Tasking is the first step in the Change Detection workflow and the only way to obtain imagery for use with Capella’s Change Detection product. There are several requirements for imagery to be available for use with Change Detection. As the product continues to be enhanced, these requirements will be updated.
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Concept |
Requirement |
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Organization Access |
To task images that include Change Detection, the Organization must be enabled to do so by a Capella Administrator. |
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Tasked vs Archive imagery |
Change Detection can only be initiated at the time a Repeat Task to obtain new imagery is submitted. Capella’s Change Detection product is not currently available utilizing imagery from the Archive. A detailed overview of Repeat Tasking is available on this support site and is crucial to review in advance of tasking for Change Detection. |
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Image Mode |
Change Detection is available on the following Image Modes using the Geocoded Terrain Corrected (GEO) product type only:
Importantly, Spotlight and Sliding Spotlight must be tasked as Standard Products (Product Guide). Stripmap images may be tasked with custom length and width. Extended Products can not be tasked with Change Detection for any Image Mode. GEO is the only product type that is currently used in Change Detection. |
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Acquisition Geometry |
Obtaining tasked imagery with compatible acquisition geometry is critical to ensuring useful Change Maps. Repeat Tasks requested with Change Detection can only be acquired when the Maintain Scene Framing setting is set to true. This setting will acquire all repeat images with the same Observation Direction, Orbital Plane, and Orbit State as the first image in the repeat series. The Observation Direction, Orbital Plane, and Orbit State for the first image in the repeat series may be set by the user or will be set automatically based on the first accepted task. |
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Look Angle Tolerance |
The user may select a Look Angle Tolerance between 0° and 10°. 10° is the default selection if no other choice is made. A larger Look Angle Tolerance (e.g. 10°) will result in more collection opportunities for the repeat series, making tasks more likely to be accepted by the scheduler. The tradeoff for this increase in opportunities is that image artifacts (parallax, differential layover, etc) are also more likely be detected as changes. A smaller Look Angle Tolerance (e.g. 0°) will help reduce the quantity of changes detected based on image artifacts. However, a smaller tolerance will results in fewer collection opportunities and tasks that are less likely to be accepted in competitive areas. This concept is further elaborated on in “Revisit: Important considerations for tasking with Change Detection.” |
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Image quantities and comparison sequence |
Change Detection requires a minimum of two tasked images to run. A time series of images may be acquired for as long as the user specifies in the Repeat Task. Change Detection will only be run between each subsequent image—e.g. images 1 & 2, images 2 & 3, images 3 & 4, and so on. |