Monthly Archives: April 2017

Aperture Synthesis and Azimuth Resolution in Synthetic Aperture Radar – Lecture Notes

Teaching the fundamentals of Synthetic Aperture Radar (SAR) system design and imaging mechanism to remote sensing students / professionals is always a difficult task. Remote sensing students / professionals generally do not have an in-depth background of signal processing and radar system design, and as an instructor, I always have to think over how much I need to tell them about SAR system design, without diving into the detailed mathematics of signal processing and imaging mechanism. Normally, I go in-depth towards the imaging geometry and an understanding of the Doppler history curve, and briefly go over the signal-processing heavy concepts like pulse compression and matched filtering. A good fundamental understanding of the SAR system design, imaging geometry, and image formation is essential for remote sensing students / professionals to have a background context knowledge when they select SAR data and process / analyze it for different remote sensing applications.

For the past few years, I have been teaching a graduate course in Radar Remote Sensing and also run an annual Summer School on Earth Remote Sensing with SAR at our research group GREL. One of the core issues in understanding the aperture synthesis process is the requirement for enhancement of the azimuth / along-track resolution. It is always interesting to discuss in class how in normal imaging radar the azimuth resolution depends inversely on the antenna along-track length, while in fully-focussed SAR the azimuth resolution becomes half of the antenna along-track length. This is a significant reversal: In normal imaging radar, we need a bigger antenna in along-track dimension to get better azimuth resolution, while in SAR, the smaller the antenna in the along-track dimension, the better the azimuth resolution.

AzimuthResolutionSAR

To explain how aperture synthesis changes the azimuth resolution to half of the along-track antenna length, I have made some detailed notes for my ongoing graduate class on Radar Remote Sensing. These notes require just basic knowledge of geometry, algebra, and sum series in mathematics. I would like to share them with the wider scientific audience, please access the PDF notes here: Aperture Synthesis and Azimuth Resolution.

ApertureSynthesis

The synthetic aperture length is defined in the figure above. The azimuth resolution in fully-focussed SAR becomes half of the antenna along-track dimension.

I have taken the help of two excellent resources on SAR remote sensing in developing these notes:

For more in-depth understanding and analysis of how SAR is used for remote sensing, you can consider attending the next Summer School on Earth Remote Sensing with SAR, which I will be offering this summer. The summer school is coming up in July, 2018, and it will be open for international participants; formal dates will be announced soon. Keep watching the GREL website for updates.

Big Earth Data Documentary

Recently I ran into this wonderful documentary about how scientists are handling the huge amounts of remote sensing and earth science data being collected in the current age.

The documentary spends a lot of time talking about how remote sensing is used for oceanography and marine security monitoring, looking at concerns like monster waves, oil spills, surface ice content, ship routing through polar oceans, etc.

The EarthServer project is mentioned, which establishes “big earth data analytics, rapid ad-hoc processing and filtering on massive geodata.” Satellite images are shown to be useful also for automatic counting of houses or camps, and for disaster damage assessment. The use of GRACE satellite system for Earth gravimetry and water content measurement is mentioned.

For background information regarding the documentary, go here.