On kps – kilo pixel swath
By Dr. Armando Guevara
In an effort to help the understanding of customers when it comes to buying sensors (all things being equal –apples to apples- with regards to all sensors having the same geometric and radiometric quality) the time has come to establish a measure of sensor efficiency with regards to collection capacity per unit of time.
Consider that the terminology of “frame” no longer makes sense and it is increasingly confusing to the end customer when bidding for a frame system, e.g. large frame, medium frame etc. -and then vendors show up with frames termed “large” or “medium” etc. and they are all of different size. The term “megapixel” is also confusing. Say, a 39 megapixel CCD camera based system is approximately 7.2×5.4k pixels with an effective swath of 7K pixels. At the end of the day what the customers really cares about is: “At a defined GSD how much area can I collect in a given unit time”. The answer to this is effectively affected by the swath of the sensor in number of pixels.
A kps is the number of pixels across track covered by a sensor on the ground, in other words, the number of pixels in the swath. 1 KPS = one thousand pixels swath. kps – a base measure to establishing digital aerial camera collection efficiency. It is often difficult to differentiate the competing claims of different digital aerial camera manufacturers when it comes to efficiency. There are many aspects that contribute to the efficiency, but one simple measure is for the same aircraft speed, how much area is collected per hour of flying?
There are many factors that go into the design of a successful aerial imaging project, including but not limited to one camera focal length, CCD size and flying height. For digital cameras, the project is designed for a specific nominal ground sample distance or GSD. No matter what flying height, focal length, or CCD size, the amount of area covered is the nominal GSD times the number of pixels in the width of the CCD array. For a typical 39 megapixel camera, the published width of the array is 7,216 pixels. An Iris One 30 system (3×11 MPix camera modules) has an effective swath width of 12,024 pixels, and an Iris One 50 (5x 11 MPix camera modules) has an effective swath width of 20040 pixels. To make the math easy, assume we fly each camera system to collect 1- foot pixels (30 cms);
• A 39 megapixel camera will collect a swath 7,216′ wide
• Iris One 30 system will collect a swath 11,490′ wide
• Iris One 50 system will collect a swath 18,971′ wide
Normal block collection of a project will factor in a 30% side lap between flight lines.
• A 39 megapixel camera will have an effective swath 5051′ wide
• Iris One 30 will collect a swath 8,043′ wide
• Iris One 50 will collect a swath 13,280′ wide
With a flying speed of 150 miles an hour times 5,280 feet in a mile, the aircraft travels approximately 792,000 feet an hour.
Visual Intelligence®, Iris One™, iOne™, Isis Earth™, Isis Sky™, ARCA™, CoCo™ and DigitalFilm™ are some of Visual Intelligence’s (“VI”) Trade Marked products based and covered under one or more of the following VI Patents: 7,127,348 (“System”); 7,893,957 (“ARCA”); 7,725,258 (“CoCo”); 7,212,938; 6,928,194; 7,630,579. For more information, please see VI PATENTS