About the Rapid Response MODIS mosaic of the Arctic
Changes to the Mosaic
On March 26, 2017 the source data for the mosaic changed from Collection 5 to Collection 6. The projection used and the number of tiles also changed. Details are provided below.
In the future, the mosaic will be phased out and replaced by imagery from NASA's Global Imagery Browse Services (GIBS), which includes these layers plus many more. More information is available about GIBS and this imagery is also accessible with the interactive Worldview tool.
Data included in the image
A true color image is generated each day for Terra and Aqua. A 367 false-color image is also generated for Terra. Band 6 on Aqua is not functional.
The image is composed of data collected during a single day (UTC time). Because Aqua and Terra are in a polar orbit, MODIS captures many images of the Arctic throughout the day. To select the data used in the mosaic, the Rapid Response System chooses the data that are closest to the center of each swath, where edge distortion is minimized. This mosaicing technique creates the diagonal lines that give the image its "pie slice" appearance.
A single static daily image like this one is not the best way to represent the multiple polar overpasses of the MODIS instrument. We are working on better ways to present imagery from all the MODIS (and other instrument) overpasses.
For Collection 5, the images are mapped using the Polar Stereographic projection with origin ("down") at 0 longitude and +90 latitude with a +70 standard parallel (also known as latitude of true scale) onto a sphere with a radius of 6371.007181 kilometers. This corresponds to a scale at natural origin of 0.969858730377.
For Collection 6, the images are mapped using the EPSG:3413 projection, details on this projection can be found here. This is projected onto the WGS84 spheroid and "down" is -45 degrees longitude.
Information on using the mosaic image in GIS and image processing software packages is available on our FAQ page.
The mosaic is laid out in a 8 by 8 tiling scheme, centered on the south pole. Each tile is 1024 by 1024 pixels in size. The tiles are numbered starting with row 0 column 0 in the lower left corner. For Collection 5 only the central 6 by 6 tiles (row 1 column 1 to row 6 column 6) were generated. For Collection 6 all 8 by 8 tiles are being generated.
The complete mosaic can be downloaded as a single image at 4km, 2km, and 1km resolutions. By clicking on each individual tile within the mosaic, a page featuring that tile will come up, and the 250m image for that tile can be downloaded.
Our About Rapid Response Imagery page provides more information on usage guidelines, product quality, and algorithms for the Antarctic imagery.
Our News column contains information on problems with the Rapid Response system and the MODIS instruments on Aqua and Terra.
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