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A daily view of all the goings-on at ASTRON and JIVE.

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    © ASTRON

    At April 20th the general assembly of the Dutch Electronics and Radio Society (Nederlands Elektronica en Radio Genootschap, NERG) decided to dissolve the society after more than 90 years. The current activities of the NERG will be taken over by the telecommunication branch of the Royal Netherlands Society of Engineers. The general assembly was followed by a mini-symposium with presentations about the remarkable and rich history of the society marking foundations for radio astronomy in the Netherlands.

    The Dutch Electronics and Radio Society was established as the Dutch Radio Society (Nederlandsch Radio Genootschap, NRG) at May 29th 1920. The goal of the organization was the advancement of scientific research in the, at that time new, field of radio communication. Among the first members were three Nobel prize laureates: Lorentz, Van der Waals and Zeeman. Radio communication at that time was an important topic in the Netherlands, to become independent of foreign telegraph cables to communicate with their colonies, especially the Dutch East Indies.

    In 1922 the NRG was one of the initiators of the establishment of the URSI as the international radio science organization. The N(E)RG hosted the Dutch URSI committee until the Royal Dutch Academy of Arts and Sciences took over that role in 2005.

    After World War II the field of radio broadened to what we nowadays call electronics. For that reason the society changed its name to Dutch Radio and Electronics Society in 1963. Radio astronomy as new application of radio science also got the attention of the NRG. The detection of the neutral hydrogen line by Muller in 1951 was published in the journal of the NRG in 1952 (see the insert). In later issues of the journal of the N(E)RG other developments at ASTRON were published, including for the JCMT, the WSRT and LOFAR(*).

    All the issues of the journal of the N(E)RG (Tijdschrift van het N(E)RG) are available online now via https://www.kivi.nl/afdelingen/telecommunicatie/nerg/archief-nerg-tijdschriften-nederlands-electronica-en-radiogenootschap

    On the picture above Bart Smolders(*), chairman of the NERG, hands over the gavel to Willem van der Kamp, chairman of the telecommunication branch of the Royal Netherlands Society of Engineers.

    (*) Editor's note: A future AJDI will be devoted to the various ASTRON employees who have been awarded prestigious prizes by the NERG. Also Prof Smolders, the present (and last) chairman of the NERG, is an esteemed ex-colleague.


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    © R.H. van den Brink

    In the first week of April 2016 the second six APERTIF PAF FrontEnds were assembled and tested. The first six FrontEnds were installed in RT2, RT4, RT5, RT8, RT9 and RTA. The next six FrontEnds were ready in Februari 2016, but waiting for the LNAs to be assembled.

    The new FrontEnds were assembled in one day by a large team of APERTIF members and volunteers. Two days later the FrontEnds were tested by Mark Ruiter and Lute van de Bult. They will now be installed in RT3, RT6, RT7, RTB, RTC and RTD, which will complete APERTIF-12

    (*) APERTIF-12 is the second part of the APERTIF project, which is divided into two delivery phases. In the first phase (APERTIF-6), six dishes are fitted with the single-polarization version of the APERTIF system. In the second phase (APERTIF-12), another six dished will be fitted with the APERTIF system, and all twelve dishes are upgraded to a dual-polarized system.


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    © ASTRON

    Some time ago, a number of ASTRON colleagues flew off to Cape Town for a SKA MIDPREP/AAMID workshop to discuss and work towards SKA-2, in particular the Mid-Frequency Aperture Array (MFAA) component. At the airport, a shuttle bus was arranged which could fit six persons. However one of our colleagues, who will rename nameless, had some "over-sized" luggage with him which was certainly too large for the shuttle bus and its occupants.

    After many calls, it took the cab driver almost 45 minutes to find a solution to this. Two buses were required - one for the over-sized box (now clearly observed to be containing a racing bike) and it's owner, and another for the rest of our party, now somewhat wilting after the 12 hour plane journey and the unexpected delay. The latter were packed into the second bus like sardines in a tin.

    It was "erg gezellig" according to the person shown above right in the image, no doubt considering that this team building exercise would lead to a significant improvement in cross-cutting institute collaborations.


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  • 05/23/16--17:00: Farewell Erik vd Wal
  • © ASTRON

    Erik van der Wal (right on picture) will leave ASTRON 1 June 2016, after 11 years working as RF expert at ASTRON. We will surely miss him as RF expert and good colleague in the radio group.

    Erik started his career as the RF system designer for EMRBACE, a 10.000 element dense phased array demonstrator.

    His broad excellent knowledge and experience helped the team to design this wonderful system. Major hurdles had to be taken to get the tile design right. Topics such as beam squint, beamforming , calibrate ability, RF layout, produce ability and reliability had to be sorted out. Erik played a major role in these topics.

    Erik and Sieds Damstra teamed up, for the design of the required printed circuit boards. This Frisian couple proved to be a strong development team that successfully delivered the PCB boards for the EMBRACE tile. At this time a second (Frisian) RF design team was formed. Erik and Mark started to work on the RF design of the tile and later on the testing and commissioning of the EMBRACE instrument using a 200 channel LOFAR backend. This valuable experience from EMBRACE was used in later system like APERTIF and SKA MFAA.

    His experience and knowledge went further than RF. He also oversees other areas quite well, like antennas, calibration, (embedded) software and digital signal processing. This made Erik the ideal person to ask for advice. He loved it to explain and to coach other colleagues in their work, and to get their knowledge and understanding to a higher level. We are Erik grateful for the detailed discussions and feedback we had.

    An other recent development project where Erik worked on was Apertif. For Apertif Erik contributed on the RF system, and especially the down conversion system, called DCU. It's wide bandwidth and harsh RFI environment made it very difficult the best frequency mixing scheme. Erik liked difficult technical ''puzzles', and this was one of them he liked, and he found a very nice solution.

    Erik was interested in technology in the broadest sense. In coffee breaks numerous discussions led to new insights, ideas and concepts.

    Erik, thank you for the very nice time with you at ASTRON.


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  • 05/24/16--17:00: Giant solar radio source
  • © NASA/SDO, LOFAR, Sijie Yu, Eduard Kontar

    Radio observations of the outer solar corona provide the unique link between near-Sun phenomena and the effects of solar activity that extend throughout the heliosphere.

    Researchers sponsored by EU-network RadioSun use radio images obtained by the Low Frequency Array (LOFAR) to study giant radio sources associated with a Coronal Mass Ejections.

    See also: http://www.astro.gla.ac.uk/?p=4460


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    © ASTRON

    Now that complex boards like the ASTRON/JIVE UniBoard and UniBoard2 are being used all over the world, knowing the status and the location of those boards is increasingly important. With the help of Henk Vosmeijer, we now have a database to keep track of them. By means of a QR-code on the board, we can easily access the database, and update the status where needed.

    Via the following link you can have a look at typical item in the database. http://www.astron.nl/RDBE/view.php?id=3


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  • 05/26/16--17:00: Touching base: Grant Hampson
  • © Madroon Community Consultants (MCC)

    It is always good to see a former colleague, who has left for pastures with a different shade of green. On the one hand it is sad to see them go, but it is a small world, and it is good to gain an influential friend in one of our sister institutes. Especially in the age of SKA, where all institutes have to work closely together.

    Grant Hampson worked at ASTRON as a postdoc from 1997 to 2004, where he did sterling work on mid-frequency aperture arrays like OSMA and THEA. After that he moved to Ohio to work with Steve Ellingson (another friend), and then on to CSIRO in Sydney (lots of friends). There he worked on the broadband upgrade of ATCA, a digital filter bank for Parkes, and was leader of the digital systems for ASKAP/BETA. At present he is Head of Design for ASKAP 2.0.

    He looks back with pleasure on his time with ASTRON, especially because he was allowed to work on end-to-end systems. He also feels that his personal contacts in Dwingeloo greatly facilitate the work of the multi-national (ASTRON/CSIRO/NZA) SKA CSP Low.CBF group, for who's dPDR he was visiting us.

    Since Grant and his family like the outdoors, they have chosen to live quite a long way from Sydney, on lake Macquarie near the Pacific coast. He has promised to send a few pictures, for a future AJDI.


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  • 05/29/16--17:00: LFAA AAVS1 fibre deployment
  • © ICRAR/Curtin

    The Local Infrastructure work package (LINFRA, lead: ICRAR/Curtin) of the SKA Low Frequency Aperture Array (LFAA) has been making impressive progress. This daily image reports on the deployment of the fiberoptic cable installation.

    As the AAVS1 system will use RF over Fibre (RFoF) technology, we need to make sure that the antennas are connected via a stable fibre link to the digitisers in the Central Processing Facility (CPF) on the MRO site (which also holds the ASKAP and MWA processing racks)

    As can be seen on the pictures, the large drum of cable has arrived at the MRO and has been deployed to the four AAVS1 stations.

    On end of the fibre optic cable will be connected to the Antenna Power and Interface Unit (APIU), situated in the centre of each station.

    A separate, 25 meter, fibre optic cable will connect the antennas to the APIU, within each station.

    The other end will be connected to the RFoF receiver modules, mounted at the digitisers boards, located at the CPF.


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  • 05/30/16--17:00: GUIs for UniBoard
  • © DESP

    To enhance the workflow and the work ability in general for the UniBoards the DESP group had a long-cherished desire to have a GUI (Graphical User Interface) that allows monitoring and control of basic functionality of the UniBoards. Occupied by "normal" projects none of the DESP team members was able to fulfill this longing.

    Fortunately our trainee Reinier van der Walle accepted the challenge and he created two very usable GUIs.

    1. Flash gui

    The Flashgui allows us to easily update the firmware of an UniBoard. It allows us also to update the firmware in a complete system that is based on UniBoards. For instance the 12x8=96 UniBoards that are located at the dishes in Westerbork can all be updated via a single instance of the GUI. Since the GUI is build on an existing layer of python code it will also be possible to use the GUI for future boards like UniBoard2 and the Gemini board that is developed in cooperation with CSIRO.

    2. Monitoring gui

    The monitoring GUI allows us to read back control related data from the UniBoards and display it in a graphical way. Typical parameters to be read are the data rates of the serial links and FPGA temperatures. The GUI is based on Kst Plot, a real-time large-dataset viewing and plotting tool.

    Renier has successfully demonstrated the GUIs. In particular the Flash GUI is already intensively used in the Apertif commissioning work. The photo shows the moment of fame where Reinier presented his work to the whole DESP team.

    Well done Reinier!

    On behalf of the DESP team,

    Renier van der Walle

    Hajee Pepping


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  • 05/31/16--17:00: An online tutorial for TaQL
  • © TJD

    The table query language TaQL, developed by Ger van Diepen, can be used for quickly inspecting and modifying casacore tables like Measurement Sets. For example, you can easily flag certain bad solutions, inspect and edit the metadata, subtract two data columns in an MS, or quickly convert between J2000 and ITRF. TaQL can be used from python, C++ or just from the command line.

    A much-heard criticism on TaQL is that the language is difficult. That is of course not true, once you have learned it. To make the learning process easier, we developed a tutorial with lots of exercises.

    The tutorial is located at taql.astron.nl.

    This tutorial runs in a web browser. The backend is based on Jupyter and runs, through tmpnb, in a number of dynamically started Docker containers.


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    © NRAO/ICRAR

    Astronomers (including Maddox & Oosterloo from Astron and Hess, Lucero & Verheijen from the Kapteyn Institute) have detected the faint radio emission from atomic hydrogen, the most abundant element in the Universe, in a galaxy nearly 5 billion (5 thousand million) light-years from Earth. This doubles the distance record for this type of detection.

    The discovery comes from the first 178 hours of VLA observations of a program called the 'COSMOS HI Large Extragalactic Survey', or CHILES, led by Jacqueline van Gorkom of Columbia University. The CHILES project eventually will use more than 1000 hours of VLA observing time.

    The evolution of galaxies is largely determined by the balance between how much a galaxy grows by capturing gas from the inter-galactic environment, and how much mass it loses due to interactions with other galaxies, or due to furious bursts of star formation. By looking farther out in distance, one is looking farther back in time, so observations of very distant galaxies give insights into how in the past galaxies drew in gas, processed it, and lost it again. Ultimately, the CHILES project will look 6 billion years back in time, thus covering almost half the lifespan of the Universe.

    The data give a first glimpse of galaxy evolution in action, 5 billion years ago: the hydrogen gas (orange in the image above) belongs to a massive, barred spiral galaxy which may be interacting with a small neighbour galaxy. Due to this interaction, it is losing a lot of gas. Nevertheless, there must still be a lot of gas left (nearly 100 billion times the mass of the Sun) because the galaxy is forming stars at a rate of about 85 suns every year (i.e. about 30 times more than our own Galaxy does).

    The results of this work are published in the Astrophysical Journal Letters ( http://xxx.lanl.gov/abs/1606.00013 )


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    © Jochen Heidt

    The Large Binocular Telescope (LBT) is a relatively young telescope. Having seen first light in 2005 it is certainly the most advanced optical/NIR 8m-class telescope at present. Its 1st generation instruments which are now close to completion offer a wide range of of observing modes, some of which are world-leading.

    I will give a brief review on the development of the LBT project, present its current instrumentation and give an outline of its scientific perspective. Special emphasis will be given to the LUCI instruments, which are NIR imager and multi-object spectrographs for the LBT and which are developed at my home institution. Finally, some recently obtained LBT results focusing on potential supermassive binary black hole systems will be discussed.


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    © ASTRON

    Some time ago, a number of ASTRON colleagues flew off to Cape Town for a SKA MIDPREP/AAMID workshop to discuss and work towards SKA-2, in particular the Mid-Frequency Aperture Array (MFAA) component. At the airport, a shuttle bus was arranged which could fit six persons. However one of our colleagues, who will rename nameless, had some "over-sized" luggage with him which was certainly too large for the shuttle bus and its occupants.

    After many calls, it took the cab driver almost 45 minutes to find a solution to this. Two buses were required - one for the over-sized box (now clearly observed to be containing a racing bike) and it's owner, and another for the rest of our party, now somewhat wilting after the 12 hour plane journey and the unexpected delay. The latter were packed into the second bus like sardines in a tin.

    It was "erg gezellig" according to the person shown above right in the image, no doubt considering that this team building exercise would lead to a significant improvement in cross-cutting institute collaborations.


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    © Robert van der Horn

    Dear all,

    After two years in the Karoo desert, we "the environmentals" finally got some fresh air.

    The guys from Astron made the effort to come over and check us from head to toe. It was about time because we could use the fresh air and we needed our batteries to be charged as well. Herewith we would like to thank the guys from Astron for their visit and good care, and we hope to see you soon, after all we are good friends.

    Yours sincerely,

    The Environmentals.


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  • 06/07/16--17:00: ASTRON bikes in the rain
  • © Madroon Community Consultants (MCC)

    This is a very Dutch picture. In any other country, the participants of a conference or school are left to fend for themselves, to walk to their hotel in apprehensive groups, by way of dark and foreign-looking places. But in Holland everyone gets a nice bicycle, with actually working lights, which offers a large measure of freedom and independence. As a final courtesy, we even supply a nice plastic bag with a prestigious logo, to shield the saddle against the unlikely contingency of a drop of moisturizing rain.

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    © Manolis Papastergis (Kapteyn)

    The "too big to fail" (TBTF) problem is a pressing observational challenge to the standard cosmological model at small scales. Put simply, it refers to the fact that it is very challenging to explain both the internal kinematics and the observed number density of dwarfs in the LCDM context. Even though the problem was first identified in the satellite population of the Milky Way, it has now become clear that it concerns dwarf galaxies in general.

    In this talk, I first plan to give an overview of the observational evidence that supports the statements above. I then plan to discuss two promising non-cosmological solutions to the problem: The first comes from the theory side, and consists of incorporating a number of baryonic feedback effects into our theoretical model. The second comes from the observational side, and has to do with the ability of HI kinematics to accurately trace the underlying dark mater potential of dwarfs. I will conclude by showing how present and future observations of HI in nearby field dwarfs can help us distinguish between cosmological and non-cosmological solutions for TBTF.


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    © Alec Hirschauer (Indiana University)

    Metals refer to elements other than hydrogen and helium in astronomy; these elements are formed by stars. Metal-poor galaxies lack these elements compared to other galaxies and are one of the best testbeds for understanding conditions early in the Universe. The gas out of which metal-poor galaxies are forming stars has a similar metal content as the gas forming stars in the early Universe. In addition, the amount of helium found in extremely metal-poor galaxies can be compared to predictions for the primordial abundance from Big Bang nucleosynthesis.

    The above images show AGC 198681, also known as Leoncino, or "little lion", as it is found in the constellation Leo Minor. This galaxy was recently identified as being the most metal-poor gas-rich galaxy known (Hirschauer+ 2016). Leoncino was originally found by the ALFALFA HI survey and identified as a low mass dwarf galaxy. Subsequent observations of its only HII region revealed it to have an extremely low oxygen abundance, making it the lowest-abundance star-forming galaxy known in the Local Universe. The left image above shows an HST image of this source with neutral hydrogen (HI) contours from Westerbork overlaid; the right image is a zoom-in on the optical galaxy. The WSRT observations localize the ALFALFA HI detection to this galaxy. They also hint at signs of interaction in this system, although further observations are needed to confirm this.

    Interestingly, two of the five lowest-abundance star-forming galaxies known have been discovered by the ALFALFA HI survey. This highlights an important parameter space for HI surveys, including the upcoming surveys with Apertif at ASTRON.

    More information can be found in the paper on Leoncino: Hirschauer et al. 2016, ApJ, 822, 108.


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    © Credit: B. Saxton (NRAO/AUI/NSF)/G. Tremblay et al./NASA/ESA Hubble/ALMA (ESO/NAOJ/NRA)

    On June 9th an international team of astronomers, including ASTRON astronomers Raymond Oonk and Michael Wise, reported witnessing a cosmic weather event in the form cold molecular gas clouds falling in towards the central supermassive black hole in the centrally dominant galaxy of the bright Abell 2597 galaxy cluster. This galaxy cluster is located at a distance of about 1 billion light-years from us.

    These new ALMA (Atacama Large Millimeter/submillimeter Array) observations show for the first time unambiguous observational evidence for a chaotic, cold 'rain' feeding a supermassive black hole with a mass about 300 million times that of our Sun. The infalling clouds were revealed by narrow absorption features from carbon monoxide (CO) against the central line of sight towards the black hole.

    The observed molecular cloud velocities, in combination with detailed very long baseline radio interferometric observations of cold atomic gas, place these clouds very the near (less than 300 lightyears) the black hole and on rapidly infalling orbits. Each of these clouds has a size of a few tens of light-years across and contains about a million solar masses of cold molecular gas. The discovered clouds are likely part of a much larger, centralized, clumpy distribution of cold clouds that provide the necessary fuel for the black hole regulating the thermal balance in the core of this galaxy cluster.

    Image: The background image (blue) is from the NASA/ESA Hubble Space Telescope. The foreground (red) is ALMA data showing the distribution of carbon monoxide gas in and around the galaxy. The pull-out box shows the ALMA data of the "shadow" (black) produced by absorption of the millimetre-wavelength light emitted by electrons whizzing around powerful magnetic fields generated by the galaxy's supermassive black hole. The shadow indicates that cold clouds of molecular gas are raining in on the black hole. Credit: B. Saxton (NRAO/AUI/NSF)/G. Tremblay et al./NASA/ESA Hubble/ALMA (ESO/NAOJ/NRA)

    The results have been published in Nature in a paper entitled "Cold, clumpy accretion onto an active supermassive black hole", by Grant R. Tremblay, J.B.R. Oonk et al. ( http://nature.com/articles/doi:10.1038/nature17969 ).


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    © Ger de Bruyn

    With the completion of threePolishstations, designated PL610, PL611 and PL612, in November 2015, the International LOFAR Telescope (ILT) has increased its maximum baseline to more than 1300 km. At a frequency of 173 MHz this allows it to make images with a resolution (PSF) of about 0.2"x0.3" . All that is required is a bright enough, compact radio source to (self-)calibrate the rapidly changing ionospheric phases.

    3C196 is a double source with an overall extent of about 9"; it is associated with a quasar at a redshift of 0.87 which gives it a modes linear size of 70 kpc. On Dutch baselines, which span a maximum baseline of 120 km, we still see strong beating effects between the two dominant hotspots and it has proven difficult to remove the source perfectly from our EoR data using the four-component model created by Pandey (which is used by many LOFAR users to pre-calibrate their data). In order to get to a dynamic range in excess of one million we obviously need longer baselines to determine the structure at sub-arcsecond resolution !

    Over the years, the EoR group has acquired many datasets with international baselines and a 116 MHz 0.50" PSF image of the source was shown last year at the Assen LOFAR conference. But we also needed such resolution for many other sources in our 10x10 agree deep images. So on 26 Feb 2016, just before 3C196 shifts into the daylight, we set out to use the multi-beaming capacity of LOFAR to target 20 compact sources, including 3C196, in an 8-hour experiment. Each target was allocated 4 groups of 6 subbands at respectively 116, 136, 155 and 171 MHz. Each subband had 32 channels and the correlator used 1s integration, in order to permit imaging over areas as large as the size of the international station beam (about 2 degrees). The 3 Polish stations worked flawlessly for 8 hours and we were lucky with a benign ionosphere. The other 9 international stations suffered about 1-2 hours of data-loss. The longer baselines and the higher frequency combined to double the resolution to about 0.25".

    Beautiful fringes were seen on the baselines from the LOFAR CORE (adding up all core stations) to the three Polish stations, as can be seen in the 4 plots. Since the Sun rises in Poland before it does over the Netherlands, the first few hours of data show strong differential Faraday rotation due to the different TEC over the two locations. This manifests itself as significant flux in the XY and YX cross-correlations (green and red).

    A high dynamic range image made from just 1 MHz of bandwidth at the highest frequency (171 MHz) is also shown. It reveals a wealth of structure; the NE hot spot is still not resolved. What makes the radio source somewhat special is that is is probably distorted by gravitational lensing due to a massive foreground barred spiral galaxy at a redshift of 0.43 entered. This galaxy is located about 2" South-East of the quasar core which is midway between the two hotspots.

    Transferring the self-calibratied complex gains, derived from the self-calibrated data to other beams, allows us to image compact sources up to 3 degrees away from 3C196, and with flux densities of only 0.1 Jy (in 1 MHz bandwidth). We expect to go much fainter, though. These results are shown today at the VLBI Busy week.


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    © Maaijke Mevius, Emanuela Orru, Richard Fallows

    The ionosphere has always been known to pose a particular challenge when calibrating LOFAR data, particularly in the low band below 80MHz. Recently Poland joined LOFAR with 3 stations, at the same time offering a range of ionospheric expertise and instrumentation. This prompted a fresh effort to bring together radio astronomers and ionospheric physicists, which was formally started with the first LOFAR Ionospheric Workshop, held in Warsaw on the 2nd and 3rd June 2016.

    Starting with a series of talks explaining in basic terms what everybody does to overcome the language barrier, presentations also detailed the wealth of ionospheric information which could be brought to bear on the calibration issue, from high-resolution GPS measurements of the Total Electron Content to radar soundings using ionosondes, riometers measuring absorption due to the lower ionosphere and in-situ satellite information.

    Further presentations detailed the progress already made by the radio astronomers in calibrating their data, the particular challenges they are facing and the kinds of data products which could be offered to help with studies of the ionosphere. This lead to very useful discussions and the launch of several working groups, with a second workshop planned in Leiden next spring.

    All-in-all, a very productive meeting which will hopefully progress as a long and fruitful collaboration between the two communities!


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