W o r k p ac k ag es

E n g in eer in gr ep o r ts

S im u la tio n s ,an a ly s es , . . .

BDT Radio – 1a – CMV 2009/09/01

LOFAR – the science

Epoch of Reionisation

Wide-area Surveys

Transients

Cosmic Rays

Magnetism

Solar System Science

BDT Radio – 1a – CMV 2009/09/01

RCU B oard

A /D

B ac k plane& RF S hie ld

D is tributedB eam form ing

GbE

Sta

tio

nG

bE

sw

itch

(2

4 p

ort

s)

Gb

E s

wit

ch f

ab

ric

(23

1 o

utp

uts

)

W A N fibrec onnec t ions

S y nc .

Delay

B uffering

Corre lator /B eam form ers

(B lue G ene /L)

Calibrat ionRF I M it igat ion

S torage

c alibrat ion

Im age c reat ion

Us er applic at ionsRSP board 24

Station 77

Centra l P roc es s ing F ac ilit ies

A rc hiveE x port and

G RID

RS P B oard

W A N

Ionos phere

Outputc ontro l

Filter

Filter

Filter

Filter

B eamformer

BDT Radio – 1a – CMV 2009/09/01

to receiver

1..16on/off delaystep

on/off delaystep

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

Sampling

I: 0 - 100 II: 100 - 200 III: 200- 300

200 M Hz clockNyquist Zones

0 100 200 300

160 M Hz clockNyquist Zones

frequency [M Hz]

o bse rv ationmo de I10 - 90

Filte rs30

10 90 110

optiona l

ob se rv ationmo de II

110 - 190

ob se rv ationmo de IV210 - 250

ob se rv ationmo de III170 - 230

I : 0-80 II: 80 - 160 III: 160 - 240

BDT Radio – 1a – CMV 2009/09/01

Timing

Rubidium (Rb) laser reduces variance in the GPS-PPS to < 4 ns rms over 105 sec. The output of the Rb reference is distributed to the Time Distribution Sub-rack (TDS).Reference frequency is converted to the sampling frequency: using 10 MHz reference and Phase Locked Loops (PLL) in combination with a Voltage Controlled Crystal Oscillator (VCXO), the jitter of the output clock signals are minimized. Within a sub-rack all clock distribution is done differentially to reduce noise picked up by the clock traces and to reduce Electro Magnetic Interference (EMI) by the clock.

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01

CEntral Processing Facility

25000 Tbyte/day

10 Tbyte/day

250 Tbyte/ day

BDT Radio – 1a – CMV 2009/09/01

BDT Radio – 1a – CMV 2009/09/01