A satellite camera that employs image motion compensation technology has many applications. Some of these applications include photogrammetry mapping, acquiring data regarding natural disasters, surveying land resources, monitoring the environment, etc. This type of satellite camera also works as the most efficient aerial remote-sensing light sensor. It can achieve higher ground resolutions from high altitudes when in flight, providing superior aerial surveying productivity. But how?
What is image motion compensation?
If we were to give an image motion compensation definition, this would be the description of pictures according to how a reference picture transformed into a current picture. A reference picture here could mean a picture from the past or even a future picture. Only a high-precision satellite camera can take pics on the go. Some of the most important features of this type of visual equipment are automatic velocity/altitude system ratio, image motion compensation mechanism & control. These systems are more performant if they provide high accuracy.
For instance, remote-sensing Chinese satellites provide higher accuracy than cameras that use image motion compensation systems. When designing a satellite camera that uses this system, engineers consider how picture points on film are displaced because of Earth’s relative motion to a camera’s platform. In this case, the camera’s platform is the satellite. Any satellite camera equipped with a picture stabilizing system must also have a high-resolution lens. This device features an optical correlator and an additional sensor for measuring the motion of a black and swiftly moving focus plane picture of high accuracy. A higher processing burden on both the encoder and decoder is one of the main disadvantages of a satellite camera compensating for its movement.
How image motion compensation works in satellite camera
Now that you understand image motion compensation meaning, let’s dig a bit deeper — how do these satellite camera mechanisms work? Let’s start with a moving film method. It is about moving the film according to the speed of what you are filming and in a direction that doesn’t change. So, the relative motion of image points with a film needs compensation. A satellite camera’s focal plane has a flattening plate for a film. This plate is negative pressure or a clamp plate flattening. An advanced satellite camera uses negative pressure flattening because this method is more precise. When expositing, the film flattens on a flattening plate until the two have the same integrity. A transfer mechanism electrical motor moves images at the same speeds and in the corresponding direction.
However, there’s more. Satellite cameras also have to use a control system that controls the electrical motor’s rotation speed. It’s important to have same speeds for the flattening plate and the electrical motor. Velocity and altitude are two variables that determine the speed of an electrical motor and flattening plate in a satellite camera. Both change the motor’s speed too. So, this system should be very precise, work steadily, and have an advanced speed-control system. Image sequences motion compensation is necessary for this method. An imaging controller starts calculating the imaging cycle first. After, it adjusts each imaging cycle’s timing sequences. This matters a lot for photogrammetry mapping.
What is image processing motion compensation?
Picture processing motion compensation stands for a process of determining motion vectors. These vectors describe how a 2D picture transforms into another 2D one, usually because a video sequence’s frames are adjacent. Problems often arise when a motion is in 3D because it is the projection of 3D images onto a 2D plane. Luckily, picture-processing motion compensation reduces redundancy. It is based on the simple principle that most motion in an image consists of an element being displaced. Image processing motion compensation takes every macroblock in a picture and compares it with all other macroblocks. These macroblocks form vertical and/or horizontal displacements in small increments, usually of half-pixel. Image processing motion compensation stops when a fit macroblock is identified. Then, a receiver gets instructions to employ that macroblock’s contents and replace them to a new position with their motion vector. Image processing motion compensation in a satellite camera should be fast and reliable. For this reason, optical engineers compete to build the most advanced systems.
The image motion compensation system of a satellite camera is very complex. A satellite’s computer works for the image-motion compensation system to determine leading-in velocity/altitude in accordance with the satellite’s orbital parameters. Then, a computerized phase-locked control device moves the film’s flattening plate at the same speeds as the images move, following the same direction. Using image motion compensation systems in different remote sensing initiatives involves working with an 80–100 lp/mm optical resolution satellite camera that can obtain great images of ground objects.
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