Intelligence and Collections: Synthetic Aperture Radar, by Crusoe

An effective partisan must have a baseline understanding of many things to operate effectively within a set area of operations.  This understanding includes capabilities and equipment employed by a potential adversary that can be used against you.  Most of us are actively following OSINT feeds on social media as well as what is posted on American Partisan.  I personally like to understand what it is I am looking at.  The purpose of this series of articles is to demystify literal and non-literal intelligence tools that are used every single day and provide that baseline.  Drawing from real world experience and academic pursuits my goal is to help you understand strength, weaknesses, opportunities, and threats (SWOT).

What is SAR and why is it important?  Synthetic Aperture Radar is a collection method of using pulsed microwave signals sent from either an aircraft or satellite to a specific area and then processing those signals to provide a detailed geographic picture.  It is similar with how a bat uses sonar to “see” the world around it.  Waves of sonar energy are sent out and the bat uses the return signal to navigate through foliage or caves as it flies to its next spot. (Manley 2020) Now just substitute sonar energy with microwave energy and now you have the basic idea of how this works.  Now that we have a reference point, let us dive into the weeds a little bit to add more clarity to the subject.

When trying to understand non-passive collection methods it is important to dig a little deeper to provide a more rounded understanding of the topic.  Non-passive collection sources that use radar or microwave technology are reliant upon an energy beam being sent to the target area and the resulting return signal to ascertain what the composition of the area is.  For this case we are using microwave signals, as noted above, and these signals are sent in the 300MHz to 300 GHz range, but what makes this collection method different is the use of multiple wavelengths (or bands) to penetrate the obstacles.  (Crockett & Long 2013) The different bands use varying wavelengths which allow the radar to penetrate through different mediums and thus allow the user to “see” through clouds, foliage, ice, etc. (Herndon et al. 2020) Another interesting concept related to radar is the “scattering” of the signal which is a property of the radar wavelength against the object the radar is attempting to penetrate.  When the processer receives the return radar signal it calculates the scattering, wavelength band, and polarization to create an image.

(Herndon et al. 2020)

Now let us contrast that to what optical imagery is capable of.  Optical imagery is a passive system, one that does not emit energy, and relies upon radiation emitted along the electromagnetic spectrum to discern what it is seeing.  These radiation wavelengths are predominately between the ultraviolet and near infrared spectrum and are visible using optical sensors on whatever platform it is mounted on.  (TRESTE, n.d.)  The benefit of optical sensors is that they can produce much clearer images, for example Google Earth, and are easier to interpret, but with every positive there is a negative.  A significant limitation of optical sensors is the wavelengths within the ultraviolet spectrum cannot penetrate through weather, clouds or even tree foliage so what you see is exactly what it has captured.  The best way to understand the difference between the two is to stack both sensor products next to each other. When looking at the below image it clearly shows the crisp optical picture and within the clouds to the left is a corresponding SAR shot that shows the ability of the sensor to penetrate through the cloud layer.

(spacialmate.com, n.d.)

Every collection method has both pros and cons, and this is certainly true for both optical and SAR sensors.  As stated in this article, optical sensors are best at providing clear images that are easy to manipulate while SAR sensors can also provide imagery but not with the same amount of clarity.  The SAR sensor’s strength is its ability to penetrate through different mediums which enables it to provide a level of image sophistication that the optical sensor cannot achieve.  The use of multiple bands of microwave wavelengths can provide the customer the real time information that is required.  As technology advances, I expect the clarity of the SAR picture to become clearer and rival that which is captured by the optical sensors alone.  As with any intelligence collection method, the strength of the information gathered is multiplied by the number of assets collecting.  There is still a place for optical sensors but layered with a SAR overlay the image becomes more useable.

References:

• Crockett, Mark T. and David Long. 2013. “An Introduction to Synthetic Aperture Radar: A High-Resolution Alternative to Optical Imaging.” Semantic Scholar. https://www.semanticscholar.org/paper/An-Introduction-to-Synthetic-Aperture-Radar%3A-a-to-Crockett-Long/0789d51dbbc41fd9c4e6afb46963854fce784791
• Herndon, Kelsey, Franz Meyer, Africa Flores, Emil Cherrington, and Leah Kucera. “What is Synthetic Aperture Radar?” Earth Science Data Systems. April 16, 2020. https://earthdata.nasa.gov/learn/backgrounders/what-is-sar
• Manley, Scott. “Satellites Use “this Weird Trick’ to See More Than They Should-Synthetic Aperture Radar Explained.” YouTube. December 30, 2020. https://www.youtube.com/watch?v=g-YICKbcC-A
• com. (n.d.) “Image of Optical vs. Synthetic Aperture Radar.” Accessed online December 28, 2021. https://spatialmate.com/wp-content/uploads/2020/01/3-1.jpg
• TRIbal Earth Science & Technology Education Program. n.d. “History of Remote Sensing.” Accessed on-line December 28, 2021.