Frequently Asked Questions about RFView® for MAK ONE

What does SAR stand for?
Synthetic Aperture Radar

How does a SAR sensor work?
SAR works by sending radar signals out and listening for their returns. The farther something is from the emitter, the longer it takes for the signal to return. Generally speaking, the bottom of the SAR image contains the first returns, and the top of the image contains the last returns. For this reason, the direction in which the sensor is pointed must be closer to parallel with the ground than straight down.

Why are some SAR images wedge-shaped?
The closer the sensor is to the aimpoint and the larger the area of interest is, the more wedge-shaped the returned image will be. For conceptual purposes, you can think of the SAR image as capturing all the “stuff” that is in the sensor’s FOV, but that “stuff” is being viewed from above. However, that is not how SAR imaging works in the real world.

Why does the heading of the SAR sensor’s movement matter?
A SAR sensor must travel through the air to capture an image. The heading of the sensor’s movement is the direction the aircraft – the one carrying the SAR sensor – is flying. SAR sensors are commonly referred to as side-looking sensors. They send out multiple radar signals and gather their returns as they move past the portion of the terrain they are imaging. SAR sensors produce the best images when the sensor is pointing at 90 degrees from their direction of forward motion. They don’t produce usable images when the head is in the same or opposite direction that the sensor is pointing. The reason for this is that the SAR sensor is looking for Doppler shifts in the return signal that occur when the sensor moves perpendicular to what it is trying to image.

Why does the speed at which a SAR sensor is moving matter?
The longer a radar’s aperture/antenna is, the better resolution it has. A SAR sensor creates a synthetic aperture by moving through the air and capturing different returns along that path. For a completely static scene, it does not matter whether the sensor is moving at 300 or 3,000 meters/second. However, this speed has a significant impact on trying to image a scene that has a moving object in it. Assuming the desired resolution is a constant, the required synthetic aperture length would also be a constant. The speed at which the sensor travels dictates how long it will take to collect the data needed for an image. The less time spent capturing a single SAR image means the less distortion there will be for moving objects in that image.

Does the power of the radar matter?
This is the amount of output power the radar produces in watts. Because the SAR sensor has autogain capabilities, changing this value might not have much impact on the final SAR image, provided the autogain controls can still produce a reasonable image. Other factors, such as coverage and distance, can also affect the final signal-to-noise ratio.

What is the downrange size of a SAR image?
It is the real-world size of the portion of the terrain that should be captured in the SAR image, measured in the direction the sensor is pointing.

What is the cross-range size of a SAR image?
It is the real-world size of the portion of the terrain that should be captured in the SAR image, measured along the direction of the radar's movement. If the SAR sensor is pointed 90 degrees from the direction of motion, which is ideal, the down-range and cross-range directions are perpendicular to each other.

What are the different orientations of SAR images?

• North Up: The contents of the scene display such that the world’s north direction is towards the top of the image.

• Track Up: The contents of the scene display such that the heading of the aircraft is towards the top of the image.

• LOS Up: With Line-of-Sight Up, the pixels at the bottom of the image are closest to the sensor (first to return), and the pixels at the top of the image are farthest away (last to return).

Are VR-TheWorld databases supported?
Yes, and they will produce the best-looking SAR images of any database format in RFView for MAK ONE 1.0 for the following three reasons:

1. Low-resolution worldwide land use data is used to tell RFView where to place trees.

2. Open Street Map data is used to generate roads and bodies of water, such as lakes and rivers.

3. Land that is not defined as roads or water is defined as ground.

Are CDB databases supported?
Yes, but RFView for MAK ONE 1.0 does not make use of the material or land use raster/texture data that CDB databases might contain. The structure of CDB databases should enable us to readily incorporate this data into a future release. If you are interested in this feature, contact info@mak.com to learn more.

Are there any videos that explain what RFView for MAK ONE is?
Yes, there was a webinar on this topic: MAKtv Webinar: RFView for MAK ONE

Are there any videos that explain how to demo RFView for MAK ONE?
MAK’s VP of Products, Jim Kogler, made two videos that explain how to use RFView for MAK ONE, why it can be challenging to capture “good” SAR images, and also walk the user through how to use VR-Forces to place entities in the scene to be used by RFView for MAK ONE. These videos can be found here:

• MAKtv: RFView for MAK ONE demo (Part 1) and

• MAKtv: RFView for MAK ONE demo (Part 2)

What is layover?
SAR sensors rely on the time-of-flight of radar returns to position objects in the downrange dimension. When the radar signal returns to the SAR sensor from the top of a tall building, before the signal returns from the bottom of that building, the top of the building will appear closer to the sensor than the bottom of the building. Therefore, this building will appear to lean towards the sensor in the SAR image. This is called layover and can occur with man-made structures or the terrain.

Why do moving entities look odd?
SAR sensors rely on the time-of-flight of radar returns to position objects in the downrange dimension. SAR sensors rely on Doppler shifts within the returned radar signal to identify the location of objects in the crossrange dimension. If an entity is moving, the time-of-flight and Doppler shift of the return from that entity can mislead the sensor. Because of this, a moving entity can appear in an incorrect location and/or be smudged in the SAR image. However, the shadow cast by that entity will remain in the correct location.

Why do rotating articulated parts look odd?
SAR sensors rely on Doppler shifts within the returned radar signal to identify the location of objects in the cross-range dimension. The Doppler shift returned from a rotating structure will be misleading to a SAR sensor and will generally result in that structure appearing as a streak in the cross-range dimension. However, the shadow cast by the rotating structure will remain in the correct location.

What are the hardware requirements for RFView for MAK ONE?

The requirements for RFView for MAK ONE are similar to VR-Vantage; please see Hardware Requirements. The RFView SideCar and VR-Vantage applications will both consume CPU, GPU, and RAM resources, but neither application needs to maintain a specific frame rate. The majority of the time that RFView for MAK ONE uses to generate a SAR image is commonly consumed by VR-Vantage loading the required portion of the database. Assuming this data has been cached by VR-Vantage, having a fast SSD is important. The overall performance difference between generating a SAR image with an NVIDIA RTX 4070, 4080, and 4090 graphics card is negligible. However, be sure that your graphics card has sufficient video RAM for your use case. In our testing, 16 GB works well when using the MAK Earth (online) database.