Experimental planetary radar captures incredible high-res Moon images

Jan 27, 2020
Experimental planetary radar captures incredible high-res Moon images
By Michael Irving
January 28, 2021

Astronomers have captured stunning new high-resolution radar images of the Moon, using an experimental instrument mounted on a ground-based telescope. This proof of concept test paves the way for a more powerful radar telescope that could see as far as our planet Neptune.

The new technology was developed by the Green Bank Observatory (GBO), National Radio Astronomy Observatory (NRAO) and Raytheon Intelligence & Space. The new radar transmitter was fitted onto the Green Bank Telescope (GBT), which allows it to beam radar signals into space. The reflected signals are then captured by the Very Long Baseline Array (VLBA)*, a series of radio antennas spread across North America, and processed to produce images.

hadley rille.jpg

In this new radar image, mountains, craters and a snaking feature called Hadley Rille can be clearly seen

The team conducted the first proof of concept test last November, and the results are incredible. On a large-scale image of the Moon, the instrument was sensitive enough that you can zoom in on specific features on the surface, down to objects as small as 5 m (16.4 ft) wide. Near the landing site of the Apollo 15 mission, for example, an ancient lava tube named Hadley Rille can be clearly seen snaking its way across the landscape, flanked by mountains and passing a crater called Hadley C.

apollo 15 landing site.jpg

The radar image of the Apollo 15 lunar landing site and surrounds, pulled out of a wider map of the Moon
Sophia Dagnello, NRAO/GBO/Raytheon/AUI/NSF/USGS

Building on this test, the team now plans to develop a 500-kW radar system that will be able to image objects further out in the solar system. Ultimately, the researchers say, this next-gen radar telescope could be used to capture high resolution images of objects as far away as Uranus and Neptune.

“The planned system will be a leap forward in radar science, allowing access to never before seen features of the Solar System from right here on Earth,” says Karen O’Neil, site director of the Green Bank Observatory.

Source: NRAO, the National Radio Astronomy Observatory, is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Founded in 1956.

* The Very Long Baseline Array is a network of ten observing stations located across the United States. Each station consists of a 25-meter radio antenna dish and a control building. Radio signals captured by each antenna are amplified, digitized and recorded. The recorded data are then sent to Socorro, NM to be processed by a powerful computer known as a correlator**. By combining their data, the stations form one of the world’s most powerful radio cameras.

The VLBA stations are located in areas with limited radio interference, and widely spread across the country. The distance between any two stations is known as their baseline. The longer the baseline, the better the angular resolution. The most widely separated antennas are at Mauna Kea in Hawaii and St. Croix in the U.S. Virgin Islands, which are 8,611 km apart. While each VLBA antenna is identical, each location is unique. Each station also has a webcam, so you can view them in real time (http://www.vlba.nrao.edu/sites/SITECAM/NLcam.shtml)
  1. St. Croix – U.S. Virgin Islands
  2. Hancock – New Hampshire
  3. North Liberty – Iowa
  4. Fort Davis – Texas
  5. Los Alamos – New Mexico
  6. Pie Town – New Mexico
  7. Kitt Peak – Arizona
  8. Owens Valley – California
  9. Brewster – Washington
  10. Mauna Kea – Hawaii
Observing superfast jet material from a neutron star merger
Measuring the precise locations and distances of Fast Radio Bursts
Settling the controversy over the distance to the Pleiades
Mapping the spiral arms of our galaxy
Observing the rotation of an asteroid passing near Earth
Tracking the collision of powerful stellar winds
Measuring water masers to accurately determine cosmic distances

At a Glance:
Number of Dishes10
Dish Sizes25 meters (82 feet)
Antennae Weight~ 218 tons
Total Collecting Area19,635 square meters
Receiver Frequencies0.3 GHz – 96 GHz (90 cm – 3 mm)
Resolution0.17 – 22 milliarcseconds
Array SizeMaximum baseline of 8,611 km (5,350 mi)

** The digital correlator compares the data from each antenna to create a radio image. The correlator at most observatories is a specialized computer. The VLBA uses a software correlator which is especially well suited to job. The software doesn’t process the data in real time, but instead reads the data from the hard drives. As the power of computers improves, the software correlator becomes more powerful, allowing more data to be processed.

VLBA-DiFX is the name that NRAO has given to its new VLBI correlator. It is a software correlator that uses Adam Deller's Distributed FX (DiFX)*** as the base and has software written around it for nearly seamless integration with the VLBA. The correlator runs on a cluster of commodity computers containing multi-core Intel processors. A bank of about 24 Mark5 units feed the correlator directly from data recorded at the antennas.

VLBA-DiFX is one of three components of the recent VLBA Sensitivity Upgrade Project, the other two being a digital back end to replace the aging analog baseband-converters, samplers, and formatters, and the Mark5C recorder which will provide 4 times the record rate of the Mark5A units that are currently in use.

Users whose observations are correlated using DiFX are encouraged to include the following statement in any publication of those results: "This work made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under licence", and to cite the following paper: Deller, A. T., Tingay, S. J., Bailes, M., & West, C. 2007, PASP, 119, 318.

*** Adam Deller, Steven Tingay, Matthew Bailes & Craig West, Swinburne University, Hawthorn VIC Australia; E-mail: adeller@astro.swin.edu.au, stingay@astro.swin.edu.au,
mbailes@astro.swin.edu.au, cwest@astro.swin.edu.au

This paper describes the development of a general-purpose software correlator code known as
Distributed FX (DiFX). The code was developed primarily to facilitate an upgrade of the Long
Baseline Array (LBA) network for Very Long Baseline Interferometry (VLBI) in Australia, en-
abling an upgrade from the S2 tape-based recording system to a PC-EVN disk-based system. This
upgrade has brought 4-8 fold increases in bandwidth and greatly expanded the available correla-
tion parameter space. This expansion in correlator capability has led to a range of new science,
both with the LBA and other VLBA arrays outside Australia, and these applications are briefly

See: https://www.atnf.csiro.au/vlbi/correlation/deller.pdf

See: https://safe.nrao.edu/wiki/bin/view/VLBA/Correlation

I find it incredible that the radar mounted on The Green Bank Observatory can be used to bounce signals off solid celestial bodies in our solar system which are then received and collated by the Very Long Baseline Array*, the VLBA, radio antennas spread across North America and the Caribbean. And that this raw data is able to be collimated, using software developed by a team in Australia, into such incredibly clear images for us to examine. The views of our solar system are improving every day.

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