BDT Radio – 1a – CMV 2009/09/01 Basic Detection Techniques Radio Detection Techniques Marco de Vos, ASTRON / Literature: Selected chapters from Krauss, Radio Astronomy, 2 nd edition, 1986, Cygnus- Quasar Books, Ohio, ISBN Perley et al., Synthesis Imaging in Radio Astronomy, 1994, BookCrafters, ISBN Selected LOFAR and APERTIF documents Lecture slides

BDT Radio – 1a – CMV 2009/09/01 Overview 1a (2009/09/01): Introduction Measurement properties, EM radiation, wavelength regimes, coherent & incoherent detection, caveats in interpretation. Historical example: detection of 21cm line Tour d’horizon, system perspective 1b (2009/09/04): Single pixel feeds Theory: basic properties, sky noise, system noise, Aeff/Tsys, receiver systems, mixing, filtering Case study: the LOFAR Low Band Antenna 2a (2009/10/06): Array antennas Theory: 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 arrays Theory: 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

Measurement process Atmospheric effects Imaging system Instrumentation Conditioning of radiation before detection Spectroscopes, photometers, phase modulators, … Detectors From photon/free space wave to … Digital signal processing Real-time conditioning of detected data Calibration & Modelling Determining and removing instrumental signatures Deriving physical quantities from measurements Assessing significance by comparison with predictions

BDT Radio – 1a – CMV 2009/09/01 Observables Neutrinos Matter (cosmic rays, meteorites, moon rocks) Gravitational waves (<=c) EM waves Directionality (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)

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 plate Electrical: CCD (photo excitation), photomultipliers (photo emission) X-ray/gamma-ray detectors: scintillators, … Phase not preserved!!! Incoherent detection Often integrating (e.g. CCD) Inherently broadband Need instrumentation to get spectral resolution/accuracy Sensitive 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 energy Bolometer: 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 response Need 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 waves Active dipole antenna Dish + feed horn + LNA Requires full receiver chain, up to A/D conversion Radio mm 300K) IR (downconversion by mixing with laser LOs) Phase is preserved Separation of polarizations Typically narrow band But tunable, and with high spectral resolution For 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

“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 techniques Very 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 Universe Information 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 ). 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

Connecting Europe …

BDT Radio – 1a – CMV 2009/09/01 Giant radio telescopes of the world m Jodrell Bank, UK ~ m Parkes, Australia ~ m Effelsberg, Germany ~ m Arecibo, Puerto Rico ~ m GreenBank Telescope (GBT), USA

BDT Radio – 1a – CMV 2009/09/01 EVLA 27 x 25m dish

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

A systems perspective

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

Sampling

BDT Radio – 1a – CMV 2009/09/01 Subband separation Wideband input signal 80 or 100 MHz Separate into 512 small sub-bands kHz or kHz bandwidths Out-of-band rejection of a sub-band filter > 80 dB. Polyphase pre-filter, followed by FFT Optional near-perfect reconstruction of time-series

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

CEntral Processing Facility Tbyte/day 10 Tbyte/day 250 Tbyte/ day

BDT Radio – 1a – CMV 2009/09/01