This is my piece for Accretionary Wedge #60 ‘Momentous Discoveries in Geology’. Enjoy!
GBinSAR? What is this all about?
I am going to talk about a very momentous discovery in geology, the development of a type of radar that helps in monitoring ground movements. It has a long name, you must be warned: ‘Ground-Based Interferometric Synthetic Aperture Radar.’ Or, GBinSAR for short. And it’s a pretty useful bit of kit – it can be used to monitor ground movements of anything from earthquakes and volcanoes, landslides and slope failures, and even glacier movement. So how did this space tech come down to land?
First we need to know about Synthetic Aperture Radar!
Okay, so synthetic aperture radar uses microwaves to get a backscattered image of the environment – this basically means that microwaves bounce off whatever surfaces the instrument is aimed at, and returns a signal which is picked up by the same device. The resolution of a SAR instrument is very high, so it is easy to pick up tiny fluctuations that may suggest something has changed.
Now we can take it down to land!
So normally SAR instruments operate from satellites in space, but they’re quite wide-range, and sometimes for a particular slope, volcano or glacier you need an even higher, more precise resolution. So we do something very simple – we bring the SAR instrument down to the ground, and set up a couple of stations around the target area, and the radar image can then be made by combining the signal from both instruments. This is exactly what Ground-Based Synthetic Aperture Radar does.
So we have GB SAR, what about the ‘in’?
When you combine two different signals, you’re calculating the interference between them to form the image. This is what’s known as interferometry, and it explains the ‘in’ part of GBinSAR. Interferometry is mega-cool; it was first used on Venus and the Moon! It’s a beautiful example of how space tech has ended up being useful for geohazard mitigation on Earth, so all opposers of blue sky science, take note!
All right, but who invented this stuff?
The original SAR was first conceived back in 1938, by Sir Watson-Watt, and was called the ‘Bedspring Antenna’. SAR technology did not actually come into proper use until 1978 when the SEASAT satellite was first put up.
The movement from space satellites to ground-based inSAR did not happen officially until 1999, when the EU’s Joint Research Centre did some dam experiments and published the first paper on the subject. Since then companies such as Ellegi-LiSA labs in Italy have worked towards creating saleable models. The LiSA model from this lab is currently the most widely used.
Okay, so tell me more about where it’s been used. I want some examples!
GBinSAR is used all over the world to monitor any geological surface that might be likely to start making a run for it. For instance, in Japan it is used to monitor landslides in unstable areas easily affected by typhoon rains, such as the Tottori prefecture, and this has led to some very successful evacuations recently.
On the island volcano of Stromboli, GBinSAR is used to constantly monitor minor changes on the main volcanic debris slope, so that landslide-tsunamis can be mitigated. It’s possibly the best tech to use here, as erecting monitoring equipment on an active debris slope is nigh on impossible, so having this multiple-receiver setup placed around the sides of the slope allows high-resolution data to be captured without causing too much damage to the hardware.
This technology is also used in civil engineering. It’s been used to monitor deformation of dams in Poland, and even structural deformation of bridges!
So this is an awesome piece of tech, and it’s really changed the world of hazard mitigation. I’d definitely say that the idea of converting space-based Synthetic Aperture Radar to a ground-based model is one of the greatest geological revelations ever, because it has helped save lives and provide early warning systems for disasters. Although it’s something that goes by unnoticed most of the time, let’s give some applause to the humble GBinSAR device and its space-age predecessor.
1.) Guido Luzi, ‘Ground Based SAR Interferometry: a Novel Tool for Geoscience’, Geoscience and Remote Sensing New Achievements 2010
2.) Kazuo Ouchi, ‘Recent Trend and Advance of Synthetic Aperture Radar with Selected Topics’, Remote Sensing 5, 2013, pp. 716 – 807
3.) D. Tarchi, H. Rudolf, G. Luzi, L. Chiarantini, P. Coppo, A. J. Sieber, ‘SAR interferometry for structural changes detection: a demonstration on a dam,’ Proceedings of IGARSS’99 Hamburg pp 1522 – 1524
4.) D. Leva, C. Rivolta, I. Binda Rosetti, S, Kuzuoka, T. Mizuno, ‘Using a ground based interferometric synthetic aperture radar (GBinSAR) sensor to monitor a landslide in Japan’, Geoscience and Remote Sensing Symposium, 2005, Volume 6, 2005
5.) Teresa Nolesini, Federico Di Traglia, Chiara Del Ventisette, Sandro Moretti, Nicola Casagli, ‘Deformations and slope instability on Stromboli volcano: Integration of GBinSAR data and analog modelling’, Geomorphology 180 – 181, 2013, pp. 242 – 254
6.) Rafal Kocierz, Przemyslaw Kuras, Tomasz Owerko and Lukasz Ortyl, ‘Assessment of Usefulness of Radar Interferometer for Mesuring Displacements and Deformations of Dams’, Joint International Symposium on Deformation Monitoring, 2011
7.) Stefan Pradelok, P. Kuras, T.Owerko, L. Ortyl, R. Kocierz, O. Sukta, ‘Advantages of radar interferometry for assessment of dynamic deformation of bridge,’ Proceedings of Bridge Maintenance, Safety, Management, Resilience and Sustainability, Sixth International IAMBAS Conference, 2012