Abraham, Here are my comments on the beam measurement paper. Please don't be dismayed by the length, they are mostly text level corrections, with a few higher level questions or comments. Overall the paper looks quite good, and was especially informative for a novice on the collaboration like myself.
-Ben Saliwanchik ------------------------------------------------ Abstract: 1) "HERA is a hexagonal array of large (14 m) dishes with suspended dipole feeds with element collecting area of 100m^2." -> "HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds and an element collecting area of 100m^2." 2) "HERA-127 should detect the EOR with a signal-to-noise of 25-30 with a single season of observations." -> "with a signal-to-noise ratio of 25-30" 3) "Even with more pessimistic assumptions, using only previously demonstrated techniques, the signifi cance of an EOR detection remains above 5 \sigma." -> "the significance of the EOR detection" Section 1: 4) "where the smooth frequency evolution of the foreground emission separates from the spectrally unsmooth cosmological signal" -> "separates it from the spectrally unsmooth cosmological signal." 5) "to achieve coherent integration on the very low surface brightness 21 cm signal." -> "coherent integration of" 6) "progressively larger hex patterns," -> "hexagonal" 7) "A central lesson of first generation instruments is it is essential" -> "is that it is essential" 8) "The complement of the wedge is knows as the 'EOR window'." -> "is known as" 9) "To be sure, all are subject to the same geometric limits on foreground frequency- dependence limiting foreground bounding foreground emission within the wedge," -> "To be sure, all are subject to the same geometric limits on foreground frequency-dependence which limit foreground emission to within the wedge," 10) "This second effect makes intermediate length baselines of tens to hundreds of meters sensitive to the very bright diffuse emission would not see from near zenith." -> "bright diffuse emission that would not be seen from near the zenith." 11) "In this work we study angular response of the dish and its implications for power spectrum measurements." -> "we study the angular response" 12) "The 352 dishes are positioned in a compact, hexagonal array permitting redundant baseline calibration and coherent integration in ~k space" - Earlier in the section 331 is given as the final number of elements. 13) "We characterize the dish beam at various feed heights to map out the focus and study beam errors due to feed misalignment." - Was misalignment in the horizontal plane also explored? If not, are there future plans to investigate those additional degrees of freedom? 14) "when foreground are must at risk of leaking into the EOR window." -> "when foregrounds are most at risk of leaking into the EOR window." 15) "then review the ORBCOMM beam measurement system, in Section 3." -> "then review the ORBCOMM beam measurement system in Section 3." Section 2: 16) "More significant is frequency structure introduced by time domain reflections between the suspended feed detailed by Ewall-Wice et al." -> "reflections between the suspended feeds" 17) "The dipoles themselves is modeled as a copper pipe of diameter XX, we neglect the dielectric PVC in which the copper pipe is actually enclosed." -> "The dipoles themselves are modeled as a copper pipe of diameter XX. We neglect the dielectric PVC in which the copper pipe is actually enclosed" - Also, don't forget to insert the actual pipe diameter! 18) "In the CST model we again model the dish as a 14m diameter solid aluminum paraboloid with f/D = 0:32 but now neglect the 1m hole at zenith, effectively assuming the concrete and earth ground behind it are perfectly reflective." - Why is only one of these scenarios tested with each modeling package? Shouldn't both scenarios be tested with both software methods? 19) "The actual material properties are somewhere in between, though difficult to predict theoretically." - Can the reflectivity of concrete at these wavelengths be measured to improve the accuracy of the model? Alternately, why doesn't the metal mesh cover the central hole? Section 3: 20) "We briefly review the beam mapping system detailed by Neben et al. (2015), then discuss application of system for HERA dish measurements." -> "then discuss the application of the system" 21) "yielding typically 200-300 satellite pass." -> "yielding typically 200-300 satellite passes." 22) "or in the off state of of a pulsing sequence." -> "or in the off state of a pulsing sequence." 23) "though we experiment with other locations at first in our to characterize the environmental systematics of these measurements," -> "though we experimented with other locations at first to characterize the environmental systematics of these measurements," 24) "(2) 100m apart on a NS line, 100,m south of the HERA dish." -> "(2) 100m apart on a NS line, 100 m south of the HERA dish." 25) "Figure ?? shows the results from these experiments in the form of the ratio of the power responses of the two antennas." - Broken reference to Figure 4. 26) "Systematics at the few percent level are observed in within 20deg of zenith, and at the 10 - -20% level farther out." -> "Systematics at the few percent level are observed within 20deg of zenith, and at the 10-20% level farther out." Section 4: 27) "We exclude times when the received power is within 20 dB of the background level determined at between passes," -> "determined between passes," 28) "Figure 5 shows the measured power patterns for these three feed heights for the EW (left panel) and the NS (right panel) feed polarization." -> "feed polarizations." 29) "These maps are plotted in sine-projection with dashed circles marking zenith angles of 20deg, 40deg, 60deg, 80deg." -> "20deg, 40deg, 60deg, and 80deg." 30) "The data agree with both models to within a dB in the main lobe," -> "to within 1 dB" or "to within a decibel" 31) "The collecting areas range are shown in Table 1" -> "The collecting areas at each feed height are shown in Table 1" 32) "The measured collecting areas are a 30-50% lower than the geometric area." -> "The measured collecting areas are 30-50% lower than the geometric area." 33) "and all modes whose frequency dependence is larger than that of source at the edge of the main lobe are used." -> "larger than that of the source" 34) Was the beam pattern measured with the feed height greater than 5.3 m to ensure that the dish goes back out of focus after that point? How do we know the focus isn't at, say 5.5 m? Figure 6 suggests the simulations are quite accurate, but it seems like a good thing to check experimentally, given how much of a difference the feed height makes in detection S/N. Section 5: 35) "The added frequency dependence of the changing overall gain and beam shape versus frequency is addressed by the other papers in this series." - Add reference. 36) "This reduces the magnitude of emission near the edge of the EOR window, reducing the risk it leaks inside." -> "reducing the risk of it leaking inside the window." 37) "Dashed lines mark zenith angles 20deg, 40deg, 60deg, 80deg." -> "20deg, 40deg, 60deg, and 80deg." 38) "In contrast several hours later, the galactic center is fully below the western horizon, leaving only a slight brightening near the eastern horizon due to the weaker galactic anticenter." -> "In contrast, several hours later the galactic center is fully below the western horizon," 39) "In contrast, all three model agree much more closely when there is little or no edge brightening" -> "all three models agree" Section 6: 40) "the large 14m dish achieves sufficient sensitivity at a reasonably data processing and analysis cost." -> "at a reasonable data processing and analysis cost." 41) "We present in this paper beam pattern measurements at 137MHz" -> "In this paper we present beam pattern measurements at 137MHz" 42) "We begin with the power pattern measurements using the beam mapping system of Neben et al. (2015) which we deploy at the prototype three-element HERA array" -> "which we deployed at the prototype three-element HERA array" 43) "then roughly track the typical sidelobe levels at 20-30 dB below zenith though fail to reproduce the exact sidelobe amplitudes and locations." -> "20-30 dB below zenith, though they fail to reproduce" 44) "These papers demonstrate that in the best case, a combination of bandpass calibration and delay space CLEANing can mitigate foregrounds to a manageable level, while in the worst case, HERA can still achieve a XX-XX \sigma detection of the EOR parameters from the power spectrum by simply excluding a very conservative buffer outside the wedge." - Don't forget to insert missing significance! On Wed, Jan 27, 2016 at 10:53 PM, Abraham Richard Neben <[email protected]> wrote: > Hi Everyone, > > Please send me comments on this paper by next friday (Feb 5). We want to > post this to the arxiv before the proposal is submitted, but we also don’t > want to take people’s editing time away from the proposal. > > Abraham > > > > > > On Jan 26, 2016, at 1:13 PM, Abraham Richard Neben <[email protected]> > wrote: > > > > Hi Everyone, > > > > Here is our paper on HERA beam measurements and science implications for > review by the collaboration. The other dish papers (on reflectometry and > foreground simulations) aren’t far behind. > > > > Please take a look and send any comments! > > > > Best, > > > > Abraham > > > > > > > > <DishBeamMeasurementsPaper_rev2.pdf> > > -- Dr. Benjamin Saliwanchik Astrophysics and Cosmology Research Unit Department of Mathematics University of KwaZulu-Natal, SA
