The aim of the ECHO project is high precision calibration of wide-field radio instruments. A transmitter mounted to a drone provides a known signal at a known location. The goal is to make full sky maps of antenna beams accurate with variation everywhere less than 1%. A secondary goal is to build an open source project useful as a community resource.
LWA Sevilleta station, October 2019: ECHO transmitter is visible on LWATV! We’re scanning a transmitter across the array in a spiral pattern on 100m radius sphere. Definitely not in the far field so one should expect quite a bit of distortion.
For a while I used the glob. These are left for posterity -dcj 12 May 2020
Our first paper about the drone calibrator is out on the arxiv today! Using data from our field tests last year we measured the stability and accuracy of the beam maps. The repeatability compared well to measurements made using satellites (thats the plot on the right) and the measurements matched up well with the models. There were a few issues though. The main thing seems to be the stability of the antenna attachment to the drone. We're sensitive to even a degree of rotation! Overall, though the thing worked a lot better than I was expecting, quite frankly.
The paper is here: https://arxiv.org/abs/1610.02607
Last week the ECHO team took the (relatively) short drive from Tempe up to Prescott, Arizona and Embry Riddle Aeronautical University to do some more testing at a new location. The Embry-Riddle Physics department has put together a very nice campus observatory which is predominantly devoted to radio science, both astronomy and aerospace. Under the leadership of Professor Andri Gretarsson, they have set up a set of three MWA tiles with which they plan to observe pulsars, and antenna elements from LWA and from LOFAR. On this trip we got shown around the site, made a preliminary map of one MWA tile, and discussed plans in the works to build a HERA dish.
We only had a few hours in the afternoon to map the tile, so we hurried through three sorties and hoped for the best. Getting home and processing the data we were pleased to see the expected square sidelobe pattern (shown below). The errors are still a bit high due to a low sample count, so we'll be heading back up as soon as we can to get more data.
This week several students and I traveled to Green Bank, WV for some high precision testing of the ECHO drone. The goal was to test our beam mapping accuracy on an antenna for which we had good models. This was also a week reserved for focused work; its our opportunity to put in a solid amount of time in the field to work out the kinks in the mapping process. After some rain delays on day 1 the weather was beautiful for flying. Over the course of four days we flew around 25 flights and made four complete beam maps. This is described in more detail in our field report memo:
Report on ECHO measurements of Orbcomm dipoles in Green Bank. D. Jacobs (2015)
We had a good time and learned a lot; students and PI. Physics student Jacob took some truly excellent photos, check out the complete album here.
ECHO is the External Calibrator for Hydrogen Observatories, a drone-mounted calibrator designed to help us get 1 part in 10,000 precision in cosmology telescopes targeting the first half-billion years of cosmic time. ECHO is supported by the National Science Foundation and Arizona NASA Space-Grant.
This semester I start work in earnest on a new project thats been simmering in the background, the External Calibrator for Hydrogen Observatories (ECHO) an experimental method to provide an airborne calibration source for wide-field radio arrays observing Hydrogen at cosmological distances. In particular, accurate maps of the primary beam (the response of the receiver dipoles as a function of position on the sky) have been found to be crucial at multiple stages analysis of data from PAPER/MWA/LOFAR etc but have historically been measured through indirect means such as the amplitude of satellites or radio galaxies passing overhead. ECHO aims to provide a direct measurement with a system where all parameters are under the experimenter’s control.
At this point we are designing and building our transmitter (don't need much power for a radio telescope!) and selecting a new drone platform. We've hired a small team of undergraduates to take point.
This project is supported by National Science Foundation and the Bowman Low frequency Cosmology lab in the School for Earth and Space Exploration.