Landsat Variable Window Product

Variable window products are map oriented image products where users can select the framing dimensions of the scenes they require. The variable window product is designed to remove the limitations of Path Image products by providing more flexibility in choosing imagery to cover an area of interest, either across multiple scenes or as smaller areas within existing scenes.

The advantage of map oriented image products is that the pixels are aligned to the map grid rather than parallel to the path of the satellite (swath), allowing them to be used with software and other products that require map grids.   

To define a variable window product in the ACRES digital catalogue a particular path and date of imagery is nominated and a rectangular window is specified by the latitude and longitude of the scene centre with the scene extent in kilometres east-west and north-south. All imagery from that path (image swath) falling inside the specified window is then extracted to the produce the Map orientated  product.

Variable Window Products are only available for image data processed as Map Oriented Image and Orthocorrected Image scenes.

Some examples of variable windows are displayed in the following [jpg_22k] image.
Select for higher resolution 111k_image):

• A - window wholly within path
• B - window straddling the path
• C - window cutting one side of path

The resulting map oriented product is aligned to the Map Grid of Australia (MGA) with the pixel rows aligned east-west, instead of being aligned perpendicular to the direction of satellite travel.

For Map Oriented Image products, the coordinate values are only approximate, although the relative accuracy is within a few pixels.

Window Size

The product is extracted only from the path specified. If the nominated window extends outside the image swath, that area will be filled with blank pixels. The maximum size window that can be specified is 310 km × 530 km. The E-W extent is larger than the width of the available imagery due to the satellite path being tilted N-E by 9 to 13 degrees, depending on the latitude. Note that the maximum N-S extent is larger than the path oriented scene size of 184.8 km. This allows for much more data to be ordered in a single data set.

Comparison of a Full Scene Path Image to a digital Variable Window Product-[jpg_22k].
Select for higher resolution 46k_image)

Sample window for larger ETM+ or TM Image-[jpg_26k].
Select for higher resolution 46k_image)

Pixel Sizes

• are slightly smaller than the original imagery to avoid aliasing and loss of information content
• are multiples of each other to allow ready registration
• fit neatly into one hundred metre grid intervals