Support the Arctic Sea Ice Forum and Blog

Author Topic: AMSR2 on Worldview  (Read 3333 times)

Andreas T

  • Nilas ice
  • Posts: 1126
    • View Profile
  • Liked: 11
  • Likes Given: 2
AMSR2 on Worldview
« on: March 29, 2016, 12:27:24 PM »
I recently spotted that  these channels are available on Worldview:
 Sea Ice Brightness Temperature 6km 89H GCOM-W1 / AMSR2
as well as the .... 89V .... version
I am trying to learn what it tells me and how it can be useful.
What is great on Worldview is of course how easy it is to switch between aligned images from visible  to IR and AMSR, and to flick from one date to the next for comparison.
I have attached some views of Wrangel island as an example. Coastline overlay has to be moved to the top to show in AMSR, it took me a while to figure that out   ::)
The resolution of AMSR is clearly lower than IR which is lower than visible as one would expect.
Leads show up warmer in both IR and AMSR and surface temperature changes due to weather show up in both too. But in IR view of the surface is obscured by cloud or fog. AMSR also shows patterns in the ice which persist over long times which seem to indicate different thickness. These areas cool more rapidly and warm up more slowly than others.
But this is me guessing and drawing conclusions from comparing these images. Does anyone have more information or can point me to sources.
This could be a very useful tool for us but it seems it is not straightforward to interpret  it.


Andreas T

  • Nilas ice
  • Posts: 1126
    • View Profile
  • Liked: 11
  • Likes Given: 2
Re: AMSR2 on Worldview
« Reply #1 on: March 31, 2016, 12:25:47 AM »
Since AMSR2 makes visible lasting patterns in the ice, I had a go at tracking identifiable floes in the drift towards Fram strait. I just tracked 6 floes over 12 days, the marks are for 18, 21 ,24 ,27, 30th March overlaid on the image from the 18th. It doesn't provide a lot of information, if anything I am surprised how much they do move in parallel, I expected more of a funneling together. This is mainly an exercise what this could do to show up deformation of larger ice areas.

seaicesailor

  • Guest
Re: AMSR2 on Worldview
« Reply #2 on: April 04, 2016, 12:41:44 AM »
Awesome Andreas! Did not know this product. Do you think one can infer snow cover from the IR images or thickness or combination of both? thank you
i am going to have my own look on it too

Andreas T

  • Nilas ice
  • Posts: 1126
    • View Profile
  • Liked: 11
  • Likes Given: 2
Re: AMSR2 on Worldview
« Reply #3 on: April 04, 2016, 02:36:17 PM »
I have to say that my knowledge of this is from the basic physics and a bit of reading around, so if someone has better information I would like to hear it.
IR is emitted from the surface because snow, ice and water are opaque at that wavelength (11 micrometer) and emissivity is pretty close, though higher for fine freshly fallen snow than for bare ice, so I doubt you could easily "read" snow cover from this data.
Snow surfaces should change temperature more quickly than bare ice, and with warmer water below the ice, snow surfaces would be colder in cold air and clear sky. But that depends on rates of heat transfer (wind) how quickly air temperatures change, so I doubt this helps. My guess is that there are just too many unknowns. Fog and cloud add further obstacles (absorption and emission by water vapour is low at that frequency so there need to be liquid droplets to obscure the surface emission)
I don't know enough about the microwave emission picked up by AMSR, but emissivity does depend on the state the water is in, that is why it can be used to distinguish  ice from water. I haven't yet found information about the effect of snow. In the data shown on worldview temperature has an effect as one would expect, we are looking at thermal radiation from the surface. You can see that in rapid changes in changing weather conditions (but again clouds, i.e. thicker layers of waterdroplets can change what we see) Whether the persistent patterns which can be seen are caused by ice temperature (relating to thickness), snowcover, or age (structure, salinity?) I do not know.
One place I am keeping an eye on is north west of Franz Josef Land where a large area which appears blue in AMSR is drifting towards open water. The weeks to come may tell us more about how resilient i.e. thick this ice is.

Andreas T

  • Nilas ice
  • Posts: 1126
    • View Profile
  • Liked: 11
  • Likes Given: 2
Re: AMSR2 on Worldview
« Reply #4 on: April 04, 2016, 02:46:42 PM »
Another place where one could learn more about interpretation of these images is off the northeast coast of Greenland. The landfast ice there shows some patterns which seem to relate to age of that ice, which briefly broke in Sept 2015 but then froze together without drifting far.

Andreas T

  • Nilas ice
  • Posts: 1126
    • View Profile
  • Liked: 11
  • Likes Given: 2
Re: AMSR2 on Worldview
« Reply #5 on: April 04, 2016, 05:51:35 PM »
I should have looked on Jim's site earlier! He links to this great JAXA ADS site
 https://ads.nipr.ac.jp/vishop/vishop-monitor.html?N
which lets you play animations of AMSR data (36H,36V,18V bands) albeit in low resolution but great for following the movement over the whole winter. I still don't know how to interpret the different colour codes.
 It also has a sea ice thickness map which tells me my guess of greater thickness in the blue band was wrong!
Still learning.

seaicesailor

  • Guest
Re: AMSR2 on Worldview
« Reply #6 on: April 05, 2016, 12:11:43 AM »
Andreas, take that thickness map with a grain of salt, it is ok in Winter but I have seen abrupt changes sometimes. Also it becomes totally unreliable as soon as surface melt starts. Wipneus showed this problem last year.

oren

  • Young ice
  • Posts: 4488
    • View Profile
  • Liked: 877
  • Likes Given: 1287
Re: AMSR2 on Worldview
« Reply #7 on: April 05, 2016, 05:35:24 PM »
Great resource, thanks for bringing it up!