Landsat 8 off-nadir images


One interesting feature of the new Landsat 8 satellite launched earlier this year is the capability to record off-nadir images.  Normally earth observation satellites look straight down at the earth surface.  The capability to tilt the view sidewards allows recording images outside the normal schedule (which repeats the same view only after 16 days in case of Landsat) and to record images north and south of the normal coverage.

Landsat regularly covers everything up to about 82°40′ latitude which leaves out only the northmost parts of Greenland and Ellesmere Island in the north and central Antarctica in the south.  The off-nadir capability of Landsat 8 allows covering all land surface in the north and will significantly reduce the coverage gap in the south.  Unfortunately recording off-nadir scenes seems to be quite a major interruption of the normal recording operation so it does not happen very often.  Until now there is only one sequence of off-nadir scenes covering the normally uncovered areas in the north from May 17 this year.  I assembled these scenes into a single image you can see below:

This mosaic consisting of several Landsat scenes is over 30000 pixel wide in full size (without pansharpening). In May almost everything is snow covered so contrasts are quite low.  There is also some cloud cover over Greenland on the right although the date was obviously chosen for good weather conditions.  Ellesmere Island on the left is mostly free of clouds. Note map projection is EPSG:3413 which is polar stereographic centered at 45 degrees west.  For comparison here is a MODIS mosaic from late summer 2011 showing the same area:

Which parts of this area are outside the regular Landsat coverage can be seen in the following image. Also drawn in there are the extents of the following magnified crops:

Best contrasts and least disturbance by the clouds can be found in the infrared channels so the following magnified crops are contrast enhanced infrared images. The low noise of Landsat 8 data allows stretching the contrast significantly to emphasize small shading variations.

The first crop shows the remains of the Serson Ice Shelf which is the southmost ice shelf on Ellesmere Island. More details on this ice shelf can be found here and here.

The second crop contains the Milne Ice Shelf which is the second largest of the remaining arctic ice shelves and the most stable one. Some cloud cover obscures the northern part. The typical wavy surface structure of the ice shelves is well visible here which makes it possible to distinguish the ice shelf from the normal sea ice. On lower resolution satellite images these waves are not visible making it difficult to make this distinction.

In the bottom left corner a small ice shelf area called the Peterson Ice Shelf.

This crop contains the Ward Hunt Ice Shelf, largest of the Arctic ice shelves. Recent ice losses have split it into two parts opening up the Disraeli Fjord on the bottom right. The fjords and coastal areas around the ice shelf are filled with land fast sea ice while in the upper part of the crop you can see the more mobile pack ice of the Arctic Ocean.

This last crop from much further to the east shows the only larger ice shelf area in northern Greenland in the Hunt Fjord between Cape Kane in the west and Cape Washington in the east. Many of the fjords in northern Greenland are filled with multiyear sea ice that only breaks up every few years but here is the only one where this has developed into a permanent ice shelf. Despite the strong disturbance by clouds you can clearly see the wave structures on the ice.

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